| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:CommonStockValue us-gaap:ConsolidatedEntities srt:ParentCompany | NA | NA | 0.384 | NA | NA | NA | 0.398 | NA | NA | NA | 0.403 | NA | NA | NA | 0.408 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:CommonStockValue us-gaap:StatementClassOfStock us-gaap:CommonClassA | ▁▁▁▁▁▂▂▂▂▂▂▂▂▂▂▃▃▃▃▄▄▄▅▅▆▆▆▆▆▇▆▆▇▇▇▇▇▇▇▇█ | 0.275 | 0.274 | 0.272 | 0.272 | 0.272 | 0.286 | 0.285 | 0.284 | 0.284 | 0.286 | 0.288 | 0.293 | 0.293 | 0.293 | 0.293 | 0.294 | 0.304 | 0.307 | 0.306 | 0.308 | 0.31 | 0.31 | 0.325 | 0.334 | 0.337 | 0.347 | 0.348 | 0.348 | 0.349 | 0.35 | 0.349 | 0.349 | 0.35 | 0.35 | 0.351 | 0.358 | 0.358 | 0.358 | 0.356 | 0.36 | 0.37 | NA | 0.368 | NA | NA |
| us-gaap:CommonStockValue us-gaap:StatementClassOfStock us-gaap:CommonClassB | ▁▃▃▃▃▄▄▄▄████████████████████████████████ | 0.111 | 0.112 | 0.112 | 0.112 | 0.112 | 0.113 | 0.113 | 0.113 | 0.113 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | NA | 0.115 | NA | NA |
| us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding | ▄ | 38.741486 | NA | NA | NA | 39.203404 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 46.658031 | NA | 47.321797 | 47.292147 | 47.184079 | NA | 48.253888 | 48.488046 | 48.363035 | NA | 48.938333 | 49.934648 |
| us-gaap:WeightedAverageNumberOfSharesOutstandingBasic | ▄ | 38.741486 | NA | NA | NA | 39.203404 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 46.658031 | NA | 47.086098 | 47.049055 | 46.989773 | NA | 48.059747 | 48.302779 | 48.171317 | NA | 48.938333 | 49.735398 |
| us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted | NA | 38.603555 | NA | 38.538476 | 39.203404 | 39.955514 | NA | 39.877129 | 40.050065 | 40.373295 | NA | 40.988965 | 40.886617 | 40.950528 | NA | 41.553316 | 42.32654 | 42.291857 | NA | 42.642213 | 42.6357 | 43.088092 | NA | 45.047777 | 45.946415 | 46.29059 | NA | 46.43268 | 46.529377 | 46.527917 | NA | 46.496612 | 46.626853 | 46.658031 | NA | 47.460308 | 47.434915 | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:CommonShareholders | NA | 38.031267 | NA | 37.988584 | 38.641794 | 39.405454 | NA | 39.356311 | 39.518652 | 39.855122 | NA | 40.441783 | 40.411359 | 40.54187 | NA | 41.146424 | 41.91399 | 41.851064 | NA | 42.19958 | 42.193769 | 42.630806 | NA | 44.570519 | 45.451888 | 45.799873 | NA | 45.948255 | 46.075869 | 46.110952 | NA | 46.086743 | 46.210571 | 46.272324 | NA | 47.086182 | 47.049055 | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:UnvestedRestrictedStockShareholders | NA | 0.572288 | NA | 0.549892 | 0.56161 | 0.55006 | NA | 0.520818 | 0.531413 | 0.518173 | NA | 0.547182 | 0.475258 | 0.408658 | NA | 0.406892 | 0.41255 | 0.440793 | NA | 0.442633 | 0.441931 | 0.457286 | NA | 0.477258 | 0.494527 | 0.490717 | NA | 0.484425 | 0.453508 | 0.416965 | NA | 0.409869 | 0.416282 | 0.385707 | NA | 0.374126 | 0.38586 | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:EarningsPerShareBasic | ▄ | 2.16 | NA | NA | NA | 2.21 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 1.2 | 0.78 | 0.87 | 0.91 | 1.37 | 0.98 | 0.76 | 1.13 | 1.73 | -0.01 | 1.0 |
| us-gaap:EarningsPerShareBasic us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:CommonShareholders | ▄ | 2.16 | NA | NA | NA | 2.21 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:EarningsPerShareBasic us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:UnvestedRestrictedStockShareholders | ▄ | 2.16 | NA | NA | NA | 2.21 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:EarningsPerShareDiluted | ▄ | 2.16 | NA | NA | NA | 2.21 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 1.19 | 0.77 | 0.87 | 0.91 | 1.37 | 0.98 | 0.76 | 1.13 | 1.73 | -0.01 | 0.99 |
| us-gaap:EarningsPerShareDiluted us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:CommonShareholders | ▄ | 2.16 | NA | NA | NA | 2.21 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:EarningsPerShareDiluted us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:UnvestedRestrictedStockShareholders | ▄ | 2.16 | NA | NA | NA | 2.21 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:EarningsPerShareBasicAndDiluted | NA | 3.2 | 6.1 | 1.86 | 2.21 | -1.01 | 1.06 | 0.83 | 0.61 | 1.03 | 0.53 | 1.05 | 1.21 | 2.78 | 1.17 | 1.11 | 0.68 | 1.18 | 2.32 | 1.98 | 0.61 | 1.11 | 1.86 | 1.09 | 1.54 | 1.4 | 1.59 | 1.84 | 1.61 | 1.59 | 1.52 | 1.35 | 2.17 | 1.46 | 1.2 | 0.78 | 0.87 | 0.91 | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:EarningsPerShareBasicAndDiluted us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:CommonShareholders | NA | 3.2 | 6.029999999999999 | 1.86 | 2.21 | -1.01 | 1.06 | 0.83 | 0.61 | 1.03 | 0.5300000000000002 | 1.05 | 1.21 | 2.78 | 1.1699999999999995 | 1.11 | 0.68 | 1.18 | 2.3199999999999994 | 1.98 | 0.61 | 1.11 | 1.8599999999999994 | 1.09 | 1.54 | 1.4 | 1.5899999999999999 | 1.84 | 1.61 | 1.59 | 1.5199999999999996 | 1.35 | 2.17 | 1.46 | 1.1999999999999997 | 0.78 | 0.87 | 0.91 | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:EarningsPerShareBasicAndDiluted us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities nni:UnvestedRestrictedStockShareholders | NA | 3.2 | 6.029999999999999 | 1.86 | 2.21 | -1.01 | 1.06 | 0.83 | 0.61 | 1.03 | 0.5300000000000002 | 1.05 | 1.21 | 2.78 | 1.1699999999999995 | 1.11 | 0.68 | 1.18 | 2.3199999999999994 | 1.98 | 0.61 | 1.11 | 1.8599999999999994 | 1.09 | 1.54 | 1.4 | 1.5899999999999999 | 1.84 | 1.61 | 1.59 | 1.5199999999999996 | 1.35 | 2.17 | 1.46 | 1.1999999999999997 | 0.78 | 0.87 | 0.91 | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| COGS Ratio us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:CommunicationsServices,nni:CommunicationsSegment | NA | NA | 19.253 | 20.211 | 18.998 | 18.181 | 17.499 | 16.47 | 15.758 | 14.543 | 13.326 | 11.818 | 10.32 | 9.189 | 8.123 | 6.751 | 5.719 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| COGS Ratio us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:EducationTechnologyServicesAndPaymentProcessingServices,nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | ▅█▄▅▃▆▄▅▃▆▃▃▂▃▁▂▁ | 76.702 | 95.258 | 65.096 | 74.121 | 59.304 | 83.675 | 63.578 | 74.251 | 60.342 | 79.159 | 54.59 | 58.409 | 48.742 | 60.221 | 43.326 | 50.358 | 43.48 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| COGS Ratio us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | ▁▂▂▂▂▅▅█▄▅▄▄▂▂▁▁▁ | 0.21 | 0.263 | 0.259 | 0.367 | 0.42 | 1.991 | 2.069 | 3.499 | 1.659 | 2.017 | 1.526 | 1.513 | 0.748 | 0.665 | 0.007 | 0.005 | 0.003 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| COGS Ratio us-gaap:ProductOrService nni:CommunicationsServices | NA | NA | 19.253 | 20.211 | 18.998 | 18.181 | 17.499 | 16.47 | 15.758 | 14.543 | 13.326 | 11.818 | 10.32 | 9.189 | 8.123 | 6.751 | 5.719 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| COGS Ratio us-gaap:ProductOrService nni:EducationTechnologyServicesAndPaymentProcessingServices | ▅█▄▅▃▆▄▅▃▆▃▃▂▃▁▂▁ | 76.702 | 95.258 | 65.097 | 74.121 | 59.304 | 83.675 | 63.578 | 74.251 | 60.342 | 79.159 | 54.589 | 58.409 | 48.742 | 60.221 | 43.326 | 50.358 | 43.48 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| EBT Margin us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:AssetGenerationAndManagementSegment | ▁▁▂▂▂▄▆▇███▇▇▅▅▅▅ | 129.965 | 126.402 | 137.006 | 137.959 | 150.583 | 185.926 | 208.575 | 233.225 | 243.295 | 246.867 | 248.621 | 236.039 | 226.509 | 200.334 | 195.56 | 194.971 | 191.368 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| EBT Margin us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | ▁▂▂▂▂▅▅█▄▅▄▄▂▂▁▁▁ | 0.21 | 0.263 | 0.259 | 0.367 | 0.42 | 1.991 | 2.069 | 3.499 | 1.659 | 2.017 | 1.526 | 1.513 | 0.748 | 0.665 | 0.007 | 0.005 | 0.003 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| EBT Margin us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:LoanServicingAndSystemsSegment | ▁▁▁▁▁▅▇██▇▆▆▅▄▃▃▂ | 0.03 | 0.034 | 0.033 | 0.034 | 0.052 | 0.317 | 0.452 | 0.532 | 0.55 | 0.497 | 0.42 | 0.381 | 0.293 | 0.257 | 0.152 | 0.147 | 0.12 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| Net profit Margin us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:AssetGenerationAndManagementSegment | ▁▁▂▂▂▄▆▇███▇▇▅▅▅▅ | 129.965 | 126.402 | 137.006 | 137.959 | 150.583 | 185.926 | 208.575 | 233.225 | 243.295 | 246.867 | 248.621 | 236.039 | 226.509 | 200.334 | 195.56 | 194.971 | 191.368 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| Net profit Margin us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | ▁▂▂▂▂▅▅█▄▅▄▄▂▂▁▁▁ | 0.21 | 0.263 | 0.259 | 0.367 | 0.42 | 1.991 | 2.069 | 3.499 | 1.659 | 2.017 | 1.526 | 1.513 | 0.748 | 0.665 | 0.007 | 0.005 | 0.003 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| Net profit Margin us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:LoanServicingAndSystemsSegment | ▁▁▁▁▁▅▇██▇▆▆▅▄▃▃▂ | 0.03 | 0.034 | 0.033 | 0.034 | 0.052 | 0.317 | 0.452 | 0.532 | 0.55 | 0.497 | 0.42 | 0.381 | 0.293 | 0.257 | 0.152 | 0.147 | 0.12 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
|---|
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:ComprehensiveIncomeNetOfTax | ▄▅█▄▄▁▃▃▃▃▃▃▃▅▃▃▃▃▅▄▃▃▄▃▄▄▄▄▄▄▄▄▅▄▄▃▃▃▄▃▃▃ | 85.786 | 126.518 | 236.809 | 72.554 | 88.856 | -42.645 | 42.462 | 32.958 | 24.211 | 41.26 | 21.534 | 44.198 | 49.117 | 113.073 | 48.531 | 46.239 | 27.673 | 50.611 | 103.5 | 86.147 | 22.457 | 47.093 | 82.758 | 48.548 | 69.32 | 64.502 | 73.647 | 84.749 | 77.884 | 71.646 | 69.617 | 65.955 | 98.79 | 70.316 | 61.38 | 35.304 | 40.38 | 43.746 | 64.879 | 47.451 | 37.125 | 54.88 | NA | NA | NA |
| us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest | ▆▆▂▆▇█▆▇▇▇▇▇▇▆▃▃▁▄█▇▇▇▇▇▇▇ | -0.854 | -0.694 | -3.385 | -0.327 | 0.128 | 0.767 | -0.547 | -0.077 | 0.059 | 0.056 | 0.049 | 0.199 | 0.104 | -0.74 | -2.385 | -2.768 | -4.086 | -2.106 | 0.585 | 0.069 | 0.028 | 0.068 | 0.168 | 0.022 | 0.054 | 0.041 | NA | 0.157 | 0.693 | 0.513 | NA | 0.216 | 0.614 | 0.271 | 0.019 | 0.124 | 0.136 | 0.152 | 0.0 | 0.0 | 0.0 | 0.0 | NA | NA | NA |
| us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest | ▄▅█▄▄▁▃▃▃▃▃▃▃▅▃▃▃▃▅▄▃▃▄▃▄▄▄▄▄▄▄▄▅▄▄▃▃▃▄▃▃▃ | 84.932 | 125.824 | 233.424 | 72.227 | 88.984 | -41.878 | 41.915 | 32.881 | 24.27 | 41.316 | 21.583 | 44.397 | 49.221 | 112.333 | 46.146 | 43.471 | 23.587 | 48.505 | 104.085 | 86.216 | 22.485 | 47.161 | 82.926 | 48.57 | 69.374 | 64.543 | 73.955 | 84.906 | 78.577 | 72.159 | 70.185 | 66.171 | 99.404 | 70.587 | 61.399 | 35.428 | 40.516 | 43.898 | 64.879 | 47.451 | 37.125 | 54.88 | NA | NA | NA |
| us-gaap:CostOfGoodsAndServicesSold | ▅▇▆█▄▇▆█▄▆▄▅▂▃▂▃▁ | 21.676 | 27.052 | 24.354 | 31.157 | 21.119 | 28.388 | 24.329 | 30.907 | 20.972 | 25.818 | 20.513 | 23.397 | 15.182 | 17.4 | 14.383 | 17.783 | 11.718 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:GainLossOnInvestments | ▄▃▃▁█▂ | 15.591 | 8.498 | 11.884 | -10.152 | 53.151 | -1.025 | NA | 1.948 | 4.258 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 0.994 | 4.254 | NA | NA | 6.939 | -4.084 | NA | NA | NA | NA | NA |
| us-gaap:GainsLossesOnExtinguishmentOfDebt | NA | NA | 1.416 | 0.105 | NA | NA | -0.874 | -14.014 | NA | NA | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | ▄▅█▄▄▁▃▃▃▃▂▃▃▅▃▃▃▄▅▅▃▃▅▄▄▄ | 109.25 | 157.765 | 302.18 | 90.332 | 107.874 | -49.898 | 50.855 | 41.964 | 30.887 | 53.038 | 17.076 | 57.008 | 63.05 | 149.161 | 40.23 | 69.097 | 40.683 | 76.675 | 153.06 | 132.078 | 41.214 | 72.462 | 130.913 | 75.976 | 111.319 | 102.436 | NA | 131.889 | 118.765 | 114.91 | NA | 93.49 | 156.603 | 106.797 | NA | 58.822 | 56.408 | 66.523 | NA | 71.861 | 58.231 | NA | NA | NA | NA |
| us-gaap:IncomeTaxExpenseBenefit | ▅▆█▅▅▃▄▄▄▄▃▄▄▆▃▅▅▅▇▇▄▅▇▅▆▆▅▆▆▆▁▅▇▆▁▅▄▅▁▅▅▆▇▃▅ | 26.237 | 34.861 | 70.573 | 19.156 | 21.264 | -10.133 | 9.022 | 8.829 | 6.209 | 11.391 | -4.599 | 13.882 | 13.511 | 35.976 | -5.486 | 25.562 | 16.032 | 28.755 | 54.128 | 47.715 | 15.036 | 24.433 | 47.395 | 26.999 | 40.356 | 37.63 | 30.036 | 46.513 | 43.078 | 40.611 | -37.556 | 30.444 | 54.746 | 38.447 | -36.099 | 21.87 | 14.878 | 23.23 | -39.008 | 24.41 | 21.106 | 32.928 | 51.057 | -0.226 | 29.996 |
| us-gaap:IncomeTaxesPaidNet | ▄▃▄▃▄▃▃▃▄▃▄▃▅▁▅▅▆▃▅▅▇▃▆▆█▃▆▆█▄▆▆█▄▅▅▇▃▆▆▅▅▅▅ | 14.03 | 0.199 | 16.272 | 5.464 | 7.869 | 0.08 | 2.852 | 3.291 | 11.538 | -0.009 | 6.964 | 0.799 | 23.279 | -30.569 | 25.29 | 25.238 | 45.013 | 1.18 | 27.782 | 31.645 | 54.665 | 1.323 | 42.832 | 37.192 | 67.166 | 0.045 | 36.962 | 35.16 | 70.328 | 13.378 | 40.096 | 44.878 | 64.377 | 5.489 | 27.96 | 29.685 | 54.193 | 2.92 | 35.54 | 34.309 | 31.038 | 32.293 | 28.181 | 25.887 | NA |
| us-gaap:InterestExpense | ▂▁▂▂▃▆▆▇████▇▆▅▅▅▄▄▄▄▄▃▃▃▃▃▃▃▂▂▂▂▂▃▃▃▃▃▂▂▂▂▃▂ | 49.991 | 27.773 | 52.283 | 58.423 | 85.248 | 134.118 | 148.106 | 172.488 | 186.963 | 191.77 | 182.732 | 180.175 | 171.45 | 135.55 | 123.401 | 121.65 | 113.236 | 106.899 | 107.336 | 96.386 | 94.052 | 90.408 | 80.866 | 77.164 | 72.626 | 71.554 | 72.061 | 71.937 | 69.235 | 60.004 | 59.135 | 55.315 | 58.127 | 58.358 | 65.391 | 66.402 | 67.476 | 69.297 | 64.062 | 60.866 | 51.054 | 52.307 | 54.515 | 68.243 | 59.243 |
| us-gaap:InterestIncomeExpenseNet | ▄▆▅▄▂▁▂▂▂▁▃▂▁▂▃▃▄▃▄▆▅▆▇▇▇▆▇█▇▆▇▇▆▆▅▄▄▄▅▆▅▄▆▅▆ | 83.592 | 101.33 | 86.556 | 81.322 | 66.635 | 55.073 | 64.252 | 66.457 | 59.825 | 58.816 | 69.539 | 59.773 | 57.739 | 67.307 | 73.235 | 75.234 | 79.841 | 76.925 | 78.96 | 99.795 | 92.2 | 101.609 | 112.215 | 111.993 | 105.096 | 102.595 | 112.492 | 117.487 | 107.713 | 98.871 | 108.736 | 104.922 | 101.419 | 98.798 | 90.598 | 85.266 | 84.567 | 84.856 | 93.291 | 96.761 | 88.736 | 85.777 | 96.335 | 92.213 | 97.414 |
| us-gaap:InterestPaidNet | ▁█ | 39.218 | 39.686 | NA | NA | 83.986 | 125.184 | 138.879 | 163.655 | NA | NA | 165.612 | 165.802 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:NetIncomeLoss | ▄▅█▄▄▁▃▃▃▃▃▃▃▅▃▃▃▃▅▄▃▃▄▃▄▄▄▄▄▄▄▄▅▄▃▃▃▃▄▃▃▃▄▂▃ | 83.867 | 123.598 | 234.991 | 71.503 | 86.482 | -40.532 | 42.38 | 33.212 | 24.619 | 41.591 | 21.626 | 42.927 | 49.435 | 113.925 | 48.1 | 46.303 | 28.737 | 50.026 | 98.346 | 84.294 | 26.15 | 47.961 | 83.35 | 48.955 | 70.909 | 64.765 | 73.611 | 85.219 | 74.994 | 73.786 | 70.52 | 62.83 | 101.243 | 68.079 | 56.634 | 36.828 | 41.394 | 43.141 | 64.879 | 47.451 | 37.125 | 54.88 | 85.087 | -0.368 | 49.993 |
| us-gaap:NetIncomeLossAttributableToNoncontrollingInterest | ▆▆▂▆▇█▆▇▇▇▇▇▇▆▃▃▁▄█▇▇▇▇▇▇▇▇▇███▇█▇▇▇▇▇▇▇▇▇ | -0.854 | -0.694 | -3.385 | -0.327 | 0.128 | 0.767 | -0.546 | -0.077 | 0.059 | 0.056 | 0.048 | 0.199 | 0.104 | -0.74 | -2.386 | -2.768 | -4.086 | -2.106 | 0.585 | 0.069 | 0.028 | 0.068 | 0.168 | 0.022 | 0.054 | 0.041 | 0.308 | 0.157 | 0.693 | 0.513 | 0.568 | 0.216 | 0.614 | 0.271 | 0.019 | 0.124 | 0.136 | 0.152 | 0.0 | 0.0 | 0.0 | 0.0 | NA | NA | NA |
| us-gaap:NetIncomeLossAttributableToNoncontrollingInterest us-gaap:ConsolidationItems us-gaap:CorporateNonSegment | ▅▇▁▆▇█▆▇▇▇ | -0.854 | 0.017 | -3.385 | -0.327 | 0.128 | 0.767 | -0.547 | -0.077 | 0.059 | 0.056 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:NetIncomeLossAttributableToNoncontrollingInterest us-gaap:ConsolidationItems us-gaap:IntersegmentElimination | NA | -0.711 | NA | NA | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:OperatingExpenses | ▅▅█▇▆▇▇▇▆▆▆▆▆▄▃▃▂▂▂▁▁▂▂▂▂▂▂▂▂▁▂▁▁▁▂▁▂▂▁▁▁▁▃▅▂ | 171.791 | 172.673 | 213.352 | 191.148 | 185.692 | 190.91 | 199.922 | 202.7 | 181.115 | 179.088 | 187.783 | 185.445 | 176.225 | 151.653 | 136.392 | 125.333 | 119.017 | 114.987 | 115.801 | 106.792 | 107.412 | 111.512 | 117.223 | 120.938 | 115.828 | 115.228 | 114.906 | 117.445 | 112.79 | 107.369 | 111.607 | 107.607 | 102.904 | 106.865 | 109.244 | 104.937 | 108.211 | 111.172 | 102.691 | 104.778 | 100.557 | 99.632 | 131.274 | 160.287 | 108.221 |
| us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax | ▁█ | -0.001 | 0.001 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:OtherComprehensiveIncomeLossNetOfTax | ▅▆▅▅▆▂▄▄▄▄▄▅▄▃▄▄▃▄█▅▁▃▃▄▃▄▄▄▆▂▃▆▂▆█▃▃▄ | 1.919 | 2.92 | 1.818 | 1.051 | 2.374 | -2.113 | 0.082 | -0.254 | -0.408 | -0.331 | -0.092 | 1.271 | -0.318 | -0.852 | 0.43 | -0.064 | -1.064 | 0.585 | 5.154 | 1.853 | -3.693 | -0.868 | -0.592 | -0.407 | -1.589 | -0.263 | 0.036 | -0.47 | 2.89 | -2.14 | -0.903 | 3.125 | -2.453 | 2.237 | 4.746 | -1.524 | -1.014 | 0.605 | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:OtherIncome | NA | NA | -12.35 | 1.502 | 60.127 | 8.281 | 26.522 | 13.439 | 16.152 | 9.067 | 9.998 | 16.673 | 9.58 | 18.198 | 7.952 | 19.756 | 12.485 | 12.632 | 15.218 | 15.15 | 9.765 | 13.796 | 6.684 | 6.523 | 7.504 | 6.918 | 12.906 | 7.65 | 15.315 | 18.131 | 15.981 | 8.613 | 12.288 | 9.416 | 7.023 | 12.699 | 8.8 | 10.954 | 12.264 | 3.931 | 6.826 | 6.492 | 6.122 | 9.432 | 8.496 | |
| us-gaap:OtherIncome us-gaap:ConsolidationItems us-gaap:CorporateNonSegment | NA | NA | -17.466 | -2.737 | 57.089 | 2.083 | 4.127 | 7.231 | 8.624 | 3.344 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:OtherIncome us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:AssetGenerationAndManagementSegment | NA | NA | 2.238 | 1.004 | 0.732 | 3.215 | 18.553 | 3.384 | 4.888 | 3.525 | 3.691 | 3.267 | 2.772 | 3.351 | 2.705 | 2.753 | 3.057 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:OtherIncome us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:CommunicationsSegment | NA | NA | 0.305 | 0.511 | 0.392 | 0.353 | 0.49 | 0.532 | 0.362 | 0.125 | 0.125 | 0.95 | 0.0 | 0.0 | NA | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:OtherIncome us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | NA | NA | 0.0 | 0.373 | 0.0 | 0.0 | 0.259 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:OtherIncome us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:LoanServicingAndSystemsSegment | NA | NA | 2.524 | 2.353 | 1.914 | 2.63 | 3.094 | 2.291 | 2.277 | 2.074 | 2.088 | 1.948 | 1.956 | 1.292 | 0.0 | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:ProfitLoss | ▄▅█▄▄▁▃▃▃▃▃▃▃▅▃▃▃▃▅▄▃▃▄▃▄▄▄▄▄▄▄▄▅▄▃▃▃▃▄▃▃▃ | 83.013 | 122.904 | 231.606 | 71.176 | 86.61 | -39.765 | 41.834 | 33.135 | 24.678 | 41.647 | 21.674 | 43.126 | 49.539 | 113.185 | 45.714 | 43.535 | 24.651 | 47.92 | 98.931 | 84.363 | 26.178 | 48.029 | 83.518 | 48.977 | 70.963 | 64.806 | 73.919 | 85.376 | 75.687 | 74.299 | 71.088 | 63.046 | 101.857 | 68.35 | 56.653 | 36.952 | 41.53 | 43.293 | 64.879 | 47.451 | 37.125 | 54.88 | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax dei:LegalEntity,us-gaap:MajorCustomers,us-gaap:ConcentrationRiskByType nni:NelnetServicing,nni:DepartmentOfEducation,us-gaap:CustomerConcentrationRisk | █▁ | 35.4 | 34.9 | NA | 36.3 | 37.4 | 38.7 | NA | 38.6 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:CommunicationsServices,nni:CommunicationsSegment | NA | NA | 19.253 | 20.211 | 18.998 | 18.181 | 17.499 | 16.47 | 15.758 | 14.543 | 13.326 | 11.818 | 10.32 | 9.189 | 8.123 | 6.751 | 5.719 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:EducationTechnologyServicesAndPaymentProcessingServices,nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | ▅█▄▅▃▆▄▅▃▆▃▃▂▃▁▂▁ | 76.702 | 95.258 | 65.096 | 74.121 | 59.304 | 83.675 | 63.578 | 74.251 | 60.342 | 79.159 | 54.59 | 58.409 | 48.742 | 60.221 | 43.326 | 50.358 | 43.48 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nni:LoanServicingAndSystems,nni:LoanServicingAndSystemsSegment | █████████████▆▁▁▁ | 112.094 | 111.517 | 113.99 | 113.794 | 111.042 | 112.735 | 113.086 | 113.286 | 113.985 | 114.898 | 112.762 | 112.579 | 114.545 | 100.141 | 55.921 | 55.95 | 56.899 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:MajorCustomers nni:BusinessRevenue | NA | NA | NA | 4.918 | 4.619 | 4.471 | 4.433 | 4.025 | 3.816 | 3.414 | 3.197 | 2.861 | 2.535 | 2.381 | 2.219 | 2.013 | 1.814 | 1.696 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:MajorCustomers nni:CommunicationsRevenueCustomer | NA | NA | NA | 20.211 | 18.998 | 18.181 | 17.499 | 16.47 | 15.758 | 14.543 | 13.326 | 11.818 | 10.32 | 9.189 | 8.123 | 6.751 | 5.719 | 5.106 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:MajorCustomers nni:OtherCustomerRevenue | NA | NA | NA | 0.12 | 0.17 | 0.151 | 0.073 | 0.048 | 0.052 | 0.064 | 0.062 | 0.061 | 0.058 | 0.061 | 0.059 | 0.058 | 0.085 | 0.059 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:MajorCustomers nni:ResidentialRevenue | NA | NA | NA | 15.173 | 14.209 | 13.559 | 12.993 | 12.397 | 11.89 | 11.065 | 10.067 | 8.896 | 7.727 | 6.747 | 5.845 | 4.68 | 3.82 | 3.351 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:CommunicationRevenueServiceOffering | NA | NA | NA | 20.211 | 18.998 | 18.181 | 17.499 | 16.47 | 15.758 | 14.543 | 13.326 | 11.818 | 10.32 | 9.189 | 8.123 | 6.751 | 5.719 | 5.106 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:CommunicationsServices | NA | NA | 19.253 | 20.211 | 18.998 | 18.181 | 17.499 | 16.47 | 15.758 | 14.543 | 13.326 | 11.818 | 10.32 | 9.189 | 8.123 | 6.751 | 5.719 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:EducationTechnologyAndServices | ▆█▃▃▃▄▂▂▃▄▂▂▂▃▁▁▂▃ | 24.733 | 32.322 | 15.065 | 15.84 | 14.927 | 20.054 | 11.706 | 13.067 | 14.096 | 19.709 | 10.744 | 11.419 | 12.018 | 16.975 | 8.735 | 9.831 | 10.825 | 15.147 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:EducationTechnologyServicesAndPaymentProcessingServices | ▅█▄▅▃▆▄▅▃▆▃▃▂▃▁▂▁ | 76.702 | 95.258 | 65.097 | 74.121 | 59.304 | 83.675 | 63.578 | 74.251 | 60.342 | 79.159 | 54.589 | 58.409 | 48.742 | 60.221 | 43.326 | 50.358 | 43.48 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:FFELPServicing | ▂▂▂▃▃▄▄▄▅▅▆▆█▆▁▁▁▂ | 4.703 | 4.67 | 4.74 | 4.912 | 4.917 | 5.614 | 5.835 | 6.089 | 6.424 | 6.695 | 7.283 | 7.422 | 9.147 | 7.691 | 3.849 | 3.979 | 3.636 | 4.077 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:GovernmentServicingGreatLakes | █▇▇██████████▆▁▁▁▁ | 43.863 | 43.302 | 42.862 | 45.35 | 45.213 | 46.446 | 46.371 | 46.234 | 45.973 | 47.077 | 46.191 | 45.671 | 45.682 | 30.754 | 0.0 | 0.0 | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:GovernmentServicingNelnet | ▂▁▁▃▄▆▇▆█▇▆▆▇▇▆▆▇▆ | 35.376 | 34.872 | 34.493 | 36.295 | 37.36 | 38.65 | 39.247 | 38.645 | 40.459 | 39.64 | 39.076 | 38.907 | 39.781 | 39.327 | 38.42 | 38.594 | 39.809 | 39.007 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:Internet | NA | NA | NA | 12.794 | 11.93 | 11.199 | 10.598 | 9.899 | 9.297 | 8.449 | 7.522 | 6.456 | 5.395 | 4.696 | 3.998 | 3.205 | 2.569 | 2.202 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:LoanServicingAndSystems | █████████████▆▁▁▁ | 112.094 | 111.517 | 113.99 | 113.794 | 111.042 | 112.735 | 113.086 | 113.286 | 113.985 | 114.898 | 112.761 | 112.579 | 114.545 | 100.141 | 55.921 | 55.95 | 56.899 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:LoanServicingAndSystemsRevenue | █████████████▆▁▁▁▁ | 112.094 | 111.517 | 113.99 | 113.794 | 111.042 | 112.735 | 113.086 | 113.286 | 113.985 | 114.898 | 112.762 | 112.579 | 114.545 | 100.141 | 55.921 | 55.95 | 56.899 | 54.229 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:OtherCommunicationRevenue | NA | NA | NA | 0.04 | 0.038 | 0.055 | 0.082 | 0.016 | 0.016 | 0.029 | 0.03 | 0.02 | 0.017 | 0.021 | 0.02 | 0.018 | 0.046 | 0.019 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:OtherServiceOffering | █▇█▇▆▆▇▆▆▆▆▆▆▆▄▄▁▄ | 0.423 | 0.348 | 0.393 | 0.384 | 0.262 | 0.292 | 0.359 | 0.286 | 0.28 | 0.298 | 0.293 | 0.263 | 0.281 | 0.277 | 0.1 | 0.101 | -0.101 | 0.145 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:OutsourcedServicesRevenueAndOther | ▅▇█▅▃▂▂▂▂▂▂▂▂▁▁▁▂▁ | 7.962 | 11.671 | 14.532 | 8.883 | 4.705 | 2.098 | 2.049 | 2.264 | 2.123 | 2.265 | 2.26 | 2.371 | 2.382 | 1.679 | 1.438 | 1.351 | 2.007 | 0.991 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:PaymentProcessing | ▅▇▅█▃▇▅█▃▆▃▅▂▃▂▄▁▃ | 25.008 | 33.038 | 25.975 | 35.42 | 21.168 | 31.742 | 25.42 | 35.138 | 21.311 | 28.979 | 21.381 | 26.956 | 16.026 | 19.926 | 16.281 | 22.541 | 13.885 | 18.945 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:PrivateEducationAndConsumerLoanServicing | █▄▃▃▃▄▄▅▄▅▅▅▄█▃▃▂▁ | 12.816 | 8.548 | 7.759 | 7.928 | 8.196 | 8.609 | 8.762 | 9.561 | 8.985 | 9.48 | 9.484 | 10.007 | 8.882 | 13.101 | 7.525 | 7.596 | 7.121 | 5.817 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:SoftwareServices | ▄▅▆▇▇██▇▇▆▅▅▅▄▁▁▁▁ | 7.374 | 8.454 | 9.604 | 10.426 | 10.651 | 11.318 | 10.822 | 10.493 | 10.021 | 9.741 | 8.468 | 8.201 | 8.671 | 7.589 | 4.689 | 4.43 | 4.326 | 4.337 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:Telephone | NA | NA | NA | 2.931 | 2.812 | 2.691 | 2.643 | 2.487 | 2.395 | 2.167 | 2.075 | 1.957 | 1.825 | 1.689 | 1.585 | 1.413 | 1.344 | 1.262 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:Television | NA | NA | NA | 4.446 | 4.218 | 4.236 | 4.176 | 4.068 | 4.05 | 3.898 | 3.699 | 3.385 | 3.083 | 2.783 | 2.52 | 2.115 | 1.76 | 1.623 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService nni:TuitionPaymentPlanServices | ▅▇▄▃▄█▅▅▄▇▃▂▂▄▁▁▂▃ | 26.538 | 29.55 | 23.663 | 22.477 | 22.947 | 31.587 | 26.093 | 25.76 | 24.655 | 30.173 | 22.172 | 19.771 | 20.417 | 23.043 | 18.21 | 17.885 | 18.871 | 21.787 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService us-gaap:AdministrativeService | ▃▄▇▇▃▇█▆▆▆▆▅▅▄▁▁▁ | 0.701 | 1.113 | 2.524 | 2.353 | 0.922 | 2.243 | 2.831 | 2.084 | 2.051 | 1.872 | 1.824 | 1.756 | 1.756 | 1.161 | 0.0 | 0.0 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService us-gaap:InvestmentAdvice | ▂▄▄▆▃▄▁▁▁▁▃▂▂▂▁█▃ | 1.145 | 2.697 | 2.688 | 4.463 | 1.914 | 2.802 | 0.747 | 0.753 | 0.731 | 0.711 | 1.84 | 1.183 | 1.394 | 1.593 | 1.062 | 5.852 | 2.294 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
|---|
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:Assets | ▂▁▁▁▁▂▂▂▃▃▃▃▃▂▂▃▃▄▅▅▆▇▇█▇▇▇▇█▅▅▄▄▄▄▃▃▃▄▄▃ | 23028.863 | 22167.208 | 22646.16 | 22222.526 | 22611.208 | 23280.628 | 23708.97 | 23936.719 | 24219.8 | 24721.927 | 25220.968 | 25104.925 | 25209.244 | 23898.402 | 23964.435 | 24768.71 | 25323.087 | 26141.22 | 27180.108 | 27669.611 | 28715.798 | 29589.347 | 30485.905 | 31045.395 | 30246.823 | 29955.794 | 30098.143 | 30698.649 | 31371.022 | 27487.007 | 27770.849 | 26536.928 | 26303.177 | 26645.224 | 26607.895 | 24408.844 | 25269.142 | 25446.312 | 25852.217 | 26236.227 | 24871.511 | NA | 25893.892 | NA | NA |
| us-gaap:Liabilities | ▂▁▁▁▂▂▂▂▃▃▃▃▃▃▃▃▄▄▅▅▆▇▇█▇▇▇▇█▅▆▅▅▅▅▄▄▄▅▅▄ | 20200.245 | 19418.107 | 20017.811 | 19819.695 | 20270.422 | 20954.828 | 21317.876 | 21582.054 | 21893.182 | 22391.633 | 22906.189 | 22777.797 | 22922.541 | 21653.176 | 21799.048 | 22638.27 | 23192.678 | 24013.553 | 25109.183 | 25688.515 | 26809.582 | 27702.421 | 28593.747 | 29209.996 | 28441.331 | 28174.301 | 28372.465 | 29041.092 | 29790.894 | 25973.333 | 26326.859 | 25159.015 | 24983.582 | 25418.82 | 25442.682 | 23232.606 | 24124.244 | 24338.439 | 24786.012 | 25224.744 | 23882.727 | NA | 24987.259 | NA | NA |
