NWE


Line plots across dimensions of each concept
Line plots across concepts
Tables

Table of contents



us-gaap:CommonStockValue
us-gaap:StatementEquityComponents
us-gaap:SharesIssued

us-gaap:CommonStockSharesIssued

us-gaap:CommonStockSharesAuthorized

us-gaap:PreferredStockSharesAuthorized

us-gaap:CommonStockSharesOutstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareDiluted

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:CostOfGoodsAndServicesSold

us-gaap:CostOfRevenue
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:CostsAndExpenses

us-gaap:GrossProfit
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments

us-gaap:IncomeTaxExpenseBenefit
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:IncomeTaxesPaidNet

us-gaap:InterestAndDebtExpense
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:InterestPaidNet

us-gaap:NetIncomeLoss
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments
us-gaap:StatementEquityComponents

us-gaap:OperatingIncomeLoss
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossNetOfTax
us-gaap:OtherComprehensiveIncomeLocation
us-gaap:StatementEquityComponents

us-gaap:OtherNonoperatingIncomeExpense
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax
us-gaap:MajorCustomers
us-gaap:MajorCustomers, us-gaap:StatementBusinessSegments
us-gaap:MajorCustomers, us-gaap:StatementGeographical
us-gaap:MajorCustomers, us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments

us-gaap:Revenues
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:ProductOrService
us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments

us-gaap:Assets
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments

us-gaap:Liabilities

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents

us-gaap:AssetsCurrent

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:AccountsReceivableNetCurrent

us-gaap:InventoryNet

us-gaap:InventoryRawMaterialsAndSupplies

us-gaap:OtherAssetsCurrent

us-gaap:PropertyPlantAndEquipmentGross
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:Goodwill
us-gaap:StatementBusinessSegments

us-gaap:OtherAssetsNoncurrent

us-gaap:AccountsPayableCurrent

us-gaap:AccruedLiabilitiesCurrent

us-gaap:LiabilitiesCurrent

us-gaap:OtherAccruedLiabilitiesCurrent

us-gaap:LongTermDebt
us-gaap:DebtInstrument, us-gaap:LongtermDebtType

us-gaap:LongTermDebtNoncurrent

us-gaap:DeferredIncomeTaxLiabilitiesNet
us-gaap:RetirementPlanType
us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent

us-gaap:OtherLiabilitiesNoncurrent

us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents

us-gaap:CommonStockValue

us-gaap:AdditionalPaidInCapital

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax
us-gaap:OtherComprehensiveIncomeLocation
us-gaap:StatementEquityComponents

us-gaap:TreasuryStockValue

us-gaap:StockIssuedDuringPeriodValueNewIssues
us-gaap:StatementEquityComponents

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:DeferredIncomeTaxExpenseBenefit

us-gaap:DepreciationDepletionAndAmortization
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:IncreaseDecreaseInAccountsPayable

us-gaap:IncreaseDecreaseInAccountsReceivable

us-gaap:IncreaseDecreaseInInventories

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetIncomeLoss
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments
us-gaap:StatementEquityComponents

us-gaap:ShareBasedCompensation

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:PaymentsToAcquireInvestments

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:ProceedsFromIssuanceOfLongTermDebt

us-gaap:PaymentsOfDividendsCommonStock
us-gaap:DebtInstrument
us-gaap:DebtInstrumentInterestRateStatedPercentage
us-gaap:DebtInstrument, us-gaap:LongtermDebtType

us-gaap:EffectiveIncomeTaxRateContinuingOperations

us-gaap:DeferredTaxLiabilities

us-gaap:UnrecognizedTaxBenefits

nwe:AmortizationOfDebtIssueCostsDiscountAndDeferredHedgeGain
us-gaap:LossContingenciesByNatureOfContingency
nwe:AnnualRiverbedRentExposure
us-gaap:StatementEquityComponents
nwe:CommonStockAverageSharePrice

nwe:EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxes

nwe:EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxesPercent

nwe:IncomeTaxReconciliationAcceleratedTaxDepreciationFlowThroughAdjustment

nwe:IncomeTaxReconciliationDeductionsAcceleratedTaxDepreciationFlowThroughAdjustment
us-gaap:ShortTermDebtType
nwe:MaximumRatioOfIndebtednessToNetCapitalThresholdPercentage
us-gaap:ProductOrService
nwe:OtherEnergySalesRevenue
us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:PublicUtilitiesRegulatoryProceeding
nwe:PublicUtilitiesRequestToRecognizePensionContributionOver5Years
us-gaap:ShortTermDebtType, us-gaap:VariableRate
nwe:ShortTermDebtBasisSpreadOnVariableRate
us-gaap:StatementEquityComponents
nwe:StockIssuedValueNetOfFees

us-gaap:AccrualForEnvironmentalLossContingenciesPayments1

us-gaap:AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts
us-gaap:StatementEquityComponents

us-gaap:CapitalExpendituresIncurredButNotYetPaid

us-gaap:CommonStockDividendsPerShareDeclared
us-gaap:StatementScenario, us-gaap:LongtermDebtType
us-gaap:DebtInstrumentDecreaseForgiveness
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanActuarialGainLoss
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanInterestCost
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanServiceCost

us-gaap:DividendsCommonStock
us-gaap:StatementEquityComponents

us-gaap:EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsOther

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities

us-gaap:EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost

us-gaap:EffectiveIncomeTaxRateReconciliationOtherAdjustments

us-gaap:EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent

us-gaap:EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes

us-gaap:EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
us-gaap:ShortTermDebtType
us-gaap:ExtinguishmentOfDebtAmount

us-gaap:GainLossOnSaleOfOtherAssets

us-gaap:IncomeTaxReconciliationDeductionsOther

us-gaap:IncomeTaxReconciliationDeductionsQualifiedProductionActivities

us-gaap:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate

us-gaap:IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost

us-gaap:IncomeTaxReconciliationOtherAdjustments

us-gaap:IncomeTaxReconciliationOtherReconcilingItems

us-gaap:IncomeTaxReconciliationPriorYearIncomeTaxes

us-gaap:IncomeTaxReconciliationStateAndLocalIncomeTaxes

us-gaap:IncreaseDecreaseInAccruedLiabilities

us-gaap:IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction

us-gaap:IncreaseDecreaseInOtherCurrentAssets

us-gaap:IncreaseDecreaseInOtherNoncurrentAssets

us-gaap:IncreaseDecreaseInOtherNoncurrentLiabilities

us-gaap:IncreaseDecreaseInOtherRegulatoryAssets

us-gaap:IncreaseDecreaseInRegulatoryLiabilities
us-gaap:PublicUtilitiesRegulatoryProceeding

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
us-gaap:StatementEquityComponents
us-gaap:InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet
us-gaap:StatementEquityComponents
us-gaap:InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions
us-gaap:LossContingenciesByNatureOfContingency
us-gaap:LossContingencyDamagesSoughtValue

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
us-gaap:OtherComprehensiveIncomeLocation
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossBeforeTax

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax

us-gaap:OtherComprehensiveIncomeLossTax

us-gaap:PaymentsOfFinancingCosts

us-gaap:PensionContributions
us-gaap:RetirementPlanName

us-gaap:ProceedsFromRepaymentsOfLinesOfCredit

us-gaap:ProceedsFromRepurchaseOfEquity

us-gaap:ProceedsFromShortTermDebt

us-gaap:PropertyPlantAndEquipmentAdditions
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
us-gaap:OtherComprehensiveIncomeLocation

us-gaap:RegulatedOperatingRevenueElectricNonNuclear

us-gaap:RegulatedOperatingRevenueGas

us-gaap:RepaymentsOfShortTermDebt
us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodSharesNewIssues
us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodSharesShareBasedCompensation
us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodSharesTreasuryStockReissued

us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation
us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodValueTreasuryStockReissued
us-gaap:StatementEquityComponents

us-gaap:TaxesExcludingIncomeAndExciseTaxes
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

us-gaap:UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses
us-gaap:ConsolidationItems, us-gaap:ProductOrService
us-gaap:StatementBusinessSegments

dei:EntityCommonStockSharesOutstanding
us-gaap:RetirementPlanType
nwe:AssetDefinedBenefitPlanNoncurrent
us-gaap:StatementEquityComponents
nwe:CommonStockAggregateGrossSalesPriceMaximum

nwe:CreditFacilityBorrowingsandLetterofCreditAmountOutstanding

nwe:CustomerAdvances

nwe:DeferredTaxAssetsCustomerAdvances

nwe:DeferredTaxAssetsEnvironmentalLiability

nwe:DeferredTaxAssetsUnbilledRevenue

nwe:DeferredTaxLiabilitiesExcessTaxDepreciation

nwe:DeferredTaxLiabilitiesFlowThroughDepreciation

nwe:Deferredtaxassetsproductiontaxcredits
us-gaap:RegulatoryAsset, us-gaap:RetirementPlanType
nwe:DefinedBenefitPlanActuarialNetGainsLossesInRegulatoryAssets
us-gaap:RegulatoryAsset, us-gaap:RetirementPlanType
nwe:DefinedBenefitPlanAmortizationOfPriorServiceCostCreditRegulatoryAssets
us-gaap:EnvironmentalRemediationContingency
nwe:EnvironmentalRemediationObligationMaximum
us-gaap:EnvironmentalRemediationContingency
nwe:EnvironmentalRemediationObligationMinimum
us-gaap:EnvironmentalRemediationContingency, us-gaap:EnvironmentalRemediationSite
nwe:EnvironmentalRemediationObligationToBeIncurredDuringNext5Years
us-gaap:CreditFacility
nwe:LineOfCreditFacilityMaximumPercentageOfTotalAvailabilityProvidedByASingleLender

nwe:MinimumExpectedFutureEmployerPensionContributionsRemainderofFiscalYear

nwe:NumberOfCustomers

nwe:QualifyingFacilityLiability
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
nwe:RabbiTrustInvestmentFairValueDisclosure
us-gaap:FairValueByMeasurementBasis, us-gaap:FairValueByMeasurementFrequency
us-gaap:PublicUtilitiesRegulatoryProceeding
nwe:RegulatoryAssetForCOVIDUncollectableAccounts
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
nwe:RestrictedCashFairValueDisclosure
us-gaap:FairValueByMeasurementBasis, us-gaap:FairValueByMeasurementFrequency
us-gaap:EnvironmentalRemediationContingency
us-gaap:AccrualForEnvironmentalLossContingencies
us-gaap:EnvironmentalRemediationContingency, us-gaap:EnvironmentalRemediationSite

us-gaap:AccrualForEnvironmentalLossContingenciesGross
us-gaap:EnvironmentalRemediationContingency
us-gaap:EnvironmentalRemediationContingency, us-gaap:EnvironmentalRemediationSite

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent

us-gaap:AccruedEnvironmentalLossContingenciesNoncurrent

us-gaap:AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax

us-gaap:AllowanceForDoubtfulAccountsReceivableCurrent

us-gaap:AssetRetirementObligation

us-gaap:AssetRetirementObligationsNoncurrent

us-gaap:BuildingsAndImprovementsGross

us-gaap:CapitalLeaseObligationsCurrent

us-gaap:CapitalLeaseObligationsNoncurrent

us-gaap:ContractualObligation
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredTaxAssetsGross

us-gaap:DeferredTaxAssetsHedgingTransactions

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards
us-gaap:IncomeTaxAuthority, us-gaap:TaxPeriod
us-gaap:DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration

us-gaap:DeferredTaxAssetsOther

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions

us-gaap:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals

us-gaap:DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill

us-gaap:DeferredTaxLiabilitiesRegulatoryAssetsAndLiabilities
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAmountsRecognizedInBalanceSheet
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
us-gaap:Range, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanBenefitObligation
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
us-gaap:FairValueByMeasurementBasis, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanFairValueOfPlanAssets
us-gaap:FairValueByMeasurementBasis, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanFundedStatusOfPlan
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation

us-gaap:DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:RetirementPlanSponsorLocation, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanWeightedAverageAssetAllocations
us-gaap:RetirementPlanSponsorLocation, us-gaap:RetirementPlanType

us-gaap:EmployeeRelatedLiabilitiesCurrent

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized

us-gaap:EnergyRelatedInventoryNaturalGasInStorage
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
us-gaap:FairValueNetAssetLiability
us-gaap:FairValueByMeasurementBasis, us-gaap:FairValueByMeasurementFrequency

us-gaap:FinanceLeaseLiability

us-gaap:FinanceLeaseLiabilityCurrent

us-gaap:FinanceLeaseLiabilityNoncurrent
us-gaap:BalanceSheetLocation
us-gaap:FinanceLeaseRightOfUseAsset
us-gaap:PropertyPlantAndEquipmentByType

us-gaap:InterestPayableCurrent

us-gaap:InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet
us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService
us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation
us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantProportionateOwnershipShare

us-gaap:LandAndLandImprovements
us-gaap:CreditFacility
us-gaap:LineOfCreditFacilityMaximumBorrowingCapacity

us-gaap:LineOfCreditFacilityRemainingBorrowingCapacity

us-gaap:LongTermDebtFairValue

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
us-gaap:IncomeTaxAuthority
us-gaap:OperatingLossCarryforwards

us-gaap:OtherAccruedLiabilitiesNoncurrent
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased
us-gaap:OtherCommitment

us-gaap:PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesNoncurrent
us-gaap:RetirementPlanType
us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities
us-gaap:RetirementPlanType
us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent

us-gaap:PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation

us-gaap:PublicUtilitiesPropertyPlantAndEquipmentAmountOfAcquisitionAdjustments1

us-gaap:PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress

us-gaap:PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing

us-gaap:PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment

us-gaap:PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistribution

us-gaap:PurchaseObligationDueAfterFifthYear

us-gaap:PurchaseObligationDueInFifthYear

us-gaap:PurchaseObligationDueInFourthYear

us-gaap:PurchaseObligationDueInNextTwelveMonths

us-gaap:PurchaseObligationDueInSecondYear

us-gaap:PurchaseObligationDueInThirdYear
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligation
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueAfterFifthYear
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInFifthYear
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInFourthYear
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInSecondYear
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInThirdYear
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased, us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueWithinOneYear
us-gaap:BalanceSheetLocation
us-gaap:RegulatoryAssets
us-gaap:BalanceSheetLocation, us-gaap:RegulatoryAsset
us-gaap:PublicUtilitiesRegulatoryProceeding

us-gaap:RegulatoryAssetsCurrent

us-gaap:RegulatoryAssetsNoncurrent
us-gaap:BalanceSheetLocation
us-gaap:RegulatoryLiabilities
us-gaap:BalanceSheetLocation, us-gaap:RegulatoryLiability
us-gaap:PublicUtilitiesRegulatoryProceeding
us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:SubsequentEventType

us-gaap:RegulatoryLiabilityCurrent

us-gaap:RegulatoryLiabilityNoncurrent

us-gaap:RestrictedCash

us-gaap:RestrictedCashAndCashEquivalentsAtCarryingValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
us-gaap:AwardType, us-gaap:PlanName
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
us-gaap:AwardType, us-gaap:PlanName