| us-gaap:LiabilitiesAndStockholdersEquity | ▂▁▁▁▁▂▂▂▃▃▃▃▃▂▂▃▃▄▅▅▆▇▇█▇▇▇▇█▅▅▄▄▄▄▃▃▃▄▄▃ | 23028.863 | 22167.208 | 22646.16 | 22222.526 | 22611.208 | 23280.628 | 23708.97 | 23936.719 | 24219.8 | 24721.927 | 25220.968 | 25104.925 | 25209.244 | 23898.402 | 23964.435 | 24768.71 | 25323.087 | 26141.22 | 27180.108 | 27669.611 | 28715.798 | 29589.347 | 30485.905 | 31045.395 | 30246.823 | 29955.794 | 30098.143 | 30698.649 | 31371.022 | 27487.007 | 27770.849 | 26536.928 | 26303.177 | 26645.224 | 26607.895 | 24408.844 | 25269.142 | 25446.312 | 25852.217 | 26236.227 | 24871.511 | NA | 25893.892 | NA | NA |
| us-gaap:StockholdersEquity | ██▇▆▆▆▆▆▆▆▆▆▆▆▅▅▅▅▅▅▄▄▄▄▄▄▄▃▃▃▂▂▂▂▁▁▁▁▁ | 2833.8 | 2752.19 | 2632.042 | 2399.485 | 2336.796 | 2320.68 | 2386.712 | 2350.15 | 2322.326 | 2325.996 | 2304.464 | 2316.864 | 2276.869 | 2235.753 | 2149.529 | 2111.851 | 2115.194 | 2108.187 | 2061.655 | 1972.085 | 1897.3 | 1878.254 | 1884.432 | 1835.153 | 1805.192 | 1781.222 | 1725.448 | 1657.289 | 1579.742 | 1512.919 | 1443.662 | 1377.863 | 1319.482 | 1226.123 | 1165.208 | 1175.821 | 1144.605 | 1107.716 | 1066.205 | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:CashAndCashEquivalentsAtCarryingValue | ▅▄▃▂▂▅▃▄▂▂▃▂▂▂▂▆▂▃▂▂▁▁▂▃▅▂▃▂▂▃▂▁▂▁▂▂▁▁▁▂▃▁▇█▇ | 212.989 | 144.229 | 121.249 | 96.316 | 67.54 | 204.844 | 133.906 | 160.979 | 84.4 | 74.881 | 121.347 | 83.537 | 67.867 | 69.286 | 66.752 | 254.391 | 69.239 | 108.16 | 69.654 | 67.154 | 59.253 | 51.034 | 63.529 | 114.498 | 182.28 | 100.046 | 130.481 | 74.579 | 92.099 | 107.102 | 63.267 | 51.391 | 68.584 | 50.066 | 66.031 | 93.674 | 56.255 | 60.7 | 42.57 | 92.094 | 116.341 | 48.137 | 283.801 | 316.361 | 274.761 |
| us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents | ▅▂▂▁▁▅█▆▄▄▇▃▂▂▂▅▃▃▇ | 1077.373 | 947.191 | 958.395 | 901.541 | 921.315 | 1100.338 | 1222.601 | 1138.207 | 1053.997 | 1051.625 | 1192.391 | 995.466 | 964.353 | 925.272 | 942.066 | 1085.153 | 986.28 | 989.494 | 1170.317 | NA | NA | NA | 1040.924 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:PropertyPlantAndEquipmentGross | ▄ | 311.049 | NA | 283.152 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 130.285 | NA | NA | NA | 109.658 | NA | NA | NA | 102.701 | NA | NA | NA | 111.433 | NA | NA | NA | NA | NA | NA |
| us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment | ▄ | 182.522 | NA | 159.625 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 84.391 | NA | NA | NA | 75.829 | NA | NA | NA | 70.832 | NA | NA | NA | 76.614 | NA | NA | NA | NA | NA | NA |
| us-gaap:AmortizationOfIntangibleAssets | ████▇▇█████▇▇▆▂▂▂▂▃▃▃▃▃▂▂▂▂▂▂▁▁▁▁ | 8.3 | 8.4 | 8.0 | 8.0 | 7.4 | 7.4 | 8.0 | 8.0 | 8.3 | 8.5 | 8.3 | 7.9 | 7.8 | 6.2 | 2.3 | 2.3 | 2.4 | 2.4 | 3.2 | 3.2 | 2.7 | 2.5 | 2.6 | 2.4 | 2.4 | 2.4 | 2.1 | 2.0 | 1.4 | 1.0 | 0.8 | 0.8 | 0.8 | NA | 5.0 | 4.6 | 4.7 | NA | 4.7 | 4.5 | 4.0 | NA | NA | NA | NA |
| us-gaap:PropertyPlantAndEquipmentNet | ▃▃▃██████▇██▇▇▆▅▄▃▃▃▂▂▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ | 128.527 | 130.45 | 123.527 | 360.49 | 350.043 | 351.097 | 348.259 | 342.401 | 337.418 | 335.07 | 344.784 | 339.73 | 328.016 | 299.837 | 248.051 | 208.441 | 181.098 | 143.062 | 123.786 | 107.505 | 96.079 | 88.708 | 80.482 | 46.706 | 48.047 | 51.003 | 45.894 | 44.647 | 35.498 | 33.302 | 33.829 | 33.013 | 34.392 | 31.107 | 31.869 | 32.752 | 33.105 | 34.119 | 34.819 | 33.335 | 34.593 | NA | 30.573 | NA | NA |
| us-gaap:Goodwill | ▅▅▅████████▇▇█▅▆▆▆▆▆▆▆▆▃▃▃▃▃▃▁▁▁▁▁▁▁▁▁▁▁▁ | 142.092 | 142.092 | 142.092 | 156.912 | 156.912 | 156.912 | 156.912 | 156.912 | 156.912 | 156.912 | 156.912 | 153.802 | 153.802 | 158.456 | 138.759 | 147.312 | 147.312 | 147.312 | 147.312 | 147.312 | 147.312 | 147.312 | 146.0 | 126.2 | 126.2 | 126.2 | 126.2 | 126.2 | 126.2 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | 117.118 | NA | 117.118 | NA | NA |
| us-gaap:IntangibleAssetsNetExcludingGoodwill | ▄▅▅▄▅▅▆▆▇▇█▇▇█▃▃▃▄▄▄▄▄▄▃▃▃▃▃▄▁▁▁▁▁▁▂▂▂▂▃▃ | 58.464 | 66.718 | 75.07 | 58.701 | 66.733 | 74.127 | 81.532 | 89.499 | 97.477 | 105.795 | 114.29 | 95.66 | 102.489 | 107.192 | 38.427 | 40.742 | 43.077 | 45.434 | 47.813 | 50.964 | 54.141 | 48.827 | 51.062 | 35.386 | 37.784 | 40.183 | 42.582 | 42.876 | 44.849 | 9.089 | 6.132 | 6.932 | 7.731 | 8.556 | 9.393 | 14.36 | 19.006 | 23.682 | 28.374 | 33.074 | 37.564 | NA | 38.712 | NA | NA |
| us-gaap:FiniteLivedIntangibleAssetsNet | ▃▄▅▃▄▄▅▆▇▇█▆▇▇▁▁▂▂▂▂▃▂▂▁▁▁▂▂▂ | 58.464 | 66.718 | 75.07 | 58.701 | 66.733 | 74.127 | 81.532 | 89.499 | 97.477 | 105.795 | 114.29 | 95.66 | 102.489 | 107.192 | 38.427 | 40.742 | 43.077 | 45.434 | 47.813 | 50.964 | 54.141 | 48.827 | 51.062 | 35.386 | 37.784 | 40.183 | 42.582 | 42.876 | 44.849 | NA | 6.132 | NA | NA | NA | 9.393 | 14.36 | 19.006 | NA | 28.374 | NA | NA | NA | NA | NA | NA |
| us-gaap:OperatingLeaseRightOfUseAsset | NA | NA | 18.301 | NA | NA | NA | 32.77 | 34.264 | 31.822 | 33.928 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:EquitySecuritiesFvNi | █▇▅▃▃▃▁▂▂▂▂ | 69.123 | 59.853 | 42.041 | 30.466 | 29.972 | 26.163 | 12.9 | 17.302 | 18.098 | 18.37 | 17.647 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
|---|
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:LongTermDebt | ▃▁▃▃▅██ | 19381.835 | 18754.715 | 19320.726 | 19215.053 | 19726.158 | 20466.73 | 20529.054 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:DebtAndCapitalLeaseObligations | NA | NA | 19320.726 | NA | NA | NA | 20529.054 | 20910.19 | 21294.192 | 21835.723 | 22218.74 | 22251.433 | 22468.364 | 21227.349 | 21356.573 | 22240.279 | 22790.78 | 23594.516 | 24668.49 | 25320.878 | 26399.686 | 27349.891 | 28172.682 | 28827.603 | 28070.423 | 27815.324 | 28027.35 | 28737.456 | 29492.56 | 25589.287 | 25955.289 | 24858.455 | 24690.952 | 25125.177 | 25098.835 | 22884.096 | 23836.25 | 24060.609 | 24434.54 | 24926.512 | 23605.413 | NA | 24672.472 | NA | NA | |
| us-gaap:MinorityInterest | ▁▂▁▃▄▄▄▄▄▄▅▅▅▅▇█▇█▅▅▅▅▅▃▃▃▃▃▃▃▃▂▃▃▂▃▃▃▂ | -5.182 | -3.089 | -3.693 | 3.346 | 3.99 | 5.12 | 4.382 | 4.515 | 4.292 | 4.298 | 10.315 | 10.264 | 9.834 | 9.473 | 15.858 | 18.589 | 15.215 | 19.48 | 9.27 | 9.011 | 8.916 | 8.672 | 7.726 | 0.246 | 0.3 | 0.271 | 0.23 | 0.268 | 0.386 | 0.755 | 0.328 | 0.05 | 0.113 | 0.281 | 0.005 | 0.417 | 0.293 | 0.157 | 0.0 | NA | NA | NA | NA | NA | NA |
| us-gaap:MinorityInterest us-gaap:ConsolidatedEntities srt:ParentCompany | NA | NA | 0.377 | NA | NA | NA | 5.172 | NA | NA | NA | 4.188 | NA | NA | NA | 4.07 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo | NA | NA | 3.857 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree | NA | NA | 2.938 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour | NA | NA | 1.562 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive | NA | NA | 1.424 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive | NA | NA | 4.437 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:StockholdersEquity | ██▇▆▆▆▆▆▆▆▆▆▆▆▅▅▅▅▅▅▄▄▄▄▄▄▄▃▃▃▂▂▂▂▁▁▁▁▁ | 2833.8 | 2752.19 | 2632.042 | 2399.485 | 2336.796 | 2320.68 | 2386.712 | 2350.15 | 2322.326 | 2325.996 | 2304.464 | 2316.864 | 2276.869 | 2235.753 | 2149.529 | 2111.851 | 2115.194 | 2108.187 | 2061.655 | 1972.085 | 1897.3 | 1878.254 | 1884.432 | 1835.153 | 1805.192 | 1781.222 | 1725.448 | 1657.289 | 1579.742 | 1512.919 | 1443.662 | 1377.863 | 1319.482 | 1226.123 | 1165.208 | 1175.821 | 1144.605 | 1107.716 | 1066.205 | NA | NA | NA | NA | NA | NA |
| us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | ██▇▆▆▆▆▆▆▆▆▆▆▆▆▆▆▆▅▅▅▅▅▄▄▄▄▄▄▃▃▃▃▂▂▂▂▂▂▂▂▁▁▁▁ | 2828.618 | 2749.101 | 2628.349 | 2402.831 | 2340.786 | 2325.8 | 2391.094 | 2354.665 | 2326.618 | 2330.294 | 2314.779 | 2327.128 | 2286.703 | 2245.226 | 2165.387 | 2130.44 | 2130.409 | 2127.667 | 2070.925 | 1981.096 | 1906.216 | 1886.926 | 1892.158 | 1835.399 | 1805.492 | 1781.493 | 1725.678 | 1657.557 | 1580.128 | 1513.674 | 1443.99 | 1377.913 | 1319.595 | 1226.404 | 1165.213 | 1176.238 | 1144.898 | 1107.873 | 1066.205 | 1011.483 | 988.784 | 955.367 | 906.633 | 844.614 | 873.945 |
| us-gaap:CommonStockValue us-gaap:ConsolidatedEntities srt:ParentCompany | NA | NA | 0.384 | NA | NA | NA | 0.398 | NA | NA | NA | 0.403 | NA | NA | NA | 0.408 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:CommonStockValue us-gaap:StatementClassOfStock us-gaap:CommonClassA | ▁▁▁▁▁▂▂▂▂▂▂▂▂▂▂▃▃▃▃▄▄▄▅▅▆▆▆▆▆▇▆▆▇▇▇▇▇▇▇▇█ | 0.275 | 0.274 | 0.272 | 0.272 | 0.272 | 0.286 | 0.285 | 0.284 | 0.284 | 0.286 | 0.288 | 0.293 | 0.293 | 0.293 | 0.293 | 0.294 | 0.304 | 0.307 | 0.306 | 0.308 | 0.31 | 0.31 | 0.325 | 0.334 | 0.337 | 0.347 | 0.348 | 0.348 | 0.349 | 0.35 | 0.349 | 0.349 | 0.35 | 0.35 | 0.351 | 0.358 | 0.358 | 0.358 | 0.356 | 0.36 | 0.37 | NA | 0.368 | NA | NA |
| us-gaap:CommonStockValue us-gaap:StatementClassOfStock us-gaap:CommonClassB | ▁▃▃▃▃▄▄▄▄████████████████████████████████ | 0.111 | 0.112 | 0.112 | 0.112 | 0.112 | 0.113 | 0.113 | 0.113 | 0.113 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | NA | 0.115 | NA | NA |
| us-gaap:AdditionalPaidInCapital | ▂▂▁▁▁▂▂▁▁▁▁▂▁▁▁▁▁▁▁▁▂▁▁▁▁▃▃▃▄▄▄▄▄▅▅███▇█ | 10.158 | 5.859 | 3.794 | 1.704 | 1.867 | 9.14 | 5.715 | 3.678 | 1.67 | 0.636 | 0.622 | 4.908 | 2.586 | 0.448 | 0.521 | 0.36 | 0.366 | 2.236 | 0.42 | 0.224 | 4.601 | 2.913 | 0.0 | 1.441 | 0.0 | 13.177 | 17.29 | 18.15 | 20.721 | 27.138 | 24.887 | 24.068 | 27.004 | 27.786 | 32.54 | 52.843 | 52.194 | 50.948 | 49.245 | 54.685 | NA | NA | 76.263 | NA | NA |
| us-gaap:RetainedEarningsAccumulatedDeficit | ██▇▆▆▆▆▆▆▆▆▆▆▆▅▅▅▅▅▅▅▄▄▄▄▄▄▄▃▃▃▂▂▂▂▂▂▁▁▁ | 2812.315 | 2736.923 | 2621.762 | 2393.113 | 2331.312 | 2310.282 | 2377.627 | 2343.185 | 2317.115 | 2321.407 | 2299.556 | 2307.573 | 2271.171 | 2231.875 | 2143.983 | 2106.895 | 2110.158 | 2100.214 | 2056.084 | 1971.862 | 1894.551 | 1873.5 | 1881.708 | 1830.387 | 1801.457 | 1762.711 | 1702.56 | 1633.577 | 1552.988 | 1482.637 | 1413.492 | 1347.609 | 1289.416 | 1192.822 | 1129.389 | 1124.806 | 1092.715 | 1056.058 | 1017.629 | 957.463 | NA | NA | 831.057 | NA | NA |
| us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax | █▇▅▄▄▃▄▄▄▄▄▄▄▄▅▄▄▅▅▂▁▃▃▄▄▅▅▅▅▄▅▅▄▅▄▁▂▃▂ | 10.941 | 9.022 | 6.102 | 4.284 | 3.233 | 0.859 | 2.972 | 2.89 | 3.144 | 3.552 | 3.883 | 3.975 | 2.704 | 3.022 | 4.617 | 4.187 | 4.251 | 5.315 | 4.73 | -0.424 | -2.277 | 1.416 | 2.284 | 2.876 | 3.283 | 4.872 | 5.135 | 5.099 | 5.569 | 2.679 | 4.819 | 5.722 | 2.597 | 5.05 | 2.813 | -1.933 | -0.409 | 0.605 | 0.0 | NA | NA | NA | NA | NA | NA |
| us-gaap:MinorityInterest | ▁▂▁▃▄▄▄▄▄▄▅▅▅▅▇█▇█▅▅▅▅▅▃▃▃▃▃▃▃▃▂▃▃▂▃▃▃▂ | -5.182 | -3.089 | -3.693 | 3.346 | 3.99 | 5.12 | 4.382 | 4.515 | 4.292 | 4.298 | 10.315 | 10.264 | 9.834 | 9.473 | 15.858 | 18.589 | 15.215 | 19.48 | 9.27 | 9.011 | 8.916 | 8.672 | 7.726 | 0.246 | 0.3 | 0.271 | 0.23 | 0.268 | 0.386 | 0.755 | 0.328 | 0.05 | 0.113 | 0.281 | 0.005 | 0.417 | 0.293 | 0.157 | 0.0 | NA | NA | NA | NA | NA | NA |
| us-gaap:MinorityInterest us-gaap:ConsolidatedEntities srt:ParentCompany | NA | NA | 0.377 | NA | NA | NA | 5.172 | NA | NA | NA | 4.188 | NA | NA | NA | 4.07 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:StockIssuedDuringPeriodValueNewIssues | ▅▆▂▂▅█▂▂▄▇▂▂▅▆▁▁▃▆▁▁▃▇▁▁▃▇▁▁▃▆▁▁▂▄▂▁▃▆▁▁▃█▂▂▂ | 1.824 | 2.091 | 0.473 | 0.553 | 1.66 | 2.941 | 0.45 | 0.524 | 1.384 | 2.494 | 0.509 | 0.58 | 1.911 | 2.173 | 0.26 | 0.278 | 0.992 | 2.09 | 0.275 | 0.282 | 0.954 | 2.708 | 0.182 | 0.268 | 0.945 | 2.468 | 0.213 | 0.213 | 0.883 | 2.246 | 0.146 | 0.264 | 0.695 | 1.273 | 0.368 | 0.271 | 0.852 | 2.426 | 0.266 | 0.315 | 1.028 | 3.089 | 0.388 | 0.602 | 0.702 |
| us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue | █▆▅▅▅▅▅▅▅▄▅▅▄▃▃▃▃▃▂▃▃▃▄▄▄▄▄▄▃▃▂▂▂▂▂▂▂▁▁▁▁▁▁▁▁ | 2.874 | 1.985 | 1.831 | 1.864 | 1.857 | 1.738 | 1.738 | 1.705 | 1.59 | 1.368 | 1.668 | 1.934 | 1.506 | 1.087 | 0.98 | 1.042 | 1.075 | 1.096 | 0.638 | 1.132 | 1.133 | 1.183 | 1.231 | 1.246 | 1.353 | 1.357 | 1.303 | 1.248 | 1.135 | 0.875 | 0.794 | 0.824 | 0.808 | 0.676 | 0.615 | 0.584 | 0.593 | 0.395 | 0.294 | 0.31 | 0.342 | 0.355 | 0.372 | 0.405 | 0.366 |
| us-gaap:MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders | ▄▁█▁▂▁▁▃▁▁▁▁▁▁▂▂▁▁▁▁▁▁▁▁▁▁▃▁▂▁▁▁▁▁▁▁ | 6.727 | 0.102 | 15.203 | 0.331 | 0.534 | 0.055 | 0.125 | 3.865 | 0.091 | 0.022 | 0.174 | 0.095 | 0.238 | 0.019 | 0.371 | 0.759 | 0.205 | 0.31 | 0.353 | 0.0 | 0.122 | 0.097 | 0.356 | -0.08 | -0.044 | 0.0 | 3.594 | -0.275 | 1.062 | -0.287 | -0.29 | -0.279 | -0.782 | 0.0 | -0.431 | 0.0 | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:NetCashProvidedByUsedInOperatingActivities | ▆▄▄█▄▁▆▆▅▁▅▅▄▄▃▅▄▅▄▅▅▅▅▅▄▆▅▅▅▅▆▄▅▅▄▅▄▅▅▄▅▅▆▃ | 138.953 | 48.658 | 39.78 | 278.636 | 38.854 | -144.455 | 155.997 | 160.753 | 121.83 | -139.665 | 77.335 | 121.926 | 13.679 | 57.952 | -2.827 | 98.203 | 58.299 | 73.833 | 66.43 | 83.598 | 70.735 | 104.494 | 84.01 | 115.37 | 62.637 | 129.348 | 94.382 | 106.595 | 67.868 | 88.604 | 184.574 | 49.42 | 68.195 | 84.991 | 38.721 | 99.33 | 60.696 | 100.571 | 98.916 | 43.73 | 86.549 | 81.667 | 179.038 | -45.581 | NA |
| us-gaap:NetCashProvidedByUsedInInvestingActivities | ▃▅▄▅▅▄▅▅▅▅▅▄▂▄▅▅▅▆▅▆▆▅▅▅▅▄▅▅▂▅▅▄▅▄▁▆▄▅▅▅▅▅█▅ | -711.784 | 468.362 | -332.418 | 236.351 | 611.614 | 105.672 | 331.951 | 337.135 | 469.179 | 386.301 | 204.154 | 149.078 | -1187.913 | 102.33 | 747.47 | 698.309 | 772.896 | 1051.415 | 595.461 | 1034.539 | 899.735 | 729.68 | 569.244 | 523.867 | 292.426 | 31.825 | 447.965 | 618.401 | -1516.385 | 340.511 | 402.658 | -180.513 | 408.726 | -134.291 | -2168.141 | 924.171 | 114.481 | 336.835 | 309.583 | 311.452 | 466.336 | 352.452 | 2493.233 | 251.921 | NA |
| us-gaap:NetCashProvidedByUsedInFinancingActivities | ▆▄▅▄▄▅▄▄▄▄▅▅▇▅▄▄▄▃▄▃▄▄▄▄▅▅▄▄▇▄▄▅▄▅█▄▅▄▄▄▄▄▁▅ | 703.044 | -528.147 | 349.492 | -534.761 | -829.491 | -83.48 | -403.554 | -413.678 | -588.637 | -387.402 | -84.564 | -239.891 | 1213.315 | -177.076 | -932.282 | -611.36 | -870.116 | -1086.742 | -659.391 | -1110.236 | -962.251 | -846.669 | -704.223 | -707.019 | -272.829 | -191.608 | -486.445 | -742.516 | 1433.514 | -385.28 | -575.356 | 113.9 | -458.403 | 33.335 | 2101.777 | -986.082 | -179.622 | -419.276 | -458.023 | -379.429 | -484.681 | -669.783 | -2704.831 | -164.74 | NA |
| us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect | ▇▄▅▄▁▂▆▆▄▂█▅▅▄▂▆▄▁ | 130.182 | -11.204 | 56.854 | -19.774 | -179.023 | -122.263 | 84.394 | 84.21 | 2.372 | -140.766 | 196.925 | 31.113 | 39.081 | -16.794 | -143.087 | 98.873 | -3.214 | -180.823 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:DeferredIncomeTaxExpenseBenefit | ▄▆▆▄▅▁▄▅▃▄▃▄▅▆▆▄▂▄█▅▂▄▆▃▄▄▄▆▄▄▃▃▆▅▅▃▂▃▅▃▃▄▅▃ | 2.768 | 15.405 | 18.949 | 3.787 | 11.238 | -26.0 | 2.327 | 5.431 | -12.216 | -2.807 | -12.593 | 2.28 | 4.411 | 16.883 | 13.468 | 0.237 | -13.496 | -1.753 | 34.638 | 12.627 | -16.0 | -4.26 | 14.95 | -11.02 | 2.895 | 0.224 | -1.732 | 15.738 | 3.156 | 2.497 | -10.74 | -7.965 | 16.37 | 4.874 | 5.312 | -8.658 | -13.293 | -7.19 | 8.19 | -7.201 | -8.815 | 0.1 | 8.565 | -11.521 | NA |
| us-gaap:DepreciationDepletionAndAmortization | ▅▅▆▆▆▆▆▆▆▆▆▆▆▆▅▄▄▄▅▃▄▄▄▄▄▄▄▄▃▃▃▂▂▃█▂▁▄▆▂ | 38.339 | 38.415 | 49.298 | 49.893 | 50.519 | 48.763 | 50.143 | 48.398 | 47.173 | 46.948 | 47.866 | 47.591 | 45.924 | 43.301 | 37.997 | 33.021 | 32.495 | 34.31 | 38.559 | 21.69 | 31.22 | 31.078 | 32.691 | 30.854 | 29.966 | 30.225 | 29.651 | 29.112 | 27.207 | 21.999 | 21.154 | 19.17 | 19.081 | 20.079 | 63.104 | 18.153 | 7.452 | 28.072 | 49.01 | 18.621 | NA | NA | NA | NA | NA |
| us-gaap:IncreaseDecreaseInAccountsReceivable | ▅▅▅▄▅▁█▅▄▆▃▆▄▅▄▅▆▅▄▅▄▄▄▅▅▅▄▅▄▅▄▄▄▅▄▅▅▅▅▅▅▅▄█ | 5.615 | 3.831 | 4.595 | -3.867 | 10.577 | -52.185 | 48.312 | 1.665 | -10.599 | 16.571 | -18.387 | 17.728 | -2.223 | -0.177 | -14.61 | 10.382 | 14.302 | 1.972 | -9.436 | 11.444 | -3.501 | -5.961 | -15.149 | 3.747 | 4.925 | 5.416 | -8.574 | 1.189 | -5.063 | 5.758 | -6.879 | -3.065 | -7.223 | 9.601 | -7.761 | 4.398 | 2.786 | 0.561 | 4.76 | 4.782 | 1.3 | 0.198 | -16.099 | 42.063 | NA |
| us-gaap:NetCashProvidedByUsedInOperatingActivities | ▆▄▄█▄▁▆▆▅▁▅▅▄▄▃▅▄▅▄▅▅▅▅▅▄▆▅▅▅▅▆▄▅▅▄▅▄▅▅▄▅▅▆▃ | 138.953 | 48.658 | 39.78 | 278.636 | 38.854 | -144.455 | 155.997 | 160.753 | 121.83 | -139.665 | 77.335 | 121.926 | 13.679 | 57.952 | -2.827 | 98.203 | 58.299 | 73.833 | 66.43 | 83.598 | 70.735 | 104.494 | 84.01 | 115.37 | 62.637 | 129.348 | 94.382 | 106.595 | 67.868 | 88.604 | 184.574 | 49.42 | 68.195 | 84.991 | 38.721 | 99.33 | 60.696 | 100.571 | 98.916 | 43.73 | 86.549 | 81.667 | 179.038 | -45.581 | NA |
| us-gaap:NetIncomeLoss | ▄▅█▄▄▁▃▃▃▃▃▃▃▅▃▃▃▃▅▄▃▃▄▃▄▄▄▄▄▄▄▄▅▄▃▃▃▃▄▃▃▃▄▂▃ | 83.867 | 123.598 | 234.991 | 71.503 | 86.482 | -40.532 | 42.38 | 33.212 | 24.619 | 41.591 | 21.626 | 42.927 | 49.435 | 113.925 | 48.1 | 46.303 | 28.737 | 50.026 | 98.346 | 84.294 | 26.15 | 47.961 | 83.35 | 48.955 | 70.909 | 64.765 | 73.611 | 85.219 | 74.994 | 73.786 | 70.52 | 62.83 | 101.243 | 68.079 | 56.634 | 36.828 | 41.394 | 43.141 | 64.879 | 47.451 | 37.125 | 54.88 | 85.087 | -0.368 | 49.993 |
| us-gaap:ProfitLoss | ▄▅█▄▄▁▃▃▃▃▃▃▃▅▃▃▃▃▅▄▃▃▄▃▄▄▄▄▄▄▄▄▅▄▃▃▃▃▄▃▃▃ | 83.013 | 122.904 | 231.606 | 71.176 | 86.61 | -39.765 | 41.834 | 33.135 | 24.678 | 41.647 | 21.674 | 43.126 | 49.539 | 113.185 | 45.714 | 43.535 | 24.651 | 47.92 | 98.931 | 84.363 | 26.178 | 48.029 | 83.518 | 48.977 | 70.963 | 64.806 | 73.919 | 85.376 | 75.687 | 74.299 | 71.088 | 63.046 | 101.857 | 68.35 | 56.653 | 36.952 | 41.53 | 43.293 | 64.879 | 47.451 | 37.125 | 54.88 | NA | NA | NA |
| us-gaap:ShareBasedCompensation | ▂▂█▂▂▂▂▂▂▁▂▂▂▁▁▁▁▁▁▁▁▁▁ | 2.928 | 2.052 | 11.201 | 1.957 | 1.724 | 1.857 | 1.833 | 1.81 | 1.662 | 1.476 | 1.758 | 2.046 | 1.574 | 1.161 | 1.046 | 1.11 | 1.139 | 1.121 | 0.785 | 1.175 | 1.146 | 1.242 | 1.227 | NA | NA | NA | 1.335 | 1.282 | NA | NA | 0.816 | 0.955 | NA | NA | 0.854 | 0.754 | 0.712 | 0.7 | 0.455 | 0.482 | 0.535 | 0.557 | 0.561 | 0.6 | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:NetCashProvidedByUsedInInvestingActivities | ▃▅▄▅▅▄▅▅▅▅▅▄▂▄▅▅▅▆▅▆▆▅▅▅▅▄▅▅▂▅▅▄▅▄▁▆▄▅▅▅▅▅█▅ | -711.784 | 468.362 | -332.418 | 236.351 | 611.614 | 105.672 | 331.951 | 337.135 | 469.179 | 386.301 | 204.154 | 149.078 | -1187.913 | 102.33 | 747.47 | 698.309 | 772.896 | 1051.415 | 595.461 | 1034.539 | 899.735 | 729.68 | 569.244 | 523.867 | 292.426 | 31.825 | 447.965 | 618.401 | -1516.385 | 340.511 | 402.658 | -180.513 | 408.726 | -134.291 | -2168.141 | 924.171 | 114.481 | 336.835 | 309.583 | 311.452 | 466.336 | 352.452 | 2493.233 | 251.921 | NA |
| us-gaap:PaymentsToAcquirePropertyPlantAndEquipment | ▂▃▆▆▄▅▄▄▄▄▅▅▆▅█▆▇▅▄▃▃▃▁▁▁▂▂▃▂▁▂▁▂▁▁▁▁▁▁▁▂▁▂▁ | 10.886 | 17.898 | 32.614 | 33.704 | 21.433 | 25.561 | 24.818 | 23.966 | 18.902 | 24.813 | 28.543 | 31.471 | 36.941 | 28.068 | 49.349 | 35.842 | 44.345 | 26.469 | 20.781 | 17.244 | 14.319 | 15.258 | 4.005 | 3.237 | 1.147 | 8.372 | 4.797 | 12.669 | 5.876 | 3.146 | 5.29 | 2.162 | 6.78 | 2.778 | 2.574 | 2.965 | 2.099 | 2.306 | 4.391 | 1.495 | 5.289 | 2.992 | 5.274 | 2.826 | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| us-gaap:NetCashProvidedByUsedInFinancingActivities | ▆▄▅▄▄▅▄▄▄▄▅▅▇▅▄▄▄▃▄▃▄▄▄▄▅▅▄▄▇▄▄▅▄▅█▄▅▄▄▄▄▄▁▅ | 703.044 | -528.147 | 349.492 | -534.761 | -829.491 | -83.48 | -403.554 | -413.678 | -588.637 | -387.402 | -84.564 | -239.891 | 1213.315 | -177.076 | -932.282 | -611.36 | -870.116 | -1086.742 | -659.391 | -1110.236 | -962.251 | -846.669 | -704.223 | -707.019 | -272.829 | -191.608 | -486.445 | -742.516 | 1433.514 | -385.28 | -575.356 | 113.9 | -458.403 | 33.335 | 2101.777 | -986.082 | -179.622 | -419.276 | -458.023 | -379.429 | -484.681 | -669.783 | -2704.831 | -164.74 | NA |
| us-gaap:RepaymentsOfLongTermDebt us-gaap:DebtInstrument,us-gaap:SubsequentEventType us-gaap:JuniorSubordinatedDebt,us-gaap:SubsequentEvent | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | |
| us-gaap:PaymentsOfDividendsCommonStock | ███▄▄▅▅▁▁▁ | 8.475 | 8.437 | 8.435 | 7.664 | 7.733 | 7.946 | 7.939 | 7.143 | 7.171 | 7.232 | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA |
| us-gaap:PaymentsForRepurchaseOfCommonStock | ▁▁▁▁█▁▁▁▃▃▄▁▁▂▂▆▃▁▂▂▁▆▄▃▅▂▁▁▂▁▁▁▁▂▃▁▁▁▂▃▁▁▁▄ | 0.399 | 2.009 | 0.213 | 4.618 | 67.274 | 1.253 | 0.149 | 0.221 | 23.683 | 16.358 | 28.811 | 0.192 | 4.91 | 11.418 | 5.565 | 45.136 | 16.826 | 1.369 | 8.948 | 7.675 | 0.399 | 52.069 | 29.526 | 15.615 | 43.089 | 7.939 | 2.376 | 4.033 | 8.435 | 0.869 | 0.121 | 4.026 | 2.285 | 6.704 | 21.293 | 0.206 | 0.199 | 1.116 | 6.004 | 20.595 | 0.225 | 0.31 | 0.133 | 26.614 | NA |
| 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
|---|
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 384000.0 | 398000.0 | 403000.0 | 408000.0 |
| Percentage of CommonStockValue | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets srt:ParentCompany | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 275000.0 | 274000.0 | 272000.0 | 272000.0 | 272000.0 | 286000.0 | 285000.0 | 284000.0 | 284000.0 | 286000.0 | 288000.0 | 293000.0 | 293000.0 | 293000.0 | 293000.0 | 294000.0 | 304000.0 | 307000.0 | 306000.0 | 308000.0 | 310000.0 | 310000.0 | 325000.0 | 334000.0 | 337000.0 | 347000.0 | 348000.0 | 348000.0 | 349000.0 | 350000.0 | 349000.0 | 349000.0 | 350000.0 | 350000.0 | 351000.0 | 358000.0 | 358000.0 | 358000.0 | 356000.0 | 360000.0 | 370000.0 | 368000.0 |
| Percentage of CommonStockValue | 0.0 | 0.0 | 70.8 | 0.0 | 0.0 | 0.0 | 71.6 | 0.0 | 0.0 | 0.0 | 71.5 | 0.0 | 0.0 | 0.0 | 71.8 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassA | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 111000.0 | 112000.0 | 112000.0 | 112000.0 | 112000.0 | 113000.0 | 113000.0 | 113000.0 | 113000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 |
| Percentage of CommonStockValue | 0.0 | 0.0 | 29.2 | 0.0 | 0.0 | 0.0 | 28.4 | 0.0 | 0.0 | 0.0 | 28.5 | 0.0 | 0.0 | 0.0 | 28.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassB | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-06-30 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-09-30 | 2010-06-30 |
| Value | 38 | 39 | 46 | 47 | 47 | 47 | 48 | 48 | 48 | 48 | 49 |
| Percentage of WeightedAverageNumberOfDilutedSharesOutstanding | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 | 2013-03-31 | 2012-03-31 |
| Value | 38 | 38 | 46 | 46 |
| Percentage of WeightedAverageNumberOfDilutedSharesOutstanding | 98.3 | 98.6 | 99.2 | 99.6 |
| Period End | 2021-06-30 | 2020-06-30 | 2013-03-31 | 2012-03-31 |
| Value | 0.641394 | 0.56161 | 0.385707 | 0.308422 |
| Percentage of WeightedAverageNumberOfDilutedSharesOutstanding | 1.7 | 1.4 | 0.8 | 0.7 |
| Period End | 2021-06-30 | 2020-06-30 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-09-30 | 2010-06-30 |
| Value | 38 | 39 | 46 | 47 | 47 | 46 | 48 | 48 | 48 | 48 | 49 |
| Percentage of WeightedAverageNumberOfSharesOutstandingBasic | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 | 2013-03-31 | 2012-03-31 |
| Value | 38 | 38 | 46 | 46 |
| Percentage of WeightedAverageNumberOfSharesOutstandingBasic | 98.3 | 98.6 | 99.2 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 | 2013-03-31 | 2012-03-31 |
| Value | 0.641394 | 0.56161 | 0.385707 | 0.308422 |
| Percentage of WeightedAverageNumberOfSharesOutstandingBasic | 1.7 | 1.4 | 0.8 | 0.7 |
| Period End | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-09-30 | 2012-06-30 |
| Value | 38 | 38 | 39 | 39 | 39 | 40 | 40 | 40 | 40 | 40 | 41 | 42 | 42 | 42 | 42 | 43 | 45 | 45 | 46 | 46 | 46 | 46 | 46 | 46 | 46 | 47 | 47 |
| Percentage of WeightedAverageNumberOfShareOutstandingBasicAndDiluted | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-09-30 | 2012-06-30 |
| Value | 38 | 37 | 38 | 39 | 39 | 39 | 39 | 40 | 40 | 40 | 41 | 41 | 41 | 42 | 42 | 42 | 44 | 45 | 45 | 45 | 46 | 46 | 46 | 46 | 46 | 47 | 47 |
| Percentage of WeightedAverageNumberOfShareOutstandingBasicAndDiluted | 98.5 | 98.6 | 98.6 | 98.6 | 98.7 | 98.7 | 98.7 | 98.7 | 98.8 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 98.9 | 98.9 | 98.9 | 98.9 | 99.0 | 99.0 | 99.1 | 99.1 | 99.1 | 99.2 | 99.2 | 99.2 |
| Period End | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-09-30 | 2012-06-30 |
| Value | 0.572288 | 0.549892 | 0.56161 | 0.55006 | 0.520818 | 0.531413 | 0.518173 | 0.547182 | 0.475258 | 0.408658 | 0.406892 | 0.41255 | 0.440793 | 0.442633 | 0.441931 | 0.457286 | 0.477258 | 0.494527 | 0.490717 | 0.484425 | 0.453508 | 0.416965 | 0.409869 | 0.416282 | 0.385707 | 0.374126 | 0.38586 |
| Percentage of WeightedAverageNumberOfShareOutstandingBasicAndDiluted | 1.5 | 1.4 | 1.4 | 1.4 | 1.3 | 1.3 | 1.3 | 1.3 | 1.2 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.1 | 1.1 | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 | 0.9 | 0.9 | 0.8 | 0.8 | 0.8 |
| Period End | 2021-06-30 | 2020-06-30 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 2.16 | 2.21 | 1.2 | 0.78 | 0.87 | 0.91 | 1.37 | 0.98 | 0.76 | 1.13 | 1.73 | -0.01 | 1.0 |
| Percentage of EarningsPerShareBasic | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 2.16 | 2.21 |
| Percentage of EarningsPerShareBasic | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 2.16 | 2.21 |
| Percentage of EarningsPerShareBasic | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 2.16 | 2.21 | 1.19 | 0.77 | 0.87 | 0.91 | 1.37 | 0.98 | 0.76 | 1.13 | 1.73 | -0.01 | 0.99 |
| Percentage of EarningsPerShareDiluted | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 2.16 | 2.21 |
| Percentage of EarningsPerShareDiluted | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 2.16 | 2.21 |
| Percentage of EarningsPerShareDiluted | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 3.2 | 6.1 | 1.86 | 2.21 | -1.01 | 1.06 | 0.83 | 0.61 | 1.03 | 0.53 | 1.05 | 1.21 | 2.78 | 1.17 | 1.11 | 0.68 | 1.18 | 2.32 | 1.98 | 0.61 | 1.11 | 1.86 | 1.09 | 1.54 | 1.4 | 1.59 | 1.84 | 1.61 | 1.59 | 1.52 | 1.35 | 2.17 | 1.46 | 1.2 | 0.78 | 0.87 | 0.91 |
| Percentage of EarningsPerShareBasicAndDiluted | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 3.2 | 6.03 | 1.86 | 2.21 | -1.01 | 1.06 | 0.83 | 0.61 | 1.03 | 0.53 | 1.05 | 1.21 | 2.78 | 1.17 | 1.11 | 0.68 | 1.18 | 2.32 | 1.98 | 0.61 | 1.11 | 1.86 | 1.09 | 1.54 | 1.4 | 1.59 | 1.84 | 1.61 | 1.59 | 1.52 | 1.35 | 2.17 | 1.46 | 1.2 | 0.78 | 0.87 | 0.91 |
| Percentage of EarningsPerShareBasicAndDiluted | 100.0 | 98.9 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 3.2 | 6.03 | 1.86 | 2.21 | -1.01 | 1.06 | 0.83 | 0.61 | 1.03 | 0.53 | 1.05 | 1.21 | 2.78 | 1.17 | 1.11 | 0.68 | 1.18 | 2.32 | 1.98 | 0.61 | 1.11 | 1.86 | 1.09 | 1.54 | 1.4 | 1.59 | 1.84 | 1.61 | 1.59 | 1.52 | 1.35 | 2.17 | 1.46 | 1.2 | 0.78 | 0.87 | 0.91 |
| Percentage of EarningsPerShareBasicAndDiluted | 100.0 | 98.9 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | 85 | 126 | 236 | 72 | 88 | -42.645 | 42 | 32 | 24 | 41 | 21 | 44 | 49 | 113 | 48 | 46 | 27 | 50 | 103 | 86 | 22 | 47 | 82 | 48 | 69 | 64 | 73 | 84 | 77 | 71 | 69 | 65 | 98 | 70 | 61 | 35 | 40 | 43 | 64 | 47 | 37 | 54 |
| Percentage of ComprehensiveIncomeNetOfTax | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 64.2 | 98.0 | 170.6 | 51.9 | 58.5 | -22.5 | 20.0 | 13.8 | 9.8 | 16.5 | 8.5 | 18.4 | 21.4 | 55.7 | 24.7 | 23.5 | 14.3 | 27.5 | 55.6 | 43.9 | 12.1 | 24.5 | 42.9 | 25.7 | 39.0 | 37.0 | 39.9 | 44.7 | 44.0 | 45.1 | 41.5 | 41.2 | 61.9 | 44.7 | 39.3 | 23.3 | 26.6 | 28.4 | 41.2 | 30.1 | 26.6 | 39.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | -854000.0 | -694000.0 | -3385000.0 | -327000.0 | 128000.0 | 767000.0 | -547000.0 | -77000.0 | 59000.0 | 56000.0 | 49000.0 | 199000.0 | 104000.0 | -740000.0 | -2385000.0 | -2768000.0 | -4086000.0 | -2106000.0 | 585000.0 | 69000.0 | 28000.0 | 68000.0 | 168000.0 | 22000.0 | 54000.0 | 41000.0 | 157000.0 | 693000.0 | 513000.0 | 216000.0 | 614000.0 | 271000.0 | 19000.0 | 124000.0 | 136000.0 | 152000.0 | 0 | 0 | 0 | 0 |
| Percentage of ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | -0.5 | -2.4 | -0.2 | 0.1 | 0.4 | -0.3 | -0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | -0.4 | -1.2 | -1.4 | -2.1 | -1.1 | 0.3 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.1 | 0.4 | 0.3 | 0.1 | 0.4 | 0.2 | 0.0 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | 84 | 125 | 233 | 72 | 88 | -41.878 | 41 | 32 | 24 | 41 | 21 | 44 | 49 | 112 | 46 | 43 | 23 | 48 | 104 | 86 | 22 | 47 | 82 | 48 | 69 | 64 | 73 | 84 | 78 | 72 | 70 | 66 | 99 | 70 | 61 | 35 | 40 | 43 | 64 | 47 | 37 | 54 |
| Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 63.6 | 97.5 | 168.1 | 51.7 | 58.6 | -22.1 | 19.7 | 13.8 | 9.8 | 16.5 | 8.6 | 18.5 | 21.5 | 55.4 | 23.5 | 22.1 | 12.2 | 26.4 | 55.9 | 43.9 | 12.1 | 24.6 | 42.9 | 25.7 | 39.0 | 37.1 | 40.1 | 44.8 | 44.4 | 45.4 | 41.8 | 41.3 | 62.3 | 44.9 | 39.4 | 23.4 | 26.6 | 28.5 | 41.2 | 30.1 | 26.6 | 39.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 21 | 27 | 24 | 31 | 21 | 28 | 24 | 30 | 20 | 25 | 20 | 23 | 15 | 17 | 14 | 17 | 11 |
| Percentage of CostOfGoodsAndServicesSold | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 16.2 | 21.0 | 17.5 | 22.3 | 13.9 | 15.0 | 11.5 | 12.9 | 8.5 | 10.3 | 8.1 | 9.8 | 6.6 | 8.6 | 7.3 | 9.0 | 6.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 5.572 | 5.914 | 5.743 | 5.582 | 5.327 | 5.236 | 5.101 | 4.759 | 5.034 | 4.31 | 3.865 | 3.717 | 3.161 | 2.632 | 2.203 |
| Percentage of CostOfGoodsAndServicesSold | 22.9 | 19.0 | 27.2 | 19.7 | 21.9 | 16.9 | 24.3 | 18.4 | 24.5 | 18.4 | 25.5 | 21.4 | 22.0 | 14.8 | 18.8 |
| Percentage of InterestAndDividendIncomeOperating | 4.0 | 4.2 | 3.8 | 3.0 | 2.5 | 2.2 | 2.1 | 1.9 | 2.0 | 1.8 | 1.7 | 1.8 | 1.6 | 1.3 | 1.1 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsServices nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 21 | 27 | 18 | 25 | 15 | 22 | 19 | 25 | 15 | 21 | 15 | 19 | 11 | 13 | 11 | 15 | 9.515 |
| Percentage of CostOfGoodsAndServicesSold | 100.0 | 100.0 | 77.1 | 81.0 | 72.8 | 80.3 | 78.1 | 83.1 | 75.7 | 81.6 | 75.5 | 81.6 | 74.5 | 78.6 | 78.0 | 85.2 | 81.2 |
| Percentage of InterestAndDividendIncomeOperating | 16.2 | 21.0 | 13.5 | 18.1 | 10.1 | 12.1 | 8.9 | 10.7 | 6.4 | 8.4 | 6.1 | 8.0 | 4.9 | 6.7 | 5.7 | 7.7 | 4.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServices nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 5.572 | 5.914 | 5.743 | 5.582 | 5.327 | 5.236 | 5.101 | 4.759 | 5.034 | 4.31 | 3.865 | 3.717 | 3.161 | 2.632 | 2.203 |
| Percentage of CostOfGoodsAndServicesSold | 22.9 | 19.0 | 27.2 | 19.7 | 21.9 | 16.9 | 24.3 | 18.4 | 24.5 | 18.4 | 25.5 | 21.4 | 22.0 | 14.8 | 18.8 |
| Percentage of InterestAndDividendIncomeOperating | 4.0 | 4.2 | 3.8 | 3.0 | 2.5 | 2.2 | 2.1 | 1.9 | 2.0 | 1.8 | 1.7 | 1.8 | 1.6 | 1.3 | 1.1 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 510100.0 | 237950.0 | 0.0 | 431000.0 | 386500.0 | 371700.0 | 0.0 | 263200.0 | 220300.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 21 | 27 | 18 | 25 | 15 | 22 | 19 | 25 | 15 | 21 | 15 | 19 | 11 | 13 | 11 | 15 | 9.515 |
| Percentage of CostOfGoodsAndServicesSold | 100.0 | 100.0 | 77.1 | 81.0 | 72.8 | 80.3 | 78.1 | 83.1 | 75.7 | 81.6 | 75.5 | 81.6 | 74.5 | 78.6 | 78.0 | 85.2 | 81.2 |
| Percentage of InterestAndDividendIncomeOperating | 16.2 | 21.0 | 13.5 | 18.1 | 10.1 | 12.1 | 8.9 | 10.7 | 6.4 | 8.4 | 6.1 | 8.0 | 4.9 | 6.7 | 5.7 | 7.7 | 4.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 10321.9 | 10285.9 | 0.0 | 6878.2 | 3661.0 | 1145.5 | 0.0 | 733.7 | 956.7 | 1044.1 | 0.0 | 1261.5 | 1513.0 | 2057.6 | 0.0 | 303020.0 | 317166.7 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 5.573 | 5.914 | 5.743 | 5.582 | 5.327 | 5.236 | 5.101 | 4.759 | 5.033 | 4.31 | 3.865 | 3.717 | 3.161 | 2.632 | 2.203 |
| Percentage of CostOfGoodsAndServicesSold | 22.9 | 19.0 | 27.2 | 19.7 | 21.9 | 16.9 | 24.3 | 18.4 | 24.5 | 18.4 | 25.5 | 21.4 | 22.0 | 14.8 | 18.8 |
| Percentage of InterestAndDividendIncomeOperating | 4.0 | 4.2 | 3.8 | 3.0 | 2.5 | 2.2 | 2.1 | 1.9 | 2.0 | 1.8 | 1.7 | 1.8 | 1.6 | 1.3 | 1.1 |
| Percentage of InterestAndDividendIncomeOperating nni:CommunicationsServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 21 | 27 | 18 | 25 | 15 | 22 | 19 | 25 | 15 | 21 | 15 | 19 | 11 | 13 | 11 | 15 | 9.515 |
| Percentage of CostOfGoodsAndServicesSold | 100.0 | 100.0 | 77.1 | 81.0 | 72.8 | 80.3 | 78.1 | 83.1 | 75.7 | 81.6 | 75.5 | 81.6 | 74.5 | 78.6 | 78.0 | 85.2 | 81.2 |
| Percentage of InterestAndDividendIncomeOperating | 16.2 | 21.0 | 13.5 | 18.1 | 10.1 | 12.1 | 8.9 | 10.7 | 6.4 | 8.4 | 6.1 | 8.0 | 4.9 | 6.7 | 5.7 | 7.7 | 4.9 |
| Percentage of InterestAndDividendIncomeOperating nni:EducationTechnologyServicesAndPaymentProcessingServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2012-12-31 | 2012-09-30 | 2011-12-31 | 2011-09-30 |
| Value | 15 | 8.498 | 11 | -10.152 | 53 | -1.025 | 1.948 | 4.258 | 0.994 | 4.254 | 6.939 | -4.084 |
| Percentage of GainLossOnInvestments | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 11.7 | 6.6 | 8.6 | -7.3 | 35.0 | -0.5 | 0.8 | 1.7 | 0.6 | 2.8 | 4.4 | -2.6 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 1.094 | -22.219 |
| Percentage of GainLossOnInvestments | 7.0 | -261.5 |
| Percentage of InterestAndDividendIncomeOperating | 0.8 | -17.2 |
| Percentage of InterestAndDividendIncomeOperating nni:ALLOVotingMembershipInterestsInvestment | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-06-30 | 2020-03-31 |
| Value | -2.302 | -1.679 | 2.04 | -2.839 |
| Percentage of GainLossOnInvestments | -14.8 | -19.8 | 3.8 | 277.0 |
| Percentage of InterestAndDividendIncomeOperating | -1.7 | -1.3 | 1.3 | -1.5 |
| Percentage of InterestAndDividendIncomeOperating nni:SolarInvestment | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2019-12-31 | 2019-09-30 | 2018-12-31 | 2018-09-30 |
| Value | 1416000.0 | 105000.0 | -874000.0 | -14014000.0 | 0 | 0 |
| Percentage of GainsLossesOnExtinguishmentOfDebt | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 1.0 | 0.1 | -0.4 | -5.9 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 |
| Value | 109 | 157 | 302 | 90 | 107 | -49.898 | 50 | 41 | 30 | 53 | 17 | 57 | 63 | 149 | 40 | 69 | 40 | 76 | 153 | 132 | 41 | 72 | 130 | 75 | 111 | 102 | 131 | 118 | 114 | 93 | 156 | 106 | 58 | 56 | 66 | 71 | 58 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 81.8 | 122.2 | 217.6 | 64.6 | 71.0 | -26.4 | 23.9 | 17.6 | 12.5 | 21.2 | 6.8 | 23.8 | 27.5 | 73.5 | 20.5 | 35.1 | 21.1 | 41.7 | 82.2 | 67.3 | 22.1 | 37.7 | 67.8 | 40.2 | 62.6 | 58.8 | 69.6 | 67.1 | 72.3 | 58.3 | 98.2 | 68.0 | 38.8 | 37.1 | 43.2 | 45.6 | 41.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -2.142 | -29.65 | 210 | -23.426 | 37 | -22.646 | -13.637 | -11.216 | -8.822 | -14.073 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | -2.0 | -18.8 | 69.6 | -25.9 | 34.5 | 45.4 | -26.8 | -26.7 | -28.6 | -26.5 |
| Percentage of InterestAndDividendIncomeOperating | -1.6 | -23.0 | 151.5 | -16.8 | 24.5 | -12.0 | -6.4 | -4.7 | -3.6 | -5.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -140.6 | -2379.6 | 0.0 | -1423.2 | 3113.9 | -1456.3 | 0.0 | -392.3 | -390.7 | -685.5 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 78 | 141 | 82 | 89 | 51 | -60.945 | 50 | 25 | 12 | 26 | 18 | 51 | 56 | 115 | 60 | 57 | 34 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | 72.2 | 89.8 | 27.2 | 99.5 | 47.6 | 122.1 | 99.8 | 61.2 | 41.5 | 50.1 | 107.3 | 90.5 | 89.1 | 77.6 | 150.2 | 83.4 | 84.5 |
| Percentage of InterestAndDividendIncomeOperating | 59.1 | 109.7 | 59.3 | 64.3 | 33.8 | -32.2 | 23.9 | 10.7 | 5.2 | 10.6 | 7.3 | 21.5 | 24.5 | 57.0 | 30.7 | 29.3 | 17.8 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 60.7 | 112.0 | 0.0 | 65.2 | 34.1 | -32.8 | 0.0 | 11.0 | 5.3 | 10.8 | 0.0 | 21.9 | 24.8 | 57.8 | 0.0 | 29.6 | 18.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -14.31 | -4.539 | -7.057 | -7.284 | -8.66 | -9.466 | -6.49 | -6.329 | -7.734 | -10.185 | -10.634 | -9.263 | -8.791 | -7.423 | -5.866 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | -4.7 | -5.0 | -6.5 | 14.6 | -17.0 | -22.6 | -21.0 | -11.9 | -45.3 | -17.9 | -16.9 | -6.2 | -21.9 | -10.7 | -14.4 |
| Percentage of InterestAndDividendIncomeOperating | -10.3 | -3.2 | -4.6 | -3.9 | -4.1 | -4.0 | -2.6 | -2.5 | -3.1 | -4.2 | -4.6 | -4.6 | -4.5 | -3.8 | -3.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -649000.0 | -316450.0 | 0.0 | -1018500.0 | -1063400.0 | -926300.0 | 0.0 | -742300.0 | -586600.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 17 | 30 | 12 | 15 | 11 | 27 | 9.542 | 16 | 11 | 24 | -1.557 | 9.988 | 7.421 | 17 | 3.865 | 9.264 | 7.991 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | 15.8 | 19.6 | 4.0 | 16.7 | 10.8 | -54.8 | 18.8 | 39.9 | 35.7 | 47.1 | -9.1 | 17.5 | 11.8 | 11.8 | 9.6 | 13.4 | 19.6 |
| Percentage of InterestAndDividendIncomeOperating | 12.9 | 24.0 | 8.7 | 10.8 | 7.7 | 14.5 | 4.5 | 7.0 | 4.5 | 10.0 | -0.6 | 4.2 | 3.2 | 8.7 | 2.0 | 4.7 | 4.1 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 8205.7 | 11777.2 | 0.0 | 4098.9 | 2783.6 | 1373.8 | 0.0 | 478.0 | 664.2 | 1238.5 | 0.0 | 660.1 | 992.1 | 2647.2 | 0.0 | 185280.0 | 266366.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 15 | 16 | 11 | 13 | 14 | 13 | 12 | 20 | 22 | 21 | 18 | 13 | 17 | 20 | 7.193 | 9.585 | 8.716 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | 14.2 | 10.2 | 3.9 | 14.8 | 13.5 | -27.3 | 25.3 | 48.3 | 72.4 | 41.3 | 111.1 | 23.0 | 28.0 | 13.4 | 17.9 | 13.9 | 21.4 |
| Percentage of InterestAndDividendIncomeOperating | 11.6 | 12.5 | 8.5 | 9.5 | 9.6 | 7.2 | 6.0 | 8.5 | 9.1 | 8.7 | 7.5 | 5.5 | 7.7 | 9.9 | 3.7 | 4.9 | 4.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 51710.0 | 47305.9 | 0.0 | 39235.3 | 28073.1 | 4297.5 | 0.0 | 3807.1 | 4068.0 | 4408.2 | 0.0 | 3447.2 | 6035.5 | 7796.1 | 0.0 | 6520.4 | 7263.3 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -0.268 | -1.254 |
| Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest | -0.2 | -0.8 |
| Percentage of InterestAndDividendIncomeOperating | -0.2 | -1.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | -13.1 | -91.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 26 | 34 | 70 | 19 | 21 | -10.133 | 9.022 | 8.829 | 6.209 | 11 | -4.599 | 13 | 13 | 35 | -5.486 | 25 | 16 | 28 | 54 | 47 | 15 | 24 | 47 | 26 | 40 | 37 | 30 | 46 | 43 | 40 | -37.556 | 30 | 54 | 38 | -36.099 | 21 | 14 | 23 | -39.008 | 24 | 21 | 32 | 51 | -0.226 | 29 |
| Percentage of IncomeTaxExpenseBenefit | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 19.6 | 27.0 | 50.8 | 13.7 | 14.0 | -5.4 | 4.2 | 3.7 | 2.5 | 4.5 | -1.8 | 5.8 | 5.9 | 17.7 | -2.8 | 13.0 | 8.3 | 15.6 | 29.1 | 24.3 | 8.1 | 12.7 | 24.5 | 14.3 | 22.7 | 21.6 | 16.3 | 24.6 | 24.3 | 25.6 | -22.4 | 19.0 | 34.3 | 24.5 | -23.1 | 14.4 | 9.8 | 15.1 | -24.8 | 15.5 | 15.1 | 23.8 | 33.8 | -0.1 | 19.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -0.497 | -10.133 | 48 | -8.146 | 4.312 | -3.592 | -6.457 | -3.935 | -3.321 | -4.716 |
| Percentage of IncomeTaxExpenseBenefit | -1.9 | -29.1 | 68.8 | -42.5 | 20.3 | 35.4 | -71.6 | -44.6 | -53.5 | -41.4 |
| Percentage of InterestAndDividendIncomeOperating | -0.4 | -7.8 | 35.0 | -5.8 | 2.8 | -1.9 | -3.0 | -1.6 | -1.3 | -1.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -32.6 | -813.2 | 0.0 | -494.9 | 360.5 | -231.0 | 0.0 | -137.6 | -147.1 | -229.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 18 | 33 | 19 | 21 | 12 | -14.627 | 12 | 6.16 | 3.074 | 6.372 | 4.397 | 12 | 13 | 27 | 22 | 21 | 13 |
| Percentage of IncomeTaxExpenseBenefit | 72.2 | 97.5 | 28.0 | 112.7 | 58.0 | 144.4 | 135.1 | 69.8 | 49.5 | 55.9 | -95.6 | 89.2 | 99.8 | 77.2 | -418.4 | 85.7 | 81.4 |
| Percentage of InterestAndDividendIncomeOperating | 14.2 | 26.3 | 14.2 | 15.4 | 8.1 | -7.7 | 5.7 | 2.6 | 1.2 | 2.5 | 1.7 | 5.2 | 5.9 | 13.7 | 11.7 | 11.1 | 6.8 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 14.6 | 26.9 | 0.0 | 15.6 | 8.2 | -7.9 | 0.0 | 2.6 | 1.3 | 2.6 | 0.0 | 5.2 | 6.0 | 13.9 | 0.0 | 11.2 | 6.8 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -3.434 | -1.089 | -1.694 | -1.748 | -2.078 | -2.272 | -1.558 | -1.519 | -1.855 | -2.444 | -2.552 | -2.223 | -3.341 | -2.821 | -2.229 |
| Percentage of IncomeTaxExpenseBenefit | -4.9 | -5.7 | -8.0 | 17.3 | -23.0 | -25.7 | -25.1 | -13.3 | 40.3 | -17.6 | -18.9 | -6.2 | 60.9 | -11.0 | -13.9 |
| Percentage of InterestAndDividendIncomeOperating | -2.5 | -0.8 | -1.1 | -0.9 | -1.0 | -1.0 | -0.6 | -0.6 | -0.7 | -1.0 | -1.1 | -1.1 | -1.7 | -1.4 | -1.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -155800.0 | -75950.0 | 0.0 | -244400.0 | -255200.0 | -222300.0 | 0.0 | -282100.0 | -222900.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 4.136 | 7.434 | 2.907 | 3.61 | 2.806 | 6.565 | 2.29 | 4.014 | 2.645 | 5.995 | -0.374 | 2.397 | 1.781 | 4.225 | 1.468 | 3.52 | 3.037 |
| Percentage of IncomeTaxExpenseBenefit | 15.8 | 21.3 | 4.1 | 18.8 | 13.2 | -64.8 | 25.4 | 45.5 | 42.6 | 52.6 | 8.1 | 17.3 | 13.2 | 11.7 | -26.8 | 13.8 | 18.9 |
| Percentage of InterestAndDividendIncomeOperating | 3.1 | 5.8 | 2.1 | 2.6 | 1.8 | 3.5 | 1.1 | 1.7 | 1.1 | 2.4 | -0.1 | 1.0 | 0.8 | 2.1 | 0.7 | 1.8 | 1.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 1969.5 | 2826.6 | 0.0 | 983.7 | 668.1 | 329.7 | 0.0 | 114.7 | 159.4 | 297.2 | 0.0 | 158.4 | 238.1 | 635.3 | 0.0 | 70400.0 | 101233.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 3.723 | 3.86 | 2.836 | 3.201 | 3.504 | 3.269 | 3.082 | 4.861 | 5.37 | 5.258 | 4.555 | 3.152 | 4.245 | 5.003 | 3.718 | 4.937 | 4.918 |
| Percentage of IncomeTaxExpenseBenefit | 14.2 | 11.1 | 4.0 | 16.7 | 16.5 | -32.3 | 34.2 | 55.1 | 86.5 | 46.2 | -99.0 | 22.7 | 31.4 | 13.9 | -67.8 | 19.3 | 30.7 |
| Percentage of InterestAndDividendIncomeOperating | 2.8 | 3.0 | 2.0 | 2.3 | 2.3 | 1.7 | 1.5 | 2.0 | 2.2 | 2.1 | 1.8 | 1.3 | 1.9 | 2.5 | 1.9 | 2.5 | 2.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 12410.0 | 11352.9 | 0.0 | 9414.7 | 6738.5 | 1031.2 | 0.0 | 913.7 | 976.4 | 1057.9 | 0.0 | 827.3 | 1448.8 | 1946.7 | 0.0 | 3358.5 | 4098.3 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -0.064 | -0.286 |
| Percentage of IncomeTaxExpenseBenefit | -0.2 | -0.8 |
| Percentage of InterestAndDividendIncomeOperating | -0.0 | -0.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | -3.1 | -20.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 14 | 0.199 | 16 | 5.464 | 7.869 | 0.08 | 2.852 | 3.291 | 11 | -0.009 | 6.964 | 0.799 | 23 | -30.569 | 25 | 25 | 45 | 1.18 | 27 | 31 | 54 | 1.323 | 42 | 37 | 67 | 0.045 | 36 | 35 | 70 | 13 | 40 | 44 | 64 | 5.489 | 27 | 29 | 54 | 2.92 | 35 | 34 | 31 | 32 | 28 | 25 |
| Percentage of IncomeTaxesPaidNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 10.5 | 0.2 | 11.7 | 3.9 | 5.2 | 0.0 | 1.3 | 1.4 | 4.7 | -0.0 | 2.8 | 0.3 | 10.2 | -15.1 | 12.9 | 12.8 | 23.3 | 0.6 | 14.9 | 16.1 | 29.4 | 0.7 | 22.2 | 19.7 | 37.8 | 0.0 | 20.0 | 18.6 | 39.7 | 8.4 | 23.9 | 28.0 | 40.4 | 3.5 | 17.9 | 19.6 | 35.6 | 1.9 | 22.6 | 21.8 | 22.2 | 23.4 | 18.7 | 16.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 49 | 27 | 52 | 58 | 85 | 134 | 148 | 172 | 186 | 191 | 182 | 180 | 171 | 135 | 123 | 121 | 113 | 106 | 107 | 96 | 94 | 90 | 80 | 77 | 72 | 71 | 72 | 71 | 69 | 60 | 59 | 55 | 58 | 58 | 65 | 66 | 67 | 69 | 64 | 60 | 51 | 52 | 54 | 68 | 59 |
| Percentage of InterestExpense | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 37.4 | 21.5 | 37.7 | 41.8 | 56.1 | 70.9 | 69.7 | 72.2 | 75.8 | 76.5 | 72.4 | 75.1 | 74.8 | 66.8 | 62.8 | 61.8 | 58.6 | 58.2 | 57.6 | 49.1 | 50.5 | 47.1 | 41.9 | 40.8 | 40.9 | 41.1 | 39.0 | 38.0 | 39.1 | 37.8 | 35.2 | 34.5 | 36.4 | 37.1 | 41.9 | 43.8 | 44.4 | 45.0 | 40.7 | 38.6 | 36.5 | 37.9 | 36.1 | 42.5 | 37.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 1.093 | 0.824 | -0.195 | 0.888 | 1.078 | 1.407 | -0.209 | 2.11 | 3.872 | 3.814 |
| Percentage of InterestExpense | 2.2 | 3.0 | -0.4 | 1.5 | 1.3 | 1.0 | -0.1 | 1.2 | 2.1 | 2.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.8 | 0.6 | -0.1 | 0.6 | 0.7 | 0.7 | -0.1 | 0.9 | 1.6 | 1.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | 71.7 | 66.1 | 0.0 | 53.9 | 90.1 | 90.5 | 0.0 | 73.8 | 171.5 | 185.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | -0.187 | -0.218 | -0.252 | -0.261 | -0.368 | -0.598 | -0.801 | -1.171 | -0.974 | -0.851 | -0.569 | -4.846 | -4.425 | -3.15 | -2.702 | -2.139 | -1.776 | -1.359 | -2.52 | -0.93 |
| Percentage of InterestExpense | -0.4 | -0.8 | -0.5 | -0.4 | -0.4 | -0.4 | -0.5 | -0.7 | -0.5 | -0.4 | -0.3 | -2.7 | -2.6 | -2.3 | -2.2 | -1.8 | -1.6 | -1.3 | -2.3 | -1.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.1 | -0.2 | -0.2 | -0.2 | -0.2 | -0.3 | -0.4 | -0.5 | -0.4 | -0.3 | -0.2 | -2.0 | -1.9 | -1.6 | -1.4 | -1.1 | -0.9 | -0.7 | -1.4 | -0.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:IntersegmentElimination | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 48 | 26 | 52 | 57 | 84 | 133 | 149 | 171 | 184 | 188 | 181 | 176 | 169 | 134 | 123 | 121 | 113 |
| Percentage of InterestExpense | 97.4 | 97.0 | 100.7 | 98.9 | 99.1 | 99.4 | 100.6 | 99.4 | 98.4 | 98.5 | 99.4 | 98.2 | 98.9 | 99.0 | 100.0 | 99.5 | 99.9 |
| Percentage of InterestAndDividendIncomeOperating | 36.4 | 20.9 | 37.9 | 41.3 | 55.6 | 70.4 | 70.2 | 71.8 | 74.6 | 75.3 | 72.0 | 73.7 | 74.0 | 66.2 | 62.7 | 61.5 | 58.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 37.4 | 21.3 | 0.0 | 41.9 | 56.1 | 71.7 | 0.0 | 73.5 | 75.6 | 76.5 | 0.0 | 74.9 | 74.9 | 67.0 | 0.0 | 62.1 | 59.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.0 | 0.016 | 0.021 | 0.017 | 0.014 | 0.012 | 0.011 | 0.008 | 0.006 | 0.003 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestExpense | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 0.0 | 4.4 | 5.0 | 0.9 | 0.0 | 0.3 | 0.7 | 0.4 | 0.0 | 0.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.023 | 0.023 | 0.024 | 0.024 | 0.028 | 0.044 | 0.045 | 0.051 | 0.019 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.003 | 0.0 | 0.0 |
| Percentage of InterestExpense | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 76.7 | 67.6 | 0.0 | 70.6 | 53.8 | 13.9 | 0.0 | 9.6 | 3.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 0.392 | 0.194 |
| Percentage of InterestExpense | 0.8 | 0.7 |
| Percentage of InterestAndDividendIncomeOperating | 0.3 | 0.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | 19.2 | 14.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 83 | 101 | 86 | 81 | 66 | 55 | 64 | 66 | 59 | 58 | 69 | 59 | 57 | 67 | 73 | 75 | 79 | 76 | 78 | 99 | 92 | 101 | 112 | 111 | 105 | 102 | 112 | 117 | 107 | 98 | 108 | 104 | 101 | 98 | 90 | 85 | 84 | 84 | 93 | 96 | 88 | 85 | 96 | 92 | 97 |
| Percentage of InterestIncomeExpenseNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.6 | 78.5 | 62.3 | 58.2 | 43.9 | 29.1 | 30.3 | 27.8 | 24.2 | 23.5 | 27.6 | 24.9 | 25.2 | 33.2 | 37.2 | 38.2 | 41.4 | 41.8 | 42.4 | 50.9 | 49.5 | 52.9 | 58.1 | 59.2 | 59.1 | 58.9 | 61.0 | 62.0 | 60.9 | 62.2 | 64.8 | 65.5 | 63.6 | 62.9 | 58.1 | 56.2 | 55.6 | 55.0 | 59.3 | 61.4 | 63.5 | 62.1 | 63.9 | 57.5 | 62.2 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 0.431 | 0.422 | 1.573 | 0.758 | 0.118 | 0.148 | 2.271 | 0.749 | -1.614 | -1.761 |
| Percentage of InterestIncomeExpenseNet | 0.5 | 0.4 | 1.8 | 0.9 | 0.2 | 0.3 | 3.5 | 1.1 | -2.7 | -3.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.3 | 0.3 | 1.1 | 0.5 | 0.1 | 0.1 | 1.1 | 0.3 | -0.7 | -0.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | 28.3 | 33.9 | 0.0 | 46.1 | 9.9 | 9.5 | 0.0 | 26.2 | -71.5 | -85.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 81 | 99 | 84 | 80 | 66 | 52 | 59 | 61 | 59 | 58 | 66 | 59 | 56 | 66 | 72 | 73 | 78 |
| Percentage of InterestIncomeExpenseNet | 97.3 | 98.1 | 97.4 | 98.6 | 99.2 | 95.6 | 92.6 | 92.9 | 99.1 | 98.7 | 96.3 | 99.0 | 98.5 | 98.2 | 98.6 | 98.2 | 98.1 |
| Percentage of InterestAndDividendIncomeOperating | 60.9 | 77.0 | 60.7 | 57.4 | 43.5 | 27.8 | 28.0 | 25.8 | 24.0 | 23.2 | 26.6 | 24.7 | 24.8 | 32.6 | 36.7 | 37.5 | 40.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 62.6 | 78.7 | 0.0 | 58.1 | 43.9 | 28.3 | 0.0 | 26.5 | 24.4 | 23.5 | 0.0 | 25.1 | 25.1 | 33.0 | 0.0 | 37.9 | 40.9 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.21 | 0.263 | 0.259 | 0.351 | 0.399 | 1.974 | 2.055 | 3.487 | 1.648 | 2.009 | 1.52 | 1.51 | 0.748 | 0.665 | 0.007 | 0.005 | 0.003 |
| Percentage of InterestIncomeExpenseNet | 0.3 | 0.3 | 0.3 | 0.4 | 0.6 | 3.6 | 3.2 | 5.2 | 2.8 | 3.4 | 2.2 | 2.5 | 1.3 | 1.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.2 | 0.2 | 0.2 | 0.3 | 0.3 | 1.0 | 1.0 | 1.5 | 0.7 | 0.8 | 0.6 | 0.6 | 0.3 | 0.3 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 100.0 | 100.0 | 0.0 | 95.6 | 95.0 | 99.1 | 0.0 | 99.7 | 99.3 | 99.6 | 0.0 | 99.8 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.007 | 0.011 | 0.009 | 0.01 | 0.024 | 0.273 | 0.407 | 0.481 | 0.531 | 0.497 | 0.42 | 0.381 | 0.293 | 0.257 | 0.149 | 0.147 | 0.12 |
| Percentage of InterestIncomeExpenseNet | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.5 | 0.6 | 0.7 | 0.9 | 0.8 | 0.6 | 0.6 | 0.5 | 0.4 | 0.2 | 0.2 | 0.2 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 23.3 | 32.4 | 0.0 | 29.4 | 46.2 | 86.1 | 0.0 | 90.4 | 96.5 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 1.649 | 1.182 |
| Percentage of InterestIncomeExpenseNet | 2.0 | 1.2 |
| Percentage of InterestAndDividendIncomeOperating | 1.2 | 0.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | 80.8 | 85.9 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2018-12-31 | 2018-09-30 |
| Value | 39 | 39 | 83 | 125 | 138 | 163 | 165 | 165 |
| Percentage of InterestPaidNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 29.4 | 30.7 | 55.3 | 66.2 | 65.4 | 68.5 | 65.6 | 69.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 83 | 123 | 234 | 71 | 86 | -40.532 | 42 | 33 | 24 | 41 | 21 | 42 | 49 | 113 | 48 | 46 | 28 | 50 | 98 | 84 | 26 | 47 | 83 | 48 | 70 | 64 | 73 | 85 | 74 | 73 | 70 | 62 | 101 | 68 | 56 | 36 | 41 | 43 | 64 | 47 | 37 | 54 | 85 | -0.368 | 49 |
| Percentage of NetIncomeLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.8 | 95.7 | 169.3 | 51.2 | 56.9 | -21.4 | 20.0 | 13.9 | 10.0 | 16.6 | 8.6 | 17.9 | 21.6 | 56.2 | 24.5 | 23.5 | 14.9 | 27.2 | 52.8 | 43.0 | 14.0 | 25.0 | 43.2 | 25.9 | 39.9 | 37.2 | 39.9 | 45.0 | 42.4 | 46.4 | 42.0 | 39.2 | 63.5 | 43.3 | 36.3 | 24.3 | 27.2 | 28.0 | 41.2 | 30.1 | 26.6 | 39.7 | 56.4 | -0.2 | 31.9 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 82 | 121 | 231 | 70 | 85 | -39.974 | 41 | 32 | 24 | 41 | 21 | 42 | 48 | 112 | 47 | 45 | 28 | 49 | 97 | 83 | 25 | 47 | 82 | 48 | 70 | 64 | 72 | 84 | 74 | 73 | 69 | 62 | 100 | 67 | 56 | 36 | 41 | 42 |
| Percentage of NetIncomeLoss | 98.3 | 98.5 | 98.6 | 98.6 | 98.6 | 98.6 | 98.7 | 98.7 | 98.7 | 98.7 | 98.4 | 98.7 | 98.8 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 98.9 | 98.9 | 98.9 | 98.9 | 98.9 | 98.9 | 99.0 | 99.0 | 99.1 | 99.1 | 99.1 | 99.1 | 99.2 | 99.2 | 99.2 | 99.2 | 99.4 |
| Percentage of InterestAndDividendIncomeOperating | 61.7 | 94.3 | 166.9 | 50.4 | 56.1 | -21.1 | 19.7 | 13.7 | 9.8 | 16.4 | 8.4 | 17.7 | 21.3 | 55.6 | 24.2 | 23.3 | 14.7 | 26.9 | 52.2 | 42.5 | 13.9 | 24.7 | 42.7 | 25.6 | 39.5 | 36.8 | 39.5 | 44.5 | 42.0 | 46.0 | 41.6 | 38.9 | 62.9 | 43.0 | 36.0 | 24.1 | 27.0 | 27.8 |
| Percentage of InterestAndDividendIncomeOperating nni:CommonShareholders | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 1.388 | 1.832 | 3.334 | 1.02 | 1.239 | -0.558 | 0.559 | 0.434 | 0.327 | 0.534 | 0.337 | 0.573 | 0.575 | 1.137 | 0.475 | 0.453 | 0.28 | 0.521 | 1.032 | 0.875 | 0.271 | 0.509 | 0.885 | 0.519 | 0.763 | 0.687 | 0.796 | 0.889 | 0.731 | 0.661 | 0.618 | 0.553 | 0.904 | 0.562 | 0.439 | 0.29 | 0.336 | 0.279 |
| Percentage of NetIncomeLoss | 1.7 | 1.5 | 1.4 | 1.4 | 1.4 | 1.4 | 1.3 | 1.3 | 1.3 | 1.3 | 1.6 | 1.3 | 1.2 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 | 0.9 | 0.9 | 0.9 | 0.8 | 0.8 | 0.8 | 0.8 | 0.6 |
| Percentage of InterestAndDividendIncomeOperating | 1.0 | 1.4 | 2.4 | 0.7 | 0.8 | -0.3 | 0.3 | 0.2 | 0.1 | 0.2 | 0.1 | 0.2 | 0.3 | 0.6 | 0.2 | 0.2 | 0.1 | 0.3 | 0.6 | 0.4 | 0.1 | 0.3 | 0.5 | 0.3 | 0.4 | 0.4 | 0.4 | 0.5 | 0.4 | 0.4 | 0.4 | 0.3 | 0.6 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 |
| Percentage of InterestAndDividendIncomeOperating nni:UnvestedRestrictedStockShareholders | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -0.791 | -19.534 | 165 | -14.953 | 32 | -19.821 | -6.633 | -7.204 | -5.56 | -9.413 |
| Percentage of NetIncomeLoss | -0.9 | -15.8 | 70.3 | -20.9 | 37.9 | 48.9 | -15.7 | -21.7 | -22.6 | -22.6 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | -15.1 | 119.0 | -10.7 | 21.6 | -10.5 | -3.1 | -3.0 | -2.3 | -3.8 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -51.9 | -1567.7 | 0.0 | -908.4 | 2742.6 | -1274.7 | 0.0 | -252.0 | -246.2 | -458.5 |
| Period End | 2021-03-31 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | 0.711 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of NetIncomeLoss | 0.6 | 0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:IntersegmentElimination | -326.1 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 59 | 107 | 62 | 68 | 39 | -46.318 | 38 | 19 | 9.732 | 20 | 13 | 39 | 42 | 87 | 37 | 35 | 21 |
| Percentage of NetIncomeLoss | 71.5 | 87.1 | 26.6 | 95.6 | 45.2 | 114.3 | 91.0 | 58.7 | 39.5 | 48.5 | 64.4 | 91.3 | 86.4 | 77.2 | 77.9 | 77.2 | 74.1 |
| Percentage of InterestAndDividendIncomeOperating | 44.9 | 83.4 | 45.1 | 48.9 | 25.7 | -24.5 | 18.2 | 8.2 | 3.9 | 8.1 | 5.5 | 16.3 | 18.6 | 43.4 | 19.0 | 18.2 | 11.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 46.1 | 85.1 | 0.0 | 49.5 | 25.9 | -24.9 | 0.0 | 8.4 | 4.0 | 8.2 | 0.0 | 16.6 | 18.9 | 43.9 | 0.0 | 18.3 | 11.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -10.876 | -3.45 | -5.363 | -5.536 | -6.582 | -7.194 | -4.932 | -4.81 | -5.879 | -7.741 | -8.082 | -7.04 | -5.45 | -4.602 | -3.637 |