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized

us-gaap:ShortTermBorrowings

us-gaap:UnbilledReceivablesCurrent

us-gaap:UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate

Plots across concepts


IncomeStatement
Other Comprehensive Income Loss Net Of Tax
Expenses
Income Tax Expense Benefit
Balance Sheet
Cash And Cash Equivalents At Carrying Value
Assets
Cash And Cash Equivalents At Carrying Value
Current Assets
Cash And Cash Equivalents At Carrying Value
NonCurrent Assets
Other Assets Noncurrent
PropertyPlantAndEquipmentNet
Property Plant And Equipment Net
Liabilities
Liabilities Current
Current Liabilities
Employee Related Liabilities Current
Noncurrent Liabilities
Other Liabilities Noncurrent
Stockholders Equity
Accumulated Other Comprehensive Income Loss Net Of Tax
Per Share
Common Stock Dividends Per Share Declared
CashFlow
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInOperatingActivities
Increase Decrease In Accounts Receivable
NetCashProvidedByUsedInInvestingActivities
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInFinancingActivities
Proceeds From Issuance Of Long Term Debt
Shares
Weighted Average Number Of Shares Outstanding Basic
AccountsReceivable
Allowance For Doubtful Accounts Receivable Current

Tables

  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:CommonStockValue █▃▂▂▂▂▂▂▂▂▁▁0.5510.5420.5410.5410.5410.5410.5410.540.540.540.5390.539
 us-gaap:SharesIssued us-gaap:StatementEquityComponents us-gaap:CommonStock█▃▂▂▂▂▂▂▂▂▁▁55.11854.23854.14554.14554.14554.14553.99953.99653.99653.99653.88953.889
 us-gaap:SharesIssued us-gaap:StatementEquityComponents us-gaap:TreasuryStock▃▅▃▅▆█▁▂▂▃▅▆3.5583.5633.5583.5643.5713.5783.5473.553.5533.5563.5663.569
us-gaap:CommonStockSharesIssued █▁55.11757554.238266NA54.144775NANA53.999189NANANA53.88941NA
us-gaap:CommonStockSharesAuthorized ▄▄▄▄200.0200.0200.0200.0NANA200.0NANANA200.0NA
us-gaap:PreferredStockSharesAuthorized ▄▄50.050.0NA50.0NANA50.0NANANA50.0NA
us-gaap:CommonStockSharesOutstanding █▁51.56001350.675207NA50.581098NANA50.452191NANANA50.323649NA
us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding █▁51.1213250.7368NA50.67409350.63900550.70528NA50.77923750.77515250.729364NA50.460543
us-gaap:WeightedAverageNumberOfSharesOutstandingBasic █▄▄▄▄▃▂▂▂▂▁▁50.98918250.63144850.58350.57656450.56972550.50679450.44850.44386650.44068550.38083950.32150.317813
us-gaap:EarningsPerShareBasic ▃▇▅▂▁▅▆▁▄█▇▂0.721.251.060.580.431.01.190.430.941.451.320.56
us-gaap:EarningsPerShareDiluted ▃▇▅▂▁▅▆▁▅█▇▂0.721.241.060.580.431.01.180.420.941.441.310.56
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
 Cost Ratio us-gaap:ConsolidationItems,us-gaap:ProductOrService us-gaap:OperatingSegments,us-gaap:ElectricityUsRegulated▁█241.44270.071NANA217.938244.625NANANANANANA
 Cost Ratio us-gaap:ConsolidationItems,us-gaap:ProductOrService us-gaap:OperatingSegments,us-gaap:NaturalGasUsRegulated▁█56.777130.732NANA51.42290.63NANANANANANA
 Cost Ratio us-gaap:StatementBusinessSegments nwe:ElectricDomesticRegulatedNANANA244.155217.938244.625NA241.237219.659273.037NANA
 Cost Ratio us-gaap:StatementBusinessSegments nwe:GasDomesticRegulatedNANANA36.45551.42290.63NA33.59951.06111.183NANA
 Gross Margin us-gaap:ConsolidationItems,us-gaap:ProductOrService us-gaap:OperatingSegments,us-gaap:ElectricityUsRegulated▁█241.44270.071NANA217.938244.625NANANANANANA
 Gross Margin us-gaap:ConsolidationItems,us-gaap:ProductOrService us-gaap:OperatingSegments,us-gaap:NaturalGasUsRegulated▁█56.777130.732NANA51.42290.63NANANANANANA
 Gross Margin us-gaap:StatementBusinessSegments nwe:ElectricDomesticRegulatedNANANA244.155217.938244.625NA241.237219.659273.037NA245.159
 Gross Margin us-gaap:StatementBusinessSegments nwe:GasDomesticRegulatedNANANA36.45551.42290.63NA33.59951.06111.183NA34.715
 Operating Margin us-gaap:ConsolidationItems,us-gaap:ProductOrService us-gaap:OperatingSegments,us-gaap:ElectricityUsRegulated▁█241.44270.071NANA217.938244.625NANANANANANA
 Operating Margin us-gaap:ConsolidationItems,us-gaap:ProductOrService us-gaap:OperatingSegments,us-gaap:NaturalGasUsRegulated▁█56.777130.732NANA51.42290.63NANANANANANA
 Operating Margin us-gaap:StatementBusinessSegments nwe:ElectricDomesticRegulatedNANANA244.155217.938244.625NA241.237219.659273.037NA245.159
 Operating Margin us-gaap:StatementBusinessSegments nwe:GasDomesticRegulatedNANANA36.45551.42290.63NA33.59951.06111.183NA34.715
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
 TTM Greenblatt ROC _ _▃▆▄▂▁▅▆▁▂█▄▁59.04380.98566.49649.65544.83975.21484.65146.35648.82397.0264.74247.808
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:ComprehensiveIncomeNetOfTax ▃▇▆▂▁▅▆▁▅█▇▂37.21262.9555.50129.57621.59950.91859.91121.82647.68872.98167.02128.227
us-gaap:CostOfGoodsAndServicesSold ▂█▃▂▁▄▃▂▁▆▂▂67.965144.51385.83768.03861.04391.27282.31464.22755.744115.73572.36972.247
us-gaap:CostOfRevenue ▂█▃▂▁▄▃▂▁▆▂▂67.965144.51385.83768.03861.04391.27282.31464.22755.744115.73572.36972.247
us-gaap:CostsAndExpenses ▂█▃▂▁▄▃▁▁▆239.174319.818246.949230.955224.521260.041243.484228.48221.896287.2NANA
us-gaap:GrossProfit ▄▇▃▂▁▅▅▁▂█▄▁230.252256.29227.608212.572208.317243.983245.821210.609214.975268.485236.447207.627
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments ▃▇▅▂▁▅▆▁▂█▄▂38.60263.04947.80826.76320.77648.89860.15522.22525.43674.37943.12427.824
us-gaap:IncomeTaxExpenseBenefit ██▆▇▇▇██▁█▁▇1.365-0.022-5.743-2.703-0.718-1.8060.1730.555-22.2261.573-23.368-0.358
us-gaap:IncomeTaxesPaidNet NANA0.0150.0450.00.055-6.8050.00.00.0680.00.0
us-gaap:InterestAndDebtExpense ▅▅█▆▇▇▇▆▅▆▆▁23.47323.5124.51423.67724.28724.33424.04523.72223.51123.7923.78622.035
us-gaap:InterestPaidNet █▁29.70913.765NA13.10527.56114.554NA13.41528.82213.278NANA
us-gaap:NetIncomeLoss ▃▇▅▂▁▅▆▁▅█▇▂37.23763.07153.55129.46621.49450.70459.98221.6747.66272.80666.49228.182
us-gaap:OperatingIncomeLoss ▃▆▄▂▁▅▆▁▂█▄▁59.04380.98566.49649.65544.83975.21484.65146.35648.82397.0264.74247.808
us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax ▄▁▃▃▃▆▂▅▁▅█▂0.021-0.076-0.003-0.003-0.0080.101-0.0530.042-0.0870.0630.157-0.068
us-gaap:OtherComprehensiveIncomeLossNetOfTax ▁▁█▂▂▂▁▂▁▂▃▂-0.025-0.1211.950.110.1050.214-0.0710.1560.0260.1750.5290.045
 us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation us-gaap:AccumulatedDefinedBenefitPlansAdjustment▁█-0.159-0.158NANANANANANANANANANA
 us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation us-gaap:AccumulatedTranslationAdjustment█▁0.021-0.076NANA-0.0080.101NANANANANANA
 us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesNANANA0.1130.1130.113NA0.1140.1130.112NA0.113
 us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedTranslationAdjustmentNANANA-0.003-0.0080.101NA0.042-0.0870.063NA-0.068
 us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:ComprehensiveIncomeNANANA0.110.1050.214NA0.1560.0260.175NA0.045
us-gaap:OtherNonoperatingIncomeExpense ▅██▃▃▁▂▂▃▄▅▅3.0325.5745.8260.7850.224-1.982-0.451-0.4090.1241.1492.1682.051
us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax ▄█▅▂▂▆▅▁▂█▄▁301.3366.6316.0279.0265.8346.0328.0264.7266.7371.9307.5257.5
us-gaap:Revenues ▃█▃▂▁▅▄▁▁▇▃▂298.217400.803313.445280.61269.36335.255328.135274.836270.719384.22308.816279.874
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:Assets ██▇▅▄▄▄▃▂▂▂▁6566.246502.8136389.4496075.6395971.7755966.9435910.7025810.185720.4355700.6555644.3765500.098
us-gaap:Liabilities ██▇▅▄▄▃▃▂▂▂▁4388.9254388.9784310.3544021.0893918.2193906.4673871.6083805.6563710.3573710.8633701.9943600.198
us-gaap:LiabilitiesAndStockholdersEquity ██▇▅▄▄▄▃▂▂▂▁6566.246502.8136389.4496075.6395971.7755966.9435910.7025810.185720.4355700.6555644.3765500.098
us-gaap:StockholdersEquity █▆▆▅▅▅▅▄▄▃▂▁2177.3152113.8352079.0952054.552053.5562060.4762039.0942004.5242010.0781989.7921942.3821899.9
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:AssetsCurrent ▇█▅▃▂▆▄▂▁▄▃▁347.732358.711308.68281.328263.586330.302301.727265.822252.994288.131277.685247.222
us-gaap:CashAndCashEquivalentsAtCarryingValue ▁▂▁▁▂█▁▁▁▁▂▁5.9428.9255.8113.5127.46456.3935.1455.0464.2173.9597.866.912
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents ▂▂▂▁▂█▁▁▁▁▂▁19.59821.8917.09614.00916.41365.14312.0714.10112.45911.03415.31114.093
us-gaap:AccountsReceivableNetCurrent ▄▇█▂▁▆█▁▁█▇▁143.497162.999168.229133.115125.104155.911167.405126.373126.025169.64162.373127.93
us-gaap:InventoryNet █▄▅█▅▃▃▃▂▁▂▃69.94656.82761.0169.05561.22453.23653.92555.16851.78147.55550.81552.738
us-gaap:InventoryRawMaterialsAndSupplies NANA44.311NANANA42.791NANANA36.926NA
us-gaap:OtherAssetsCurrent █▇▇▇▄▂▄▄▂▁▂▃19.36517.82717.37218.08913.32511.42513.89514.08711.1929.77110.75512.877
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:PropertyPlantAndEquipmentGross NANA6916.107NANANA6553.928NANANA6286.104NA
 us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:FiniteLivedIntangibleAssetsByMajorClass us-gaap:ComputerSoftwareIntangibleAssetNANA260.156NANANA235.187NANANANANA
us-gaap:PropertyPlantAndEquipmentNet █▇▇▆▅▄▄▃▂▂▂▁5071.8264993.2554952.9354860.7594784.0174717.5154700.9244650.9514588.3984537.9094521.3184460.15
us-gaap:Goodwill ▁▁▁▁▁▁▁██▁▁▁357.586357.586357.586357.586357.586357.586357.586357.986357.986357.586357.586357.586
us-gaap:OtherAssetsNoncurrent ▅█▆▅▅▅▆▅▄▄▁▁64.52175.11868.80464.50765.09964.60566.33464.6461.05959.82250.20651.097
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:AccountsPayableCurrent ▆▅█▄▃▂▇▂▁▅▆▂89.62280.225100.38874.66369.466.50796.6966.5558.88581.54887.04362.019
us-gaap:AccruedLiabilitiesCurrent ▄█▂█▂▅▁▅▁▆▃▇230.444270.879207.514269.722211.452237.947202.021243.093197.293245.986216.792263.142
us-gaap:LiabilitiesCurrent ▃▅▇█▆▃▃▃▁▃▃▃348.452386.447466.423493.516428.866348.315334.267333.684275.786347.242347.009349.713
us-gaap:OtherAccruedLiabilitiesCurrent NANA59.477NANANA49.099NANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:LongTermDebt NANA2315.261NANANA2233.281NANANA2102.345NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:NewMarketTaxCreditFinancing,us-gaap:SecuredDebtNANA26.977NANANA26.977NANANA26.977NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:RevolvingCreditFacilityDue2023,us-gaap:LineOfCreditNANA222.0NANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontana2.00Due2023,us-gaap:SecuredDebtNANA144.66NANANA144.66NANANA144.66NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue20253.11,us-gaap:SecuredDebtNANA75.0NANANA75.0NANANA75.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2028,us-gaap:SecuredDebtNANA35.0NANANA35.0NANANA35.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2030,us-gaap:SecuredDebtNANA100.0NANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2042,us-gaap:SecuredDebtNANA60.0NANANA60.0NANANA60.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2043,us-gaap:SecuredDebtNANA15.0NANANA15.0NANANA15.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2044,us-gaap:SecuredDebtNANA450.0NANANA450.0NANANA450.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2045,us-gaap:SecuredDebtNANA125.0NANANA125.0NANANA125.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2047,us-gaap:SecuredDebtNANA250.0NANANA250.0NANANA250.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2049,us-gaap:SecuredDebtNANA150.0NANANA150.0NANANA0.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2052,us-gaap:SecuredDebtNANA40.0NANANA40.0NANANA40.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2026,us-gaap:SecuredDebtNANA60.0NANANA60.0NANANA60.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue20262.66,us-gaap:SecuredDebtNANA45.0NANANA45.0NANANA45.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2030,us-gaap:SecuredDebtNANA50.0NANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2040,us-gaap:SecuredDebtNANA70.0NANANA70.0NANANA70.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2042,us-gaap:SecuredDebtNANA30.0NANANA30.0NANANA30.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2043,us-gaap:SecuredDebtNANA50.0NANANA50.0NANANA50.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2044,us-gaap:SecuredDebtNANA30.0NANANA30.0NANANA30.0NA
 us-gaap:LongTermDebt us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2052,us-gaap:SecuredDebtNANA20.0NANANA20.0NANANA20.0NA
us-gaap:LongTermDebtNoncurrent █▇▅▃▃▄▄▃▃▂▂▁2503.3472464.1212315.2612188.9012157.742239.4062233.2812176.0572158.9912080.4622102.3452016.091
us-gaap:DeferredIncomeTaxLiabilitiesNet █▆▅▂▃▂▁494.477480.879471.777456.735462.522451.97447.986NANANANANA
 us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap:RetirementPlanType us-gaap:OtherPostretirementBenefitPlansDefinedBenefitNANA2.774NANANA4.463NANANA4.235NA
 us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap:RetirementPlanType us-gaap:PensionPlansDefinedBenefitNANA128.324NANANA119.496NANANA126.988NA
us-gaap:OtherLiabilitiesNoncurrent ▄█▆▄▂▂▁▃▁▅▄▂398.134417.213410.703398.124391.012393.155387.152394.996388.913405.843399.822391.326
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:StockholdersEquity █▆▆▅▅▅▅▄▄▃▂▁2177.3152113.8352079.0952054.552053.5562060.4762039.0942004.5242010.0781989.7921942.3821899.9
us-gaap:CommonStockValue █▃▂▂▂▂▂▂▂▂▁▁0.5510.5420.5410.5410.5410.5410.5410.540.540.540.5390.539
us-gaap:AdditionalPaidInCapital █▃▃▃▃▂▂▂▂▂▁▁1575.1591517.3551513.7871514.821513.511512.1481508.971505.6051504.291502.9931499.071496.218
us-gaap:RetainedEarningsAccumulatedDeficit ██▇▆▆▆▅▄▅▄▂▁707.598702.058670.111646.65647.272655.865635.246604.048611.159592.278548.253509.24
us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax ███▄▃▃▃▃▃▃▂▁-7.415-7.39-7.269-9.219-9.329-9.434-9.648-9.577-9.733-9.759-9.934-10.463
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation us-gaap:AccumulatedDefinedBenefitPlansAdjustment▁▅█1.6431.8021.96NA0.120.120.12NANANA0.251NA
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges█▄▁-10.503-10.616-10.729NA-10.955-11.068-11.181NANANA-11.633NA
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation us-gaap:AccumulatedTranslationAdjustment▃▁█1.4451.4241.5NA1.5061.5141.413NANANA1.448NA
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation us-gaap:OtherComprehensiveIncomeNANA-7.269NANANA-9.648NANANA-9.934NA
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNANANA0.120.120.120.120.2510.2510.2510.2510.038
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesNANANA-10.842-10.955-11.068-11.181-11.294-11.408-11.521-11.633-11.792
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedTranslationAdjustmentNANANA1.5031.5061.5141.4131.4661.4241.5111.4481.291
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:ComprehensiveIncomeNANANA-9.219-9.329-9.434-9.648-9.577-9.733-9.759-9.934-10.463
us-gaap:TreasuryStockValue ██▇▇▇█▂▂▂▃▁▁98.57898.7398.07598.24298.43898.64496.01596.09296.17896.2695.54695.634
us-gaap:StockIssuedDuringPeriodValueNewIssues 56.666NA0.3450.3660.4290.2590.2320.2320.212.450.2010.283
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:NetCashProvidedByUsedInOperatingActivities ▂▃▁▅▃█▂▅▁▅▁▅38.92165.59929.634103.29661.057158.16242.859109.24833.189111.42435.56799.291
us-gaap:NetCashProvidedByUsedInInvestingActivities ▃▆▁▃▄▆▇▄▆█▅▇-104.986-77.854-122.775-106.51-98.148-78.371-73.277-95.847-81.45-65.577-93.062-76.864
us-gaap:NetCashProvidedByUsedInFinancingActivities ▆▄█▃▃▂▅▃▆▁▆▂63.77317.04996.2280.81-11.639-26.71828.387-11.75949.686-50.12458.713-21.246
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect ▁█-2.2924.794NA-2.404-48.7353.073NA1.6421.425-4.277NA1.181
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:DeferredIncomeTaxExpenseBenefit █▆▆▆▇▇█▇▂▇▁█2.065-2.706-3.815-3.759-0.170.172.4860.197-17.2550.708-19.4761.268
us-gaap:DepreciationDepletionAndAmortization ██▆▅▅▆▄▄▁▆▄▄46.80946.97545.30844.28944.78245.26543.15743.16641.01645.58443.59943.581
us-gaap:IncreaseDecreaseInAccountsPayable ▅▂█▅▅▄▇▆▁▅▇▆1.549-16.59120.2243.138-0.94-6.37912.1215.741-23.6373.95415.2854.759
us-gaap:IncreaseDecreaseInAccountsReceivable ▃▄█▅▂▄█▅▁▅▇▄-19.502-5.2335.1148.011-30.807-11.49441.0320.348-43.6157.26734.443-2.045
us-gaap:IncreaseDecreaseInInventories █▂▁▆▆▃▃▅▅▃▃▆13.119-4.183-8.0457.8317.988-0.689-1.2433.3874.226-3.26-1.9236.04
us-gaap:NetCashProvidedByUsedInOperatingActivities ▂▃▁▅▃█▂▅▁▅▁▅38.92165.59929.634103.29661.057158.16242.859109.24833.189111.42435.56799.291
us-gaap:NetIncomeLoss ▃▇▅▂▁▅▆▁▅█▇▂37.23763.07153.55129.46621.49450.70459.98221.6747.66272.80666.49228.182
us-gaap:ShareBasedCompensation ▅█▁▅▅██▅▅▇▇▅1.3153.223-1.1981.1521.1533.0423.2291.1811.1792.4182.7481.197
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:NetCashProvidedByUsedInInvestingActivities ▃▆▁▃▄▆▇▄▆█▅▇-104.986-77.854-122.775-106.51-98.148-78.371-73.277-95.847-81.45-65.577-93.062-76.864
us-gaap:PaymentsToAcquirePropertyPlantAndEquipment ▆▃█▆▅▃▂▅▃▁▄▂104.3477.854122.775106.50598.11178.37173.14295.84781.4565.57790.56176.949
us-gaap:PaymentsToAcquireInvestments NANA0.00.005NANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
us-gaap:NetCashProvidedByUsedInFinancingActivities ▆▄█▃▃▂▅▃▆▁▆▂63.77317.04996.2280.81-11.639-26.71828.387-11.75949.686-50.12458.713-21.246
us-gaap:ProceedsFromIssuanceOfLongTermDebt ▁█▁▁0.099.9150.00.0NANA0.0100.0NANA0.00.0
us-gaap:PaymentsOfDividendsCommonStock █▇▅▅▅▅▃▃▃▃▁▁31.69731.12430.0930.08830.08730.08528.78428.78128.78128.78127.47927.47
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument nwe:SecuredDebtMontanaDue2030NANANA3.2099999999999998e-063.2099999999999996e-08NANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument nwe:SecuredDebtSouthDakotaDue2030NANANA3.2099999999999998e-063.2099999999999996e-08NANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2025,us-gaap:SecuredDebtNANA5.0099999999999995e-06NANANA5.01e-08NANANA5.01e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue20253.11,us-gaap:SecuredDebtNANA3.11e-06NANANA3.11e-08NANANA3.11e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2028,us-gaap:SecuredDebtNANA3.99e-06NANANA3.99e-08NANANA3.99e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2030,us-gaap:SecuredDebtNANA3.2099999999999998e-06NANANANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2039,us-gaap:SecuredDebtNANA5.71e-06NANANA5.7099999999999995e-08NANANA5.7099999999999995e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2042,us-gaap:SecuredDebtNANA4.15e-06NANANA4.15e-08NANANA4.15e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2043,us-gaap:SecuredDebtNANA4.849999999999999e-06NANANA4.8500000000000004e-08NANANA4.8500000000000004e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2044,us-gaap:SecuredDebtNANA4.18e-06NANANA4.18e-08NANANA4.176e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2047,us-gaap:SecuredDebtNANA4.03e-06NANANA4.0300000000000004e-08NANANA4.0300000000000004e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDue2052,us-gaap:SecuredDebtNANA4.2999999999999995e-06NANANA4.2999999999999995e-08NANANA4.2999999999999995e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDueJune2049,us-gaap:SecuredDebtNANA3.98e-06NANANA3.98e-08NANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtMontanaDueSeptember2049,us-gaap:SecuredDebtNANA3.98e-06NANANA3.98e-08NANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2025,us-gaap:SecuredDebtNANA5.0099999999999995e-06NANANA5.01e-08NANANA5.01e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2026,us-gaap:SecuredDebtNANA2.8e-06NANANA2.8e-08NANANA2.8e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue20262.66,us-gaap:SecuredDebtNANA2.66e-06NANANA2.66e-08NANANA2.66e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2030,us-gaap:SecuredDebtNANA3.2099999999999998e-06NANANANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2040,us-gaap:SecuredDebtNANA4.26e-06NANANA4.26e-08NANANA4.26e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2042,us-gaap:SecuredDebtNANA4.15e-06NANANA4.15e-08NANANA4.15e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2043,us-gaap:SecuredDebtNANA4.849999999999999e-06NANANA4.8500000000000004e-08NANANA4.8500000000000004e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2044,us-gaap:SecuredDebtNANA4.219999999999999e-06NANANA4.22e-08NANANA4.22e-08NA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType nwe:SecuredDebtSouthDakotaDue2052,us-gaap:SecuredDebtNANA4.2999999999999995e-06NANANA4.2999999999999995e-08NANANA4.2999999999999995e-08NA