| Percentage of NetIncomeLoss | -4.6 | -4.8 | -6.2 | 13.7 | -15.5 | -21.7 | -20.0 | -11.6 | -27.2 | -18.0 | -16.3 | -6.2 | -11.3 | -9.9 | -12.7 |
| Percentage of InterestAndDividendIncomeOperating | -7.8 | -2.5 | -3.5 | -2.9 | -3.1 | -3.0 | -2.0 | -1.9 | -2.3 | -3.2 | -3.5 | -3.5 | -2.8 | -2.3 | -1.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -493200.0 | -240500.0 | 0.0 | -774100.0 | -808200.0 | -704000.0 | 0.0 | -460200.0 | -363700.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 13 | 23 | 9.207 | 11 | 8.885 | 20 | 7.252 | 12 | 8.374 | 18 | -1.183 | 7.591 | 5.64 | 13 | 2.397 | 5.744 | 4.954 |
| Percentage of NetIncomeLoss | 15.6 | 19.0 | 3.9 | 16.0 | 10.3 | -51.3 | 17.1 | 38.3 | 34.0 | 45.6 | -5.5 | 17.7 | 11.4 | 11.7 | 5.0 | 12.4 | 17.2 |
| Percentage of InterestAndDividendIncomeOperating | 9.8 | 18.2 | 6.6 | 8.2 | 5.8 | 11.0 | 3.4 | 5.3 | 3.4 | 7.6 | -0.5 | 3.2 | 2.5 | 6.6 | 1.2 | 2.9 | 2.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 6236.2 | 8950.6 | 0.0 | 3115.3 | 2115.5 | 1044.0 | 0.0 | 363.3 | 504.8 | 941.3 | 0.0 | 501.7 | 754.0 | 2011.9 | 0.0 | 114880.0 | 165133.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 11 | 12 | 8.98 | 10 | 11 | 10 | 9.759 | 15 | 17 | 16 | 14 | 9.982 | 13 | 15 | 6.065 | 8.056 | 8.024 |
| Percentage of NetIncomeLoss | 14.1 | 9.9 | 3.8 | 14.2 | 12.8 | -25.5 | 23.0 | 46.3 | 69.1 | 40.0 | 66.7 | 23.3 | 27.2 | 13.9 | 12.6 | 17.4 | 27.9 |
| Percentage of InterestAndDividendIncomeOperating | 8.8 | 9.5 | 6.5 | 7.3 | 7.3 | 5.5 | 4.6 | 6.4 | 6.9 | 6.6 | 5.7 | 4.2 | 5.9 | 7.8 | 3.1 | 4.1 | 4.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 39300.0 | 35952.9 | 0.0 | 29820.6 | 21334.6 | 3266.2 | 0.0 | 2893.4 | 3091.6 | 3350.3 | 0.0 | 2619.9 | 4586.7 | 6163.8 | 0.0 | 5480.3 | 6686.7 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -0.204 | -0.968 |
| Percentage of NetIncomeLoss | -0.2 | -0.8 |
| Percentage of InterestAndDividendIncomeOperating | -0.2 | -0.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | -10.0 | -70.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | -0.854 | -0.694 | -3.385 | -0.327 | 0.128 | 0.767 | -0.546 | -0.077 | 0.059 | 0.056 | 0.048 | 0.199 | 0.104 | -0.74 | -2.386 | -2.768 | -4.086 | -2.106 | 0.585 | 0.069 | 0.028 | 0.068 | 0.168 | 0.022 | 0.054 | 0.041 | 0.308 | 0.157 | 0.693 | 0.513 | 0.568 | 0.216 | 0.614 | 0.271 | 0.019 | 0.124 | 0.136 | 0.152 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of NetIncomeLossAttributableToNoncontrollingInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | -0.5 | -2.4 | -0.2 | 0.1 | 0.4 | -0.3 | -0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | -0.4 | -1.2 | -1.4 | -2.1 | -1.1 | 0.3 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.2 | 0.1 | 0.4 | 0.3 | 0.3 | 0.1 | 0.4 | 0.2 | 0.0 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -0.854 | 0.017 | -3.385 | -0.327 | 0.128 | 0.767 | -0.547 | -0.077 | 0.059 | 0.056 |
| Percentage of NetIncomeLossAttributableToNoncontrollingInterest | 100.0 | -2.4 | 100.0 | 100.0 | 100.0 | 100.0 | 100.2 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | 0.0 | -2.4 | -0.2 | 0.1 | 0.4 | -0.3 | -0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -56.0 | 1.4 | 0.0 | -19.9 | 10.7 | 49.3 | 0.0 | -2.7 | 2.6 | 2.7 |
| Period End | 2021-03-31 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | -0.711 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of NetIncomeLossAttributableToNoncontrollingInterest | 102.4 | 0.0 | 0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:IntersegmentElimination | 326.1 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 171 | 172 | 213 | 191 | 185 | 190 | 199 | 202 | 181 | 179 | 187 | 185 | 176 | 151 | 136 | 125 | 119 | 114 | 115 | 106 | 107 | 111 | 117 | 120 | 115 | 115 | 114 | 117 | 112 | 107 | 111 | 107 | 102 | 106 | 109 | 104 | 108 | 111 | 102 | 104 | 100 | 99 | 131 | 160 | 108 |
| Percentage of OperatingExpenses | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 128.6 | 133.7 | 153.7 | 136.8 | 122.3 | 100.9 | 94.1 | 84.8 | 73.4 | 71.5 | 74.4 | 77.3 | 76.9 | 74.8 | 69.4 | 63.7 | 61.6 | 62.6 | 62.2 | 54.4 | 57.7 | 58.1 | 60.7 | 63.9 | 65.2 | 66.2 | 62.3 | 62.0 | 63.7 | 67.6 | 66.5 | 67.2 | 64.5 | 68.0 | 70.0 | 69.2 | 71.2 | 72.1 | 65.3 | 66.5 | 71.9 | 72.2 | 87.0 | 99.9 | 69.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 21 | 23 | 32 | 21 | 19 | 17 | 20 | 19 | 15 | 15 |
| Percentage of OperatingExpenses | 12.8 | 13.8 | 15.2 | 11.2 | 10.6 | 9.0 | 10.0 | 9.5 | 8.7 | 8.7 |
| Percentage of InterestAndDividendIncomeOperating | 16.4 | 18.5 | 23.3 | 15.3 | 12.9 | 9.0 | 9.4 | 8.0 | 6.4 | 6.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | 1441.8 | 1917.2 | 0.0 | 1303.0 | 1641.6 | 1099.3 | 0.0 | 671.4 | 701.2 | 762.6 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | -8.483 | -8.271 | -8.645 | -8.29 | -8.54 | -11.065 | -11.325 | -11.611 | -11.598 | -12.217 | -12.412 | -12.29 | -11.609 | -10.771 | -10.835 | -10.563 | -9.952 | -10.323 | -10.945 | -11.021 |
| Percentage of OperatingExpenses | -4.9 | -4.8 | -4.1 | -4.3 | -4.6 | -5.8 | -5.7 | -5.7 | -6.4 | -6.8 | -6.6 | -6.6 | -6.6 | -7.1 | -7.9 | -8.4 | -8.4 | -9.0 | -9.5 | -10.3 |
| Percentage of InterestAndDividendIncomeOperating | -6.4 | -6.4 | -6.2 | -5.9 | -5.6 | -5.8 | -5.3 | -4.9 | -4.7 | -4.9 | -4.9 | -5.1 | -5.1 | -5.3 | -5.5 | -5.4 | -5.2 | -5.6 | -5.9 | -5.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:IntersegmentElimination | 4536.4 | 3794.0 | 0.0 | 3176.2 | 2320.7 | 1850.3 | 0.0 | 991.5 | 1190.8 | 1435.6 | 0.0 | 253.6 | 262.4 | 341.9 | 0.0 | 493.8 | 560.4 | 759.6 | 0.0 | 1185.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 12 | 12 | 13 | 12 | 14 | 16 | 17 | 31 | 18 | 16 | 16 | 16 | 16 | 15 | 16 | 19 | 16 |
| Percentage of OperatingExpenses | 7.4 | 7.4 | 6.2 | 6.8 | 7.7 | 8.4 | 8.7 | 15.4 | 10.1 | 9.2 | 9.0 | 9.0 | 9.4 | 10.0 | 12.2 | 15.8 | 14.2 |
| Percentage of InterestAndDividendIncomeOperating | 9.5 | 9.8 | 9.6 | 9.3 | 9.4 | 8.5 | 8.2 | 13.0 | 7.4 | 6.6 | 6.7 | 7.0 | 7.2 | 7.5 | 8.4 | 10.0 | 8.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 9.8 | 10.0 | 0.0 | 9.4 | 9.5 | 8.6 | 0.0 | 13.3 | 7.5 | 6.7 | 0.0 | 7.1 | 7.3 | 7.6 | 0.0 | 10.1 | 8.8 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 28 | 19 | 20 | 20 | 21 | 21 | 17 | 16 | 16 | 14 | 13 | 12 | 11 | 9.992 | 8.279 |
| Percentage of OperatingExpenses | 13.3 | 10.1 | 11.1 | 10.6 | 10.7 | 10.5 | 9.7 | 9.1 | 8.6 | 7.8 | 7.8 | 8.1 | 8.6 | 8.0 | 7.0 |
| Percentage of InterestAndDividendIncomeOperating | 20.4 | 13.8 | 13.6 | 10.7 | 10.0 | 8.9 | 7.1 | 6.5 | 6.4 | 6.0 | 6.0 | 6.0 | 5.9 | 5.1 | 4.3 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1751000.0 | 812000.0 | 0.0 | 1447000.0 | 1378700.0 | 1222700.0 | 0.0 | 999200.0 | 827900.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 38 | 37 | 34 | 34 | 32 | 35 | 37 | 35 | 35 | 35 | 42 | 30 | 30 | 29 | 28 | 25 | 25 |
| Percentage of OperatingExpenses | 22.1 | 21.7 | 16.2 | 18.1 | 17.6 | 18.6 | 18.7 | 17.4 | 19.4 | 19.6 | 22.5 | 16.6 | 17.5 | 19.5 | 20.7 | 20.7 | 21.8 |
| Percentage of InterestAndDividendIncomeOperating | 28.5 | 29.0 | 24.8 | 24.7 | 21.5 | 18.8 | 17.6 | 14.8 | 14.2 | 14.0 | 16.7 | 12.9 | 13.4 | 14.6 | 14.4 | 13.2 | 13.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 18098.6 | 14257.8 | 0.0 | 9417.4 | 7771.2 | 1783.1 | 0.0 | 1010.1 | 2115.7 | 1741.6 | 0.0 | 2038.6 | 4111.2 | 4451.0 | 0.0 | 518960.0 | 865900.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 105 | 104 | 113 | 111 | 106 | 113 | 115 | 107 | 106 | 107 | 108 | 114 | 110 | 92 | 59 | 57 | 58 |
| Percentage of OperatingExpenses | 61.6 | 60.7 | 53.1 | 58.1 | 57.6 | 59.2 | 57.6 | 53.0 | 58.5 | 60.2 | 57.9 | 61.5 | 62.8 | 60.9 | 43.8 | 45.5 | 48.9 |
| Percentage of InterestAndDividendIncomeOperating | 79.2 | 81.2 | 81.6 | 79.5 | 70.4 | 59.8 | 54.2 | 45.0 | 43.0 | 43.0 | 43.1 | 47.5 | 48.3 | 45.6 | 30.4 | 29.0 | 30.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 352563.3 | 308308.8 | 0.0 | 326776.5 | 205613.5 | 35668.5 | 0.0 | 20190.8 | 19275.8 | 21685.5 | 0.0 | 29938.1 | 37788.1 | 35963.0 | 0.0 | 38826.5 | 48545.8 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 1.852 | 2.036 |
| Percentage of OperatingExpenses | 1.1 | 1.2 |
| Percentage of InterestAndDividendIncomeOperating | 1.4 | 1.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | 90.7 | 148.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -1000.0 | 1000.0 |
| Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 1919000.0 | 2920000.0 | 1818000.0 | 1051000.0 | 2374000.0 | -2113000.0 | 82000.0 | -254000.0 | -408000.0 | -331000.0 | -92000.0 | 1271000.0 | -318000.0 | -852000.0 | 430000.0 | -64000.0 | -1064000.0 | 585000.0 | 5154000.0 | 1853000.0 | -3693000.0 | -868000.0 | -592000.0 | -407000.0 | -1589000.0 | -263000.0 | 36000.0 | -470000.0 | 2890000.0 | -2140000.0 | -903000.0 | 3125000.0 | -2453000.0 | 2237000.0 | 4746000.0 | -1524000.0 | -1014000.0 | 605000.0 |
| Percentage of OtherComprehensiveIncomeLossNetOfTax | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 1.4 | 2.3 | 1.3 | 0.8 | 1.6 | -1.1 | 0.0 | -0.1 | -0.2 | -0.1 | -0.0 | 0.5 | -0.1 | -0.4 | 0.2 | -0.0 | -0.6 | 0.3 | 2.8 | 0.9 | -2.0 | -0.5 | -0.3 | -0.2 | -0.9 | -0.2 | 0.0 | -0.2 | 1.6 | -1.3 | -0.5 | 2.0 | -1.5 | 1.4 | 3.0 | -1.0 | -0.7 | 0.4 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 1919000.0 | 2920000.0 | 1818000.0 | 1051000.0 | 2374000.0 | -2113000.0 | 82000.0 | -254000.0 | -408000.0 | -331000.0 | -92000.0 | 1271000.0 | -318000.0 | -852000.0 | 430000.0 | -64000.0 | -1064000.0 | 585000.0 | 5154000.0 | 1853000.0 | -3693000.0 | -868000.0 | -592000.0 | -407000.0 | -1589000.0 | -263000.0 | 36000.0 | -470000.0 | 2890000.0 | -2140000.0 | -903000.0 | 3125000.0 | -2453000.0 | 2237000.0 | 4746000.0 | -1524000.0 | -1014000.0 | 605000.0 |
| Percentage of OtherComprehensiveIncomeLossNetOfTax | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 1.4 | 2.3 | 1.3 | 0.8 | 1.6 | -1.1 | 0.0 | -0.1 | -0.2 | -0.1 | -0.0 | 0.5 | -0.1 | -0.4 | 0.2 | -0.0 | -0.6 | 0.3 | 2.8 | 0.9 | -2.0 | -0.5 | -0.3 | -0.2 | -0.9 | -0.2 | 0.0 | -0.2 | 1.6 | -1.3 | -0.5 | 2.0 | -1.5 | 1.4 | 3.0 | -1.0 | -0.7 | 0.4 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:AccumulatedOtherComprehensiveIncome | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | -12.35 | 1.502 | 60 | 8.281 | 26 | 13 | 16 | 9.067 | 9.998 | 16 | 9.58 | 18 | 7.952 | 19 | 12 | 12 | 15 | 15 | 9.765 | 13 | 6.684 | 6.523 | 7.504 | 6.918 | 12 | 7.65 | 15 | 18 | 15 | 8.613 | 12 | 9.416 | 7.023 | 12 | 8.8 | 10 | 12 | 3.931 | 6.826 | 6.492 | 6.122 | 9.432 | 8.496 |
| Percentage of OtherIncome | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | -8.9 | 1.1 | 39.6 | 4.4 | 12.5 | 5.6 | 6.5 | 3.6 | 4.0 | 6.9 | 4.2 | 9.0 | 4.0 | 10.0 | 6.5 | 6.9 | 8.2 | 7.7 | 5.2 | 7.2 | 3.5 | 3.4 | 4.2 | 4.0 | 7.0 | 4.0 | 8.7 | 11.4 | 9.5 | 5.4 | 7.7 | 6.0 | 4.5 | 8.4 | 5.8 | 7.1 | 7.8 | 2.5 | 4.9 | 4.7 | 4.1 | 5.9 | 5.4 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -17.466 | -2.737 | 57 | 2.083 | 4.127 | 7.231 | 8.624 | 3.344 |
| Percentage of OtherIncome | 141.4 | -182.2 | 94.9 | 25.2 | 15.6 | 53.8 | 53.4 | 36.9 |
| Percentage of InterestAndDividendIncomeOperating | -12.6 | -2.0 | 37.6 | 1.1 | 1.9 | 3.0 | 3.5 | 1.3 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | 0.0 | -166.3 | 4773.3 | 134.0 | 0.0 | 252.9 | 381.9 | 162.9 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 2.238 | 1.004 | 0.732 | 3.215 | 18 | 3.384 | 4.888 | 3.525 | 3.691 | 3.267 | 2.772 | 3.351 | 2.705 | 2.753 | 3.057 |
| Percentage of OtherIncome | -18.1 | 66.8 | 1.2 | 38.8 | 70.0 | 25.2 | 30.3 | 38.9 | 36.9 | 19.6 | 28.9 | 18.4 | 34.0 | 13.9 | 24.5 |
| Percentage of InterestAndDividendIncomeOperating | 1.6 | 0.7 | 0.5 | 1.7 | 8.7 | 1.4 | 2.0 | 1.4 | 1.5 | 1.4 | 1.2 | 1.7 | 1.4 | 1.4 | 1.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 0.0 | 0.7 | 0.5 | 1.7 | 0.0 | 1.5 | 2.0 | 1.4 | 0.0 | 1.4 | 1.2 | 1.7 | 0.0 | 1.4 | 1.6 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.305 | 0.511 | 0.392 | 0.353 | 0.49 | 0.532 | 0.362 | 0.125 | 0.125 | 0.95 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of OtherIncome | -2.5 | 34.0 | 0.7 | 4.3 | 1.8 | 4.0 | 2.2 | 1.4 | 1.3 | 5.7 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.2 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.1 | 0.0 | 0.0 | 0.4 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 36200.0 | 6250.0 | 0.0 | 95000.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.0 | 0.373 | 0.0 | 0.0 | 0.259 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of OtherIncome | -0.0 | 24.8 | 0.0 | 0.0 | 1.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.3 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 0.0 | 101.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 2.524 | 2.353 | 1.914 | 2.63 | 3.094 | 2.291 | 2.277 | 2.074 | 2.088 | 1.948 | 1.956 | 1.292 | 0.0 | 0.0 | 0.0 |
| Percentage of OtherIncome | -20.4 | 156.7 | 3.2 | 31.8 | 11.7 | 17.0 | 14.1 | 22.9 | 20.9 | 11.7 | 20.4 | 7.1 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 1.8 | 1.7 | 1.3 | 1.4 | 1.5 | 1.0 | 0.9 | 0.8 | 0.8 | 0.8 | 0.9 | 0.6 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 0.0 | 6920.6 | 3680.8 | 829.7 | 0.0 | 430.6 | 414.0 | 417.3 | 0.0 | 511.3 | 667.6 | 502.7 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | 83 | 122 | 231 | 71 | 86 | -39.765 | 41 | 33 | 24 | 41 | 21 | 43 | 49 | 113 | 45 | 43 | 24 | 47 | 98 | 84 | 26 | 48 | 83 | 48 | 70 | 64 | 73 | 85 | 75 | 74 | 71 | 63 | 101 | 68 | 56 | 36 | 41 | 43 | 64 | 47 | 37 | 54 |
| Percentage of ProfitLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.1 | 95.2 | 166.8 | 50.9 | 57.0 | -21.0 | 19.7 | 13.9 | 10.0 | 16.6 | 8.6 | 18.0 | 21.6 | 55.8 | 23.2 | 22.1 | 12.8 | 26.1 | 53.1 | 43.0 | 14.1 | 25.0 | 43.3 | 25.9 | 39.9 | 37.2 | 40.1 | 45.1 | 42.8 | 46.8 | 42.3 | 39.3 | 63.8 | 43.5 | 36.3 | 24.4 | 27.3 | 28.1 | 41.2 | 30.1 | 26.6 | 39.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -1.645 | -19.517 | 161 | -15.28 | 32 | -19.054 | -7.18 | -7.281 | -5.501 | -9.357 |
| Percentage of ProfitLoss | -2.0 | -15.9 | 69.9 | -21.5 | 38.0 | 47.9 | -17.2 | -22.0 | -22.3 | -22.5 |
| Percentage of InterestAndDividendIncomeOperating | -1.2 | -15.1 | 116.5 | -10.9 | 21.7 | -10.1 | -3.4 | -3.0 | -2.2 | -3.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -107.9 | -1566.4 | 0.0 | -928.3 | 2753.3 | -1225.3 | 0.0 | -254.7 | -243.6 | -455.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 59 | 107 | 62 | 68 | 39 | -46.318 | 38 | 19 | 9.732 | 20 | 13 | 39 | 42 | 87 | 37 | 35 | 21 |
| Percentage of ProfitLoss | 72.2 | 87.6 | 27.0 | 96.0 | 45.1 | 116.5 | 92.2 | 58.9 | 39.4 | 48.5 | 64.2 | 90.9 | 86.2 | 77.7 | 81.9 | 82.1 | 86.4 |
| Percentage of InterestAndDividendIncomeOperating | 44.9 | 83.4 | 45.1 | 48.9 | 25.7 | -24.5 | 18.2 | 8.2 | 3.9 | 8.1 | 5.5 | 16.3 | 18.6 | 43.4 | 19.0 | 18.2 | 11.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 46.1 | 85.1 | 0.0 | 49.5 | 25.9 | -24.9 | 0.0 | 8.4 | 4.0 | 8.2 | 0.0 | 16.6 | 18.9 | 43.9 | 0.0 | 18.3 | 11.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -10.876 | -3.45 | -5.363 | -5.536 | -6.582 | -7.194 | -4.932 | -4.81 | -5.879 | -7.741 | -8.082 | -7.04 | -5.45 | -4.602 | -3.637 |
| Percentage of ProfitLoss | -4.7 | -4.8 | -6.2 | 13.9 | -15.7 | -21.7 | -20.0 | -11.5 | -27.1 | -17.9 | -16.3 | -6.2 | -11.9 | -10.6 | -14.8 |
| Percentage of InterestAndDividendIncomeOperating | -7.8 | -2.5 | -3.5 | -2.9 | -3.1 | -3.0 | -2.0 | -1.9 | -2.3 | -3.2 | -3.5 | -3.5 | -2.8 | -2.3 | -1.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -493200.0 | -240500.0 | 0.0 | -774100.0 | -808200.0 | -704000.0 | 0.0 | -460200.0 | -363700.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 13 | 23 | 9.207 | 11 | 8.885 | 20 | 7.252 | 12 | 8.374 | 18 | -1.183 | 7.591 | 5.64 | 13 | 2.397 | 5.744 | 4.954 |
| Percentage of ProfitLoss | 15.8 | 19.2 | 4.0 | 16.1 | 10.3 | -52.3 | 17.3 | 38.4 | 33.9 | 45.6 | -5.5 | 17.6 | 11.4 | 11.8 | 5.2 | 13.2 | 20.1 |
| Percentage of InterestAndDividendIncomeOperating | 9.8 | 18.2 | 6.6 | 8.2 | 5.8 | 11.0 | 3.4 | 5.3 | 3.4 | 7.6 | -0.5 | 3.2 | 2.5 | 6.6 | 1.2 | 2.9 | 2.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 6236.2 | 8950.6 | 0.0 | 3115.3 | 2115.5 | 1044.0 | 0.0 | 363.3 | 504.8 | 941.3 | 0.0 | 501.7 | 754.0 | 2011.9 | 0.0 | 114880.0 | 165133.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 11 | 12 | 8.98 | 10 | 11 | 10 | 9.759 | 15 | 17 | 16 | 14 | 9.982 | 13 | 15 | 3.475 | 4.648 | 3.798 |
| Percentage of ProfitLoss | 14.2 | 9.9 | 3.9 | 14.2 | 12.8 | -26.0 | 23.3 | 46.5 | 68.9 | 40.0 | 66.5 | 23.1 | 27.1 | 13.3 | 7.6 | 10.7 | 15.4 |
| Percentage of InterestAndDividendIncomeOperating | 8.8 | 9.5 | 6.5 | 7.3 | 7.3 | 5.5 | 4.6 | 6.4 | 6.9 | 6.6 | 5.7 | 4.2 | 5.9 | 7.4 | 1.8 | 2.4 | 2.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 39300.0 | 35952.9 | 0.0 | 29820.6 | 21334.6 | 3266.2 | 0.0 | 2893.4 | 3091.6 | 3350.3 | 0.0 | 2619.9 | 4586.7 | 5849.4 | 0.0 | 3161.9 | 3165.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -0.204 | -0.968 |
| Percentage of ProfitLoss | -0.2 | -0.8 |
| Percentage of InterestAndDividendIncomeOperating | -0.2 | -0.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | -10.0 | -70.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | -0.854 | -0.694 | -3.385 | -0.327 | 0.128 | 0.767 | -0.547 | -0.077 | 0.059 | 0.056 | 0.049 | 0.199 | 0.104 | 0.74 | -2.385 | -2.768 | -4.086 | 2.106 | 0.585 | 0.069 | 0.028 | 0.068 | 0.168 | 0.022 | 0.054 | 0.041 | 0.157 | 0.693 | 0.513 | 0.271 | 0.124 | 0.136 | 0.152 | 0.0 | 0.0 | 0.0 |
| Percentage of ProfitLoss | -1.0 | -0.6 | -1.5 | -0.5 | 0.1 | -1.9 | -1.3 | -0.2 | 0.2 | 0.1 | 0.2 | 0.5 | 0.2 | 0.7 | -5.2 | -6.4 | -16.6 | 4.4 | 0.6 | 0.1 | 0.1 | 0.1 | 0.2 | 0.0 | 0.1 | 0.1 | 0.2 | 0.9 | 0.7 | 0.4 | 0.3 | 0.3 | 0.4 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | -0.5 | -2.4 | -0.2 | 0.1 | 0.4 | -0.3 | -0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.4 | -1.2 | -1.4 | -2.1 | 1.1 | 0.3 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.1 | 0.4 | 0.3 | 0.2 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:NoncontrollingInterest | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | 83 | 123 | 234 | 71 | 86 | -40.532 | 42 | 33 | 24 | 41 | 21 | 42 | 49 | 113 | 48 | 46 | 28 | 50 | 98 | 84 | 26 | 47 | 83 | 48 | 70 | 64 | 85 | 74 | 73 | 68 | 36 | 41 | 43 | 47 | 37 | 54 |
| Percentage of ProfitLoss | 101.0 | 100.6 | 101.5 | 100.5 | 99.9 | 101.9 | 101.3 | 100.2 | 99.8 | 99.9 | 99.8 | 99.5 | 99.8 | 100.7 | 105.2 | 106.4 | 116.6 | 104.4 | 99.4 | 99.9 | 99.9 | 99.9 | 99.8 | 100.0 | 99.9 | 99.9 | 99.8 | 99.1 | 99.3 | 99.6 | 99.7 | 99.7 | 99.6 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.8 | 95.7 | 169.3 | 51.2 | 56.9 | -21.4 | 20.0 | 13.9 | 10.0 | 16.6 | 8.6 | 17.9 | 21.6 | 56.2 | 24.5 | 23.5 | 14.9 | 27.2 | 52.8 | 43.0 | 14.0 | 25.0 | 43.2 | 25.9 | 39.9 | 37.2 | 45.0 | 42.4 | 46.4 | 43.3 | 24.3 | 27.2 | 28.0 | 30.1 | 26.6 | 39.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:RetainedEarnings | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 |
| Value | 35 | 34 | 36 | 37 | 38 | 38 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 26.5 | 27.0 | 26.0 | 24.6 | 20.5 | 16.2 |
| Percentage of InterestAndDividendIncomeOperating nni:NelnetServicing nni:DepartmentOfEducation us-gaap:CustomerConcentrationRisk | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 19 | 20 | 18 | 18 | 17 | 16 | 15 | 14 | 13 | 11 | 10 | 9.189 | 8.123 | 6.751 | 5.719 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 55.7 | 50.8 | 47.0 | 0.0 | 42.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 13.9 | 14.5 | 12.5 | 9.6 | 8.2 | 6.9 | 6.4 | 5.8 | 5.3 | 4.9 | 4.5 | 4.5 | 4.1 | 3.4 | 3.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsServices nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 76 | 95 | 65 | 74 | 59 | 83 | 63 | 74 | 60 | 79 | 54 | 58 | 48 | 60 | 43 | 50 | 43 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 216.7 | 272.9 | 0.0 | 204.2 | 158.6 | 216.2 | 0.0 | 192.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 57.4 | 73.8 | 46.9 | 53.0 | 39.0 | 44.2 | 29.9 | 31.1 | 24.5 | 31.6 | 21.6 | 24.3 | 21.3 | 29.7 | 22.0 | 25.6 | 22.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServices nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 112 | 111 | 113 | 113 | 111 | 112 | 113 | 113 | 113 | 114 | 112 | 112 | 114 | 100 | 55 | 55 | 56 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 316.6 | 319.5 | 0.0 | 313.5 | 296.9 | 291.3 | 0.0 | 293.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 83.9 | 86.4 | 82.1 | 81.4 | 73.1 | 59.6 | 53.3 | 47.4 | 46.2 | 45.9 | 44.7 | 46.9 | 50.0 | 49.4 | 28.4 | 28.4 | 29.5 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystems nni:LoanServicingAndSystemsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 4.036 | 4.918 | 4.619 | 4.471 | 4.433 | 4.025 | 3.816 | 3.414 | 3.197 | 2.861 | 2.535 | 2.381 | 2.219 | 2.013 | 1.814 | 1.696 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 13.5 | 12.4 | 11.6 | 0.0 | 10.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 3.5 | 3.0 | 2.4 | 2.1 | 1.7 | 1.5 | 1.4 | 1.3 | 1.2 | 1.1 | 1.2 | 1.1 | 1.0 | 0.9 | 0.9 |
| Percentage of InterestAndDividendIncomeOperating nni:BusinessRevenue | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 19 | 20 | 18 | 18 | 17 | 16 | 15 | 14 | 13 | 11 | 10 | 9.189 | 8.123 | 6.751 | 5.719 | 5.106 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 55.7 | 50.8 | 47.0 | 0.0 | 42.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 14.5 | 12.5 | 9.6 | 8.2 | 6.9 | 6.4 | 5.8 | 5.3 | 4.9 | 4.5 | 4.5 | 4.1 | 3.4 | 3.0 | 2.8 |
| Percentage of InterestAndDividendIncomeOperating nni:CommunicationsRevenueCustomer | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 0.134 | 0.12 | 0.17 | 0.151 | 0.073 | 0.048 | 0.052 | 0.064 | 0.062 | 0.061 | 0.058 | 0.061 | 0.059 | 0.058 | 0.085 | 0.059 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 0.3 | 0.5 | 0.4 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating nni:OtherCustomerRevenue | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 15 | 15 | 14 | 13 | 12 | 12 | 11 | 11 | 10 | 8.896 | 7.727 | 6.747 | 5.845 | 4.68 | 3.82 | 3.351 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 41.8 | 38.0 | 35.0 | 0.0 | 32.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 10.9 | 9.4 | 7.2 | 6.1 | 5.2 | 4.8 | 4.4 | 4.0 | 3.7 | 3.4 | 3.3 | 3.0 | 2.4 | 2.0 | 1.8 |
| Percentage of InterestAndDividendIncomeOperating nni:ResidentialRevenue | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 19 | 20 | 18 | 18 | 17 | 16 | 15 | 14 | 13 | 11 | 10 | 9.189 | 8.123 | 6.751 | 5.719 | 5.106 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 55.7 | 50.8 | 47.0 | 0.0 | 42.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 14.5 | 12.5 | 9.6 | 8.2 | 6.9 | 6.4 | 5.8 | 5.3 | 4.9 | 4.5 | 4.5 | 4.1 | 3.4 | 3.0 | 2.8 |
| Percentage of InterestAndDividendIncomeOperating nni:CommunicationRevenueServiceOffering | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 19 | 20 | 18 | 18 | 17 | 16 | 15 | 14 | 13 | 11 | 10 | 9.189 | 8.123 | 6.751 | 5.719 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 55.7 | 50.8 | 47.0 | 0.0 | 42.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 13.9 | 14.5 | 12.5 | 9.6 | 8.2 | 6.9 | 6.4 | 5.8 | 5.3 | 4.9 | 4.5 | 4.5 | 4.1 | 3.4 | 3.0 |
| Percentage of InterestAndDividendIncomeOperating nni:CommunicationsServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 24 | 32 | 15 | 15 | 14 | 20 | 11 | 13 | 14 | 19 | 10 | 11 | 12 | 16 | 8.735 | 9.831 | 10 | 15 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 69.9 | 92.6 | 0.0 | 43.6 | 39.9 | 51.8 | 0.0 | 33.9 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 18.5 | 25.0 | 10.9 | 11.3 | 9.8 | 10.6 | 5.5 | 5.5 | 5.7 | 7.9 | 4.3 | 4.8 | 5.2 | 8.4 | 4.4 | 5.0 | 5.6 | 8.2 |
| Percentage of InterestAndDividendIncomeOperating nni:EducationTechnologyAndServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 76 | 95 | 65 | 74 | 59 | 83 | 63 | 74 | 60 | 79 | 54 | 58 | 48 | 60 | 43 | 50 | 43 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 216.7 | 272.9 | 0.0 | 204.2 | 158.6 | 216.2 | 0.0 | 192.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 57.4 | 73.8 | 46.9 | 53.0 | 39.0 | 44.2 | 29.9 | 31.1 | 24.5 | 31.6 | 21.6 | 24.3 | 21.3 | 29.7 | 22.0 | 25.6 | 22.5 |
| Percentage of InterestAndDividendIncomeOperating nni:EducationTechnologyServicesAndPaymentProcessingServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 4.703 | 4.67 | 4.74 | 4.912 | 4.917 | 5.614 | 5.835 | 6.089 | 6.424 | 6.695 | 7.283 | 7.422 | 9.147 | 7.691 | 3.849 | 3.979 | 3.636 | 4.077 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 13.3 | 13.4 | 0.0 | 13.5 | 13.1 | 14.5 | 0.0 | 15.8 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 3.5 | 3.6 | 3.4 | 3.5 | 3.2 | 3.0 | 2.7 | 2.5 | 2.6 | 2.7 | 2.9 | 3.1 | 4.0 | 3.8 | 2.0 | 2.0 | 1.9 | 2.2 |
| Percentage of InterestAndDividendIncomeOperating nni:FFELPServicing | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 43 | 43 | 42 | 45 | 45 | 46 | 46 | 46 | 45 | 47 | 46 | 45 | 45 | 30 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 123.9 | 124.1 | 0.0 | 124.9 | 120.9 | 120.0 | 0.0 | 119.8 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 32.8 | 33.5 | 30.9 | 32.5 | 29.8 | 24.5 | 21.8 | 19.3 | 18.6 | 18.8 | 18.3 | 19.0 | 19.9 | 15.2 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating nni:GovernmentServicingGreatLakes | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 35 | 34 | 34 | 36 | 37 | 38 | 39 | 38 | 40 | 39 | 39 | 38 | 39 | 39 | 38 | 38 | 39 | 39 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 99.9 | 99.9 | 0.0 | 100.0 | 99.9 | 99.9 | 0.0 | 100.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 26.5 | 27.0 | 24.8 | 26.0 | 24.6 | 20.4 | 18.5 | 16.2 | 16.4 | 15.8 | 15.5 | 16.2 | 17.4 | 19.4 | 19.5 | 19.6 | 20.6 | 21.2 |
| Percentage of InterestAndDividendIncomeOperating nni:GovernmentServicingNelnet | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 12 | 12 | 11 | 11 | 10 | 9.899 | 9.297 | 8.449 | 7.522 | 6.456 | 5.395 | 4.696 | 3.998 | 3.205 | 2.569 | 2.202 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 35.2 | 31.9 | 28.9 | 0.0 | 25.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 9.2 | 7.9 | 5.9 | 5.0 | 4.1 | 3.8 | 3.4 | 3.0 | 2.7 | 2.4 | 2.3 | 2.0 | 1.6 | 1.3 | 1.2 |
| Percentage of InterestAndDividendIncomeOperating nni:Internet | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 112 | 111 | 113 | 113 | 111 | 112 | 113 | 113 | 113 | 114 | 112 | 112 | 114 | 100 | 55 | 55 | 56 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 316.6 | 319.5 | 0.0 | 313.5 | 296.9 | 291.3 | 0.0 | 293.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 83.9 | 86.4 | 82.1 | 81.4 | 73.1 | 59.6 | 53.3 | 47.4 | 46.2 | 45.9 | 44.7 | 46.9 | 50.0 | 49.4 | 28.4 | 28.4 | 29.5 |
| Percentage of InterestAndDividendIncomeOperating nni:LoanServicingAndSystems | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 112 | 111 | 113 | 113 | 111 | 112 | 113 | 113 | 113 | 114 | 112 | 112 | 114 | 100 | 55 | 55 | 56 | 54 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 316.6 | 319.5 | 0.0 | 313.5 | 296.9 | 291.3 | 0.0 | 293.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 83.9 | 86.4 | 82.1 | 81.4 | 73.1 | 59.6 | 53.3 | 47.4 | 46.2 | 45.9 | 44.7 | 46.9 | 50.0 | 49.4 | 28.4 | 28.4 | 29.5 | 29.5 |
| Percentage of InterestAndDividendIncomeOperating nni:LoanServicingAndSystemsRevenue | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 0.038 | 0.04 | 0.038 | 0.055 | 0.082 | 0.016 | 0.016 | 0.029 | 0.03 | 0.02 | 0.017 | 0.021 | 0.02 | 0.018 | 0.046 | 0.019 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating nni:OtherCommunicationRevenue | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 0.423 | 0.348 | 0.393 | 0.384 | 0.262 | 0.292 | 0.359 | 0.286 | 0.28 | 0.298 | 0.293 | 0.263 | 0.281 | 0.277 | 0.1 | 0.101 | -0.101 | 0.145 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 1.2 | 1.0 | 0.0 | 1.1 | 0.7 | 0.8 | 0.0 | 0.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.3 | 0.3 | 0.3 | 0.3 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | -0.1 | 0.1 |
| Percentage of InterestAndDividendIncomeOperating nni:OtherServiceOffering | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 7.962 | 11 | 14 | 8.883 | 4.705 | 2.098 | 2.049 | 2.264 | 2.123 | 2.265 | 2.26 | 2.371 | 2.382 | 1.679 | 1.438 | 1.351 | 2.007 | 0.991 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 22.5 | 33.4 | 0.0 | 24.5 | 12.6 | 5.4 | 0.0 | 5.9 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 6.0 | 9.0 | 10.5 | 6.4 | 3.1 | 1.1 | 1.0 | 0.9 | 0.9 | 0.9 | 0.9 | 1.0 | 1.0 | 0.8 | 0.7 | 0.7 | 1.0 | 0.5 |
| Percentage of InterestAndDividendIncomeOperating nni:OutsourcedServicesRevenueAndOther | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 25 | 33 | 25 | 35 | 21 | 31 | 25 | 35 | 21 | 28 | 21 | 26 | 16 | 19 | 16 | 22 | 13 | 18 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 70.6 | 94.7 | 0.0 | 97.6 | 56.6 | 82.0 | 0.0 | 91.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 18.7 | 25.6 | 18.7 | 25.3 | 13.9 | 16.8 | 12.0 | 14.7 | 8.6 | 11.6 | 8.5 | 11.2 | 7.0 | 9.8 | 8.3 | 11.4 | 7.2 | 10.3 |
| Percentage of InterestAndDividendIncomeOperating nni:PaymentProcessing | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 12 | 8.548 | 7.759 | 7.928 | 8.196 | 8.609 | 8.762 | 9.561 | 8.985 | 9.48 | 9.484 | 10 | 8.882 | 13 | 7.525 | 7.596 | 7.121 | 5.817 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 36.2 | 24.5 | 0.0 | 21.8 | 21.9 | 22.2 | 0.0 | 24.8 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 9.6 | 6.6 | 5.6 | 5.7 | 5.4 | 4.6 | 4.1 | 4.0 | 3.6 | 3.8 | 3.8 | 4.2 | 3.9 | 6.5 | 3.8 | 3.9 | 3.7 | 3.2 |
| Percentage of InterestAndDividendIncomeOperating nni:PrivateEducationAndConsumerLoanServicing | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 7.374 | 8.454 | 9.604 | 10 | 10 | 11 | 10 | 10 | 10 | 9.741 | 8.468 | 8.201 | 8.671 | 7.589 | 4.689 | 4.43 | 4.326 | 4.337 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 20.8 | 24.2 | 0.0 | 28.7 | 28.5 | 29.2 | 0.0 | 27.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 5.5 | 6.5 | 6.9 | 7.5 | 7.0 | 6.0 | 5.1 | 4.4 | 4.1 | 3.9 | 3.4 | 3.4 | 3.8 | 3.7 | 2.4 | 2.3 | 2.2 | 2.4 |
| Percentage of InterestAndDividendIncomeOperating nni:SoftwareServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 2.601 | 2.931 | 2.812 | 2.691 | 2.643 | 2.487 | 2.395 | 2.167 | 2.075 | 1.957 | 1.825 | 1.689 | 1.585 | 1.413 | 1.344 | 1.262 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 8.1 | 7.5 | 7.0 | 0.0 | 6.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 2.1 | 1.9 | 1.4 | 1.2 | 1.0 | 1.0 | 0.9 | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 | 0.7 | 0.7 | 0.7 |
| Percentage of InterestAndDividendIncomeOperating nni:Telephone | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-21 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 4.178 | 4.446 | 4.218 | 4.236 | 4.176 | 4.068 | 4.05 | 3.898 | 3.699 | 3.385 | 3.083 | 2.783 | 2.52 | 2.115 | 1.76 | 1.623 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 0.0 | 12.2 | 11.3 | 10.9 | 0.0 | 10.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 3.2 | 2.8 | 2.2 | 2.0 | 1.7 | 1.6 | 1.6 | 1.5 | 1.4 | 1.3 | 1.4 | 1.3 | 1.1 | 0.9 | 0.9 |
| Percentage of InterestAndDividendIncomeOperating nni:Television | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 26 | 29 | 23 | 22 | 22 | 31 | 26 | 25 | 24 | 30 | 22 | 19 | 20 | 23 | 18 | 17 | 18 | 21 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 75.0 | 84.7 | 0.0 | 61.9 | 61.4 | 81.6 | 0.0 | 66.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 19.9 | 22.9 | 17.0 | 16.1 | 15.1 | 16.7 | 12.3 | 10.8 | 10.0 | 12.0 | 8.8 | 8.2 | 8.9 | 11.4 | 9.3 | 9.1 | 9.8 | 11.9 |
| Percentage of InterestAndDividendIncomeOperating nni:TuitionPaymentPlanServices | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.701 | 1.113 | 2.524 | 2.353 | 0.922 | 2.243 | 2.831 | 2.084 | 2.051 | 1.872 | 1.824 | 1.756 | 1.756 | 1.161 | 0.0 | 0.0 | 0.0 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 2.0 | 3.2 | 0.0 | 6.5 | 2.5 | 5.8 | 0.0 | 5.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.5 | 0.9 | 1.8 | 1.7 | 0.6 | 1.2 | 1.3 | 0.9 | 0.8 | 0.7 | 0.7 | 0.7 | 0.8 | 0.6 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:AdministrativeService | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 1.145 | 2.697 | 2.688 | 4.463 | 1.914 | 2.802 | 0.747 | 0.753 | 0.731 | 0.711 | 1.84 | 1.183 | 1.394 | 1.593 | 1.062 | 5.852 | 2.294 |
| Percentage of RevenueFromContractWithCustomerExcludingAssessedTax | 3.2 | 7.7 | 0.0 | 12.3 | 5.1 | 7.2 | 0.0 | 2.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.9 | 2.1 | 1.9 | 3.2 | 1.3 | 1.5 | 0.4 | 0.3 | 0.3 | 0.3 | 0.7 | 0.5 | 0.6 | 0.8 | 0.5 | 3.0 | 1.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:InvestmentAdvice | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 23028 | 22167 | 22646 | 22222 | 22611 | 23280 | 23708 | 23936 | 24219 | 24721 | 25220 | 25104 | 25209 | 23898 | 23964 | 24768 | 25323 | 26141 | 27180 | 27669 | 28715 | 29589 | 30485 | 31045 | 30246 | 29955 | 30098 | 30698 | 31371 | 27487 | 27770 | 26536 | 26303 | 26645 | 26607 | 24408 | 25269 | 25446 | 25852 | 26236 | 24871 | 25893 |
| Percentage of Assets | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 3009 | 2557 | 2772 | 2316 |
| Percentage of Assets | 13.3 | 10.8 | 11.0 | 9.7 |
| Percentage of Assets | 13.3 | 10.8 | 11.0 | 9.7 |
| Percentage of Assets srt:ParentCompany | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2017-12-31 | 2016-12-31 | 2015-12-31 |
| Value | 1489 | 1148 | 1225 | 770 | 732 | 679 | 627 | 685 | 595 | 546 | 563 | 877 | 682 | 624 |
| Percentage of Assets | 6.5 | 5.2 | 5.4 | 3.5 | 3.2 | 2.9 | 2.6 | 2.9 | 2.5 | 2.2 | 2.2 | 3.7 | 2.5 | 2.0 |
| Percentage of Assets | 6.5 | 5.2 | 5.4 | 3.5 | 3.2 | 2.9 | 2.6 | 2.9 | 2.5 | 2.2 | 2.2 | 3.7 | 2.5 | 2.0 |
| Percentage of Assets us-gaap:CorporateNonSegment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2015-12-31 |
| Value | -281.008 | -210.017 | -197.534 | -134.183 | -132.5 | -131.004 | -147.884 | -212.392 | -190.437 | -164.453 | -134.174 | -337.236 | -398.297 | -327.824 | -411.415 | -305.454 | -276.429 | -267.405 | -256.687 | -267.147 | -218.923 |
| Percentage of Assets | -1.2 | -0.9 | -0.9 | -0.6 | -0.6 | -0.6 | -0.6 | -0.9 | -0.8 | -0.7 | -0.5 | -1.3 | -1.6 | -1.4 | -1.7 | -1.2 | -1.1 | -1.0 | -0.9 | -1.0 | -0.7 |
| Percentage of Assets | -1.2 | -0.9 | -0.9 | -0.6 | -0.6 | -0.6 | -0.6 | -0.9 | -0.8 | -0.7 | -0.5 | -1.3 | -1.6 | -1.4 | -1.7 | -1.2 | -1.1 | -1.0 | -0.9 | -1.0 | -0.7 |
| Percentage of Assets us-gaap:IntersegmentElimination | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 20783 | 20367 | 20773 | 20686 | 21136 | 21905 | 22128 | 22520 | 22907 | 23475 | 23806 | 23927 | 24092 | 22804 | 22910 | 23724 | 24433 |
| Percentage of Assets | 90.3 | 91.9 | 91.7 | 93.1 | 93.5 | 94.1 | 93.3 | 94.1 | 94.6 | 95.0 | 94.4 | 95.3 | 95.6 | 95.4 | 95.6 | 95.8 | 96.5 |
| Percentage of Assets | 90.3 | 91.9 | 91.7 | 93.1 | 93.5 | 94.1 | 93.3 | 94.1 | 94.6 | 95.0 | 94.4 | 95.3 | 95.6 | 95.4 | 95.6 | 95.8 | 96.5 |
| Percentage of Assets us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 305 | 301 | 301 | 303 | 306 | 302 | 297 | 286 | 271 | 252 | 228 | 214 | 179 | 150 |
| Percentage of Assets | 1.4 | 1.3 | 1.3 | 1.3 | 1.3 | 1.3 | 1.2 | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 | 0.7 | 0.6 |
| Percentage of Assets | 1.4 | 1.3 | 1.3 | 1.3 | 1.3 | 1.3 | 1.2 | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 | 0.7 | 0.6 |
| Percentage of Assets us-gaap:OperatingSegments nni:CommunicationsSegment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 424 | 372 | 436 | 382 | 351 | 302 | 506 | 413 | 336 | 294 | 471 | 243 | 235 | 193 | 250 | 208 | 230 |
| Percentage of Assets | 1.8 | 1.7 | 1.9 | 1.7 | 1.6 | 1.3 | 2.1 | 1.7 | 1.4 | 1.2 | 1.9 | 1.0 | 0.9 | 0.8 | 1.0 | 0.8 | 0.9 |
| Percentage of Assets | 1.8 | 1.7 | 1.9 | 1.7 | 1.6 | 1.3 | 2.1 | 1.7 | 1.4 | 1.2 | 1.9 | 1.0 | 0.9 | 0.8 | 1.0 | 0.8 | 0.9 |
| Percentage of Assets us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 205 | 191 | 190 | 211 | 221 | 223 | 290 | 222 | 267 | 273 | 226 | 276 | 253 | 281 | 122 | 98 | 99 |
| Percentage of Assets | 0.9 | 0.9 | 0.8 | 1.0 | 1.0 | 1.0 | 1.2 | 0.9 | 1.1 | 1.1 | 0.9 | 1.1 | 1.0 | 1.2 | 0.5 | 0.4 | 0.4 |
| Percentage of Assets | 0.9 | 0.9 | 0.8 | 1.0 | 1.0 | 1.0 | 1.2 | 0.9 | 1.1 | 1.1 | 0.9 | 1.1 | 1.0 | 1.2 | 0.5 | 0.4 | 0.4 |
| Percentage of Assets us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 |
| Value | 407 | 296 | 216 |
| Percentage of Assets | 1.8 | 1.3 | 1.0 |
| Percentage of Assets | 1.8 | 1.3 | 1.0 |
| Percentage of Assets us-gaap:OperatingSegments nni:NelnetBank | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 20200 | 19418 | 20017 | 19819 | 20270 | 20954 | 21317 | 21582 | 21893 | 22391 | 22906 | 22777 | 22922 | 21653 | 21799 | 22638 | 23192 | 24013 | 25109 | 25688 | 26809 | 27702 | 28593 | 29209 | 28441 | 28174 | 28372 | 29041 | 29790 | 25973 | 26326 | 25159 | 24983 | 25418 | 25442 | 23232 | 24124 | 24338 | 24786 | 25224 | 23882 | 24987 |
| Percentage of Liabilities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 87.7 | 87.6 | 88.4 | 89.2 | 89.6 | 90.0 | 89.9 | 90.2 | 90.4 | 90.6 | 90.8 | 90.7 | 90.9 | 90.6 | 91.0 | 91.4 | 91.6 | 91.9 | 92.4 | 92.8 | 93.4 | 93.6 | 93.8 | 94.1 | 94.0 | 94.1 | 94.3 | 94.6 | 95.0 | 94.5 | 94.8 | 94.8 | 95.0 | 95.4 | 95.6 | 95.2 | 95.5 | 95.6 | 95.9 | 96.1 | 96.0 | 96.5 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 377 | 165 | 463 | 162 |
| Percentage of Liabilities | 1.9 | 0.8 | 2.0 | 0.7 |
| Percentage of Assets | 1.7 | 0.7 | 1.8 | 0.7 |
| Percentage of Assets srt:ParentCompany | 12.5 | 6.5 | 16.7 | 7.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 23028 | 22167 | 22646 | 22222 | 22611 | 23280 | 23708 | 23936 | 24219 | 24721 | 25220 | 25104 | 25209 | 23898 | 23964 | 24768 | 25323 | 26141 | 27180 | 27669 | 28715 | 29589 | 30485 | 31045 | 30246 | 29955 | 30098 | 30698 | 31371 | 27487 | 27770 | 26536 | 26303 | 26645 | 26607 | 24408 | 25269 | 25446 | 25852 | 26236 | 24871 | 25893 |
| Percentage of LiabilitiesAndStockholdersEquity | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 3009 | 2557 | 2772 | 2316 |
| Percentage of LiabilitiesAndStockholdersEquity | 13.3 | 10.8 | 11.0 | 9.7 |
| Percentage of Assets | 13.3 | 10.8 | 11.0 | 9.7 |
| Percentage of Assets srt:ParentCompany | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 |
| Value | 2833 | 2752 | 2632 | 2399 | 2336 | 2320 | 2386 | 2350 | 2322 | 2325 | 2304 | 2316 | 2276 | 2235 | 2149 | 2111 | 2115 | 2108 | 2061 | 1972 | 1897 | 1878 | 1884 | 1835 | 1805 | 1781 | 1725 | 1657 | 1579 | 1512 | 1443 | 1377 | 1319 | 1226 | 1165 | 1175 | 1144 | 1107 | 1066 |
| Percentage of StockholdersEquity | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 12.3 | 12.4 | 11.6 | 10.8 | 10.3 | 10.0 | 10.1 | 9.8 | 9.6 | 9.4 | 9.1 | 9.2 | 9.0 | 9.4 | 9.0 | 8.5 | 8.4 | 8.1 | 7.6 | 7.1 | 6.6 | 6.3 | 6.2 | 5.9 | 6.0 | 5.9 | 5.7 | 5.4 | 5.0 | 5.5 | 5.2 | 5.2 | 5.0 | 4.6 | 4.4 | 4.8 | 4.5 | 4.4 | 4.1 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 2632 | 2386 | 2304 | 2149 |
| Percentage of StockholdersEquity | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 11.6 | 10.1 | 9.1 | 9.0 |
| Percentage of Assets srt:ParentCompany | 87.5 | 93.3 | 83.1 | 92.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | 2009-12-31 | 2008-12-31 |
| Value | 212 | 144 | 121 | 96 | 67 | 204 | 133 | 160 | 84 | 74 | 121 | 83 | 67 | 69 | 66 | 254 | 69 | 108 | 69 | 67 | 59 | 51 | 63 | 114 | 182 | 100 | 130 | 74 | 92 | 107 | 63 | 51 | 68 | 50 | 66 | 93 | 56 | 60 | 42 | 92 | 116 | 48 | 283 | 316 | 274 | 338 | 189 |
| Percentage of CashAndCashEquivalentsAtCarryingValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.9 | 0.7 | 0.5 | 0.4 | 0.3 | 0.9 | 0.6 | 0.7 | 0.3 | 0.3 | 0.5 | 0.3 | 0.3 | 0.3 | 0.3 | 1.0 | 0.3 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.2 | 0.4 | 0.6 | 0.3 | 0.4 | 0.2 | 0.3 | 0.4 | 0.2 | 0.2 | 0.3 | 0.2 | 0.2 | 0.4 | 0.2 | 0.2 | 0.2 | 0.4 | 0.5 | 0.0 | 1.1 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 69 | 73 | 36 | 21 |
| Percentage of CashAndCashEquivalentsAtCarryingValue | 57.5 | 54.6 | 30.4 | 31.5 |
| Percentage of Assets | 0.3 | 0.3 | 0.1 | 0.1 |
| Percentage of Assets srt:ParentCompany | 2.3 | 2.9 | 1.3 | 0.9 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2013-12-31 |
| Value | 212 | 144 | 121 | 96 | 67 | 204 | 133 | 160 | 84 | 74 | 121 | 83 | 67 | 69 | 66 | 254 | 69 | 108 | 69 | 67 | 59 | 51 | 63 | 114 | 182 | 100 | 130 | 74 | 92 | 63 |
| Percentage of CashAndCashEquivalentsAtCarryingValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.9 | 0.7 | 0.5 | 0.4 | 0.3 | 0.9 | 0.6 | 0.7 | 0.3 | 0.3 | 0.5 | 0.3 | 0.3 | 0.3 | 0.3 | 1.0 | 0.3 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.2 | 0.4 | 0.6 | 0.3 | 0.4 | 0.2 | 0.3 | 0.2 |
| Percentage of Assets us-gaap:FairValueInputsLevel1 us-gaap:EstimateOfFairValueFairValueDisclosure | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2012-12-31 |
| Value | 212 | 144 | 121 | 96 | 67 | 204 | 133 | 160 | 84 | 74 | 121 | 83 | 67 | 69 | 66 | 254 | 69 | 108 | 69 | 67 | 59 | 51 | 63 | 114 | 182 | 100 | 130 | 74 | 92 | 107 | 63 | 66 |
| Percentage of CashAndCashEquivalentsAtCarryingValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.9 | 0.7 | 0.5 | 0.4 | 0.3 | 0.9 | 0.6 | 0.7 | 0.3 | 0.3 | 0.5 | 0.3 | 0.3 | 0.3 | 0.3 | 1.0 | 0.3 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.2 | 0.4 | 0.6 | 0.3 | 0.4 | 0.2 | 0.3 | 0.4 | 0.2 | 0.2 |
| Percentage of Assets us-gaap:CarryingReportedAmountFairValueDisclosure | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2012-12-31 |
| Value | 212 | 144 | 121 | 96 | 67 | 204 | 133 | 160 | 84 | 74 | 121 | 83 | 67 | 69 | 66 | 254 | 69 | 108 | 69 | 67 | 59 | 51 | 63 | 114 | 182 | 100 | 130 | 74 | 92 | 107 | 63 | 66 |
| Percentage of CashAndCashEquivalentsAtCarryingValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.9 | 0.7 | 0.5 | 0.4 | 0.3 | 0.9 | 0.6 | 0.7 | 0.3 | 0.3 | 0.5 | 0.3 | 0.3 | 0.3 | 0.3 | 1.0 | 0.3 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.2 | 0.4 | 0.6 | 0.3 | 0.4 | 0.2 | 0.3 | 0.4 | 0.2 | 0.2 |
| Percentage of Assets us-gaap:EstimateOfFairValueFairValueDisclosure | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2015-12-31 |
| Value | 1077 | 947 | 958 | 901 | 921 | 1100 | 1222 | 1138 | 1053 | 1051 | 1192 | 995 | 964 | 925 | 942 | 1085 | 986 | 989 | 1170 | 1040 |
| Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 4.7 | 4.3 | 4.2 | 4.1 | 4.1 | 4.7 | 5.2 | 4.8 | 4.4 | 4.3 | 4.7 | 4.0 | 3.8 | 3.9 | 3.9 | 4.4 | 3.9 | 3.8 | 4.3 | 3.4 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 | 2016-12-31 | 2015-12-31 |
| Value | 162 | 82 | 53 | 65 | 37 | 34 |
| Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents | 17.0 | 6.8 | 4.5 | 6.9 | 3.2 | 3.3 |
| Percentage of Assets | 0.7 | 0.3 | 0.2 | 0.3 | 0.1 | 0.1 |
| Percentage of Assets srt:ParentCompany | 5.4 | 3.2 | 1.9 | 2.8 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 311 | 283 | 130 | 109 | 102 | 111 |
| Percentage of PropertyPlantAndEquipmentGross | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 1.4 | 1.3 | 0.4 | 0.4 | 0.4 | 0.4 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 207 | 172 | 98 | 77 | 72 | 79 |
| Percentage of PropertyPlantAndEquipmentGross | 66.6 | 61.0 | 75.6 | 70.9 | 70.7 | 71.7 |
| Percentage of Assets | 0.9 | 0.8 | 0.3 | 0.3 | 0.3 | 0.3 |
| Percentage of Assets nni:ComputerEquipmentAndSoftware | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 54 | 52 | 11 | 10 | 9.711 | 9.144 |
| Percentage of PropertyPlantAndEquipmentGross | 17.5 | 18.5 | 8.7 | 9.5 | 9.5 | 8.2 |
| Percentage of Assets | 0.2 | 0.2 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:Building | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 |
| Value | 8.169 | 18 |
| Percentage of PropertyPlantAndEquipmentGross | 2.6 | 6.5 |
| Percentage of Assets | 0.0 | 0.1 |
| Percentage of Assets us-gaap:ConstructionInProgress | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 23 | 21 | 12 | 9.843 | 9.583 | 10 |
| Percentage of PropertyPlantAndEquipmentGross | 7.5 | 7.7 | 9.4 | 9.0 | 9.3 | 9.5 |
| Percentage of Assets | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:FurnitureAndFixtures | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 3.642 | 3.642 | 0.7 | 0.7 | 0.7 | 0.7 |
| Percentage of PropertyPlantAndEquipmentGross | 1.2 | 1.3 | 0.5 | 0.6 | 0.7 | 0.6 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:Land | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 9.387 | 9.168 | 3.645 | 3.618 | 6.502 | 7.321 |
| Percentage of PropertyPlantAndEquipmentGross | 3.0 | 3.2 | 2.8 | 3.3 | 6.3 | 6.6 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:LeaseholdImprovements | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 4.857 | 4.857 | 3.877 | 7.398 | 3.61 | 3.766 |
| Percentage of PropertyPlantAndEquipmentGross | 1.6 | 1.7 | 3.0 | 6.7 | 3.5 | 3.4 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:TransportationEquipment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 19 | 19 | 18 | 17 | 15 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Percentage of Assets nni:Centraloffice nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 6.088 | 6.064 | 5.902 | 5.574 | 4.943 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets nni:ComputerEquipmentAndSoftware nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 188 | 172 | 185 | 177 | 167 | 160 | 161 | 150 | 145 | 137 | 146 | 142 | 124 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 61.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.8 | 0.8 | 0.8 | 0.8 | 0.7 | 0.7 | 0.7 | 0.6 | 0.6 | 0.5 | 0.6 | 0.6 | 0.5 |
| Percentage of Assets nni:ComputerEquipmentAndSoftware nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 273 | 265 | 258 | 254 | 215 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 1.2 | 1.2 | 1.1 | 1.1 | 0.9 |
| Percentage of Assets nni:Networkplantandfiber nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 52 | 52 | 39 | 38 | 38 | 37 | 38 | 38 | 37 | 50 | 49 | 47 | 24 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 18.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 |
| Percentage of Assets us-gaap:Building nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 4.129 | 1.62 | 1.088 | 0.054 | 6.344 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:ConstructionInProgress nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 20 | 18 | 30 | 21 | 20 | 13 | 3.74 | 2.709 | 2.568 | 3.578 | 2.073 | 4.708 | 4.127 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 6.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:ConstructionInProgress nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 31 | 29 | 27 | 27 | 21 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Percentage of Assets us-gaap:EquipmentLeasedToOtherParty nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 22 | 21 | 22 | 22 | 21 | 21 | 24 | 23 | 23 | 22 | 22 | 21 | 15 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 7.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Percentage of Assets us-gaap:FurnitureAndFixtures nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 3.642 | 3.642 | 1.4 | 1.4 | 1.4 | 1.4 | 1.4 | 1.4 | 1.4 | 3.328 | 3.328 | 3.328 | 2.628 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 1.3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:Land nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 9.167 | 9.168 | 9.621 | 9.08 | 9.538 | 9.517 | 10 | 8.991 | 8.844 | 9.327 | 9.31 | 9.271 | 7.759 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 3.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:LeaseholdImprovements nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 3.761 | 3.737 | 3.733 | 3.702 | 3.219 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:OtherCapitalizedPropertyPlantAndEquipment nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 7.157 | 6.895 | 6.663 | 6.611 | 6.58 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:TransportationEquipment nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 4.857 | 4.857 | 4.897 | 5.032 | 5.032 | 5.049 | 5.049 | 5.049 | 5.067 | 5.123 | 4.447 | 4.425 | 3.813 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 1.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:TransportationEquipment nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 346 | 332 | 322 | 315 | 273 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 1.6 | 1.5 | 1.4 | 1.3 | 1.1 |
| Percentage of Assets nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 301 | 283 | 293 | 275 | 264 | 249 | 244 | 230 | 224 | 231 | 237 | 233 | 182 |
| Percentage of PropertyPlantAndEquipmentGross | 0.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 1.4 | 1.3 | 1.3 | 1.2 | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 | 0.9 | 0.9 | 0.9 | 0.8 |
| Percentage of Assets nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 182 | 159 | 84 | 75 | 70 | 76 |
| Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.8 | 0.7 | 0.3 | 0.3 | 0.3 | 0.3 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 105 | 94 | 84 | 73 | 38 |
| Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.5 | 0.4 | 0.4 | 0.3 | 0.2 |
| Percentage of Assets nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 171 | 159 | 174 | 162 | 151 | 142 | 147 | 138 | 129 | 123 | 119 | 111 | 105 |
| Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment | 0.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.8 | 0.7 | 0.8 | 0.7 | 0.7 | 0.6 | 0.6 | 0.6 | 0.5 | 0.5 | 0.5 | 0.4 | 0.4 |
| Percentage of Assets nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2011-12-31 | 2011-09-30 | 2011-06-30 |
| Value | 8.3 | 8.4 | 8.0 | 8.0 | 7.4 | 7.4 | 8.0 | 8.0 | 8.3 | 8.5 | 8.3 | 7.9 | 7.8 | 6.2 | 2.3 | 2.3 | 2.4 | 2.4 | 3.2 | 3.2 | 2.7 | 2.5 | 2.6 | 2.4 | 2.4 | 2.4 | 2.1 | 2.0 | 1.4 | 1.0 | 0.8 | 0.8 | 0.8 | 5.0 | 4.6 | 4.7 | 4.7 | 4.5 | 4.0 |
| Percentage of AmortizationOfIntangibleAssets | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 128 | 130 | 123 | 360 | 350 | 351 | 348 | 342 | 337 | 335 | 344 | 339 | 328 | 299 | 248 | 208 | 181 | 143 | 123 | 107 | 96 | 88 | 80 | 46 | 48 | 51 | 45 | 44 | 35 | 33 | 33 | 33 | 34 | 31 | 31 | 32 | 33 | 34 | 34 | 33 | 34 | 30 |
| Percentage of PropertyPlantAndEquipmentNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.6 | 0.6 | 0.5 | 1.6 | 1.5 | 1.5 | 1.5 | 1.4 | 1.4 | 1.4 | 1.4 | 1.4 | 1.3 | 1.3 | 1.0 | 0.8 | 0.7 | 0.5 | 0.5 | 0.4 | 0.3 | 0.3 | 0.3 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 |
| Value | 241 | 237 | 238 | 241 | 235 |
| Percentage of PropertyPlantAndEquipmentNet | 66.9 | 68.0 | 67.9 | 69.3 | 68.4 |
| Percentage of Assets | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 |
| Percentage of Assets nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2017-12-31 |
| Value | 130 | 123 | 119 | 112 | 112 | 106 | 97 | 91 | 94 | 108 | 118 | 122 | 77 |
| Percentage of PropertyPlantAndEquipmentNet | 100.0 | 100.0 | 33.1 | 32.0 | 32.1 | 30.7 | 28.5 | 27.2 | 28.2 | 31.6 | 34.7 | 37.2 | 31.1 |
| Percentage of Assets | 0.6 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.4 | 0.4 | 0.4 | 0.4 | 0.5 | 0.5 | 0.3 |
| Percentage of Assets nni:NonCommunications | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 | 2009-12-31 |
| Value | 142 | 142 | 142 | 156 | 156 | 156 | 156 | 156 | 156 | 156 | 156 | 153 | 153 | 158 | 138 | 147 | 147 | 147 | 147 | 147 | 147 | 147 | 146 | 126 | 126 | 126 | 126 | 126 | 126 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 117 | 143 |
| Percentage of Goodwill | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.6 | 0.6 | 0.6 | 0.7 | 0.7 | 0.7 | 0.7 | 0.7 | 0.6 | 0.6 | 0.6 | 0.6 | 0.6 | 0.7 | 0.6 | 0.6 | 0.6 | 0.6 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.5 | 0.5 | 0.5 | 0.5 | 0.4 | 0.5 | 0.5 | 0.0 |
| Period End | 2020-12-31 |
| Value | 6.292 |
| Percentage of Goodwill | 4.4 |
| Percentage of Assets | 0.0 |
| Percentage of Assets nni:HigherSchoolPublishingCompany | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 76 | 76 | 76 | 70 | 70 | 70 | 70 | 70 | 67 |
| Percentage of Goodwill | 53.9 | 53.9 | 53.9 | 44.8 | 44.8 | 44.8 | 44.8 | 44.8 | 48.4 |
| Percentage of Assets | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 |
| Percentage of Assets us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 18.1 | 20.6 | 17.5 | 18.4 | 20.0 | 23.2 | 13.9 | 14.9 | 26.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 23 | 23 | 23 | 23 | 23 | 23 | 23 | 23 | 8.596 |
| Percentage of Goodwill | 16.6 | 16.6 | 16.6 | 15.1 | 15.1 | 15.1 | 15.1 | 15.1 | 6.2 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 |
| Percentage of Assets us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 11.5 | 12.3 | 12.4 | 11.2 | 10.7 | 10.6 | 8.1 | 10.4 | 7.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 58 | 66 | 75 | 58 | 66 | 74 | 81 | 89 | 97 | 105 | 114 | 95 | 102 | 107 | 38 | 40 | 43 | 45 | 47 | 50 | 54 | 48 | 51 | 35 | 37 | 40 | 42 | 42 | 44 | 9.089 | 6.132 | 6.932 | 7.731 | 8.556 | 9.393 | 14 | 19 | 23 | 28 | 33 | 37 | 38 |