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue


Common
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value551000.0542000.0541000.0541000.0541000.0541000.0541000.0540000.0540000.0540000.0539000.0539000.0539000.0531000.0530000.0522000.0521000.0521000.0520000.0520000.0520000.0520000.0518000.0507000.0507000.0507000.0505000.0428000.0428000.0428000.0423000.0421000.0420000.0414000.0408000.0408000.0407000.0399000.0398000.0398000.0398000.0398000.0398000.0395000.0
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Shares Issued

us-gaap:SharesIssued us-gaap:StatementEquityComponents

us-gaap:SharesIssued

us-gaap:CommonStock


Shares
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-312007-12-31
Value5554545454545353535353535353525252525151515151505050504242424242403939393939
Percentage of SharesIssued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:TreasuryStock


Shares
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-312007-12-31
Value3.5583.5633.5583.5643.5713.5783.5473.553.5533.5563.5663.5693.5743.5793.6093.6123.623.6413.6263.633.6453.6483.6173.623.6243.6453.6073.613.6133.6163.5953.5973.5713.5633.573.5633.5330.363
Percentage of SharesIssued6.56.66.66.66.66.66.66.66.66.66.66.66.66.76.86.96.97.07.07.07.07.07.07.17.17.27.18.48.58.58.58.68.88.99.09.09.00.9

Common Stock Shares Issued

us-gaap:CommonStockSharesIssued

us-gaap:CommonStockSharesIssued


Common
Period End2021-06-302021-03-312020-09-302019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312011-06-302011-03-312010-12-312009-12-31
Value55545453535251515042403939398203979939566
Percentage of CommonStockSharesIssued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Common Stock Shares Authorized

us-gaap:CommonStockSharesAuthorized

us-gaap:CommonStockSharesAuthorized


Common
Period End2021-06-302021-03-312020-12-312020-09-302019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312011-06-302011-03-312010-12-312009-12-31
Value200200200200200200200200200200200200200200200000200000200000
Percentage of CommonStockSharesAuthorized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Preferred Stock Shares Authorized

us-gaap:PreferredStockSharesAuthorized

us-gaap:PreferredStockSharesAuthorized


Preferred
Period End2021-06-302021-03-312020-09-302019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312011-06-302011-03-312010-12-312009-12-31
Value50505050505050505050505050500005000050000
Percentage of PreferredStockSharesAuthorized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Common Stock Shares Outstanding

us-gaap:CommonStockSharesOutstanding

us-gaap:CommonStockSharesOutstanding


Common
Period End2021-06-302021-03-312020-09-302019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312011-06-302011-03-312010-12-312009-12-31
Value51505050504948484638373636362523622936003
Percentage of CommonStockSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Weighted Average Number Of Diluted Shares Outstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding


Weighted
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value51505050505050505050494848484848484747473939383838373736363636363636
Percentage of WeightedAverageNumberOfDilutedSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Weighted Average Number Of Shares Outstanding Basic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic


Weighted
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value50505050505050505050505049494848484848484848484747464339393838383837373736363636363636363636
Percentage of WeightedAverageNumberOfSharesOutstandingBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareBasic


Earnings
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.721.251.060.580.431.01.190.430.941.451.320.560.881.180.980.750.451.170.910.920.740.790.940.510.661.090.870.770.21.170.670.410.371.011.58-0.10.310.880.940.410.30.90.630.40.320.79
Percentage of EarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted

us-gaap:EarningsPerShareDiluted


Earnings
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.721.241.060.580.431.01.180.420.941.441.310.560.871.180.980.750.441.170.920.920.730.790.930.510.651.090.850.770.21.170.680.40.371.011.57-0.10.310.880.930.410.30.890.630.40.320.79
Percentage of EarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Comprehensive Income Net Of Tax

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTax


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value376255292150592147726728435848362156464335374523305127297.481452615143757-4.029113230141032221411
Percentage of ComprehensiveIncomeNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.417.20.010.68.114.70.08.217.919.60.011.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Cost Of Goods And Services Sold

us-gaap:CostOfGoodsAndServicesSold

us-gaap:CostOfGoodsAndServicesSold


Cost
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value67144856861918264551157272329610997
Percentage of CostOfGoodsAndServicesSold100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax22.639.40.024.423.026.40.024.320.931.10.028.10.00.00.00.0

Cost Of Revenue

us-gaap:CostOfRevenue

us-gaap:CostOfRevenue


Cost
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value67144856861918264551157272329610997
Percentage of CostOfRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax22.639.40.024.423.026.40.024.320.931.10.028.10.00.00.00.0

us-gaap:CostOfRevenue us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Cost
Period End2021-06-302021-03-312020-06-302020-03-31
Value49804863
Percentage of CostOfRevenue72.455.579.169.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax16.321.918.218.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Cost
Period End2021-06-302021-03-312020-06-302020-03-31
Value18641227
Percentage of CostOfRevenue27.644.520.930.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax6.217.54.87.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:CostOfRevenue us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Cost
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value614863584276
Percentage of CostOfRevenue89.979.169.991.576.566.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.918.218.422.216.020.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated24.522.125.624.819.930.2

nwe:GasDomesticRegulated


Cost
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value6.88312275.4591338
Percentage of CostOfRevenue10.120.930.18.523.533.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax2.54.87.92.14.910.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated23.726.928.319.524.833.1

Costs And Expenses

us-gaap:CostsAndExpenses

us-gaap:CostsAndExpenses


Costs
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value239319246230224260243228221287254233212225280246207217276
Percentage of CostsAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax79.487.20.082.884.575.20.086.383.277.20.00.00.00.00.00.00.00.00.0

Gross Profit

us-gaap:GrossProfit

us-gaap:GrossProfit


Gross
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value230256227212208243245210214268236207229245235212199247222204211217217199191233204157157202182157153180213142148170159145141176151134132
Percentage of GrossProfit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax76.469.90.076.278.470.50.079.680.672.20.080.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:GrossProfit us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Gross
Period End2021-06-302021-03-312020-06-302020-03-31
Value192189169180
Percentage of GrossProfit83.574.181.474.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax63.851.863.852.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Gross
Period End2021-06-302021-03-312020-06-302020-03-31
Value38663863
Percentage of GrossProfit16.525.918.625.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.618.114.618.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:GrossProfit us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Gross
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value183169180182176196178190181174183163180167176176157163172155172150127118132129131117126166118118124115121109124108110102
Percentage of GrossProfit86.181.474.186.682.373.086.082.873.874.386.481.973.175.386.483.472.675.086.581.473.773.381.275.165.770.983.577.070.278.383.179.772.772.383.177.770.571.582.277.6
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax65.663.852.368.966.452.769.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated73.277.672.677.182.776.978.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Gross
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value29386328377228396460283666552735595426356154293969522534534523294643243151422329
Percentage of GrossProfit13.918.625.913.417.727.014.017.226.225.713.618.126.924.713.616.627.425.013.518.626.326.718.824.934.328.816.322.829.521.616.620.127.127.616.622.129.328.217.622.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax10.614.618.310.614.219.511.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated101.681.865.1100.571.961.999.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value386347262048602225744327466051392263423438405030396136118.95533117164274-12.3614403415104130191240
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.817.20.09.67.814.10.08.49.520.00.010.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Income Tax Expense Benefit

us-gaap:IncomeTaxExpenseBenefit

us-gaap:IncomeTaxExpenseBenefit


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value1.365-0.022-5.743-2.703-0.718-1.8060.1730.555-22.2261.573-23.368-0.3583.1021.9143.3362.7750.586.677-3.407-9.6592.9472.4725.4216.3898.21110-1.032-18.4371.2047.9935.3361.8152.1065.04416-8.5882.5658.0120.7680.635-0.5169.1787.734.7291.12112
Percentage of IncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.5-0.00.0-1.0-0.3-0.50.00.2-8.30.40.0-0.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:IncomeTaxExpenseBenefit us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Income
Period End2021-06-302021-03-312020-06-302020-03-31
Value0.804-0.115-0.756-0.656
Percentage of IncomeTaxExpenseBenefit58.9522.7105.336.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.3-0.0-0.3-0.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Income
Period End2021-06-302021-03-312020-06-302020-03-31
Value0.2082.0220.3370.737
Percentage of IncomeTaxExpenseBenefit15.2-9190.9-46.9-40.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.60.10.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:IncomeTaxExpenseBenefit us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Income
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value-1.197-0.756-0.6561.4151.7131.8092.1832.6490.498-0.1394.1530.5232.887-3.792-7.9463.3311.0153.5866.5533.5586.2530.915-5.2351.6734.1371.1138.4120.0764.30418-5.7625.913.1743.0513.4073.673.9211.4496.5514.405
Percentage of IncomeTaxExpenseBenefit44.3105.336.3255.0-7.7115.0-609.885.426.0-4.2149.790.243.2111.382.3113.041.166.2102.643.362.4-88.728.4139.051.820.9463.53.685.3117.967.1230.439.6397.3536.5-711.242.718.7138.5393.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.4-0.3-0.20.50.60.50.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated-0.5-0.3-0.30.60.80.71.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Income
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value-0.6070.3370.7370.2320.354-1.079-0.362-0.4922.2262.884-2.334-0.8176.9511.113-1.169-1.2783.0212.131-1.883-1.2174.7214.129-0.926-0.0654.3253.981-3.521.9011.7721.214-3.102-1.013.592.244-3.016-0.3264.573.142-3.543-1.155
Percentage of IncomeTaxExpenseBenefit22.5-46.9-40.841.8-1.6-68.6101.1-15.9116.386.5-84.1-140.9104.1-32.712.1-43.4122.239.3-29.5-14.847.1-400.15.0-5.454.174.6-193.990.335.17.536.1-39.444.8292.2-475.063.249.840.6-74.9-103.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.20.10.20.10.1-0.3-0.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated-2.10.70.80.80.7-0.9-1.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllOtherSegments


Income
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value0.353-1.929-0.899-0.299-1.887-0.969-1.092-24.2930.84314-2.1790.945-0.810.5910.9560.874-3.161-0.728-0.5440.894-1.564-0.2961.7195.87-0.958-6.076-12.276-0.404-0.4690.242-3.0770.129-1.032-4.090.276
Percentage of IncomeTaxExpenseBenefit25.98768.233.341.6104.5-560.1-196.8109.353.6-61.1608.730.5-42.317.734.5150.7-47.321.45.630.3-63.3-5.526.971.5-9.6588.866.6-33.6-5.94.5-169.56.1-20.5-25.4-3.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.1-0.5-0.3-0.1-0.50.0-0.4-9.10.20.0-0.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AllOtherSegments0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Income Taxes Paid Net

us-gaap:IncomeTaxesPaidNet

us-gaap:IncomeTaxesPaidNet


Income
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value15000.045000.0055000.0-6805000.00068000.000055000.0-1000.00061000.00026000.0-2948000.0-1311000.00027000.07000.08000.07000.013000.03000.05000.04000.038000.01000000.002279000.0-335000.0-1237000.0018000.001000000.01000000.000
Percentage of IncomeTaxesPaidNet100.0100.00.0100.0100.00.00.0100.00.00.00.0100.0100.00.00.0100.00.00.0100.0100.0100.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.00.0100.00.0100.0100.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Interest And Debt Expense

us-gaap:InterestAndDebtExpense

us-gaap:InterestAndDebtExpense


Interest
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value23232423242424232323232223222223232322212624242222231918191919171716151715151616161716161617
Percentage of InterestAndDebtExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax7.86.40.08.59.17.00.09.08.86.40.08.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:InterestAndDebtExpense us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Interest
Period End2021-06-302021-03-312020-06-302020-03-31
Value20202120
Percentage of InterestAndDebtExpense88.888.288.585.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax6.95.78.16.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Interest
Period End2021-06-302021-03-312020-06-302020-03-31
Value1.4221.4881.6461.604
Percentage of InterestAndDebtExpense6.16.36.86.6
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.50.40.60.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:InterestAndDebtExpense us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Interest
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value21212019191919201919202121201924222019191916141415151414141215131313131313121211
Percentage of InterestAndDebtExpense89.988.585.582.182.082.186.587.685.088.489.290.089.990.390.791.390.085.386.586.185.284.274.675.676.077.383.984.184.283.285.684.485.683.881.881.078.974.774.874.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax7.68.16.07.47.25.37.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated8.59.88.48.29.07.78.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Interest
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value1.5741.6461.6041.5881.5011.511.4361.1611.8541.4561.4181.51.5461.5711.2491.8141.9553.1292.5622.7482.9942.6392.6272.5952.7572.442.562.5672.4262.4032.3632.232.0672.3272.7112.7292.6652.8913.1163.456
Percentage of InterestAndDebtExpense6.66.86.66.76.46.36.55.08.16.56.16.46.66.85.96.98.013.011.612.013.013.314.013.613.812.515.015.014.515.513.314.012.914.416.216.215.517.619.121.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.60.60.50.60.60.40.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated5.43.51.75.72.81.35.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllOtherSegments


Interest
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value1.2021.2930.8171.1581.9141.9182.6532.7252.7452.2541.5291.7181.5961.1411.0870.8440.8170.6550.7010.4880.4990.4030.4030.4470.4230.5152.1422.0632.041.990.1940.1630.2260.20.199
Percentage of InterestAndDebtExpense5.15.53.54.87.98.011.211.611.59.56.97.46.95.14.73.63.52.83.31.82.01.71.81.91.82.611.410.810.210.21.11.01.31.31.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.40.40.30.40.60.01.01.00.70.00.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AllOtherSegments0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Interest Paid Net

us-gaap:InterestPaidNet

us-gaap:InterestPaidNet


Interest
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value2913132714132813
Percentage of InterestPaidNet100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax9.93.84.710.44.25.110.83.6

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value376353292150592147726628435847362156444435384523305137307.746452615143758-3.77211323414103222141128
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.417.20.010.68.114.70.08.217.919.60.010.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Net
Period End2021-06-302021-03-312020-06-302020-03-31
Value39382230
Percentage of NetIncomeLoss105.461.3105.260.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax13.010.58.58.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Net
Period End2021-06-302021-03-312020-06-302020-03-31
Value-0.40523-0.08120
Percentage of NetIncomeLoss-1.138.0-0.441.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.16.5-0.06.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Net
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value3722303227433444373041233331513819313319332928102316201522470.65102320218.1672217179.397
Percentage of NetIncomeLoss128.6105.260.0151.958.559.4123.0101.063.763.6114.0109.759.771.7115.3106.951.868.9139.162.665.380.593.2139.151.864.9132.0109.758.380.3-17.294.773.059.2144.074.470.577.7124.680.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax13.68.58.812.410.511.613.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated15.210.312.213.913.017.015.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Net
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value-8.386-0.08120-9.551-1.66633-7.1782.4212219-4.409-0.2122012-6.516-0.891714-7.44-1.639179.143-7.387-0.4192410-3.412-0.2881711-3.486-1.0611010-5.6150.021118.309-2.51-1.325
Percentage of NetIncomeLoss-28.5-0.441.0-44.1-3.545.7-25.55.538.040.3-12.1-1.036.427.7-14.6-2.545.932.0-31.3-5.333.524.6-24.5-5.454.141.7-21.8-2.047.019.092.4-9.333.530.0-37.70.235.236.8-17.5-11.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-3.0-0.06.0-3.6-0.68.9-2.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated-28.8-0.221.4-34.1-3.228.4-24.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllOtherSegments


Net
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-1.5890.478-0.049-1.034-0.535-1.06-1.68721-3.704-16.6730.703-2.844-1.001-1.89-0.671-1.9082.1852.097-0.304-1.5820.874-0.408-1.857130.607-1.8779.436-2.606-2.68-1.721-1.593-1.108-1.9920.438-0.936
Percentage of NetIncomeLoss-4.30.8-0.2-4.8-1.1-1.8-7.845.0-5.1-25.12.5-6.5-1.7-3.9-1.8-8.73.94.8-0.7-4.42.3-0.9-7.842.71.2-5.031.3-33.6-5.9-6.6-10.2-7.7-5.30.724.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.50.1-0.0-0.4-0.20.0-0.68.0-1.00.00.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AllOtherSegments0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value376353292150592147726628435847362156454435384523305137307.7464526
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0104.1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.417.20.010.68.114.70.08.217.919.60.010.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Operating Income Loss

us-gaap:OperatingIncomeLoss

us-gaap:OperatingIncomeLoss


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value59806649447584464897644769847161438564566361724861835030257149313257894.40928554931265845332757
Percentage of OperatingIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax19.622.10.017.816.921.70.017.518.326.10.018.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingIncomeLoss us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Operating
Period End2021-06-302021-03-312020-06-302020-03-31
Value58564249
Percentage of OperatingIncomeLoss99.469.794.566.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax19.515.415.914.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Operating
Period End2021-06-302021-03-312020-06-302020-03-31
Value0.189261.59323
Percentage of OperatingIncomeLoss0.332.73.630.6
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.17.20.66.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:OperatingIncomeLoss us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Operating
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value5642495449655467564865445747616442535641584635254233412938789.664293935382439293423
Percentage of OperatingIncomeLoss113.694.566.5117.5100.667.2115.097.167.268.9105.7102.167.074.0109.8101.768.374.1117.467.169.491.0114.9103.059.068.0131.190.467.687.8219.2102.272.072.2120.594.568.565.9104.488.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax20.215.914.420.618.417.521.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated22.619.420.123.023.025.624.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Operating
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value-7.8781.59323-7.3870.24234-6.543.2812623-6.057-0.0182814-6.781-0.6252219-7.268-0.8082415-6.0221.6963117-5.253.9822114-4.766-0.191614-6.1522.0691814-3.1161.099
Percentage of OperatingIncomeLoss-15.93.630.6-15.90.535.2-13.74.731.032.5-9.8-0.033.922.6-12.1-1.035.726.5-15.0-1.329.630.6-19.46.844.335.6-16.712.237.416.1-108.1-0.729.229.0-19.37.931.931.7-9.44.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-2.80.66.7-2.80.19.2-2.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated-27.13.423.8-26.40.529.2-22.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllOtherSegments


Operating
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value0.185-1.921.1020.8692.1820.493-0.738-0.535-2.303-0.26-0.636-1.31.512-1.0142.561-0.907-0.7252.1661.301-0.437-2.517-0.456-1.165200.831-10.9041.414-2.457-2.361-1.845-4.502-0.844-2.825-3.48-0.489
Percentage of OperatingIncomeLoss0.3-2.42.21.92.90.6-1.6-1.1-2.4-0.4-1.3-1.91.8-1.44.2-2.1-0.93.42.3-0.7-4.1-0.6-2.434.21.0-21.64.6-9.8-3.3-3.7-14.3-2.6-5.0-3.9-11.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.1-0.50.40.30.60.0-0.3-0.2-0.60.0-0.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AllOtherSegments0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value21000.0-76000.0-3000.0-3000.0-8000.0101000.0-53000.042000.0-87000.063000.0157000.0-68000.086000.095000.0-5000.0-144000.0-104000.051000.0109000.026000.08000.0-118000.0113000.0233000.0-56000.0268000.0110000.0134000.0-82000.0103000.085000.0-54000.086000.049000.026000.0-79000.046000.0-47000.0124000.0-168000.018000.0
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.0-0.00.0-0.0-0.00.00.00.0-0.00.00.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value21000.0-76000.0-3000.0-3000.0-8000.0101000.0-53000.042000.0-87000.063000.0157000.0-68000.086000.095000.0-5000.0-144000.0-104000.051000.0109000.026000.08000.0-118000.0113000.0233000.0-56000.0268000.0110000.0134000.0-82000.0103000.085000.0
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.0-0.00.0-0.0-0.00.00.00.0-0.00.00.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Other Comprehensive Income Loss Net Of Tax

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value-25000.0-121000.01950000.0110000.0105000.0214000.0-71000.0156000.026000.0175000.0529000.045000.0199000.0208000.0861000.0-52000.0-11000.0144000.0398000.0-1480000.045000.0-81000.0460000.0-322000.0-147000.0179000.0-10077000.0-1060000.0-265000.0-80000.0867000.0-237000.0-97000.0-134000.0-912000.0-257000.0-145000.0-25000.0-3982000.0-351000.0-279000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.0-0.00.00.00.00.10.00.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


Other
Period End2021-06-302021-03-31
Value-159000.0-158000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax636.0130.6
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.1-0.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AccumulatedDefinedBenefitPlansAdjustment0.00.0

us-gaap:AccumulatedTranslationAdjustment


Other
Period End2021-06-302021-03-312020-06-302020-03-31
Value21000.0-76000.0-8000.0101000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax-84.062.8-7.647.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.0-0.0-0.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AccumulatedTranslationAdjustment0.00.00.00.0

us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-31
Value113000.0113000.0113000.0114000.0113000.0112000.0113000.0113000.0113000.092000.093000.093000.0-1506000.037000.037000.037000.0-555000.0-91000.0-89000.0-10269000.0-1194000.0-183000.0-183000.0-181000.0-183000.0-183000.0-183000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax102.7107.652.873.1434.664.0251.156.854.3-176.9-845.564.6101.882.2-45.78.0172.461.9-49.7101.9112.669.1228.8-20.977.2188.7136.6
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value-3000.0-8000.0101000.042000.0-87000.063000.0-68000.086000.095000.0-144000.0-104000.051000.026000.08000.0-118000.0113000.0233000.0-56000.0268000.0110000.0134000.0-82000.0103000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax-2.7-7.647.226.9-334.636.0-151.143.245.7276.9945.535.4-1.817.8145.724.6-72.438.1149.7-1.1-12.630.9-128.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.0-0.00.00.0-0.00.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ComprehensiveIncome


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-31
Value110000.0105000.0214000.0156000.026000.0175000.045000.0199000.0208000.0-52000.0-11000.0144000.0-1480000.045000.0-81000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.10.10.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Other Nonoperating Income Expense

us-gaap:OtherNonoperatingIncomeExpense

us-gaap:OtherNonoperatingIncomeExpense


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value3.0325.5745.8260.7850.224-1.982-0.451-0.4090.1241.1492.1682.0510.876-1.1292.5060.792.1231.51.372-0.1211.1953.1022.1543.7690.9950.6655.468-0.4392.982.1890.9773.1170.9282.7151.2380.9741.1760.9841.6740.3461.1060.8051.4242.3151.8530.753
Percentage of OtherNonoperatingIncomeExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.01.50.00.30.1-0.60.0-0.20.00.30.00.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherNonoperatingIncomeExpense us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Other
Period End2021-06-302021-03-312020-06-302020-03-31
Value2.2152.8290.9590.613
Percentage of OtherNonoperatingIncomeExpense73.150.8428.1-30.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.70.80.40.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Other
Period End2021-06-302021-03-312020-06-302020-03-31
Value1.0360.9830.3090.095
Percentage of OtherNonoperatingIncomeExpense34.217.6137.9-4.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.30.30.10.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:OtherNonoperatingIncomeExpense us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value1.5590.9590.613-0.677-0.22-0.5610.926-0.0520.491.1141.2470.9170.7061.110.9820.6870.4671.5271.8321.6591.2821.5541.3371.0550.812-0.8652.2130.7022.0110.8120.4050.8010.6121.1380.0860.7240.6151.4392.1091.949
Percentage of OtherNonoperatingIncomeExpense198.6428.1-30.9165.5-177.4-48.845.1-5.9-43.444.5157.843.247.180.9-811.657.515.170.948.6166.7192.828.4-304.635.437.1-88.571.075.674.165.641.668.162.268.024.965.576.4101.191.1105.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.60.40.2-0.3-0.1-0.20.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated0.60.40.2-0.3-0.1-0.20.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value0.4590.3090.095-0.344-0.053-0.4770.436-0.1910.1080.5360.7320.4890.2280.4040.3450.2710.3090.4720.5070.70.1420.4480.3360.4150.125-0.5140.8780.1980.6770.3980.5410.3490.3450.5070.2320.3550.164-0.0420.179-0.123
Percentage of OtherNonoperatingIncomeExpense58.5137.9-4.884.1-42.7-41.521.3-21.8-9.621.492.723.015.229.4-285.122.710.021.913.570.421.48.2-76.513.95.7-52.628.221.324.932.155.529.735.130.367.132.120.4-2.97.7-6.6
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.20.10.0-0.1-0.0-0.10.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated1.60.70.1-1.2-0.1-0.41.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllOtherSegments


Other
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-0.2191.762-1.233-1.044-2.69-0.6040.6120.3972.1870.1290.6891.119-1.7270.856-1.1890.7170.566-0.142-1.4480.2372.3260.1551.43-1.364-0.7593.466-2.1121.511.2522.3560.0260.0280.0270.0280.028
Percentage of OtherNonoperatingIncomeExpense-7.231.6-157.1-466.1135.7133.9-149.6320.2190.36.033.6127.7153.034.2-150.533.837.7-10.31196.719.875.07.237.9-137.1-114.163.4481.150.757.2241.10.83.01.02.32.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.10.5-0.4-0.4-0.80.00.20.10.60.00.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AllOtherSegments0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Revenue From Contract With Customer Including Assessed Tax

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value301366316279265346328264266371307257
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:MajorCustomers

nwe:CommercialCustomers


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value127145133123113143141121119147128117116142124117144
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax42.439.742.144.442.641.343.246.044.939.641.945.60.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax42.439.742.144.442.641.343.246.044.939.641.945.60.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:IndustrialCustomers


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value9.41010.09.39.39.111101012119.91011101011
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.12.83.23.33.52.63.54.03.93.33.83.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.12.83.23.33.52.63.54.03.93.33.83.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:IndustrialCustomers100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:OtherCustomers


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value9.55.15.600000000000004129.55.65.8128.05.66.4117.35.5129.05.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.21.41.84.33.61.61.84.73.01.52.14.50.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.21.41.84.33.61.61.84.73.01.52.14.50.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:OtherCustomers100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:OtherTariffBasedRevenue


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value3426232322242423232626212828544348
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax11.57.37.48.38.67.17.48.78.97.18.68.30.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax11.57.37.48.38.67.17.48.78.97.18.68.30.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:OtherTariffBasedRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value120179143110110163144961041801349710216910197171
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax39.948.945.539.741.747.344.136.639.348.543.637.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax39.948.945.539.741.747.344.136.639.348.543.637.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:Totalcustomerrevenue


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value266340292255242321303241243345281236237328249234333
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax88.592.792.691.791.492.992.691.391.192.991.491.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax88.592.792.691.791.492.992.691.391.192.991.491.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:Totalcustomerrevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:MajorCustomers, us-gaap:StatementBusinessSegments

nwe:CommercialCustomers, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value108110109116100112116114104109103110101107115104110
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax36.130.334.741.837.832.535.643.139.229.633.842.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax36.130.334.741.837.832.535.643.139.229.633.842.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value1934237.31230257.71537247.314348.61334
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax6.39.57.42.64.78.87.72.95.710.18.12.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax6.39.57.42.64.78.87.72.95.710.18.12.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:IndustrialCustomers, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value9.29.79.69.29.28.811101011119.81010101010
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.12.63.03.33.52.53.44.03.83.13.73.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.12.63.03.33.52.53.44.03.83.13.73.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:IndustrialCustomers nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:IndustrialCustomers, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value0.20.50.40.10.10.30.30.10.10.50.40.10.20.50.10.20.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.00.00.10.10.00.00.10.10.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.00.00.10.10.00.00.10.10.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:IndustrialCustomers nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:OtherCustomers, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value9.14.65.4119.25.35.4127.85.16.1117.15.0128.95.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.01.31.74.33.51.51.64.72.91.42.04.40.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.01.31.74.33.51.51.64.72.91.42.04.40.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:OtherCustomers nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:OtherCustomers, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value0.40.50.20.10.30.30.40.10.20.50.30.10.20.50.00.10.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.00.10.10.10.00.10.10.10.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.00.10.10.10.00.10.10.10.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:OtherCustomers nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0

nwe:OtherTariffBasedRevenue, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value2516141414141515151616131717453337
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax8.44.64.65.35.44.34.65.85.64.45.55.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax8.44.64.65.35.44.34.65.85.64.45.55.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:OtherTariffBasedRevenue nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:OtherTariffBasedRevenue, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value9.19.79.08.38.69.69.27.78.7109.78.510109.29.711
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.02.62.83.03.22.82.82.93.32.73.23.30.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.02.62.83.03.22.82.82.93.32.73.23.30.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:OtherTariffBasedRevenue nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value841139797851079884761128784731058872108
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax28.031.030.834.932.131.130.031.928.630.128.532.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax28.031.030.834.932.131.130.031.928.630.128.532.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value3565461325564612286846132863132463
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax11.917.814.74.89.716.314.04.710.718.415.25.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax11.917.814.74.89.716.314.04.710.718.415.25.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:Totalcustomerrevenue, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value211239222235204234231221198238208215193229226196234
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax70.165.270.384.276.867.770.783.674.664.267.983.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax70.165.270.384.276.867.770.783.674.664.267.983.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:Totalcustomerrevenue nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:Totalcustomerrevenue, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value551017020388771204410672204399223898
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax18.427.622.37.514.625.321.97.716.528.723.58.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax18.427.622.37.514.625.321.97.716.528.723.58.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:Totalcustomerrevenue nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:MajorCustomers, us-gaap:StatementGeographical

nwe:CommercialCustomers, stpr:MT


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value97110104948510510893921099791881049691110
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax32.430.232.933.932.230.433.135.234.629.531.635.50.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax32.430.232.933.932.230.433.135.234.629.531.635.50.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:MT100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, stpr:NE


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value1.84.41.90.71.54.02.20.92.15.32.50.92.46.11.12.14.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.61.20.60.30.61.20.70.30.81.40.80.30.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.61.20.60.30.61.20.70.30.81.40.80.30.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:NE100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, stpr:SD


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value2830272826333127253228252531262429
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax9.48.38.610.29.89.89.510.49.58.79.49.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax9.48.38.610.29.89.89.510.49.58.79.49.80.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:SD100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:MT


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value951431208888126119778113910777771288276134
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax31.739.038.331.733.136.736.429.230.637.635.129.90.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax31.739.038.331.733.136.736.429.230.637.635.129.90.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:MT100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:NE


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value3.98.24.01.73.57.74.51.84.29.65.11.95.0112.14.19.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.32.21.30.61.32.21.40.71.62.61.70.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.32.21.30.61.32.21.40.71.62.61.70.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:NE100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:SD