| Percentage of IntangibleAssetsNetExcludingGoodwill | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.4 | 0.4 | 0.4 | 0.5 | 0.4 | 0.4 | 0.4 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2013-12-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2011-12-31 |
| Value | 58 | 66 | 75 | 58 | 66 | 74 | 81 | 89 | 97 | 105 | 114 | 95 | 102 | 107 | 38 | 40 | 43 | 45 | 47 | 50 | 54 | 48 | 51 | 35 | 37 | 40 | 42 | 42 | 44 | 6.132 | 9.393 | 14 | 19 | 28 |
| Percentage of FiniteLivedIntangibleAssetsNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.4 | 0.4 | 0.4 | 0.5 | 0.4 | 0.4 | 0.4 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2013-12-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2011-12-31 |
| Value | 5.168 | 5.775 | 6.43 | 0.679 | 1.171 | 1.663 | 2.154 | 2.646 | 3.138 | 3.957 | 4.938 | 4.674 | 5.038 | 6.29 | 4.958 | 6.042 | 7.127 | 8.211 | 9.296 | 10 | 12 | 10 | 11 | 5.242 | 5.817 | 6.393 | 6.969 | 7.656 | 8.231 | 0.0 | 0.0 | 0.704 | 1.408 | 2.815 |
| Percentage of FiniteLivedIntangibleAssetsNet | 8.8 | 8.7 | 8.6 | 1.2 | 1.8 | 2.2 | 2.6 | 3.0 | 3.2 | 3.7 | 4.3 | 4.9 | 4.9 | 5.9 | 12.9 | 14.8 | 16.5 | 18.1 | 19.4 | 21.0 | 22.4 | 21.4 | 22.7 | 14.8 | 15.4 | 15.9 | 16.4 | 17.9 | 18.4 | 0.0 | 0.0 | 4.9 | 7.4 | 9.9 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:ComputerSoftwareIntangibleAsset | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2013-12-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2011-12-31 |
| Value | 53 | 60 | 66 | 52 | 58 | 65 | 71 | 78 | 85 | 91 | 98 | 79 | 84 | 87 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 26 | 27 | 22 | 24 | 25 | 27 | 28 | 29 | 6.132 | 9.393 | 13 | 16 | 23 |
| Percentage of FiniteLivedIntangibleAssetsNet | 91.2 | 90.1 | 89.2 | 88.6 | 87.9 | 88.0 | 88.2 | 87.7 | 87.4 | 86.8 | 86.2 | 82.7 | 82.6 | 81.4 | 62.9 | 61.8 | 60.8 | 60.0 | 59.3 | 58.1 | 57.1 | 55.0 | 54.0 | 64.9 | 64.6 | 64.4 | 64.2 | 66.7 | 66.6 | 100.0 | 100.0 | 91.1 | 86.5 | 81.9 |
| Percentage of Assets | 0.2 | 0.3 | 0.3 | 0.2 | 0.3 | 0.3 | 0.3 | 0.3 | 0.4 | 0.4 | 0.4 | 0.3 | 0.3 | 0.4 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 |
| Percentage of Assets us-gaap:CustomerRelationships | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2013-12-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2011-12-31 |
| Value | 0.833 | 1.666 | 6.018 | 6.936 | 7.207 | 7.478 | 8.326 | 9.173 | 10 | 10 | 11 | 12 | 13 | 9.074 | 9.285 | 9.497 | 9.708 | 9.919 | 10 | 10 | 10 | 10 | 5.758 | 5.888 | 6.019 | 6.15 | 6.266 | 6.383 | 0.0 | 0.0 | 0.58 | 1.159 | 2.319 |
| Percentage of FiniteLivedIntangibleAssetsNet | 1.2 | 2.2 | 10.3 | 10.4 | 9.7 | 9.2 | 9.3 | 9.4 | 9.5 | 9.5 | 12.2 | 12.3 | 12.5 | 23.6 | 22.8 | 22.0 | 21.4 | 20.7 | 19.9 | 19.1 | 21.6 | 20.9 | 16.3 | 15.6 | 15.0 | 14.4 | 14.6 | 14.2 | 0.0 | 0.0 | 4.0 | 6.1 | 8.2 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:TradeNames | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 18 | 32 | 34 | 31 | 33 |
| Percentage of OperatingLeaseRightOfUseAsset | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 |
| Value | 69 | 59 | 42 | 30 | 29 | 26 | 12 | 17 | 18 | 18 | 17 |
| Percentage of EquitySecuritiesFvNi | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.3 | 0.3 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Period End | 2020-12-31 |
| Value | 128 |
| Percentage of EquitySecuritiesFvNi | 305.9 |
| Percentage of Assets | 0.6 |
| Percentage of Assets nni:Hudl us-gaap:MiscellaneousInvestments us-gaap:VentureCapitalFunds | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 80 | 89 | 92 | 121 | 131 | 122 | 134 | 121 | 106 | 103 | 45 | 41 | 41 | 34 | 56 | 13 | 15 | 60 | 10 | 9.647 | 11 | 11 | 75 | 76 | 79 | 77 | 163 | 141 | 141 | 128 | 115 | 103 | 97 | 91 | 88 | 87 | 89 | 90 | 92 | 95 | 94 | 101 |
| Percentage of OtherAssets | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.4 | 0.4 | 0.4 | 0.5 | 0.6 | 0.5 | 0.6 | 0.5 | 0.4 | 0.4 | 0.2 | 0.2 | 0.2 | 0.1 | 0.2 | 0.1 | 0.1 | 0.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.2 | 0.2 | 0.3 | 0.3 | 0.5 | 0.5 | 0.5 | 0.5 | 0.4 | 0.4 | 0.4 | 0.3 | 0.3 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 115 | 100 | 57 | 131 |
| Percentage of OtherAssets | 125.7 | 74.5 | 126.4 | 233.4 |
| Percentage of Assets | 0.5 | 0.4 | 0.2 | 0.5 |
| Percentage of Assets srt:ParentCompany | 3.8 | 3.9 | 2.1 | 5.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 |
| Value | 19381 | 18754 | 19320 | 19215 | 19726 | 20466 | 20529 |
| Percentage of LongTermDebt | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 84.2 | 84.6 | 85.3 | 86.5 | 87.2 | 87.9 | 86.6 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 |
| Value | 19166 | 18888 | 19355 | 19349 | 19856 | 20625 | 20742 |
| Percentage of LongTermDebt | 98.9 | 100.7 | 100.2 | 100.7 | 100.7 | 100.8 | 101.0 |
| Percentage of Assets | 83.2 | 85.2 | 85.5 | 87.1 | 87.8 | 88.6 | 87.5 |
| Percentage of Assets us-gaap:VariableInterestEntityPrimaryBeneficiary | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 |
| Value | 1517 | 1222 | 1030 | 1030 |
| Percentage of LongTermDebt | 7.9 | 6.4 | 5.2 | 5.0 |
| Percentage of Assets | 6.7 | 5.5 | 4.6 | 4.4 |
| Percentage of Assets nni:ClassANotes2020 us-gaap:SeniorNotes | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 |
| Value | 295 |
| Percentage of LongTermDebt | 1.5 |
| Percentage of Assets | 1.3 |
| Percentage of Assets nni:ClassANotes20205 us-gaap:SeniorNotes | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 19320 | 20529 | 20910 | 21294 | 21835 | 22218 | 22251 | 22468 | 21227 | 21356 | 22240 | 22790 | 23594 | 24668 | 25320 | 26399 | 27349 | 28172 | 28827 | 28070 | 27815 | 28027 | 28737 | 29492 | 25589 | 25955 | 24858 | 24690 | 25125 | 25098 | 22884 | 23836 | 24060 | 24434 | 24926 | 23605 | 24672 |
| Percentage of DebtAndCapitalLeaseObligations | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 85.3 | 86.6 | 87.4 | 87.9 | 88.3 | 88.1 | 88.6 | 89.1 | 88.8 | 89.1 | 89.8 | 90.0 | 90.3 | 90.8 | 91.5 | 91.9 | 92.4 | 92.4 | 92.9 | 92.8 | 92.9 | 93.1 | 93.6 | 94.0 | 93.1 | 93.5 | 93.7 | 93.9 | 94.3 | 94.3 | 93.8 | 94.3 | 94.6 | 94.5 | 95.0 | 94.9 | 95.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 |
| Value | -5.182 | -3.089 | -3.693 | 3.346 | 3.99 | 5.12 | 4.382 | 4.515 | 4.292 | 4.298 | 10 | 10 | 9.834 | 9.473 | 15 | 18 | 15 | 19 | 9.27 | 9.011 | 8.916 | 8.672 | 7.726 | 0.246 | 0.3 | 0.271 | 0.23 | 0.268 | 0.386 | 0.755 | 0.328 | 0.05 | 0.113 | 0.281 | 0.005 | 0.417 | 0.293 | 0.157 | 0.0 |
| Percentage of MinorityInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 |
| Percentage of Assets | -0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 0.377 | 5.172 | 4.188 | 4.07 |
| Percentage of MinorityInterest | -10.2 | 118.0 | 40.6 | 25.7 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets srt:ParentCompany | 0.0 | 0.2 | 0.2 | 0.2 |
| Period End | 2020-12-31 |
| Value | 3857000.0 |
| Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearTwo | 100.0 |
| Percentage of Assets | 0.0 |
| Period End | 2020-12-31 |
| Value | 2938000.0 |
| Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearThree | 100.0 |
| Percentage of Assets | 0.0 |
| Period End | 2020-12-31 |
| Value | 1562000.0 |
| Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFour | 100.0 |
| Percentage of Assets | 0.0 |
| Period End | 2020-12-31 |
| Value | 1424000.0 |
| Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFive | 100.0 |
| Percentage of Assets | 0.0 |
| Period End | 2020-12-31 |
| Value | 4437000.0 |
| Percentage of LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive | 100.0 |
| Percentage of Assets | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 18 | 33 | 35 | 32 | 34 |
| Percentage of OperatingLeaseLiability | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Period End | 2020-12-31 |
| Value | 20 |
| Percentage of LesseeOperatingLeaseLiabilityPaymentsDue | 100.0 |
| Percentage of Assets | 0.1 |
| Period End | 2020-12-31 |
| Value | 2063000.0 |
| Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount | 100.0 |
| Percentage of Assets | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 |
| Value | 2833 | 2752 | 2632 | 2399 | 2336 | 2320 | 2386 | 2350 | 2322 | 2325 | 2304 | 2316 | 2276 | 2235 | 2149 | 2111 | 2115 | 2108 | 2061 | 1972 | 1897 | 1878 | 1884 | 1835 | 1805 | 1781 | 1725 | 1657 | 1579 | 1512 | 1443 | 1377 | 1319 | 1226 | 1165 | 1175 | 1144 | 1107 | 1066 |
| Percentage of StockholdersEquity | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 12.3 | 12.4 | 11.6 | 10.8 | 10.3 | 10.0 | 10.1 | 9.8 | 9.6 | 9.4 | 9.1 | 9.2 | 9.0 | 9.4 | 9.0 | 8.5 | 8.4 | 8.1 | 7.6 | 7.1 | 6.6 | 6.3 | 6.2 | 5.9 | 6.0 | 5.9 | 5.7 | 5.4 | 5.0 | 5.5 | 5.2 | 5.2 | 5.0 | 4.6 | 4.4 | 4.8 | 4.5 | 4.4 | 4.1 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 2632 | 2386 | 2304 | 2149 |
| Percentage of StockholdersEquity | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 11.6 | 10.1 | 9.1 | 9.0 |
| Percentage of Assets srt:ParentCompany | 87.5 | 93.3 | 83.1 | 92.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | 2010-03-31 | 2009-12-31 | 2008-12-31 |
| Value | 2828 | 2749 | 2628 | 2402 | 2340 | 2325 | 2391 | 2354 | 2326 | 2330 | 2314 | 2327 | 2286 | 2245 | 2165 | 2130 | 2130 | 2127 | 2070 | 1981 | 1906 | 1886 | 1892 | 1835 | 1805 | 1781 | 1725 | 1657 | 1580 | 1513 | 1443 | 1377 | 1319 | 1226 | 1165 | 1176 | 1144 | 1107 | 1066 | 1011 | 988 | 955 | 906 | 844 | 873 | 839 | 784 | 643 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 12.3 | 12.4 | 11.6 | 10.8 | 10.4 | 10.0 | 10.1 | 9.8 | 9.6 | 9.4 | 9.2 | 9.3 | 9.1 | 9.4 | 9.0 | 8.6 | 8.4 | 8.1 | 7.6 | 7.2 | 6.6 | 6.4 | 6.2 | 5.9 | 6.0 | 5.9 | 5.7 | 5.4 | 5.0 | 5.5 | 5.2 | 5.2 | 5.0 | 4.6 | 4.4 | 4.8 | 4.5 | 4.4 | 4.1 | 3.9 | 4.0 | 0.0 | 3.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 2632 | 2391 | 2308 | 2153 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 100.2 | 100.0 | 99.7 | 99.5 |
| Percentage of Assets | 11.6 | 10.1 | 9.2 | 9.0 |
| Percentage of Assets srt:ParentCompany | 87.5 | 93.5 | 83.3 | 93.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2015-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 0.275 | 0.274 | 0.272 | 0.272 | 0.272 | 0.286 | 0.285 | 0.284 | 0.284 | 0.286 | 0.288 | 0.293 | 0.293 | 0.293 | 0.293 | 0.294 | 0.304 | 0.307 | 0.306 | 0.308 | 0.31 | 0.325 | 0.348 | 0.349 | 0.351 | 0.356 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassA us-gaap:CommonStock | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2015-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 0.111 | 0.112 | 0.112 | 0.112 | 0.112 | 0.113 | 0.113 | 0.113 | 0.113 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 | 0.115 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassB us-gaap:CommonStock | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 |
| Value | 10 | 9.022 | 6.102 | 4.284 | 3.233 | 0.859 | 2.972 | 2.89 | 3.144 | 3.552 | 3.883 | 3.975 | 2.704 | 3.022 | 4.617 | 4.187 | 4.251 | 5.315 | 4.73 | -0.424 | -2.277 | 1.416 | 2.284 | 2.876 | 3.283 | 4.872 | 5.135 | 5.099 | 5.569 | 2.679 | 4.819 | 5.722 | 2.597 | 5.05 | 2.813 | -1.933 | -0.409 | 0.605 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 0.4 | 0.3 | 0.2 | 0.2 | 0.1 | 0.0 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | -0.0 | -0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 0.3 | 0.3 | 0.4 | 0.2 | 0.3 | 0.4 | 0.2 | 0.4 | 0.2 | -0.2 | -0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | 2010-03-31 | 2009-12-31 | 2008-12-31 |
| Value | 10 | 5.859 | 3.794 | 1.704 | 1.867 | 9.14 | 5.715 | 3.678 | 1.67 | 0.636 | 0.622 | 4.908 | 2.586 | 0.448 | 0.521 | 0.36 | 0.366 | 2.236 | 0.42 | 0.224 | 4.601 | 2.913 | 0.0 | 1.441 | 0.0 | 13 | 17 | 18 | 20 | 27 | 24 | 24 | 27 | 27 | 32 | 52 | 52 | 50 | 49 | 54 | 74 | 73 | 76 | 75 | 101 | 112 | 109 | 103 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 0.4 | 0.2 | 0.1 | 0.1 | 0.1 | 0.4 | 0.2 | 0.2 | 0.1 | 0.0 | 0.0 | 0.2 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.2 | 0.2 | 0.0 | 0.1 | 0.0 | 0.7 | 1.0 | 1.1 | 1.3 | 1.8 | 1.7 | 1.7 | 2.0 | 2.3 | 2.8 | 4.5 | 4.6 | 4.6 | 4.6 | 5.4 | 7.5 | 7.7 | 8.4 | 9.0 | 11.6 | 13.5 | 13.9 | 16.1 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.3 | 0.0 | 0.3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:AdditionalPaidInCapital | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 |
| Value | -5.182 | -3.089 | -3.693 | 3.346 | 3.99 | 5.12 | 4.382 | 4.515 | 4.292 | 4.298 | 10 | 10 | 9.834 | 9.473 | 15 | 18 | 15 | 19 | 9.27 | 9.011 | 8.916 | 8.672 | 7.726 | 0.246 | 0.3 | 0.271 | 0.23 | 0.268 | 0.386 | 0.755 | 0.328 | 0.05 | 0.113 | 0.281 | 0.005 | 0.417 | 0.293 | 0.157 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | -0.2 | -0.1 | -0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.4 | 0.4 | 0.4 | 0.4 | 0.7 | 0.9 | 0.7 | 0.9 | 0.4 | 0.5 | 0.5 | 0.5 | 0.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | -0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:NoncontrollingInterest | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 | 2010-03-31 | 2009-12-31 | 2008-12-31 |
| Value | 2812 | 2736 | 2621 | 2393 | 2331 | 2310 | 2377 | 2343 | 2317 | 2321 | 2299 | 2307 | 2271 | 2231 | 2143 | 2106 | 2110 | 2100 | 2056 | 1971 | 1894 | 1873 | 1881 | 1830 | 1801 | 1762 | 1702 | 1633 | 1552 | 1482 | 1413 | 1347 | 1289 | 1192 | 1129 | 1124 | 1092 | 1056 | 1017 | 957 | 914 | 882 | 831 | 769 | 773 | 726 | 676 | 540 |
| Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest | 99.4 | 99.6 | 99.7 | 99.6 | 99.6 | 99.3 | 99.4 | 99.5 | 99.6 | 99.6 | 99.3 | 99.2 | 99.3 | 99.4 | 99.0 | 98.9 | 99.0 | 98.7 | 99.3 | 99.5 | 99.4 | 99.3 | 99.4 | 99.7 | 99.8 | 98.9 | 98.7 | 98.6 | 98.3 | 97.9 | 97.9 | 97.8 | 97.7 | 97.3 | 96.9 | 95.6 | 95.4 | 95.3 | 95.4 | 94.7 | 92.5 | 92.4 | 91.7 | 91.1 | 88.5 | 86.6 | 86.2 | 84.0 |
| Percentage of Assets | 12.2 | 12.3 | 11.6 | 10.8 | 10.3 | 9.9 | 10.0 | 9.8 | 9.6 | 9.4 | 9.1 | 9.2 | 9.0 | 9.3 | 8.9 | 8.5 | 8.3 | 8.0 | 7.6 | 7.1 | 6.6 | 6.3 | 6.2 | 5.9 | 6.0 | 5.9 | 5.7 | 5.3 | 5.0 | 5.4 | 5.1 | 5.1 | 4.9 | 4.5 | 4.2 | 4.6 | 4.3 | 4.2 | 3.9 | 3.6 | 3.7 | 0.0 | 3.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:RetainedEarnings | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 384000.0 | 398000.0 | 403000.0 | 408000.0 |
| Percentage of CommonStockValue | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets srt:ParentCompany | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 275000.0 | 274000.0 | 272000.0 | 272000.0 | 272000.0 | 286000.0 | 285000.0 | 284000.0 | 284000.0 | 286000.0 | 288000.0 | 293000.0 | 293000.0 | 293000.0 | 293000.0 | 294000.0 | 304000.0 | 307000.0 | 306000.0 | 308000.0 | 310000.0 | 310000.0 | 325000.0 | 334000.0 | 337000.0 | 347000.0 | 348000.0 | 348000.0 | 349000.0 | 350000.0 | 349000.0 | 349000.0 | 350000.0 | 350000.0 | 351000.0 | 358000.0 | 358000.0 | 358000.0 | 356000.0 | 360000.0 | 370000.0 | 368000.0 |
| Percentage of CommonStockValue | 0.0 | 0.0 | 70.8 | 0.0 | 0.0 | 0.0 | 71.6 | 0.0 | 0.0 | 0.0 | 71.5 | 0.0 | 0.0 | 0.0 | 71.8 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassA | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2010-12-31 |
| Value | 111000.0 | 112000.0 | 112000.0 | 112000.0 | 112000.0 | 113000.0 | 113000.0 | 113000.0 | 113000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 | 115000.0 |
| Percentage of CommonStockValue | 0.0 | 0.0 | 29.2 | 0.0 | 0.0 | 0.0 | 28.4 | 0.0 | 0.0 | 0.0 | 28.5 | 0.0 | 0.0 | 0.0 | 28.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassB | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2010-12-31 |
| Value | 10 | 5.859 | 3.794 | 1.704 | 1.867 | 9.14 | 5.715 | 3.678 | 1.67 | 0.636 | 0.622 | 4.908 | 2.586 | 0.448 | 0.521 | 0.36 | 0.366 | 2.236 | 0.42 | 0.224 | 4.601 | 2.913 | 0.0 | 1.441 | 0.0 | 13 | 17 | 18 | 20 | 27 | 24 | 24 | 27 | 27 | 32 | 52 | 52 | 50 | 49 | 54 | 76 |
| Percentage of AdditionalPaidInCapital | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.3 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 3.794 | 5.715 | 0.622 | 0.521 |
| Percentage of AdditionalPaidInCapital | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets srt:ParentCompany | 0.1 | 0.2 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2010-12-31 |
| Value | 2812 | 2736 | 2621 | 2393 | 2331 | 2310 | 2377 | 2343 | 2317 | 2321 | 2299 | 2307 | 2271 | 2231 | 2143 | 2106 | 2110 | 2100 | 2056 | 1971 | 1894 | 1873 | 1881 | 1830 | 1801 | 1762 | 1702 | 1633 | 1552 | 1482 | 1413 | 1347 | 1289 | 1192 | 1129 | 1124 | 1092 | 1056 | 1017 | 957 | 831 |
| Percentage of RetainedEarningsAccumulatedDeficit | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 12.2 | 12.3 | 11.6 | 10.8 | 10.3 | 9.9 | 10.0 | 9.8 | 9.6 | 9.4 | 9.1 | 9.2 | 9.0 | 9.3 | 8.9 | 8.5 | 8.3 | 8.0 | 7.6 | 7.1 | 6.6 | 6.3 | 6.2 | 5.9 | 6.0 | 5.9 | 5.7 | 5.3 | 5.0 | 5.4 | 5.1 | 5.1 | 4.9 | 4.5 | 4.2 | 4.6 | 4.3 | 4.2 | 3.9 | 3.6 | 3.2 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 2621 | 2377 | 2299 | 2143 |
| Percentage of RetainedEarningsAccumulatedDeficit | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 11.6 | 10.0 | 9.1 | 8.9 |
| Percentage of Assets srt:ParentCompany | 87.1 | 93.0 | 82.9 | 92.6 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 |
| Value | 10 | 9.022 | 6.102 | 4.284 | 3.233 | 0.859 | 2.972 | 2.89 | 3.144 | 3.552 | 3.883 | 3.975 | 2.704 | 3.022 | 4.617 | 4.187 | 4.251 | 5.315 | 4.73 | -0.424 | -2.277 | 1.416 | 2.284 | 2.876 | 3.283 | 4.872 | 5.135 | 5.099 | 5.569 | 2.679 | 4.819 | 5.722 | 2.597 | 5.05 | 2.813 | -1.933 | -0.409 | 0.605 | 0.0 |
| Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -0.0 | -0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 6.102 | 2.972 | 3.883 | 4.617 |
| Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets srt:ParentCompany | 0.2 | 0.1 | 0.1 | 0.2 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 |
| Value | -5.182 | -3.089 | -3.693 | 3.346 | 3.99 | 5.12 | 4.382 | 4.515 | 4.292 | 4.298 | 10 | 10 | 9.834 | 9.473 | 15 | 18 | 15 | 19 | 9.27 | 9.011 | 8.916 | 8.672 | 7.726 | 0.246 | 0.3 | 0.271 | 0.23 | 0.268 | 0.386 | 0.755 | 0.328 | 0.05 | 0.113 | 0.281 | 0.005 | 0.417 | 0.293 | 0.157 | 0.0 |
| Percentage of MinorityInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 |
| Percentage of Assets | -0.0 | -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 |
| Value | 0.377 | 5.172 | 4.188 | 4.07 |
| Percentage of MinorityInterest | -10.2 | 118.0 | 40.6 | 25.7 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets srt:ParentCompany | 0.0 | 0.2 | 0.2 | 0.2 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 1824000.0 | 2091000.0 | 473000.0 | 553000.0 | 1660000.0 | 2941000.0 | 450000.0 | 524000.0 | 1384000.0 | 2494000.0 | 509000.0 | 580000.0 | 1911000.0 | 2173000.0 | 260000.0 | 278000.0 | 992000.0 | 2090000.0 | 275000.0 | 282000.0 | 954000.0 | 2708000.0 | 182000.0 | 268000.0 | 945000.0 | 2468000.0 | 213000.0 | 213000.0 | 883000.0 | 2246000.0 | 146000.0 | 264000.0 | 695000.0 | 1273000.0 | 368000.0 | 271000.0 | 852000.0 | 2426000.0 | 266000.0 | 315000.0 | 1028000.0 | 3089000.0 | 388000.0 | 602000.0 | 702000.0 |
| Percentage of StockIssuedDuringPeriodValueNewIssues | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 |
| Value | 0 | 2000.0 | 0 | 1000.0 | 0 | 1000.0 | 1000.0 | 0 | 0 | 1000.0 | 0 | 0 | 1000.0 | 2000.0 | 0 | 0 | 0 | 1000.0 | 0 |
| Percentage of StockIssuedDuringPeriodValueNewIssues | 0.0 | 0.1 | 0.0 | 0.2 | 0.0 | 0.0 | 0.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:CommonClassA us-gaap:CommonStock | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 1824000.0 | 2089000.0 | 473000.0 | 553000.0 | 1660000.0 | 2940000.0 | 449000.0 | 524000.0 | 1384000.0 | 2493000.0 | 509000.0 | 580000.0 | 1910000.0 | 2171000.0 | 260000.0 | 278000.0 | 992000.0 | 2089000.0 | 275000.0 | 282000.0 | 954000.0 | 2707000.0 | 182000.0 | 267000.0 | 945000.0 | 2467000.0 | 212000.0 | 213000.0 | 882000.0 | 2244000.0 | 146000.0 | 264000.0 | 694000.0 | 1272000.0 | 368000.0 | 271000.0 | 851000.0 | 2424000.0 | 267000.0 | 314000.0 | 1027000.0 | 3087000.0 | 388000.0 | 601000.0 | 701000.0 |
| Percentage of StockIssuedDuringPeriodValueNewIssues | 100.0 | 99.9 | 100.0 | 100.0 | 100.0 | 100.0 | 99.8 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 99.9 | 99.9 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 99.6 | 100.0 | 100.0 | 99.5 | 100.0 | 99.9 | 99.9 | 100.0 | 100.0 | 99.9 | 99.9 | 100.0 | 100.0 | 99.9 | 99.9 | 100.4 | 99.7 | 99.9 | 99.9 | 100.0 | 99.8 | 99.9 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:AdditionalPaidInCapital | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 2874000.0 | 1985000.0 | 1831000.0 | 1864000.0 | 1857000.0 | 1738000.0 | 1738000.0 | 1705000.0 | 1590000.0 | 1368000.0 | 1668000.0 | 1934000.0 | 1506000.0 | 1087000.0 | 980000.0 | 1042000.0 | 1075000.0 | 1096000.0 | 638000.0 | 1132000.0 | 1133000.0 | 1183000.0 | 1231000.0 | 1246000.0 | 1353000.0 | 1357000.0 | 1303000.0 | 1248000.0 | 1135000.0 | 875000.0 | 794000.0 | 824000.0 | 808000.0 | 676000.0 | 615000.0 | 584000.0 | 593000.0 | 395000.0 | 294000.0 | 310000.0 | 342000.0 | 355000.0 | 372000.0 | 405000.0 | 366000.0 |
| Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 2874000.0 | 1985000.0 | 1831000.0 | 1864000.0 | 1857000.0 | 1738000.0 | 1738000.0 | 1705000.0 | 1590000.0 | 1368000.0 | 1668000.0 | 1934000.0 | 1506000.0 | 1087000.0 | 980000.0 | 1042000.0 | 1075000.0 | 1096000.0 | 638000.0 | 1132000.0 | 1133000.0 | 1183000.0 | 1231000.0 | 1246000.0 | 1353000.0 | 1357000.0 | 1303000.0 | 1248000.0 | 1135000.0 | 875000.0 | 794000.0 | 824000.0 | 808000.0 | 676000.0 | 615000.0 | 584000.0 | 593000.0 | 395000.0 | 294000.0 | 310000.0 | 342000.0 | 355000.0 | 372000.0 | 405000.0 | 366000.0 |
| Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:AdditionalPaidInCapital | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 |
| Value | 6.727 | 0.102 | 15 | 0.331 | 0.534 | 0.055 | 0.125 | 3.865 | 0.091 | 0.022 | 0.174 | 0.095 | 0.238 | 0.019 | 0.371 | 0.759 | 0.205 | 0.31 | 0.353 | 0.0 | 0.122 | 0.097 | 0.356 | -0.08 | -0.044 | 0.0 | 3.594 | -0.275 | 1.062 | -0.287 | -0.29 | -0.279 | -0.782 | 0.0 | -0.431 | 0.0 |
| Percentage of MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 |
| Value | 6.727 | 0.102 | 15 | 0.331 | 0.534 | 0.055 | 0.125 | 3.865 | 0.091 | 0.022 | 0.174 | 0.095 | 0.238 | 0.019 | 0.371 | 0.759 | 0.205 | 0.31 | 0.353 | 0.0 | 0.122 | 0.097 | 0.356 | -0.08 | -0.044 | 3.594 | -0.275 | 1.062 | 0.287 | 0.29 | 0.279 | -0.782 |
| Percentage of MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | -100.0 | -100.0 | -100.0 | 100.0 |
| Percentage of Assets | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of Assets us-gaap:NoncontrollingInterest | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 138 | 48 | 39 | 278 | 38 | -144.455 | 155 | 160 | 121 | -139.665 | 77 | 121 | 13 | 57 | -2.827 | 98 | 58 | 73 | 66 | 83 | 70 | 104 | 84 | 115 | 62 | 129 | 94 | 106 | 67 | 88 | 184 | 49 | 68 | 84 | 38 | 99 | 60 | 100 | 98 | 43 | 86 | 81 | 179 | -45.581 |
| Percentage of NetCashProvidedByUsedInOperatingActivities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 104.0 | 37.7 | 28.7 | 199.4 | 25.6 | -76.4 | 73.5 | 67.3 | 49.4 | -55.7 | 30.7 | 50.8 | 6.0 | 28.6 | -1.4 | 49.9 | 30.2 | 40.2 | 35.7 | 42.6 | 38.0 | 54.4 | 43.5 | 61.0 | 35.2 | 74.3 | 51.1 | 56.3 | 38.4 | 55.8 | 109.9 | 30.8 | 42.7 | 54.1 | 24.8 | 65.5 | 39.9 | 65.2 | 62.9 | 27.7 | 61.9 | 59.1 | 118.7 | -28.4 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | -711.784 | 468 | -332.418 | 236 | 611 | 105 | 331 | 337 | 469 | 386 | 204 | 149 | -1187.913 | 102 | 747 | 698 | 772 | 1051 | 595 | 1034 | 899 | 729 | 569 | 523 | 292 | 31 | 447 | 618 | -1516.385 | 340 | 402 | -180.513 | 408 | -134.291 | -2168.141 | 924 | 114 | 336 | 309 | 311 | 466 | 352 | 2493 | 251 |
| Percentage of NetCashProvidedByUsedInInvestingActivities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | -532.8 | 362.8 | -239.4 | 169.1 | 402.7 | 55.9 | 156.3 | 141.1 | 190.1 | 154.2 | 80.9 | 62.1 | -518.3 | 50.4 | 380.1 | 354.7 | 400.3 | 572.0 | 319.6 | 527.3 | 483.1 | 380.0 | 294.8 | 276.9 | 164.5 | 18.3 | 242.7 | 326.5 | -857.0 | 214.3 | 239.9 | -112.7 | 256.2 | -85.5 | -1389.9 | 609.3 | 75.3 | 218.5 | 196.7 | 197.6 | 333.6 | 255.2 | 1652.8 | 157.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 703 | -528.147 | 349 | -534.761 | -829.491 | -83.48 | -403.554 | -413.678 | -588.637 | -387.402 | -84.564 | -239.891 | 1213 | -177.076 | -932.282 | -611.36 | -870.116 | -1086.742 | -659.391 | -1110.236 | -962.251 | -846.669 | -704.223 | -707.019 | -272.829 | -191.608 | -486.445 | -742.516 | 1433 | -385.28 | -575.356 | 113 | -458.403 | 33 | 2101 | -986.082 | -179.622 | -419.276 | -458.023 | -379.429 | -484.681 | -669.783 | -2704.831 | -164.74 |
| Percentage of NetCashProvidedByUsedInFinancingActivities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 526.3 | -409.1 | 251.7 | -382.7 | -546.1 | -44.1 | -190.0 | -173.1 | -238.5 | -154.6 | -33.5 | -100.0 | 529.4 | -87.3 | -474.1 | -310.5 | -450.7 | -591.2 | -353.9 | -565.9 | -516.6 | -440.9 | -364.7 | -373.8 | -153.5 | -110.0 | -263.6 | -392.0 | 810.1 | -242.5 | -342.7 | 71.1 | -287.3 | 21.2 | 1347.4 | -650.2 | -118.1 | -272.0 | -291.1 | -240.7 | -346.7 | -485.1 | -1793.1 | -102.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 130 | -11.204 | 56 | -19.774 | -179.023 | -122.263 | 84 | 84 | 2.372 | -140.766 | 196 | 31 | 39 | -16.794 | -143.087 | 98 | -3.214 | -180.823 |
| Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 97.5 | -8.7 | 40.9 | -14.2 | -117.9 | -64.6 | 39.7 | 35.2 | 1.0 | -56.2 | 78.1 | 13.0 | 17.1 | -8.3 | -72.8 | 50.2 | -1.7 | -98.4 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 2.768 | 15 | 18 | 3.787 | 11 | -26.0 | 2.327 | 5.431 | -12.216 | -2.807 | -12.593 | 2.28 | 4.411 | 16 | 13 | 0.237 | -13.496 | -1.753 | 34 | 12 | -16.0 | -4.26 | 14 | -11.02 | 2.895 | 0.224 | -1.732 | 15 | 3.156 | 2.497 | -10.74 | -7.965 | 16 | 4.874 | 5.312 | -8.658 | -13.293 | -7.19 | 8.19 | -7.201 | -8.815 | 0.1 | 8.565 | -11.521 |
| Percentage of DeferredIncomeTaxExpenseBenefit | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 |
| Value | 38 | 38 | 49 | 49 | 50 | 48 | 50 | 48 | 47 | 46 | 47 | 47 | 45 | 43 | 37 | 33 | 32 | 34 | 38 | 21 | 31 | 31 | 32 | 30 | 29 | 30 | 29 | 29 | 27 | 21 | 21 | 19 | 19 | 20 | 63 | 18 | 7.452 | 28 | 49 | 18 |
| Percentage of DepreciationDepletionAndAmortization | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 5.615 | 3.831 | 4.595 | -3.867 | 10 | -52.185 | 48 | 1.665 | -10.599 | 16 | -18.387 | 17 | -2.223 | -0.177 | -14.61 | 10 | 14 | 1.972 | -9.436 | 11 | -3.501 | -5.961 | -15.149 | 3.747 | 4.925 | 5.416 | -8.574 | 1.189 | -5.063 | 5.758 | -6.879 | -3.065 | -7.223 | 9.601 | -7.761 | 4.398 | 2.786 | 0.561 | 4.76 | 4.782 | 1.3 | 0.198 | -16.099 | 42 |
| Percentage of IncreaseDecreaseInAccountsReceivable | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 138 | 48 | 39 | 278 | 38 | -144.455 | 155 | 160 | 121 | -139.665 | 77 | 121 | 13 | 57 | -2.827 | 98 | 58 | 73 | 66 | 83 | 70 | 104 | 84 | 115 | 62 | 129 | 94 | 106 | 67 | 88 | 184 | 49 | 68 | 84 | 38 | 99 | 60 | 100 | 98 | 43 | 86 | 81 | 179 | -45.581 |
| Percentage of NetCashProvidedByUsedInOperatingActivities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 104.0 | 37.7 | 28.7 | 199.4 | 25.6 | -76.4 | 73.5 | 67.3 | 49.4 | -55.7 | 30.7 | 50.8 | 6.0 | 28.6 | -1.4 | 49.9 | 30.2 | 40.2 | 35.7 | 42.6 | 38.0 | 54.4 | 43.5 | 61.0 | 35.2 | 74.3 | 51.1 | 56.3 | 38.4 | 55.8 | 109.9 | 30.8 | 42.7 | 54.1 | 24.8 | 65.5 | 39.9 | 65.2 | 62.9 | 27.7 | 61.9 | 59.1 | 118.7 | -28.4 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 83 | 123 | 234 | 71 | 86 | -40.532 | 42 | 33 | 24 | 41 | 21 | 42 | 49 | 113 | 48 | 46 | 28 | 50 | 98 | 84 | 26 | 47 | 83 | 48 | 70 | 64 | 73 | 85 | 74 | 73 | 70 | 62 | 101 | 68 | 56 | 36 | 41 | 43 | 64 | 47 | 37 | 54 | 85 | -0.368 | 49 |
| Percentage of NetIncomeLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.8 | 95.7 | 169.3 | 51.2 | 56.9 | -21.4 | 20.0 | 13.9 | 10.0 | 16.6 | 8.6 | 17.9 | 21.6 | 56.2 | 24.5 | 23.5 | 14.9 | 27.2 | 52.8 | 43.0 | 14.0 | 25.0 | 43.2 | 25.9 | 39.9 | 37.2 | 39.9 | 45.0 | 42.4 | 46.4 | 42.0 | 39.2 | 63.5 | 43.3 | 36.3 | 24.3 | 27.2 | 28.0 | 41.2 | 30.1 | 26.6 | 39.7 | 56.4 | -0.2 | 31.9 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 82 | 121 | 231 | 70 | 85 | -39.974 | 41 | 32 | 24 | 41 | 21 | 42 | 48 | 112 | 47 | 45 | 28 | 49 | 97 | 83 | 25 | 47 | 82 | 48 | 70 | 64 | 72 | 84 | 74 | 73 | 69 | 62 | 100 | 67 | 56 | 36 | 41 | 42 |
| Percentage of NetIncomeLoss | 98.3 | 98.5 | 98.6 | 98.6 | 98.6 | 98.6 | 98.7 | 98.7 | 98.7 | 98.7 | 98.4 | 98.7 | 98.8 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 99.0 | 98.9 | 98.9 | 98.9 | 98.9 | 98.9 | 98.9 | 99.0 | 99.0 | 99.1 | 99.1 | 99.1 | 99.1 | 99.2 | 99.2 | 99.2 | 99.2 | 99.4 |
| Percentage of InterestAndDividendIncomeOperating | 61.7 | 94.3 | 166.9 | 50.4 | 56.1 | -21.1 | 19.7 | 13.7 | 9.8 | 16.4 | 8.4 | 17.7 | 21.3 | 55.6 | 24.2 | 23.3 | 14.7 | 26.9 | 52.2 | 42.5 | 13.9 | 24.7 | 42.7 | 25.6 | 39.5 | 36.8 | 39.5 | 44.5 | 42.0 | 46.0 | 41.6 | 38.9 | 62.9 | 43.0 | 36.0 | 24.1 | 27.0 | 27.8 |
| Percentage of InterestAndDividendIncomeOperating nni:CommonShareholders | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | 1.388 | 1.832 | 3.334 | 1.02 | 1.239 | -0.558 | 0.559 | 0.434 | 0.327 | 0.534 | 0.337 | 0.573 | 0.575 | 1.137 | 0.475 | 0.453 | 0.28 | 0.521 | 1.032 | 0.875 | 0.271 | 0.509 | 0.885 | 0.519 | 0.763 | 0.687 | 0.796 | 0.889 | 0.731 | 0.661 | 0.618 | 0.553 | 0.904 | 0.562 | 0.439 | 0.29 | 0.336 | 0.279 |
| Percentage of NetIncomeLoss | 1.7 | 1.5 | 1.4 | 1.4 | 1.4 | 1.4 | 1.3 | 1.3 | 1.3 | 1.3 | 1.6 | 1.3 | 1.2 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.0 | 1.0 | 0.9 | 0.9 | 0.9 | 0.9 | 0.8 | 0.8 | 0.8 | 0.8 | 0.6 |
| Percentage of InterestAndDividendIncomeOperating | 1.0 | 1.4 | 2.4 | 0.7 | 0.8 | -0.3 | 0.3 | 0.2 | 0.1 | 0.2 | 0.1 | 0.2 | 0.3 | 0.6 | 0.2 | 0.2 | 0.1 | 0.3 | 0.6 | 0.4 | 0.1 | 0.3 | 0.5 | 0.3 | 0.4 | 0.4 | 0.4 | 0.5 | 0.4 | 0.4 | 0.4 | 0.3 | 0.6 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 |
| Percentage of InterestAndDividendIncomeOperating nni:UnvestedRestrictedStockShareholders | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -0.791 | -19.534 | 165 | -14.953 | 32 | -19.821 | -6.633 | -7.204 | -5.56 | -9.413 |
| Percentage of NetIncomeLoss | -0.9 | -15.8 | 70.3 | -20.9 | 37.9 | 48.9 | -15.7 | -21.7 | -22.6 | -22.6 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | -15.1 | 119.0 | -10.7 | 21.6 | -10.5 | -3.1 | -3.0 | -2.3 | -3.8 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -51.9 | -1567.7 | 0.0 | -908.4 | 2742.6 | -1274.7 | 0.0 | -252.0 | -246.2 | -458.5 |
| Period End | 2021-03-31 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | 0.711 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of NetIncomeLoss | 0.6 | 0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | 0.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:IntersegmentElimination | -326.1 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 | -0.0 | -0.0 | 0.0 | -0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 59 | 107 | 62 | 68 | 39 | -46.318 | 38 | 19 | 9.732 | 20 | 13 | 39 | 42 | 87 | 37 | 35 | 21 |
| Percentage of NetIncomeLoss | 71.5 | 87.1 | 26.6 | 95.6 | 45.2 | 114.3 | 91.0 | 58.7 | 39.5 | 48.5 | 64.4 | 91.3 | 86.4 | 77.2 | 77.9 | 77.2 | 74.1 |
| Percentage of InterestAndDividendIncomeOperating | 44.9 | 83.4 | 45.1 | 48.9 | 25.7 | -24.5 | 18.2 | 8.2 | 3.9 | 8.1 | 5.5 | 16.3 | 18.6 | 43.4 | 19.0 | 18.2 | 11.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 46.1 | 85.1 | 0.0 | 49.5 | 25.9 | -24.9 | 0.0 | 8.4 | 4.0 | 8.2 | 0.0 | 16.6 | 18.9 | 43.9 | 0.0 | 18.3 | 11.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -10.876 | -3.45 | -5.363 | -5.536 | -6.582 | -7.194 | -4.932 | -4.81 | -5.879 | -7.741 | -8.082 | -7.04 | -5.45 | -4.602 | -3.637 |
| Percentage of NetIncomeLoss | -4.6 | -4.8 | -6.2 | 13.7 | -15.5 | -21.7 | -20.0 | -11.6 | -27.2 | -18.0 | -16.3 | -6.2 | -11.3 | -9.9 | -12.7 |
| Percentage of InterestAndDividendIncomeOperating | -7.8 | -2.5 | -3.5 | -2.9 | -3.1 | -3.0 | -2.0 | -1.9 | -2.3 | -3.2 | -3.5 | -3.5 | -2.8 | -2.3 | -1.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -493200.0 | -240500.0 | 0.0 | -774100.0 | -808200.0 | -704000.0 | 0.0 | -460200.0 | -363700.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 13 | 23 | 9.207 | 11 | 8.885 | 20 | 7.252 | 12 | 8.374 | 18 | -1.183 | 7.591 | 5.64 | 13 | 2.397 | 5.744 | 4.954 |
| Percentage of NetIncomeLoss | 15.6 | 19.0 | 3.9 | 16.0 | 10.3 | -51.3 | 17.1 | 38.3 | 34.0 | 45.6 | -5.5 | 17.7 | 11.4 | 11.7 | 5.0 | 12.4 | 17.2 |
| Percentage of InterestAndDividendIncomeOperating | 9.8 | 18.2 | 6.6 | 8.2 | 5.8 | 11.0 | 3.4 | 5.3 | 3.4 | 7.6 | -0.5 | 3.2 | 2.5 | 6.6 | 1.2 | 2.9 | 2.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 6236.2 | 8950.6 | 0.0 | 3115.3 | 2115.5 | 1044.0 | 0.0 | 363.3 | 504.8 | 941.3 | 0.0 | 501.7 | 754.0 | 2011.9 | 0.0 | 114880.0 | 165133.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 11 | 12 | 8.98 | 10 | 11 | 10 | 9.759 | 15 | 17 | 16 | 14 | 9.982 | 13 | 15 | 6.065 | 8.056 | 8.024 |
| Percentage of NetIncomeLoss | 14.1 | 9.9 | 3.8 | 14.2 | 12.8 | -25.5 | 23.0 | 46.3 | 69.1 | 40.0 | 66.7 | 23.3 | 27.2 | 13.9 | 12.6 | 17.4 | 27.9 |
| Percentage of InterestAndDividendIncomeOperating | 8.8 | 9.5 | 6.5 | 7.3 | 7.3 | 5.5 | 4.6 | 6.4 | 6.9 | 6.6 | 5.7 | 4.2 | 5.9 | 7.8 | 3.1 | 4.1 | 4.2 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 39300.0 | 35952.9 | 0.0 | 29820.6 | 21334.6 | 3266.2 | 0.0 | 2893.4 | 3091.6 | 3350.3 | 0.0 | 2619.9 | 4586.7 | 6163.8 | 0.0 | 5480.3 | 6686.7 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -0.204 | -0.968 |
| Percentage of NetIncomeLoss | -0.2 | -0.8 |
| Percentage of InterestAndDividendIncomeOperating | -0.2 | -0.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | -10.0 | -70.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | 83 | 122 | 231 | 71 | 86 | -39.765 | 41 | 33 | 24 | 41 | 21 | 43 | 49 | 113 | 45 | 43 | 24 | 47 | 98 | 84 | 26 | 48 | 83 | 48 | 70 | 64 | 73 | 85 | 75 | 74 | 71 | 63 | 101 | 68 | 56 | 36 | 41 | 43 | 64 | 47 | 37 | 54 |
| Percentage of ProfitLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.1 | 95.2 | 166.8 | 50.9 | 57.0 | -21.0 | 19.7 | 13.9 | 10.0 | 16.6 | 8.6 | 18.0 | 21.6 | 55.8 | 23.2 | 22.1 | 12.8 | 26.1 | 53.1 | 43.0 | 14.1 | 25.0 | 43.3 | 25.9 | 39.9 | 37.2 | 40.1 | 45.1 | 42.8 | 46.8 | 42.3 | 39.3 | 63.8 | 43.5 | 36.3 | 24.4 | 27.3 | 28.1 | 41.2 | 30.1 | 26.6 | 39.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -1.645 | -19.517 | 161 | -15.28 | 32 | -19.054 | -7.18 | -7.281 | -5.501 | -9.357 |
| Percentage of ProfitLoss | -2.0 | -15.9 | 69.9 | -21.5 | 38.0 | 47.9 | -17.2 | -22.0 | -22.3 | -22.5 |
| Percentage of InterestAndDividendIncomeOperating | -1.2 | -15.1 | 116.5 | -10.9 | 21.7 | -10.1 | -3.4 | -3.0 | -2.2 | -3.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:CorporateNonSegment | -107.9 | -1566.4 | 0.0 | -928.3 | 2753.3 | -1225.3 | 0.0 | -254.7 | -243.6 | -455.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 59 | 107 | 62 | 68 | 39 | -46.318 | 38 | 19 | 9.732 | 20 | 13 | 39 | 42 | 87 | 37 | 35 | 21 |
| Percentage of ProfitLoss | 72.2 | 87.6 | 27.0 | 96.0 | 45.1 | 116.5 | 92.2 | 58.9 | 39.4 | 48.5 | 64.2 | 90.9 | 86.2 | 77.7 | 81.9 | 82.1 | 86.4 |
| Percentage of InterestAndDividendIncomeOperating | 44.9 | 83.4 | 45.1 | 48.9 | 25.7 | -24.5 | 18.2 | 8.2 | 3.9 | 8.1 | 5.5 | 16.3 | 18.6 | 43.4 | 19.0 | 18.2 | 11.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:AssetGenerationAndManagementSegment | 46.1 | 85.1 | 0.0 | 49.5 | 25.9 | -24.9 | 0.0 | 8.4 | 4.0 | 8.2 | 0.0 | 16.6 | 18.9 | 43.9 | 0.0 | 18.3 | 11.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -10.876 | -3.45 | -5.363 | -5.536 | -6.582 | -7.194 | -4.932 | -4.81 | -5.879 | -7.741 | -8.082 | -7.04 | -5.45 | -4.602 | -3.637 |
| Percentage of ProfitLoss | -4.7 | -4.8 | -6.2 | 13.9 | -15.7 | -21.7 | -20.0 | -11.5 | -27.1 | -17.9 | -16.3 | -6.2 | -11.9 | -10.6 | -14.8 |
| Percentage of InterestAndDividendIncomeOperating | -7.8 | -2.5 | -3.5 | -2.9 | -3.1 | -3.0 | -2.0 | -1.9 | -2.3 | -3.2 | -3.5 | -3.5 | -2.8 | -2.3 | -1.9 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:CommunicationsSegment | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -493200.0 | -240500.0 | 0.0 | -774100.0 | -808200.0 | -704000.0 | 0.0 | -460200.0 | -363700.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 13 | 23 | 9.207 | 11 | 8.885 | 20 | 7.252 | 12 | 8.374 | 18 | -1.183 | 7.591 | 5.64 | 13 | 2.397 | 5.744 | 4.954 |
| Percentage of ProfitLoss | 15.8 | 19.2 | 4.0 | 16.1 | 10.3 | -52.3 | 17.3 | 38.4 | 33.9 | 45.6 | -5.5 | 17.6 | 11.4 | 11.8 | 5.2 | 13.2 | 20.1 |
| Percentage of InterestAndDividendIncomeOperating | 9.8 | 18.2 | 6.6 | 8.2 | 5.8 | 11.0 | 3.4 | 5.3 | 3.4 | 7.6 | -0.5 | 3.2 | 2.5 | 6.6 | 1.2 | 2.9 | 2.6 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:EducationTechnologyServicesAndPaymentProcessingServicesSegment | 6236.2 | 8950.6 | 0.0 | 3115.3 | 2115.5 | 1044.0 | 0.0 | 363.3 | 504.8 | 941.3 | 0.0 | 501.7 | 754.0 | 2011.9 | 0.0 | 114880.0 | 165133.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 11 | 12 | 8.98 | 10 | 11 | 10 | 9.759 | 15 | 17 | 16 | 14 | 9.982 | 13 | 15 | 3.475 | 4.648 | 3.798 |
| Percentage of ProfitLoss | 14.2 | 9.9 | 3.9 | 14.2 | 12.8 | -26.0 | 23.3 | 46.5 | 68.9 | 40.0 | 66.5 | 23.1 | 27.1 | 13.3 | 7.6 | 10.7 | 15.4 |
| Percentage of InterestAndDividendIncomeOperating | 8.8 | 9.5 | 6.5 | 7.3 | 7.3 | 5.5 | 4.6 | 6.4 | 6.9 | 6.6 | 5.7 | 4.2 | 5.9 | 7.4 | 1.8 | 2.4 | 2.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:LoanServicingAndSystemsSegment | 39300.0 | 35952.9 | 0.0 | 29820.6 | 21334.6 | 3266.2 | 0.0 | 2893.4 | 3091.6 | 3350.3 | 0.0 | 2619.9 | 4586.7 | 5849.4 | 0.0 | 3161.9 | 3165.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -0.204 | -0.968 |
| Percentage of ProfitLoss | -0.2 | -0.8 |
| Percentage of InterestAndDividendIncomeOperating | -0.2 | -0.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:OperatingSegments nni:NelnetBank | -10.0 | -70.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | -0.854 | -0.694 | -3.385 | -0.327 | 0.128 | 0.767 | -0.547 | -0.077 | 0.059 | 0.056 | 0.049 | 0.199 | 0.104 | 0.74 | -2.385 | -2.768 | -4.086 | 2.106 | 0.585 | 0.069 | 0.028 | 0.068 | 0.168 | 0.022 | 0.054 | 0.041 | 0.157 | 0.693 | 0.513 | 0.271 | 0.124 | 0.136 | 0.152 | 0.0 | 0.0 | 0.0 |
| Percentage of ProfitLoss | -1.0 | -0.6 | -1.5 | -0.5 | 0.1 | -1.9 | -1.3 | -0.2 | 0.2 | 0.1 | 0.2 | 0.5 | 0.2 | 0.7 | -5.2 | -6.4 | -16.6 | 4.4 | 0.6 | 0.1 | 0.1 | 0.1 | 0.2 | 0.0 | 0.1 | 0.1 | 0.2 | 0.9 | 0.7 | 0.4 | 0.3 | 0.3 | 0.4 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating | -0.6 | -0.5 | -2.4 | -0.2 | 0.1 | 0.4 | -0.3 | -0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.4 | -1.2 | -1.4 | -2.1 | 1.1 | 0.3 | 0.0 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.1 | 0.4 | 0.3 | 0.2 | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.0 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:NoncontrollingInterest | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-03-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 |
| Value | 83 | 123 | 234 | 71 | 86 | -40.532 | 42 | 33 | 24 | 41 | 21 | 42 | 49 | 113 | 48 | 46 | 28 | 50 | 98 | 84 | 26 | 47 | 83 | 48 | 70 | 64 | 85 | 74 | 73 | 68 | 36 | 41 | 43 | 47 | 37 | 54 |
| Percentage of ProfitLoss | 101.0 | 100.6 | 101.5 | 100.5 | 99.9 | 101.9 | 101.3 | 100.2 | 99.8 | 99.9 | 99.8 | 99.5 | 99.8 | 100.7 | 105.2 | 106.4 | 116.6 | 104.4 | 99.4 | 99.9 | 99.9 | 99.9 | 99.8 | 100.0 | 99.9 | 99.9 | 99.8 | 99.1 | 99.3 | 99.6 | 99.7 | 99.7 | 99.6 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 62.8 | 95.7 | 169.3 | 51.2 | 56.9 | -21.4 | 20.0 | 13.9 | 10.0 | 16.6 | 8.6 | 17.9 | 21.6 | 56.2 | 24.5 | 23.5 | 14.9 | 27.2 | 52.8 | 43.0 | 14.0 | 25.0 | 43.2 | 25.9 | 39.9 | 37.2 | 45.0 | 42.4 | 46.4 | 43.3 | 24.3 | 27.2 | 28.0 | 30.1 | 26.6 | 39.7 |
| Percentage of InterestAndDividendIncomeOperating us-gaap:RetainedEarnings | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2014-12-31 | 2014-09-30 | 2013-12-31 | 2013-09-30 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 2.928 | 2.052 | 11 | 1.957 | 1.724 | 1.857 | 1.833 | 1.81 | 1.662 | 1.476 | 1.758 | 2.046 | 1.574 | 1.161 | 1.046 | 1.11 | 1.139 | 1.121 | 0.785 | 1.175 | 1.146 | 1.242 | 1.227 | 1.335 | 1.282 | 0.816 | 0.955 | 0.854 | 0.754 | 0.712 | 0.7 | 0.455 | 0.482 | 0.535 | 0.557 | 0.561 | 0.6 |
| Percentage of ShareBasedCompensation | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | -711.784 | 468 | -332.418 | 236 | 611 | 105 | 331 | 337 | 469 | 386 | 204 | 149 | -1187.913 | 102 | 747 | 698 | 772 | 1051 | 595 | 1034 | 899 | 729 | 569 | 523 | 292 | 31 | 447 | 618 | -1516.385 | 340 | 402 | -180.513 | 408 | -134.291 | -2168.141 | 924 | 114 | 336 | 309 | 311 | 466 | 352 | 2493 | 251 |
| Percentage of NetCashProvidedByUsedInInvestingActivities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | -532.8 | 362.8 | -239.4 | 169.1 | 402.7 | 55.9 | 156.3 | 141.1 | 190.1 | 154.2 | 80.9 | 62.1 | -518.3 | 50.4 | 380.1 | 354.7 | 400.3 | 572.0 | 319.6 | 527.3 | 483.1 | 380.0 | 294.8 | 276.9 | 164.5 | 18.3 | 242.7 | 326.5 | -857.0 | 214.3 | 239.9 | -112.7 | 256.2 | -85.5 | -1389.9 | 609.3 | 75.3 | 218.5 | 196.7 | 197.6 | 333.6 | 255.2 | 1652.8 | 157.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 10 | 17 | 32 | 33 | 21 | 25 | 24 | 23 | 18 | 24 | 28 | 31 | 36 | 28 | 49 | 35 | 44 | 26 | 20 | 17 | 14 | 15 | 4.005 | 3.237 | 1.147 | 8.372 | 4.797 | 12 | 5.876 | 3.146 | 5.29 | 2.162 | 6.78 | 2.778 | 2.574 | 2.965 | 2.099 | 2.306 | 4.391 | 1.495 | 5.289 | 2.992 | 5.274 | 2.826 |
| Percentage of PaymentsToAcquirePropertyPlantAndEquipment | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 703 | -528.147 | 349 | -534.761 | -829.491 | -83.48 | -403.554 | -413.678 | -588.637 | -387.402 | -84.564 | -239.891 | 1213 | -177.076 | -932.282 | -611.36 | -870.116 | -1086.742 | -659.391 | -1110.236 | -962.251 | -846.669 | -704.223 | -707.019 | -272.829 | -191.608 | -486.445 | -742.516 | 1433 | -385.28 | -575.356 | 113 | -458.403 | 33 | 2101 | -986.082 | -179.622 | -419.276 | -458.023 | -379.429 | -484.681 | -669.783 | -2704.831 | -164.74 |
| Percentage of NetCashProvidedByUsedInFinancingActivities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Percentage of InterestAndDividendIncomeOperating | 526.3 | -409.1 | 251.7 | -382.7 | -546.1 | -44.1 | -190.0 | -173.1 | -238.5 | -154.6 | -33.5 | -100.0 | 529.4 | -87.3 | -474.1 | -310.5 | -450.7 | -591.2 | -353.9 | -565.9 | -516.6 | -440.9 | -364.7 | -373.8 | -153.5 | -110.0 | -263.6 | -392.0 | 810.1 | -242.5 | -342.7 | 71.1 | -287.3 | 21.2 | 1347.4 | -650.2 | -118.1 | -272.0 | -291.1 | -240.7 | -346.7 | -485.1 | -1793.1 | -102.7 |
| Period End | 2020-11-05 |
| Value | 20 |
| Percentage of RepaymentsOfLongTermDebt | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 8.475 | 8.437 | 8.435 | 7.664 | 7.733 | 7.946 | 7.939 | 7.143 | 7.171 | 7.232 |
| Percentage of PaymentsOfDividendsCommonStock | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 0.399 | 2.009 | 0.213 | 4.618 | 67 | 1.253 | 0.149 | 0.221 | 23 | 16 | 28 | 0.192 | 4.91 | 11 | 5.565 | 45 | 16 | 1.369 | 8.948 | 7.675 | 0.399 | 52 | 29 | 15 | 43 | 7.939 | 2.376 | 4.033 | 8.435 | 0.869 | 0.121 | 4.026 | 2.285 | 6.704 | 21 | 0.206 | 0.199 | 1.116 | 6.004 | 20 | 0.225 | 0.31 | 0.133 | 26 |
| Percentage of PaymentsForRepurchaseOfCommonStock | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 | 2016-12-31 | 2015-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 41 | 35 | 58 | 37 | 45 | 17 | 16 | 0.709 | 10 | -17.568 |
| Percentage of DeferredTaxLiabilities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 | 2016-12-31 | 2015-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 74 | 56 | 38 | 26 | 40 | 49 | 52 | 66 | 77 | 55 |
| Percentage of DeferredTaxAssetsNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 | 2016-12-31 | 2015-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 | 2010-12-31 |
| Value | 20 | 20 | 23 | 28 | 28 | 27 | 21 | 19 | 29 | 21 | 10 |
| Percentage of UnrecognizedTaxBenefits | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2019-12-31 | 2018-12-31 | 2017-12-31 | 2016-12-31 | 2015-12-31 | 2014-12-31 | 2013-12-31 | 2012-12-31 | 2011-12-31 |
| Value | 569000.0 | 548000.0 | 527000.0 | 254000.0 | 264000.0 | 222000.0 | 304000.0 | -239000.0 | -137000.0 | -250000.0 |
| Percentage of DeferredTaxAssetsValuationAllowance | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-11-02 |
| Value | 100 |
| Percentage of CapitalInvestedInSubsidiary | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 24 | 54 | 34 | 26 | 23 | 53 | 35 | 24 | 15 | 45 | 35 | 17 | 15 | 38 | 24 | 15 |
| Percentage of ContractWithCustomerLiabilityIncreaseDecreaseDeferredRevenue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 0.624 | 0.851 | 0.879 | 0.855 | 0.975 | 0.953 | 0.841 | 0.736 |
| Percentage of ContractWithCustomerLiabilityIncreaseDecreaseDeferredRevenue | 2.5 | 1.6 | 2.5 | 3.3 | 4.2 | 1.8 | 2.4 | 3.1 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 11 | 11 | 10 | 9.927 | 9.658 | 9.302 | 8.798 | 8.266 |
| Percentage of ContractWithCustomerLiabilityIncreaseDecreaseDeferredRevenue | 47.6 | 21.0 | 30.7 | 37.8 | 41.4 | 17.3 | 25.0 | 34.3 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 11 | 41 | 22 | 15 | 11 | 42 | 24 | 13 |
| Percentage of ContractWithCustomerLiabilityIncreaseDecreaseDeferredRevenue | 46.0 | 76.8 | 64.5 | 57.5 | 50.9 | 79.3 | 70.4 | 58.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 0.943 | 0.365 | 0.8 | 0.382 | 0.824 | 0.881 | 0.764 | 1.116 |
| Percentage of ContractWithCustomerLiabilityIncreaseDecreaseDeferredRevenue | 3.8 | 0.7 | 2.3 | 1.5 | 3.5 | 1.6 | 2.2 | 4.6 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 |
| Value | -6.989 | 34 | 1.049 | 1.91 | -16.365 | 1.668 | -24.088 | -11.539 | 17 | 17 | 66 |
| Percentage of DerivativeMarketValueAdjustmentsAndDerivativeSettlementsNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | -11.059 | 1.049 | 1.91 | -16.365 | 3.17 | 1.668 | -24.088 | -11.539 | -29.843 | 17 | 17 | 66 | 7.014 | 7.173 | -27.91 | -4.83 | 83 | 36 | -40.702 | -28.691 | 31 | -30.658 | 6.502 | -3.078 | -5.648 | 24 | 1.57 | -4.265 | -5.655 | -16.648 | 40 | 1.072 | 6.657 | -31.275 | -21.618 | -15.18 | 11 | -13.631 | 20 | -3.036 | 33 | -35.391 | 10 |
| Percentage of DerivativeMarketValueAndForeignCurrencyAdjustmentsAndDerivativeSettlementsNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | -1.615 | 38 | 3.44 | -3.911 | -20.602 | -5.63 | -37.06 |
| Percentage of DerivativeMarketValueAndForeignCurrencyGainLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | -1.615 | 38 | 3.44 | -3.911 | -20.602 | -5.63 | -37.06 |
| Percentage of DerivativeMarketValueAndForeignCurrencyGainLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | -5.374 | -4.304 | -3.987 | -2.391 | 5.821 | 4.237 | 6.1 | 7.298 | 12 | 19 | 19 | 22 | 21 | 6.766 | 2.981 | -0.573 | -0.363 | -1.378 | -3.657 | -6.261 |
| Percentage of DerivativeSettlementsExpenseIncome | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | -5.374 | -4.304 | -3.987 | -2.391 | 5.821 | 4.237 | 6.1 | 7.298 | 12 | 19 | 19 | 22 | 22 | 6.926 | 3.169 | -0.382 | -0.165 |
| Percentage of DerivativeSettlementsExpenseIncome | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.6 | 100.6 | 102.4 | 106.3 | 66.7 | 45.5 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -5.153 | -4.285 | -3.588 | -1.308 | 2.125 | 7.064 | 12 | 16 |
| Percentage of DerivativeSettlementsExpenseIncome | 95.9 | 99.6 | 150.1 | -22.5 | 50.2 | 96.8 | 93.8 | 87.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -0.221 | -0.019 | 1.197 | 7.129 | 2.112 | 0.234 | 0.807 | 2.334 |
| Percentage of DerivativeSettlementsExpenseIncome | 4.1 | 0.4 | -50.1 | 122.5 | 49.8 | 3.2 | 6.2 | 12.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -5.374 | -4.304 | -2.391 | 5.821 | 4.237 | 7.298 | 12 | 19 |
| Percentage of DerivativeSettlementsExpenseIncome | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-05-14 |
| Value | 24.5 |
| Percentage of FinancingReceivableInterestIncomePercentage | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 13 | -13.849 | -10.636 | 52 | -4.046 | 1.921 | 4.121 | -1.151 |
| Percentage of GainLossOnInvestmentsAndNotesReceivable | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 15 | 14 | 0.0 | 18 | 0.0 | 1.712 | 0.0 |
| Percentage of GainsOnSaleOfStudentLoansAndDebtRepurchasesNet | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 100.0 | 0.0 |
| Period End | 2021-06-30 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 15 | 14 | 0.0 | 18 | 0.0 | 1.712 | 0.0 |
| Percentage of GainsOnSaleOfStudentLoansAndDebtRepurchasesNet | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 100.0 | 0.0 |
| Period End | 2020-09-30 | 2020-03-31 | 2019-12-31 | 2019-06-30 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 14 | 18 | 15 | 1.712 | 0.0 | 0.0 | 0.359 | 0.116 | 0.442 | 4.98 |
| Percentage of GainsOnSaleOfStudentLoansAndDebtRepurchasesNet. | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -1247000.0 | -917000.0 | -3655000.0 | -2447000.0 | -2382000.0 | -1944000.0 | -2570000.0 | -2101000.0 | -2063000.0 |
| Percentage of IncreaseDecreaseInOperatingLeaseLiability | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -2544000.0 | -1418000.0 | -2444000.0 | -3202000.0 | -6948000.0 | 1000000.0 | -2264000.0 | -2222000.0 | -3211000.0 | -1096000.0 |
| Percentage of IncreaseDecreaseInOperatingLeaseRightOfUseAsset | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 |
| Value | -23800000.0 |
| Percentage of InterestPayableIncreaseDecreaseDueToLikelihoodOfRepayment | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -19.757 | -20.713 | -20.513 | -20.513 | -20.476 | -21.041 | -19.059 | -16.917 | -17.535 | -17.791 |
| Percentage of IntersegmentExpenses | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | -8.483 | -8.271 | -8.645 | -8.29 | -8.54 | -11.065 | -11.325 | -11.611 | -11.598 | -12.217 | -12.412 | -12.29 | -11.609 | -10.771 | -10.835 | -10.563 | -9.952 | -10.323 | -10.945 | -11.021 |
| Percentage of IntersegmentExpenses | 42.9 | 39.9 | 42.1 | 40.4 | 41.7 | 52.6 | 59.4 | 68.6 | 66.1 | 68.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 8.549 | 8.427 | 9.333 | 8.868 | 9.055 | 11 | 11 | 11 | 11 | 12 | 12 | 12 | 11 | 10 | 11 | 10 | 10 |
| Percentage of IntersegmentExpenses | -43.3 | -40.7 | -45.5 | -43.2 | -44.2 | -56.6 | -61.6 | -69.0 | -66.5 | -69.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.082 | 0.491 | 0.536 | 0.624 | 0.881 | 0.701 | 0.716 | 0.664 | 0.776 | 0.598 | 0.599 | 0.605 | 0.629 | 0.47 | 0.496 |
| Percentage of IntersegmentExpenses | -0.4 | -2.4 | -2.6 | -3.0 | -4.6 | -4.1 | -4.1 | -3.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 3.52 | 3.664 | 3.927 | 3.61 | 3.429 | 3.327 | 3.763 | 3.194 | 3.148 | 3.299 | 3.051 | 2.494 | 2.57 | 2.567 | 2.649 | 2.219 | 2.136 |
| Percentage of IntersegmentExpenses | -17.8 | -17.7 | -19.1 | -17.6 | -16.7 | -15.8 | -19.7 | -18.9 | -18.0 | -18.5 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 16 | 16 | 15 | 15 | 15 | 16 | 14 | 12 | 13 | 13 | 15 | 15 | 15 | 13 | 8.375 | 7.774 | 8.324 |
| Percentage of IntersegmentExpenses | -81.7 | -81.5 | -77.1 | -77.2 | -78.1 | -77.2 | -73.5 | -76.6 | -77.6 | -77.3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 0.037 | 0.003 |
| Percentage of IntersegmentExpenses | -0.2 | -0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | -8.483 | -8.271 | -8.645 | -8.29 | -8.54 | -11.065 | -11.325 | -11.611 | -11.598 | -12.217 | -12.412 | -12.29 | -11.609 | -10.771 | -10.835 | -10.563 | -9.952 | -10.323 |
| Percentage of IntersegmentServicingRevenue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.011 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of IntersegmentServicingRevenue | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.1 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 | -0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 8.48 | 8.268 | 8.642 | 8.287 | 8.537 | 11 | 11 | 11 | 11 | 12 | 12 | 12 | 11 | 10 | 10 | 10 | 9.952 |
| Percentage of IntersegmentServicingRevenue | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -99.9 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 | -100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 122 | 124 | 132 | 134 | 146 | 181 | 204 | 229 | 238 | 242 | 244 | 232 | 223 | 197 | 195 | 191 | 189 | 181 | 183 | 193 | 184 | 189 | 190 | 187 | 175 | 171 | 182 | 187 | 175 | 156 | 165 | 158 | 158 | 155 | 154 | 150 | 150 | 153 | 156 | 156 | 138 | 137 | 149 | 159 | 155 |
| Percentage of LoanInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-11-02 |
| Value | 44 |
| Percentage of NoncashContributionOfAssetBackedSecuritiesToSubsidiary | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 |