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value2027192019292017193121182030171728
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax6.97.66.07.47.38.46.26.77.18.46.97.10.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax6.97.66.07.47.38.46.26.77.18.46.97.10.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:SD100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:MajorCustomers, us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments

nwe:CommercialCustomers, stpr:MT, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value848685897786908782868085798390
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax28.123.727.231.929.124.927.733.131.123.326.233.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax28.123.727.231.929.124.927.733.131.123.326.233.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:MT nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, stpr:MT, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value1323185.68.219175.59.523165.58.8206.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax4.36.55.82.03.15.55.42.13.66.25.52.10.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax4.36.55.82.03.15.55.42.13.66.25.52.10.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:MT nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, stpr:NE, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value1.84.41.90.71.54.02.20.92.15.32.50.92.46.11.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.61.20.60.30.61.20.70.30.81.40.80.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.61.20.60.30.61.20.70.30.81.40.80.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:NE nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, stpr:SD, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value242424272326252621232324222424
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax8.06.67.69.88.77.77.99.98.16.27.69.50.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax8.06.67.69.88.77.77.99.98.16.27.69.50.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:SD nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:CommercialCustomers, stpr:SD, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value4.36.53.11.02.97.35.21.33.69.25.60.93.67.91.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.41.81.00.41.12.11.60.51.32.51.80.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.41.81.00.41.12.11.60.51.32.51.80.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:CommercialCustomers stpr:SD nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:MT, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value699683787088836862947367598772
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax23.226.226.328.126.625.625.425.823.625.323.726.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax23.226.226.328.126.625.625.425.823.625.323.726.30.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:MT nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:MT, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value2547379.91738368.91845349.4174010.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax8.512.812.03.56.611.111.03.47.012.311.33.70.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax8.512.812.03.56.611.111.03.47.012.311.33.70.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:MT nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:NE, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value3.98.24.01.73.57.74.51.84.29.65.11.95.0112.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.32.21.30.61.32.21.40.71.62.61.70.70.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.32.21.30.61.32.21.40.71.62.61.70.70.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:NE nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:SD, nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value141714181418151613181416141816
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax4.84.94.56.85.55.54.66.05.04.84.76.40.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax4.84.94.56.85.55.54.66.05.04.84.76.40.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:SD nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:ResidentialCustomers, stpr:SD, nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value6.4104.81.74.7105.41.75.6136.71.75.6111.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax2.12.81.50.61.83.01.60.62.13.52.20.70.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax2.12.81.50.61.83.01.60.62.13.52.20.70.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ResidentialCustomers stpr:SD nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value236255236249218249247236213254225228
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax78.669.874.889.682.272.075.389.480.268.573.488.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax78.669.874.889.682.272.075.389.480.268.573.488.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:GasDomesticRegulated


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value64110792947978128521178129
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.430.225.210.417.828.024.710.619.831.526.611.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.430.225.210.417.828.024.710.619.831.526.611.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Revenues

us-gaap:Revenues

us-gaap:Revenues


Revenues
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value298400313280269335328274270384308279261341344309283367330300293332324272270346312251270369319262260313280235244309283244251338291240244334
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax99.0109.399.2100.6101.396.9100.0103.8101.5103.3100.4108.70.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Revenuesus-gaap:
Period End2021-06-302021-03-312020-06-302020-03-31
Value241270217244
Percentage of Revenues81.067.480.973.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax80.173.782.070.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Revenuesus-gaap:
Period End2021-06-302021-03-312020-06-302020-03-31
Value561305190
Percentage of Revenues19.032.619.127.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax18.835.719.326.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:Revenues us-gaap:ProductOrService

nwe:TotalRevenue


Revenuesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value298400313280269335328274270384308279261341309283367
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax99.0109.399.2100.6101.396.9100.1103.8101.5103.3100.4108.70.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:TotalRevenue0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

nwe:TotalRevenue, nwe:ElectricDomesticRegulated


Revenuesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value241270234244217244247241219273227245209238274233266
Percentage of Revenues80.967.474.787.080.973.075.487.881.271.173.887.680.169.888.782.472.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax80.173.774.187.582.070.775.491.182.473.474.195.20.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:TotalRevenue nwe:ElectricDomesticRegulated0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:TotalRevenue, nwe:GasDomesticRegulated


Revenuesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value56130793651908033511118134521033550101
Percentage of Revenues19.032.625.313.019.127.024.712.218.928.926.212.419.930.211.317.627.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax18.935.725.113.119.326.224.712.719.229.926.313.50.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:TotalRevenue nwe:GasDomesticRegulated0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Revenuesus-gaap:
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value244217244241219273245209238262274233266255266248241248238221236225212206234227227200210199202196207195206186208198203184
Percentage of Revenues87.080.973.087.881.171.187.680.169.876.188.782.472.577.288.684.772.676.587.581.868.271.984.376.263.471.386.677.167.171.285.880.267.069.084.774.261.768.084.575.7
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax87.582.070.791.182.473.495.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated97.799.798.2101.9102.7107.1107.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Revenuesus-gaap:
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value3651903351111345210382354910175344491763449109873964135903459102803248101873764129923658
Percentage of Revenues13.019.127.012.218.928.912.419.930.223.911.317.627.522.811.415.327.423.512.518.231.828.115.723.836.628.513.322.832.828.714.019.732.930.815.225.738.231.815.324.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax13.119.326.212.719.129.913.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated125.3108.793.4120.096.795.0119.70.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Assets

us-gaap:Assets

us-gaap:Assets


Assets
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value6566650263896075597159665910581057205700564455005438540054205628555655005499539353075261527852355060498949733874379137513715363335513480348533063224321732103061300630163037289928312795
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-06-302020-03-312019-12-312018-12-31
Value5281473546384947448248084626
Percentage of Assets80.472.872.682.875.181.382.0
Percentage of Assets80.472.872.682.875.181.382.0
Percentage of Assets us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-06-302020-03-312019-12-312018-12-31
Value1279175517391189165012701174
Percentage of Assets19.527.027.219.927.721.520.8
Percentage of Assets19.527.027.219.927.721.520.8
Percentage of Assets us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


Assetsus-gaap:
Period End2020-12-312019-12-312018-12-31
Value114.6644.732
Percentage of Assets0.20.10.1
Percentage of Assets0.20.10.1
Percentage of Assets us-gaap:OperatingSegments us-gaap:AllOtherSegments100.0100.0100.0

us-gaap:Assets us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Assetsus-gaap:
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value44304353434546324568454444084351431943464498443943884363429442214180419441693994392834422694263726092583254224862438244223192268226622592157211621232136204019861960
Percentage of Assets72.972.972.879.779.979.780.280.080.080.279.979.979.879.479.679.579.579.579.678.978.769.269.669.669.669.570.070.070.170.170.270.470.570.470.570.470.470.370.470.170.1
Percentage of Assets72.972.972.879.779.979.780.280.080.080.279.979.979.879.479.679.579.579.579.678.978.769.269.669.669.669.570.070.070.170.170.270.470.570.470.570.470.470.370.470.170.1
Percentage of Assets nwe:ElectricDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:GasDomesticRegulated


Assetsus-gaap:
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value163416131616117311471151107610721065107111271114110611291093108010731076105710571052152211701144113011171082105410311032976943938938891877880887845831819
Percentage of Assets26.927.027.120.220.120.219.619.719.719.820.020.120.120.520.320.320.420.420.220.921.130.630.230.230.130.129.829.729.629.629.529.329.229.229.129.229.229.229.129.429.3
Percentage of Assets26.927.027.120.220.120.219.619.719.719.820.020.120.120.520.320.320.420.420.220.921.130.630.230.230.130.129.829.729.629.629.529.329.229.229.129.229.229.229.129.429.3
Percentage of Assets nwe:GasDomesticRegulated100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllOtherSegments


Assetsus-gaap:
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302011-12-31
Value5.14411104.5684.6194.6644.594.6364.6834.7321515152.5862.6842.8125.9726.1186.0596.2486.7237.4167.7367.8898.118.3828.5721011139.2889.9110101012
Percentage of Assets0.10.20.20.10.10.10.10.10.10.10.30.30.30.00.00.10.10.10.10.10.10.10.10.20.20.20.20.30.30.40.30.30.30.30.30.4
Percentage of Assets0.10.20.20.10.10.10.10.10.10.10.30.30.30.00.00.10.10.10.10.10.10.10.10.20.20.20.20.30.30.40.30.30.30.30.30.4
Percentage of Assets us-gaap:AllOtherSegments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Liabilities

us-gaap:Liabilities

us-gaap:Liabilities


Liabilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value43884388431040213918390638713805371037103701360035413565362239023848379138233745367936463678371635433482349627922724267626842629254825052551241823222337235122232167217522172008
Percentage of Liabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets66.867.567.566.265.665.565.565.564.965.165.665.565.166.066.869.369.368.969.569.469.369.369.771.070.069.870.372.171.971.472.372.471.872.073.273.172.072.773.272.672.172.173.071.8

Liabilities And Stockholders Equity

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:LiabilitiesAndStockholdersEquity


Liabilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value65666502638960755971596659105810572057005644550054385400542056285556550054995393530752615278523550604989497338743791375137153633355134803485330632243217321030613006301630372795
Percentage of LiabilitiesAndStockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312010-12-312009-12-312008-12-31
Value217721132079205420532060203920042010198919421899189718341798172617081709167616481627161416001518151615061477108110671074103010041002975934888901879859820787763
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets33.232.532.533.834.434.534.534.535.134.934.434.534.934.033.230.730.731.130.530.630.730.730.329.030.030.229.727.928.128.627.727.628.228.026.826.928.027.326.827.028.20.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value-7.415-7.39-7.269-9.219-9.329-9.434-9.648-9.577-9.733-9.759-9.934-10.463-10.508-10.707-8.772-9.633-9.581-9.57-9.714-10.112-8.632-8.677-8.596-9.056-8.734-8.587-8.7661.3112.3712.6362.7161.8492.3173.6568.5149.72512
Percentage of StockholdersEquity-0.3-0.3-0.3-0.4-0.5-0.5-0.5-0.5-0.5-0.5-0.5-0.6-0.6-0.6-0.5-0.6-0.6-0.6-0.6-0.6-0.5-0.5-0.5-0.6-0.6-0.6-0.60.10.20.20.30.20.20.41.01.21.6
Percentage of Assets-0.1-0.1-0.1-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.20.00.10.10.10.10.10.10.30.30.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value157515171513151415131512150815051504150214991496149414481445139513891387138413811380137913761317131613151313926925924910896849816813807805
Percentage of StockholdersEquity72.371.872.873.773.773.474.075.174.875.577.278.878.879.080.380.981.381.282.683.884.885.486.086.886.887.388.985.686.786.188.389.290.995.199.2102.6105.5
Percentage of Assets24.023.323.724.925.325.325.525.926.326.426.627.227.526.826.724.825.025.225.225.626.026.226.125.226.026.426.423.924.424.724.524.724.425.426.828.90.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value0.5510.5420.5410.5410.5410.5410.5410.540.540.540.5390.5390.5390.5310.530.5220.5210.5210.520.520.520.520.5180.5070.5070.5070.5050.4280.4280.4280.4230.4210.4080.3980.3980.3950.395
Percentage of StockholdersEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.10.1
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value707702670646647655635604611592548509508492458436424428396372351340325303302293264246231239209197172128875934
Percentage of StockholdersEquity32.533.232.231.531.531.831.230.130.429.828.226.826.826.825.525.324.925.123.722.621.621.120.420.019.919.517.922.821.722.320.319.718.515.010.77.64.5
Percentage of Assets10.810.810.510.610.811.010.710.410.710.49.79.39.39.18.57.77.67.87.26.96.66.56.25.86.05.95.36.46.16.45.65.45.04.02.92.10.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:TreasuryStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value-98.578-98.73-98.075-98.242-98.438-98.644-96.015-96.092-96.178-96.26-95.546-95.634-95.768-95.872-96.376-96.462-96.689-97.24-95.769-95.852-96.265-96.346-93.948-94.031-94.125-94.643-92.558-92.625-92.701-92.756-91.744-91.809-90.702-90.273-90.427-90.228-89.487
Percentage of StockholdersEquity-4.5-4.7-4.7-4.8-4.8-4.8-4.7-4.8-4.8-4.8-4.9-5.0-5.0-5.2-5.4-5.6-5.7-5.7-5.7-5.8-5.9-6.0-5.9-6.2-6.2-6.3-6.3-8.6-8.7-8.6-8.9-9.1-9.7-10.5-11.0-11.5-11.7
Percentage of Assets-1.5-1.5-1.5-1.6-1.6-1.7-1.6-1.7-1.7-1.7-1.7-1.7-1.8-1.8-1.8-1.7-1.7-1.8-1.7-1.8-1.8-1.8-1.8-1.8-1.9-1.9-1.9-2.4-2.4-2.5-2.5-2.5-2.6-2.8-3.0-3.20.0
Percentage of Assets us-gaap:TreasuryStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Assets Current

us-gaap:AssetsCurrent

us-gaap:AssetsCurrent


Assets
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value347358308281263330301265252288277247231258296253248244280238237250286315312317350320290316320280246265303287233263290269244271303264
Percentage of AssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.35.54.84.64.45.55.14.64.45.14.94.54.34.85.54.54.54.45.14.44.54.85.46.06.26.47.18.37.78.48.67.76.97.68.78.77.28.29.08.88.19.010.09.5

Cash And Cash Equivalents At Carrying Value

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:CashAndCashEquivalentsAtCarryingValue


Cash
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312008-12-312007-12-31
Value5.9428.9255.8113.5127.464565.1455.0464.2173.9597.866.9125.5694.7428.4737.86816125.0795.0638.9699.027111032122017161916107.7936.8849.822188.1057.7925.9285.9944.547.186.2346.5616.1497.1284.3441112
Percentage of CashAndCashEquivalentsAtCarryingValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.10.10.10.90.10.10.10.10.10.10.10.10.20.10.30.20.10.10.20.20.20.20.60.20.40.50.40.50.40.30.20.20.30.60.30.20.20.20.20.20.20.20.20.00.20.00.0

Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents


Cash
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value1921171416651214121115141210121422179.50518
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.30.30.30.20.31.10.20.20.20.20.30.30.20.20.20.30.40.30.20.4

Accounts Receivable Net Current

us-gaap:AccountsReceivableNetCurrent

us-gaap:AccountsReceivableNetCurrent


Accounts
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value143162168133125155167126126169162127129170182129123142159116115134154117122148163120130171174129116143143109102131147107106144143143
Percentage of AccountsReceivableNetCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets2.22.52.62.22.12.62.82.22.23.02.92.32.43.23.42.32.22.62.92.22.22.62.92.22.43.03.33.13.44.64.73.63.34.14.13.33.24.14.63.53.54.84.75.1

Inventory Net

us-gaap:InventoryNet

us-gaap:InventoryNet


Inventory
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value6956616961535355514750524643525650424954494653585148556252385562473854594341597244265047
Percentage of InventoryNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.10.91.01.11.00.90.90.90.90.80.91.00.90.81.01.00.90.80.91.00.90.91.01.11.01.01.11.61.41.01.51.71.31.11.61.81.31.31.92.41.50.91.71.7

Inventory Raw Materials And Supplies

us-gaap:InventoryRawMaterialsAndSupplies

us-gaap:InventoryRawMaterialsAndSupplies


Inventory
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value4442363431313028252220
Percentage of InventoryRawMaterialsAndSupplies100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.70.70.70.60.60.60.60.80.70.70.7

Other Assets Current

us-gaap:OtherAssetsCurrent

us-gaap:OtherAssetsCurrent


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value1917171813111314119.7711012148.6891111159.501111016128.83101513148.6681212141318131110108.2979.457.804108.6735.90814
Percentage of OtherAssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.30.30.30.30.20.20.20.20.20.20.20.20.30.20.20.20.30.20.20.20.30.20.20.20.30.30.30.20.30.30.40.40.50.40.30.30.30.30.30.30.30.30.20.5

Property Plant And Equipment Gross

us-gaap:PropertyPlantAndEquipmentGross

us-gaap:PropertyPlantAndEquipmentGross


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value69166553628660185739550351263892364933613195
Percentage of PropertyPlantAndEquipmentGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets108.2110.9111.4111.0104.4104.3103.1104.8104.7104.7105.2

Accumulated Depreciation Depletion And Amortization Property Plant And Equipment

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment

us-gaap:ComputerSoftwareIntangibleAsset


Accumulated
Period End2020-12-312019-12-31
Value260235
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment100.0100.0
Percentage of Assets4.14.0
Percentage of Assets us-gaap:ComputerSoftwareIntangibleAsset0.00.0

Property Plant And Equipment Net

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:PropertyPlantAndEquipmentNet


Property
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value50714993495248604784471747004650458845374521446044174364435843094261422342144161410940694059400438433781375827992747270626902573253224442435231922662230221321702141212721171964
Percentage of PropertyPlantAndEquipmentNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets77.276.877.580.080.179.179.580.080.279.680.181.181.280.880.476.676.776.876.677.277.477.376.976.576.075.875.672.372.572.272.470.871.370.269.970.170.369.368.970.971.270.569.770.3

Goodwill

us-gaap:Goodwill

us-gaap:Goodwill


Goodwill
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value357357357357357357357357357357357357357357357357357357357357357357357355355355355355355355355355355355355355355355355355355355355355
Percentage of Goodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.45.55.65.96.06.06.06.26.36.36.36.56.66.66.66.46.46.56.56.66.76.86.86.87.07.17.19.29.49.59.69.810.010.210.210.711.011.011.111.611.811.811.712.7

us-gaap:Goodwill us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Goodwillus-gaap:
Period End2020-12-312019-12-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value243243243243243243243243243243243243243243243241241241241241241241241241241241241241241241241241241241
Percentage of Goodwill68.168.168.168.168.168.168.168.168.168.168.168.168.168.168.167.967.967.967.967.967.967.967.967.967.967.967.967.967.967.967.967.967.967.9
Percentage of Assets3.84.14.34.44.54.54.54.34.44.44.44.54.64.64.64.64.84.84.86.26.46.46.56.66.86.96.97.37.57.57.57.98.07.9
Percentage of Assets nwe:ElectricDomesticRegulated0.00.00.05.55.65.65.65.45.55.65.65.75.85.85.85.86.06.17.08.99.19.29.39.59.79.99.910.410.610.610.711.211.411.3

Other Assets Noncurrent

us-gaap:OtherAssetsNoncurrent

us-gaap:OtherAssetsNoncurrent


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value6475686465646664615950515553544947454343454857575456544961333228262723244846434040383928
Percentage of OtherAssetsNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.01.21.11.11.11.11.11.11.11.00.90.91.01.01.00.90.90.80.80.80.90.91.11.11.11.11.11.31.60.90.90.80.80.80.70.71.51.41.31.31.31.31.31.0

Accounts Payable Current

us-gaap:AccountsPayableCurrent

us-gaap:AccountsPayableCurrent


Accounts
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value89801007469669666588187625654856255567957555674605256816163689263586783625852765953527592
Percentage of AccountsPayableCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.41.21.61.21.21.11.61.11.01.41.51.11.01.01.61.11.01.01.41.11.01.11.41.21.01.11.61.61.71.82.51.71.61.92.41.91.81.62.41.91.81.72.53.3

Accrued Liabilities Current

us-gaap:AccruedLiabilitiesCurrent

us-gaap:AccruedLiabilitiesCurrent


Accrued
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value230270207269211237202243197245216263215251210252200238205241181219183226175219206206167215181209179213192214176215193229202225203165
Percentage of AccruedLiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets3.54.23.24.43.54.03.44.23.44.33.84.84.04.73.94.53.64.33.74.53.44.23.54.33.54.44.25.34.45.74.95.85.06.15.56.55.56.76.07.56.77.56.75.9

Liabilities Current

us-gaap:LiabilitiesCurrent

us-gaap:LiabilitiesCurrent


Liabilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value348386466493428348334333275347347349299326632601578545613546520518571574510544614493430419463417352376449321394415475426373394303294
Percentage of LiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.35.97.38.17.25.85.75.74.86.16.16.45.56.011.710.710.49.911.210.19.89.810.811.010.110.912.412.711.411.212.511.59.910.812.99.712.212.914.813.912.413.110.010.6

Other Accrued Liabilities Current

us-gaap:OtherAccruedLiabilitiesCurrent

us-gaap:OtherAccruedLiabilitiesCurrent


Other
Period End2020-12-312019-12-31
Value5949
Percentage of OtherAccruedLiabilitiesCurrent100.0100.0
Percentage of Assets0.90.8

Long Term Debt

us-gaap:LongTermDebt

us-gaap:LongTermDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value23152233210217931793178217821712166216621182118211551155105510551055105510559059059089089111068
Percentage of LongTermDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets36.237.837.233.132.633.834.033.833.333.430.531.230.831.129.029.730.330.331.928.128.128.329.730.335.2

us-gaap:LongTermDebt us-gaap:DebtInstrument, us-gaap:LongtermDebtType

nwe:NewMarketTaxCreditFinancing, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value262626262626260.0
Percentage of LongTermDebt1.21.21.31.51.51.51.60.0
Percentage of Assets0.40.50.50.50.50.50.50.0
Percentage of Assets nwe:NewMarketTaxCreditFinancing us-gaap:SecuredDebt0.00.00.00.00.00.00.00.0

nwe:RevolvingCreditFacilityDue2023, us-gaap:LineOfCredit


Long
Period End2020-12-31
Value222
Percentage of LongTermDebt9.6
Percentage of Assets3.5
Percentage of Assets nwe:RevolvingCreditFacilityDue2023 us-gaap:LineOfCredit0.0

nwe:SecuredDebtMontana2.00Due2023, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value1441441441441440.0
Percentage of LongTermDebt6.26.56.98.18.10.0
Percentage of Assets2.32.42.62.72.60.0
Percentage of Assets nwe:SecuredDebtMontana2.00Due2023 us-gaap:SecuredDebt0.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue20253.11, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value7575757575750.0
Percentage of LongTermDebt3.23.43.64.24.24.20.0
Percentage of Assets1.21.31.31.41.41.40.0
Percentage of Assets nwe:SecuredDebtMontanaDue20253.11 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2028, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value35353535353535350.0
Percentage of LongTermDebt1.51.61.72.02.02.02.13.00.0
Percentage of Assets0.50.60.60.60.60.70.70.90.0
Percentage of Assets nwe:SecuredDebtMontanaDue2028 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2030, us-gaap:SecuredDebt


Long
Period End2020-12-31
Value100
Percentage of LongTermDebt4.3
Percentage of Assets1.6
Percentage of Assets nwe:SecuredDebtMontanaDue2030 us-gaap:SecuredDebt0.0

nwe:SecuredDebtMontanaDue2042, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value6060606060606060600.0
Percentage of LongTermDebt2.62.72.93.33.33.43.65.25.70.0
Percentage of Assets0.91.01.11.11.11.11.21.61.70.0
Percentage of Assets nwe:SecuredDebtMontanaDue2042 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2043, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value15151515151515150.0
Percentage of LongTermDebt0.60.70.70.80.80.80.91.30.0
Percentage of Assets0.20.30.30.30.30.30.30.40.0
Percentage of Assets nwe:SecuredDebtMontanaDue2043 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2044, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value4504504504504504504500.0
Percentage of LongTermDebt19.420.121.425.125.125.327.10.0
Percentage of Assets7.07.68.08.38.28.59.00.0
Percentage of Assets nwe:SecuredDebtMontanaDue2044 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2045, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value1251251251251251250.0
Percentage of LongTermDebt5.45.65.97.07.07.00.0
Percentage of Assets2.02.12.22.32.32.40.0
Percentage of Assets nwe:SecuredDebtMontanaDue2045 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2047, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2502502502500.0
Percentage of LongTermDebt10.811.211.913.90.0
Percentage of Assets3.94.24.44.60.0
Percentage of Assets nwe:SecuredDebtMontanaDue2047 us-gaap:SecuredDebt0.00.00.00.00.0

nwe:SecuredDebtMontanaDue2049, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-31
Value1501500.0
Percentage of LongTermDebt6.56.70.0
Percentage of Assets2.32.50.0
Percentage of Assets nwe:SecuredDebtMontanaDue2049 us-gaap:SecuredDebt0.00.00.0

nwe:SecuredDebtMontanaDue2052, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value4040404040404040400.0
Percentage of LongTermDebt1.71.81.92.22.22.22.43.53.80.0
Percentage of Assets0.60.70.70.70.70.80.81.11.10.0
Percentage of Assets nwe:SecuredDebtMontanaDue2052 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2026, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value60606060600.0
Percentage of LongTermDebt2.62.72.93.33.30.0
Percentage of Assets0.91.01.11.11.10.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2026 us-gaap:SecuredDebt0.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue20262.66, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value45454545450.0
Percentage of LongTermDebt1.92.02.12.52.50.0
Percentage of Assets0.70.80.80.80.80.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue20262.66 us-gaap:SecuredDebt0.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2030, us-gaap:SecuredDebt


Long
Period End2020-12-31
Value50
Percentage of LongTermDebt2.2
Percentage of Assets0.8
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2030 us-gaap:SecuredDebt0.0

nwe:SecuredDebtSouthDakotaDue2040, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value7070707070700.0
Percentage of LongTermDebt3.03.13.33.93.93.90.0
Percentage of Assets1.11.21.21.31.31.30.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2040 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2042, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value3030303030303030300.0
Percentage of LongTermDebt1.31.31.41.71.71.71.82.62.80.0
Percentage of Assets0.50.50.50.60.50.60.60.80.90.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2042 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2043, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value50505050505050500.0
Percentage of LongTermDebt2.22.22.42.82.82.83.04.30.0
Percentage of Assets0.80.80.90.90.90.91.01.30.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2043 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2044, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value303030303030300.0
Percentage of LongTermDebt1.31.31.41.71.71.71.80.0
Percentage of Assets0.50.50.50.60.50.60.60.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2044 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2052, us-gaap:SecuredDebt


Long
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value2020202020202020200.0
Percentage of LongTermDebt0.90.91.01.11.11.11.21.71.90.0
Percentage of Assets0.30.30.40.40.40.40.40.50.60.0
Percentage of Assets nwe:SecuredDebtSouthDakotaDue2052 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.0

Long Term Debt Noncurrent

us-gaap:LongTermDebtNoncurrent

us-gaap:LongTermDebtNoncurrent


Long
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value2503246423152188215722392233217621582080210220162009201617931794179317931793179417731768178217821712166216621182118211551155105510551055105510559059059059059059056.5786.123
Percentage of LongTermDebtNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets38.137.936.236.036.137.537.837.537.736.537.236.737.037.333.131.932.332.632.633.333.433.633.834.033.833.333.430.531.230.831.129.029.730.330.331.928.128.128.229.630.130.00.20.2

Deferred Income Tax Liabilities Net

us-gaap:DeferredIncomeTaxLiabilitiesNet

us-gaap:DeferredIncomeTaxLiabilitiesNet


Deferred
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-31
Value494480471456462451447
Percentage of DeferredIncomeTaxLiabilitiesNet100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets7.57.47.47.57.77.67.6

Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent

us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap:RetirementPlanType

us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Pension
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.7744.4634.2354.2495.823
Percentage of PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent100.0100.0100.0100.0100.0
Percentage of Assets0.00.10.10.10.1
Percentage of Assets us-gaap:OtherPostretirementBenefitPlansDefinedBenefit0.00.00.00.00.0

us-gaap:PensionPlansDefinedBenefit


Pension
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value128119126112121
Percentage of PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent4626.02677.52998.52655.32084.8
Percentage of Assets2.02.02.22.12.2
Percentage of Assets us-gaap:PensionPlansDefinedBenefit0.00.00.00.00.0

Other Liabilities Noncurrent

us-gaap:OtherLiabilitiesNoncurrent

us-gaap:OtherLiabilitiesNoncurrent


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value398417410398391393387394388405399391401415415438430423419410418423418407407385382293301296292384390380375395399393389333340337333296
Percentage of OtherLiabilitiesNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets6.16.46.46.66.56.66.66.86.87.17.17.17.47.77.77.87.87.77.67.67.98.07.97.88.17.77.77.68.07.97.910.611.010.910.812.012.412.212.110.911.311.211.010.6

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312010-12-312009-12-312008-12-31
Value217721132079205420532060203920042010198919421899189718341798172617081709167616481627161416001518151615061477108110671074103010041002975934888901879859820787763
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets33.232.532.533.834.434.534.534.535.134.934.434.534.934.033.230.730.731.130.530.630.730.730.329.030.030.229.727.928.128.627.727.628.228.026.826.928.027.326.827.028.20.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value-7.415-7.39-7.269-9.219-9.329-9.434-9.648-9.577-9.733-9.759-9.934-10.463-10.508-10.707-8.772-9.633-9.581-9.57-9.714-10.112-8.632-8.677-8.596-9.056-8.734-8.587-8.7661.3112.3712.6362.7161.8492.3173.6568.5149.72512
Percentage of StockholdersEquity-0.3-0.3-0.3-0.4-0.5-0.5-0.5-0.5-0.5-0.5-0.5-0.6-0.6-0.6-0.5-0.6-0.6-0.6-0.6-0.6-0.5-0.5-0.5-0.6-0.6-0.6-0.60.10.20.20.30.20.20.41.01.21.6
Percentage of Assets-0.1-0.1-0.1-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.20.00.10.10.10.10.10.10.30.30.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value157515171513151415131512150815051504150214991496149414481445139513891387138413811380137913761317131613151313926925924910896849816813807805
Percentage of StockholdersEquity72.371.872.873.773.773.474.075.174.875.577.278.878.879.080.380.981.381.282.683.884.885.486.086.886.887.388.985.686.786.188.389.290.995.199.2102.6105.5
Percentage of Assets24.023.323.724.925.325.325.525.926.326.426.627.227.526.826.724.825.025.225.225.626.026.226.125.226.026.426.423.924.424.724.524.724.425.426.828.90.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value0.5510.5420.5410.5410.5410.5410.5410.540.540.540.5390.5390.5390.5310.530.5220.5210.5210.520.520.520.520.5180.5070.5070.5070.5050.4280.4280.4280.4230.4210.4080.3980.3980.3950.395
Percentage of StockholdersEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.10.1
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value707702670646647655635604611592548509508492458436424428396372351340325303302293264246231239209197172128875934
Percentage of StockholdersEquity32.533.232.231.531.531.831.230.130.429.828.226.826.826.825.525.324.925.123.722.621.621.120.420.019.919.517.922.821.722.320.319.718.515.010.77.64.5
Percentage of Assets10.810.810.510.610.811.010.710.410.710.49.79.39.39.18.57.77.67.87.26.96.66.56.25.86.05.95.36.46.16.45.65.45.04.02.92.10.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:TreasuryStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value-98.578-98.73-98.075-98.242-98.438-98.644-96.015-96.092-96.178-96.26-95.546-95.634-95.768-95.872-96.376-96.462-96.689-97.24-95.769-95.852-96.265-96.346-93.948-94.031-94.125-94.643-92.558-92.625-92.701-92.756-91.744-91.809-90.702-90.273-90.427-90.228-89.487
Percentage of StockholdersEquity-4.5-4.7-4.7-4.8-4.8-4.8-4.7-4.8-4.8-4.8-4.9-5.0-5.0-5.2-5.4-5.6-5.7-5.7-5.7-5.8-5.9-6.0-5.9-6.2-6.2-6.3-6.3-8.6-8.7-8.6-8.9-9.1-9.7-10.5-11.0-11.5-11.7
Percentage of Assets-1.5-1.5-1.5-1.6-1.6-1.7-1.6-1.7-1.7-1.7-1.7-1.7-1.8-1.8-1.8-1.7-1.7-1.8-1.7-1.8-1.8-1.8-1.8-1.8-1.9-1.9-1.9-2.4-2.4-2.5-2.5-2.5-2.6-2.8-3.0-3.20.0
Percentage of Assets us-gaap:TreasuryStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue


Common
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value551000.0542000.0541000.0541000.0541000.0541000.0541000.0540000.0540000.0540000.0539000.0539000.0539000.0531000.0530000.0522000.0521000.0521000.0520000.0520000.0520000.0520000.0518000.0507000.0507000.0507000.0505000.0428000.0428000.0428000.0423000.0421000.0420000.0414000.0408000.0408000.0407000.0399000.0398000.0398000.0398000.0398000.0398000.0395000.0
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Additional Paid In Capital

us-gaap:AdditionalPaidInCapital

us-gaap:AdditionalPaidInCapital


Additional
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312014-12-31
Value157515171513151415131512150815051504150214991496149414481445139513891387138413811380137913761313
Percentage of AdditionalPaidInCapital100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets24.023.323.724.925.325.325.525.926.326.426.627.227.526.826.724.825.025.225.225.626.026.226.126.4

Retained Earnings Accumulated Deficit

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:RetainedEarningsAccumulatedDeficit


Retained
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value7077026706466476556356046115925485095084924584364244283963723513403253033022932642462312392091971961961721271451471281071051078759
Percentage of RetainedEarningsAccumulatedDeficit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets10.810.810.510.610.811.010.710.410.710.49.79.39.39.18.57.77.67.87.26.96.66.56.25.86.05.95.36.46.16.45.65.45.55.65.03.94.54.64.03.53.53.62.92.1

Accumulated Other Comprehensive Income Loss Net Of Tax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax


Accumulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-312008-12-31
Value-7.415-7.39-7.269-9.219-9.329-9.434-9.648-9.577-9.733-9.759-9.934-10.463-10.508-10.707-8.772-9.633-9.581-9.57-9.714-10.112-8.632-8.677-8.596-9.056-8.734-8.587-8.7661.3112.3712.6362.7161.8492.0862.1832.3173.2293.4863.6313.6564.4247.9898.2688.5149.72512
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-0.1-0.1-0.1-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.20.00.10.10.10.10.10.10.10.10.10.10.10.10.30.30.30.30.0

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:OtherComprehensiveIncomeLocation

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


Accumulated
Period End2021-06-302021-03-312020-12-312020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value1.6431.8021.960.120.120.120.2510.031-0.742-0.937-1.247
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax-22.2-24.4-27.0-1.3-1.3-1.2-2.5-0.47.610.914.2
Percentage of Assets0.00.00.00.00.00.00.00.0-0.0-0.0-0.0
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustment0.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges


Accumulated
Period End2021-06-302021-03-312020-12-312020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value-10.503-10.616-10.729-10.955-11.068-11.181-11.633-9.981-10.352-9.014-8.316
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax141.6143.7147.6117.4117.3115.9117.1113.8106.6104.994.9
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
Percentage of Assets us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges0.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment


Accumulated
Period End2021-06-302021-03-312020-12-312020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value1.4451.4241.51.5061.5141.4131.4481.1781.381.3550.797
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax-19.5-19.3-20.6-16.1-16.0-14.6-14.6-13.4-14.2-15.8-9.1
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherComprehensiveIncome


Accumulated
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value-7.269-9.648-9.934-8.772-9.714-8.596-8.766
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-0.1-0.2-0.2-0.2-0.2-0.2-0.2
Percentage of Assets us-gaap:OtherComprehensiveIncome0.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


Accumulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value0.120.120.120.120.2510.2510.2510.2510.0380.0380.0380.031-0.742-0.742-0.742-0.742-0.937-0.937-0.937-0.937-1.247-1.247-1.247-1.247-1.329-1.329-1.329-1.329-2.292-2.292-2.292-2.292-1.739-1.158-1.0240.713
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax-1.3-1.3-1.3-1.2-2.6-2.6-2.6-2.5-0.4-0.4-0.4-0.47.77.77.87.69.310.910.810.913.814.314.514.2-101.4-56.1-50.4-48.9-124.0-109.9-105.0-98.9-47.6-13.6-10.55.8
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.1-0.1-0.1-0.1-0.1-0.0-0.00.0
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges


Accumulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value-10.842-10.955-11.068-11.181-11.294-11.408-11.521-11.633-11.792-11.905-12.018-9.981-10.074-10.166-10.259-10.352-10.446-8.94-8.977-9.014-9.051-8.496-8.405-8.3161.9533.1473.333.5133.6943.8774.064.2434.9759.2771011
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax117.6117.4117.3115.9117.9117.2118.1117.1112.7113.3112.2113.8104.6106.1107.2106.6103.3103.6103.5104.999.997.397.994.9149.0132.7126.3129.3199.8185.9186.0183.1136.1109.0107.694.3
Percentage of Assets-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.20.10.10.10.10.10.10.10.10.20.30.40.0
Percentage of Assets us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment


Accumulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value1.5031.5061.5141.4131.4661.4241.5111.4481.2911.3591.2731.1781.1831.3271.4311.381.2711.2451.2371.3551.2421.0091.0650.7970.6870.5530.6350.5320.366
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax-16.3-16.1-16.0-14.6-15.3-14.6-15.5-14.6-12.3-12.9-11.9-13.4-12.3-13.9-15.0-14.2-12.6-14.4-14.3-15.8-13.7-11.6-12.4-9.152.423.324.119.615.8
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ComprehensiveIncome


Accumulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-31
Value-9.219-9.329-9.434-9.648-9.577-9.733-9.759-9.934-10.463-10.508-10.707-8.772-9.633-9.581-9.57-9.714-10.112-8.632-8.677-8.596
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2
Percentage of Assets us-gaap:ComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Treasury Stock Value

us-gaap:TreasuryStockValue

us-gaap:TreasuryStockValue


Treasury
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value9898989898989696969695959595969696979595969693949494929292929191919190909090909090909090
Percentage of TreasuryStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.51.51.51.61.61.71.61.71.71.71.71.71.81.81.81.71.71.81.71.81.81.81.81.81.91.91.92.42.42.52.52.52.62.62.62.72.82.82.82.93.03.03.03.2

Stock Issued During Period Value New Issues

us-gaap:StockIssuedDuringPeriodValueNewIssues

us-gaap:StockIssuedDuringPeriodValueNewIssues


Stock
Period End2021-06-302020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-31
Value560.3450.3660.4290.2590.2320.2320.212.450.2010.283452.129512.354
Percentage of StockIssuedDuringPeriodValueNewIssues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2021-06-302020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value560.1770.170.2230.1470.1450.1460.1281.5170.1130.092450.95650570.5910.0-0.1223850.15-0.0331312
Percentage of StockIssuedDuringPeriodValueNewIssues99.751.346.452.056.862.562.961.061.956.232.599.944.997.30.00.00.00.00.00.00.00.00.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stock
Period End2021-06-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value0.0090.00.0-0.0010.00.00.0010.00.0010.0080.00.010.00.00.00.0020.0110.00.00.0020.0770.00.00.0050.001
Percentage of StockIssuedDuringPeriodValueNewIssues0.00.00.0-0.40.00.00.00.00.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:TreasuryStock


Stock
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value0.1960.2060.1120.0860.0820.9320.190.0471.173
Percentage of StockIssuedDuringPeriodValueNewIssues53.648.043.237.139.038.067.10.155.1
Percentage of Assets0.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:TreasuryStock0.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value386529103611584210933111359974173231222115631116-1.1421423511463126458012112224117111287725119234741122305526106
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.917.99.437.023.045.713.141.312.430.011.638.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-104990000.0-77854000.0-122780000.0-106510000.0-98148000.0-78371000.0-73277000.0-95847000.0-81450000.0-65577000.0-93062000.0-76864000.0-82968000.0-52005000.0-79453000.0-77862000.0-67301000.0-51443000.0-83901000.0-81537000.0-69842000.0-51267000.0-79371000.0-182260000.0-70777000.0-51652000.0-983270000.0-113260000.0-60290000.0-50128000.0-145290000.0-62262000.0-49688000.0-38114000.0-146230000.0-78318000.0-50636000.0-47027000.0-64246000.0-52627000.0-34068000.0-37580000.0-62598000.0-61845000.0-58437000.0-57796000.0
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-34.8-21.2-38.9-38.2-36.9-22.7-22.3-36.2-30.5-17.6-30.3-29.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value6317960.81-11.639-26.71828-11.75949-50.12458-21.24610-122.15257-53.87650-97.97852-39.36370-93.822454527-83.4029403345-59.1831282332-76.7041091025-71.034407.036-9.952-83.554316.40531-45.69
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.24.730.50.3-4.4-7.78.7-4.418.6-13.519.1-8.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect


Cash
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value-2.2924.794-2.404-48.73531.6421.425-4.2771.1812.012-1.129-7.5475.1827.78
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.81.3-0.9-18.315.30.60.5-1.20.50.00.00.00.00.0

Deferred Income Tax Expense Benefit

us-gaap:DeferredIncomeTaxExpenseBenefit

us-gaap:DeferredIncomeTaxExpenseBenefit


Deferred
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value2.065-2.706-3.815-3.759-0.170.172.4860.197-17.2550.708-19.4761.2682.8762.1432.8433.20.915.41-3.464-10.2550.6454.896.8677.1109.007-39.149-3.0385.71526138.7665.1572730-5.4046.87220325.7535.9611917113.20416
Percentage of DeferredIncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Depreciation Depletion And Amortization

us-gaap:DepreciationDepletionAndAmortization

us-gaap:DepreciationDepletionAndAmortization


Depreciation
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value46464544444543434145434343434141414139393939373535353230303028282729262626262525252523222222
Percentage of DepreciationDepletionAndAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DepreciationDepletionAndAmortization us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Depreciation
Period End2021-06-302021-03-312020-06-302020-03-31
Value38383637
Percentage of DepreciationDepletionAndAmortization82.382.482.382.1

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Depreciation
Period End2021-06-302021-03-312020-06-302020-03-31
Value8.2698.2917.9368.089
Percentage of DepreciationDepletionAndAmortization17.717.617.717.9

us-gaap:DepreciationDepletionAndAmortization us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Depreciation
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value36363735333836363634343434323232323028282825232323222221232121212120202020181818
Percentage of DepreciationDepletionAndAmortization82.882.382.183.082.283.583.183.082.682.282.282.282.282.081.981.681.580.679.879.879.777.976.176.176.279.179.079.180.881.781.681.681.681.481.381.380.480.980.881.0

nwe:GasDomesticRegulated


Depreciation
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value7.6197.9368.0897.3427.2967.5337.3777.3947.5947.3937.397.3827.3837.1547.2067.3467.3617.2777.2097.2267.2567.2147.277.2417.2055.8645.8955.7125.5994.8834.864.8534.8564.7024.7084.6714.9534.3994.3784.369
Percentage of DepreciationDepletionAndAmortization17.217.717.917.017.816.516.917.017.417.717.817.817.818.018.118.418.519.420.220.220.322.123.923.823.820.821.020.819.218.318.318.418.418.518.718.619.619.119.219.0

Increase Decrease In Accounts Payable

us-gaap:IncreaseDecreaseInAccountsPayable

us-gaap:IncreaseDecreaseInAccountsPayable


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value1.549-16.591203.138-0.94-6.379125.741-23.6373.954154.759-2.244-21.605166.803-3.982-15.806201.027-6.292-11.303108.531-7.007-23.17920-3.975-8.143-18.18254.105-9.499-14.118207.613-1.118-16.099106.092-1.531-17.36918-2.366-11.538-17.467
Percentage of IncreaseDecreaseInAccountsPayable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Increase Decrease In Accounts Receivable

us-gaap:IncreaseDecreaseInAccountsReceivable

us-gaap:IncreaseDecreaseInAccountsReceivable


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-19.502-5.23358.011-30.807-11