| Value | 14 | 0.227 | 0.0 | 0.033 | 0.063 | 3.805 | 0.0 | 0.0 | 0.0 |
| Percentage of NoncashDistributionsToNoncontrollingInterestHolders | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | 219 | 239 | 225 | 251 | 190 | 219 | 182 |
| Percentage of NoninterestIncomeExpense | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | 19 | -6.184 | -2.737 | 56 | -5.7 | 7.231 | 8.624 |
| Percentage of NoninterestIncomeExpense | 8.8 | -2.6 | -1.2 | 22.6 | -3.0 | 3.3 | 4.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | -8.483 | -8.271 | -8.29 | -8.54 | -11.065 | -11.611 | -11.598 |
| Percentage of NoninterestIncomeExpense | -3.9 | -3.5 | -3.7 | -3.4 | -5.8 | -5.3 | -6.4 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | 10 | 37 | 16 | 2.642 | -21.247 | 5.052 | -19.2 |
| Percentage of NoninterestIncomeExpense | 4.8 | 15.6 | 7.5 | 1.1 | -11.1 | 2.3 | -10.5 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | 20 | 19 | 18 | 17 | 16 |
| Percentage of NoninterestIncomeExpense | 9.2 | 7.7 | 9.7 | 7.8 | 8.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | 76 | 95 | 74 | 59 | 83 | 74 | 60 |
| Percentage of NoninterestIncomeExpense | 34.9 | 39.8 | 33.0 | 23.6 | 43.9 | 33.9 | 33.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 |
| Value | 121 | 120 | 124 | 121 | 126 | 127 | 127 |
| Percentage of NoninterestIncomeExpense | 55.3 | 50.6 | 55.2 | 48.4 | 66.3 | 58.0 | 70.2 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 0.004 | 0.022 |
| Percentage of NoninterestIncomeExpense | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-06-30 | 2020-03-31 |
| Value | 22 | -4.604 | 60 | 8.281 |
| Percentage of OtherIncomeExpenseOther | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-06-30 | 2020-03-31 |
| Value | 19 | -6.184 | 57 | 2.083 |
| Percentage of OtherIncomeExpenseOther | 86.8 | 134.3 | 94.9 | 25.2 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-06-30 | 2020-03-31 |
| Value | 2.316 | 0.445 | 0.732 | 3.215 |
| Percentage of OtherIncomeExpenseOther | 10.1 | -9.7 | 1.2 | 38.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-06-30 | 2020-03-31 |
| Value | 0.701 | 1.113 | 1.914 | 2.63 |
| Percentage of OtherIncomeExpenseOther | 3.1 | -24.2 | 3.2 | 31.8 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 0.004 | 0.022 |
| Percentage of OtherIncomeExpenseOther | 0.0 | -0.5 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 3.928 | 4.223 | 4.956 | 3.967 | 3.821 | 3.912 | 2.311 | 5.458 | 4.239 | 3.399 | 5.31 | 9.193 | 2.536 | 3.38 | 6.875 | 5.57 | 2.798 | 2.637 |
| Percentage of OtherIncomeMiscellaneous | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 |
| Value | 35 |
| Percentage of PaymentForContingentConsideration | 100.0 |
| Period End | 2020-12-31 |
| Value | 25 |
| Percentage of PaymentForContingentConsideration | 71.4 |
| Period End | 2021-03-31 |
| Value | 13 |
| Percentage of PaymentsToAcquireEquitySecuritiesFvNi | 100.0 |
| Period End | 2021-06-30 |
| Value | 24.0 |
| Percentage of PercentOfIncomeBeforeTaxesAllocatedToIncomeTaxes | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 4.483 | 1.758 | 3.635 | 3.135 | 15 | 30 | 23 | 1.719 | 1.578 | 5.369 | 6.374 | 9.718 | 5.371 | 1.722 | 2.847 | 1.605 |
| Percentage of ProceedsFromInvestmentsAndNotesReceivables | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 |
| Value | 0.359 | 38 | 4.048 | -4.067 | -20.386 | 17 | -63.255 | -13.974 | 6.157 | -22.428 | 62 |
| Percentage of ProceedsFromPaymentsToClearinghouse | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-03-31 |
| Value | -2.436 | 34 |
| Percentage of ProvisionNegativeProvisionForBeneficialInterestsAndImpairmentExpense | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-03-31 |
| Value | -2.436 | 26 |
| Percentage of ProvisionNegativeProvisionForBeneficialInterestsAndImpairmentExpense | 100.0 | 77.2 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 0.5 | 0.332 |
| Percentage of ProvisionNegativeProvisionForBeneficialInterestsAndImpairmentExpenseNet | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 0.5 | 0.332 |
| Percentage of ProvisionNegativeProvisionForBeneficialInterestsAndImpairmentExpenseNet | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 |
| Value | -9.909 | 0.0 | -13.5 | -12.5 | 0.0 | 1.5 | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 | 0.35 | 0.05 | 0.0 | 0.0 | 0.19 | 0.03 | 0.1 | 0.16 | -0.34 | -0.03 | 0.0 | 0.23 | -1.3 | -0.07 | -0.15 | -0.1 |
| Percentage of PurchaseSaleofFinancingReceivables | 100.0 | 0.0 | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 |
| Value | -9.909 |
| Percentage of PurchaseSaleofFinancingReceivables | 100.0 |
| Period End | 2021-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | 0.001 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.05 | 0.15 | 0.19 | 0.03 |
| Percentage of PurchaseSaleofFinancingReceivables | 0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 |
| Value | 0.001 |
| Percentage of PurchaseSaleofFinancingReceivables | -0.0 |
| Period End | 2020-07-29 |
| Value | 25.4 |
| Percentage of SecuritizationInterestPercent | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | -7388000.0 | -7218000.0 | -7471000.0 | -8618000.0 | -9754000.0 | -9442000.0 | -8270000.0 | -8748000.0 | -9113000.0 | -9693000.0 | -9485000.0 | -9516000.0 | -10108000.0 | -11691000.0 | -11992000.0 | -9886000.0 | -10920000.0 | -12014000.0 | -10178000.0 | -8915000.0 | -10607000.0 | -10917000.0 | -11082000.0 | -11178000.0 | -10760000.0 | -10746000.0 | -11086000.0 | -11306000.0 | -11064000.0 | -10023000.0 | -9925000.0 | -8564000.0 | -8694000.0 | -9075000.0 | -12687000.0 | -8836000.0 | -12306000.0 | -10551000.0 |
| Percentage of StudentLoanDiscountAccretion | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2017-12-31 | 2017-09-30 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 |
| Value | -9.696 | 0.0 | 0.332 | 34 | 0.0 | 0.0 | 0.0 | 0.0 | 7.814 | 3.9 | 3.626 | 0.0 | -2.767 | 0.0 | 0.0 | 0.0 |
| Percentage of AssetImpairmentCharges | 100.0 | 0.0 | 100.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 | 100.0 | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-06-30 | 2019-03-31 |
| Value | 0.0 | 0.0 | 0.332 | 7.783 | 0.0 | 0.0 |
| Percentage of AssetImpairmentCharges | -0.0 | 0.0 | 100.0 | 22.8 | 0.0 | 0.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-06-30 | 2019-03-31 |
| Value | -9.696 | 0.0 | 0.0 | 26 | 0.0 | 0.0 |
| Percentage of AssetImpairmentCharges | 100.0 | 0.0 | 0.0 | 77.2 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 |
| Value | 43 | 43 | 42 | 45 | 45 | 46 | 46 | 46 |
| Percentage of BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 |
| Value | 0.0 | 14 | 0.0 | 38 | 31 | 0.0 | 7.921 | 0.0 | 0.0 | 0.0 |
| Percentage of ConsiderationReceivedForBeneficialInterestObtainedForTransferringFinancialAsset | 0.0 | 100.0 | 0.0 | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 32 | 34 | 39 | 34 | 32 | 32 | 36 | -197.045 | 27 | 32 | -26.802 | -163.798 | 22 | 23 | -24.878 |
| Percentage of ContractWithCustomerLiabilityRevenueRecognized | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 0.8 | 0.843 | 0.843 | 1.061 | 0.85 | 0.782 | 0.786 |
| Percentage of ContractWithCustomerLiabilityRevenueRecognized | 2.5 | 2.5 | 2.2 | 3.1 | 2.6 | 2.4 | 2.2 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 11 | 10 | 9.745 | 9.65 | 9.158 | 8.474 | 8.061 |
| Percentage of ContractWithCustomerLiabilityRevenueRecognized | 34.4 | 30.3 | 25.0 | 28.3 | 27.8 | 26.1 | 22.1 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 19 | 22 | 27 | 22 | 21 | 21 | 26 |
| Percentage of ContractWithCustomerLiabilityRevenueRecognized | 60.2 | 64.7 | 70.5 | 65.2 | 66.2 | 67.2 | 71.3 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 0.97 | 0.88 | 0.899 | 1.159 | 1.149 | 1.396 | 1.582 |
| Percentage of ContractWithCustomerLiabilityRevenueRecognized | 3.0 | 2.6 | 2.3 | 3.4 | 3.5 | 4.3 | 4.3 |
| Period End | 2020-12-31 |
| Value | 258 |
| Percentage of DeconsolidationGainOrLossAmount | 100.0 |
| Period End | 2020-12-22 |
| Value | 258 |
| Percentage of DeconsolidationGainOrLossAmount | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 |
| Value | 12 | 11 | 23 | 22 | 22 | 20 | 20 | 19 | 16 | 15 | 15 | 15 | 13 | 12 | 9.6 | 7.7 | 6.7 | 6.2 | 6.0 | 5.8 | 5.4 | 5.1 | 4.6 | 4.6 | 4.1 | 3.3 |
| Percentage of Depreciation | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 20 | 20 | 31 | 30 | 29 | 27 | 28 | 27 | 24 | 24 | 23 | 22 | 21 | 18 | 11 | 10 | 9.038 | 8.598 | 9.116 | 8.994 | 8.183 | 7.64 | 7.203 | 6.977 | 6.501 | 5.662 | 5.644 | 5.493 | 5.214 | 4.783 | -5.274 | 4.34 | 4.32 | 4.377 | -8.861 | 8.402 | 8.226 | 8.136 | -8.282 | 7.917 | 6.769 | 6.776 | 8.908 | 9.025 | 9.728 |
| Percentage of DepreciationAndAmortization | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 9.305 | 8.92 | 9.232 | 6.839 | 7.065 | 5.907 | 5.995 | 5.212 | 4.623 | 4.469 |
| Percentage of DepreciationAndAmortization | 46.0 | 44.2 | 29.4 | 22.6 | 24.0 | 21.4 | 20.9 | 18.8 | 18.9 | 18.5 |
| Period End | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 10 | 11 | 10 | 10 | 11 | 10 | 7.737 | 7.362 | 6.792 | 6.167 | 5.497 | 4.921 | 3.955 | 3.145 | 2.6 |
| Percentage of DepreciationAndAmortization | 32.2 | 36.8 | 36.8 | 38.0 | 38.9 | 39.4 | 31.6 | 30.4 | 28.4 | 26.8 | 25.6 | 26.7 | 33.4 | 31.3 | 28.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 2.956 | 3.071 | 2.344 | 2.366 | 2.362 | 2.387 | 2.988 | 2.997 | 3.324 | 3.51 | 3.422 | 3.435 | 3.286 | 3.341 | 2.371 | 2.316 | 2.346 |
| Percentage of DepreciationAndAmortization | 14.6 | 15.2 | 7.5 | 7.8 | 8.0 | 8.6 | 10.4 | 10.8 | 13.6 | 14.5 | 14.3 | 14.9 | 15.3 | 18.1 | 20.0 | 23.0 | 26.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 7.974 | 8.192 | 9.669 | 9.951 | 9.142 | 8.848 | 8.519 | 8.565 | 8.799 | 8.871 | 8.837 | 8.957 | 8.212 | 6.069 | 1.22 | 0.549 | 0.546 |
| Percentage of DepreciationAndAmortization | 39.4 | 40.6 | 30.8 | 32.8 | 31.1 | 32.0 | 29.7 | 30.9 | 35.9 | 36.6 | 36.9 | 39.0 | 38.2 | 32.9 | 10.3 | 5.5 | 6.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -0.509 | 36 | 3.601 | -1.039 | -22.16 | -12.094 | -36.851 | -26.712 |
| Percentage of DerivativeGainLossOnDerivativeNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -1.106 | 2.799 | -0.161 | -2.872 | 1.558 | 6.636 | 0.004 | -2.212 |
| Percentage of DerivativeGainLossOnDerivativeNet | 217.3 | 7.8 | -4.5 | 276.4 | -7.0 | -54.9 | -0.0 | 8.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -1.615 | 38 | 3.44 | -3.911 | -20.602 | -5.63 | -37.06 | -30.574 |
| Percentage of DerivativeGainLossOnDerivativeNet | 317.3 | 107.8 | 95.5 | 376.4 | 93.0 | 46.6 | 100.6 | 114.5 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-06-30 | 2013-03-31 |
| Value | -1.615 | 38 | -7.072 | 3.441 | -3.911 | -20.602 | -2.93 | -5.63 | -37.061 | -30.574 | -48.895 | -5.226 | -4.898 | 60 | 3.998 | 21 | -0.287 | 1.238 | 61 | 47 | -44.975 | -3.674 | 28 | -23.722 | 26 | -46.072 | -19.879 | -8.381 | -2.999 | -0.039 | 14 | -34.844 |
| Percentage of DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 8.475 | 8.437 | 8.435 | 7.664 | 7.733 | 7.946 | 7.939 | 7.142 | 7.172 | 7.232 | 7.3 | 6.525 | 6.508 | 6.506 | 6.528 | 5.766 | 5.907 | 5.896 | 5.895 | 5.101 | 5.099 | 5.093 | 5.366 | 4.486 | 4.559 | 4.614 | 4.628 | 4.63 | 4.643 | 4.641 | 4.637 | 4.637 | 4.649 | 4.646 | 52 | 4.737 | 4.737 | -4.712 | -4.713 | -4.811 | 4.852 | -3.387 | -23.695 | -3.435 | 3.507 |
| Percentage of DividendsCommonStockCash | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 8.475 | 8.437 | 8.435 | 7.664 | 7.733 | 7.946 | 7.939 | 7.142 | 7.172 | 7.232 | 7.3 | 6.525 | 6.508 | 6.506 | 6.528 | 5.766 | 5.907 | 5.896 | 5.895 | 5.101 | 5.099 | 5.093 | 5.366 | 4.486 | 4.559 | 4.614 | 4.628 | 4.63 | 4.643 | 4.641 | 4.637 | 4.637 | 4.649 | 4.646 | 52 | 4.737 | 4.737 | -4.712 | -4.713 | -4.811 | 4.852 | -3.387 | -23.695 | -3.435 | 3.507 |
| Percentage of DividendsCommonStockCash | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -31000.0 | -77000.0 |
| Percentage of EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents | 100.0 | 100.0 |
| Period End | 2021-06-30 |
| Value | 2.0 |
| Percentage of EquitySecuritiesFvNiRealizedGain | 100.0 |
| Period End | 2021-06-30 |
| Value | 1.1 |
| Percentage of EquitySecuritiesFvNiRealizedGain | 55.0 |
| Period End | 2021-03-31 |
| Value | 2.3 |
| Percentage of EquitySecuritiesFvNiRealizedLoss | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | -1.1 | 22 |
| Percentage of EquitySecuritiesFvNiRealizedLoss | 0.0 | 965.2 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-06-30 |
| Value | 0.525 | 0.8 | 2.1 | 2.9 | 6.1 | 4.7 | 0.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossPurchasedWithCreditDeteriorationIncrease | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-06-30 |
| Value | 0.8 | 2.1 | 2.9 | 6.1 | 4.7 | 0.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossPurchasedWithCreditDeteriorationIncrease | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 0.525 | 6.1 |
| Percentage of FinancingReceivableAllowanceForCreditLossPurchasedWithCreditDeteriorationIncrease | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2015-03-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-09-30 | 2013-06-30 |
| Value | 374000.0 | 448000.0 | 406000.0 | 514000.0 | 404000.0 | 439000.0 | 427000.0 | 424000.0 | 431000.0 | 254000.0 | 163000.0 | 150000.0 | 183000.0 | 170000.0 | 165000.0 | 161000.0 | 245000.0 | 197000.0 | 254000.0 | 279000.0 | 339000.0 | 371000.0 | 363000.0 | 442000.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossesRecovery | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 246000.0 | 283000.0 | 381000.0 | 221000.0 | 247000.0 | 276000.0 | 240000.0 | 273000.0 | 23000.0 | 9000.0 | 26000.0 | 1000.0 | 5000.0 | 0 | 0 | 0 | 0 |
| Percentage of FinancingReceivableAllowanceForCreditLossesRecovery | 54.9 | 69.7 | 74.1 | 54.7 | 56.3 | 64.6 | 56.6 | 63.3 | 9.1 | 5.5 | 17.3 | 0.5 | 2.9 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 235000.0 | 221000.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossesRecovery | 62.8 | 54.7 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | 202000.0 | 123000.0 | 133000.0 | 183000.0 | 192000.0 | 151000.0 | 184000.0 | 158000.0 | 231000.0 | 154000.0 | 124000.0 | 182000.0 | 165000.0 | 165000.0 | 161000.0 | 245000.0 | 197000.0 | 185000.0 | 243000.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossesRecovery | 45.1 | 30.3 | 25.9 | 45.3 | 43.7 | 35.4 | 43.4 | 36.7 | 90.9 | 94.5 | 82.7 | 99.5 | 97.1 | 100.0 | 100.0 | 100.0 | 100.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 139000.0 | 183000.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossesRecovery | 37.2 | 45.3 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 |
| Value | 3.039 | 2.504 | 2.591 | 5.215 | 8.926 | 11 | 8.43 | 6.598 | 7.118 | 5.864 | 4.992 | 4.148 | 5.262 | 4.466 | 3.339 | 3.955 | 3.113 | 2.663 | 3.323 | 3.516 | 3.731 | 3.45 | 3.44 | 3.174 | 3.705 | 3.825 | -30.524 | 4.144 | 4.736 | 4.052 | 4.529 | 4.048 | 3.932 | 6.762 | 5.427 | 6.507 | 6.527 | 6.264 | 4.5 | 5.153 | 5.811 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 1.95 | 2.222 | 2.723 | 2.82 | 4.35 | 5.081 | 2.759 | 2.652 | 2.006 | 1.68 | 1.403 | 1.378 | 0.595 | 0.162 | 0.033 | 0.0 | 0.0 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 77.9 | 85.8 | 52.2 | 31.6 | 36.3 | 60.3 | 41.8 | 37.3 | 34.2 | 33.7 | 33.8 | 26.2 | 13.3 | 4.9 | 0.8 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 1.464 | 2.82 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 48.2 | 31.6 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | 0.061 | 0.07 | 2.487 | 6.08 | 6.318 | 2.913 | 3.38 | 3.878 | 3.376 | 2.743 | 2.21 | 3.111 | 3.332 | 2.692 | 3.464 | 2.825 | 2.581 | 2.83 | 3.196 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 2.4 | 2.7 | 47.7 | 68.1 | 52.7 | 34.6 | 51.2 | 54.5 | 57.6 | 54.9 | 53.3 | 59.1 | 74.6 | 80.6 | 87.6 | 90.7 | 96.9 | 85.2 | 90.9 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 1.172 | 6.08 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 38.6 | 68.1 |
| Period End | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | 0.493 | 0.299 | 0.005 | 0.026 | 1.33 | 0.436 | 0.459 | 0.588 | 0.482 | 0.569 | 0.535 | 0.773 | 0.539 | 0.452 | 0.491 | 0.288 | 0.082 | 0.493 | 0.32 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 19.7 | 11.5 | 0.1 | 0.3 | 11.1 | 5.2 | 7.0 | 8.3 | 8.2 | 11.4 | 12.9 | 14.7 | 12.1 | 13.5 | 12.4 | 9.3 | 3.1 | 14.8 | 9.1 |
| Period End | 2021-06-30 | 2020-06-30 |
| Value | 0.403 | 0.026 |
| Percentage of FinancingReceivableAllowanceForCreditLossesWriteOffs | 13.3 | 0.3 |
| Period End | 2020-09-30 | 2020-06-30 |
| Value | 2.9 | 6.1 |
| Percentage of FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 |
| Value | 34 | 54 | 113 | 137 | 292 | 291 |
| Percentage of FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-05-14 |
| Value | 77 |
| Percentage of FinancingReceivableSignificantSales | 100.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2019-09-30 | 2019-06-30 |
| Value | 15 | 0.0 | 0.0 | 1.5 |
| Percentage of FinancingReceivableTransferToHeldForSaleAllowanceForCreditLossExpenseReversal | 100.0 | 0.0 | 0.0 | 100.0 |
| Period End | 2020-09-30 | 2020-06-30 | 2019-09-30 | 2019-06-30 |
| Value | 15 | 0.0 | 0.0 | 1.5 |
| Percentage of FinancingReceivableTransferToHeldForSaleAllowanceForCreditLossExpenseReversal | 100.0 | 0.0 | 0.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | -6.989 | 34 | 1.049 | 1.91 | -16.365 | 1.668 | -24.088 | -11.539 |
| Percentage of GainLossOnDerivativeInstrumentsNetPretax | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2020-07-29 | 2020-01-30 |
| Value | 14 | 18 |
| Percentage of GainLossOnSaleOfNotesReceivable | 100.0 | 100.0 |
| Period End | 2021-05-14 |
| Value | 15 |
| Percentage of GainLossOnSaleOfNotesReceivable | 0.0 |
| Period End | 2020-09-30 |
| Value | 14 |
| Percentage of GainLossOnSaleOfNotesReceivable | 0.0 |
| Period End | 2020-12-31 |
| Value | 230 |
| Percentage of GainLossOnSaleOfPreviouslyUnissuedStockBySubsidiaryOrEquityInvesteeNonoperatingIncome | 100.0 |
| Period End | 2021-06-30 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 |
| Value | 15 | 0.0 | 14 | 0.0 | 18 | 15 | 0.0 | 1.712 | 0.0 | 0.0 | 0.0 | 0.0 |
| Percentage of GainLossOnSalesOfLoansNet | 100.0 | 0.0 | 100.0 | 0.0 | 100.0 | 100.0 | 0.0 | 100.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-03-31 | 2020-03-31 |
| Value | 2.4 | 26 |
| Percentage of ImpairmentOfInvestments | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 |
| Value | -2300000.0 | 1700000.0 | -11800000.0 | 2000000.0 | 2800000.0 |
| Percentage of IncomeLossFromEquityMethodInvestments | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 40 | 0.114 | 33 | -96.084 | 90 | 33 | -3.278 | 12 | 8.245 | 36 | 54 | 33 | 101 | 59 | 33 | 1.102 | 2.98 | 1.49 | 9.46 | 1.664 | -4.137 | 0.452 | 3.384 | -0.308 | -3.041 | 3.784 | -0.902 | -7.87 | 12 | -8.881 | -4.173 | 6.812 | -8.639 | -2.341 | 39 | -18.277 | -10.245 | -12.023 | -22.67 | -22.221 | 25 | -9.668 | -99.931 | 156 |
| Percentage of IncreaseDecreaseInAccruedInterestReceivableNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 91 | 57 |
| Percentage of IncreaseDecreaseInDeposits | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | -0.605 | -23.174 | -0.911 | -3.148 | -11.114 | -3.411 | -5.06 | -4.126 | -5.687 | 0.479 | 1.021 | -2.568 | 8.974 | 4.213 | 2.215 | 0.76 | 0.637 | 0.75 | 2.837 | 2.914 | 0.976 | 7.443 | -0.125 | 2.676 | 1.195 | 1.371 | 0.695 | 0.882 | 0.819 | 0.613 | 0.119 | -0.542 | -1.101 | 1.091 | -1.866 | -1.551 | -1.094 | -0.353 | 2.669 | -1.147 | 1.506 | -3.566 | -0.574 | -2.635 |
| Percentage of IncreaseDecreaseInInterestPayableNet | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | -27.094 | -5.147 | -39.691 | 3.501 | 8.371 | -31.363 | -10.911 | 20 | -30.781 | 32 | 53 | 4.994 | -4.834 | -49.415 | 33 | -0.942 | 2.449 | -0.294 | 1.062 | -1.438 | -0.343 | 2.922 | 1.473 | -3.815 | 2.572 | -0.605 | 0.351 | -1.34 | -0.08 | -1.303 | 2.338 | 3.011 | -0.273 | -0.293 | 0.008 | -0.066 | -1.124 | -1.14 | -0.356 | -4.323 | 4.274 | -1.016 | -10.433 | 3.941 |
| Percentage of IncreaseDecreaseInOtherOperatingAssets | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | -3.288 | -10.375 | 3.174 | 59 | 15 | -42.047 | -15.601 | 60 | 1.072 | -5.741 | -5.347 | 39 | -10.367 | -36.205 | -22.889 | 28 | -14.845 | 6.954 | -9.178 | 21 | -12.557 | 2.551 | -26.714 | 22 | -20.94 | 16 | -18.088 | 14 | -16.505 | -0.185 | 4.184 | 9.045 | -22.061 | 13 | 1.408 | 19 | -19.26 | 14 | -9.622 | 13 | 1.347 | -11.637 | 7.338 | 7.437 |
| Percentage of IncreaseDecreaseInOtherOperatingLiabilities | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 |
| Value | 72 | -70.849 | 15 | 17 | 48 | -217.851 | 128 | 30 | 62 | -153.207 | 57 | 33 | 26 | -58.606 | 81 | -31.601 | 43 | -26.003 |
| Percentage of IncreaseDecreaseInPayablesToCustomers | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 133 | 129 | 138 | 139 | 151 | 189 | 212 | 238 | 246 | 250 | 252 | 239 | 229 | 202 | 196 | 196 | 193 | 183 | 186 | 196 | 186 | 192 | 193 | 189 | 177 | 174 | 184 | 189 | 176 | 158 | 167 | 160 | 159 | 157 | 155 | 151 | 152 | 154 | 157 | 157 | 139 | 138 | 150 | 160 | 156 |
| Percentage of InterestAndDividendIncomeOperating | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 1.524 | 1.246 | 1.378 | 1.646 | 1.196 | 1.555 | 2.062 | 2.859 | 2.258 | 2.053 |
| Percentage of InterestAndDividendIncomeOperating | 1.1 | 1.0 | 1.0 | 1.2 | 0.8 | 0.8 | 1.0 | 1.2 | 0.9 | 0.8 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 |
| Value | -0.187 | -0.218 | -0.252 | -0.261 | -0.368 | -0.598 | -0.801 | -1.171 | -0.974 | -0.851 | -0.569 | -4.846 | -4.425 | -3.15 | -2.702 | -2.139 | -1.776 | -1.359 | -2.52 | -0.93 |
| Percentage of InterestAndDividendIncomeOperating | -0.1 | -0.2 | -0.2 | -0.2 | -0.2 | -0.3 | -0.4 | -0.5 | -0.4 | -0.3 | -0.2 | -2.0 | -1.9 | -1.6 | -1.4 | -1.1 | -0.9 | -0.7 | -1.4 | -0.5 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 129 | 126 | 137 | 137 | 150 | 185 | 208 | 233 | 243 | 246 | 248 | 236 | 226 | 200 | 195 | 194 | 191 |
| Percentage of InterestAndDividendIncomeOperating | 97.3 | 97.9 | 98.7 | 98.7 | 99.1 | 98.3 | 98.2 | 97.6 | 98.6 | 98.5 | 98.6 | 98.4 | 98.8 | 98.8 | 99.5 | 99.0 | 99.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.21 | 0.263 | 0.259 | 0.367 | 0.42 | 1.991 | 2.069 | 3.499 | 1.659 | 2.017 | 1.526 | 1.513 | 0.748 | 0.665 | 0.007 | 0.005 | 0.003 |
| Percentage of InterestAndDividendIncomeOperating | 0.2 | 0.2 | 0.2 | 0.3 | 0.3 | 1.1 | 1.0 | 1.5 | 0.7 | 0.8 | 0.6 | 0.6 | 0.3 | 0.3 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.03 | 0.034 | 0.033 | 0.034 | 0.052 | 0.317 | 0.452 | 0.532 | 0.55 | 0.497 | 0.42 | 0.381 | 0.293 | 0.257 | 0.152 | 0.147 | 0.12 |
| Percentage of InterestAndDividendIncomeOperating | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 2.041 | 1.376 |
| Percentage of InterestAndDividendIncomeOperating | 1.5 | 1.1 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 83 | 118 | 96 | 87 | 63 | -21.226 | 51 | 56 | 50 | 51 | 64 | 49 | 54 | 63 | 69 | 69 | 77 | 75 | 75 | 93 | 90 | 99 | 109 | 108 | 102 | 100 | 108 | 115 | 106 | 96 | 105 | 99 | 96 | 93 | 87 | 80 | 77 | 78 | 86 | 91 | 83 | 82 | 90 | 86 | 91 |
| Percentage of InterestIncomeExpenseAfterProvisionForLoanLoss | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 |
| Value | 0.431 | 0.422 | 1.573 | 0.758 | 0.118 | 0.148 | 2.271 | 0.749 | -1.614 | -1.761 |
| Percentage of InterestIncomeExpenseAfterProvisionForLoanLoss | 0.5 | 0.4 | 1.6 | 0.9 | 0.2 | -0.7 | 4.4 | 1.3 | -3.2 | -3.4 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 80 | 116 | 94 | 86 | 63 | -23.622 | 46 | 51 | 50 | 51 | 61 | 48 | 53 | 62 | 68 | 67 | 75 |
| Percentage of InterestIncomeExpenseAfterProvisionForLoanLoss | 97.3 | 98.8 | 98.1 | 98.7 | 99.1 | 111.3 | 90.8 | 91.6 | 98.9 | 98.6 | 96.1 | 98.8 | 98.4 | 98.1 | 98.5 | 97.1 | 96.7 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.21 | 0.263 | 0.259 | 0.351 | 0.399 | 1.974 | 2.055 | 3.487 | 1.648 | 2.009 | 1.52 | 1.51 | 0.748 | 0.665 | 0.007 | 0.005 | 0.003 |
| Percentage of InterestIncomeExpenseAfterProvisionForLoanLoss | 0.3 | 0.2 | 0.3 | 0.4 | 0.6 | -9.3 | 4.0 | 6.2 | 3.2 | 3.9 | 2.4 | 3.1 | 1.4 | 1.1 | 0.0 | 0.0 | 0.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 |
| Value | 0.007 | 0.011 | 0.009 | 0.01 | 0.024 | 0.273 | 0.407 | 0.481 | 0.531 | 0.497 | 0.42 | 0.381 | 0.293 | 0.257 | 0.149 | 0.147 | 0.12 |
| Percentage of InterestIncomeExpenseAfterProvisionForLoanLoss | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -1.3 | 0.8 | 0.9 | 1.0 | 1.0 | 0.7 | 0.8 | 0.5 | 0.4 | 0.2 | 0.2 | 0.2 |
| Period End | 2021-06-30 | 2021-03-31 |
| Value | 1.58 | 0.76 |
| Percentage of InterestIncomeExpenseAfterProvisionForLoanLoss | 1.9 | 0.6 |
| Period End | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 |
| Value | 49 | 83 | 125 | 163 | 178 | 176 | 165 | 165 | 145 | 114 | 103 | 103 | 95 | 88 | 81 | 77 | 76 | 66 | 62 | 57 | 55 | 53 | 54 | 58 | 48 | 48 | 42 | 48 | 51 | 48 | 55 | 58 | 59 | 61 | 52 | 52 | 47 | 53 | 53 | 68 |
| Percentage of InterestPaid | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 11 | 4.986 | 6.164 | 5.238 | 5.743 | 7.398 | 7.72 | 9.882 | 8.566 | 8.253 | 8.019 | 7.628 | 5.818 | 5.134 | 1.36 | 5.129 | 3.589 | 2.617 | 2.792 | 2.46 | 2.185 | 2.029 | 2.303 | 1.456 | 1.887 | 2.205 | 1.77 | 1.562 | 1.482 | 1.979 | 2.006 | 1.562 | 1.483 | 1.617 | 1.326 | 1.14 | 1.055 | 1.095 | 0.914 | 0.672 | 0.856 | 0.726 | 1.782 | 1.169 | 1.304 |
| Percentage of InvestmentIncomeInterest | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| Period End | 2021-06-30 | 2021-03-31 | 2020-12-31 | 2020-09-30 | 2020-06-30 | 2020-03-31 | 2019-12-31 | 2019-09-30 | 2019-06-30 | 2019-03-31 | 2018-12-31 | 2018-09-30 | 2018-06-30 | 2018-03-31 | 2017-12-31 | 2017-09-30 | 2017-06-30 | 2017-03-31 | 2016-12-31 | 2016-09-30 | 2016-06-30 | 2016-03-31 | 2015-12-31 | 2015-09-30 | 2015-06-30 | 2015-03-31 | 2014-12-31 | 2014-09-30 | 2014-06-30 | 2014-03-31 | 2013-12-31 | 2013-09-30 | 2013-06-30 | 2013-03-31 | 2012-12-31 | 2012-09-30 | 2012-06-30 | 2012-03-31 | 2011-12-31 | 2011-09-30 | 2011-06-30 | 2011-03-31 | 2010-12-31 | 2010-09-30 | 2010-06-30 |
| Value | 118 | 115 | 136 | 126 | 119 | 119 | 124 | 116 | 111 | 111 | 114 | 114 | 111 | 96 | 81 | 74 | 74 | 71 | 68 | 63 | 60 | 63 | 64 | 63 | 58 | 61 | 60 | 61 | 53 | 52 | -52.12 | 48 | 47 | 47 | -48.633 | 46 | 48 | 49 | -47.026 | 44 | 42 | 43 | 43 | 41 | 40 |
| Percentage of LaborAndRelatedExpense | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |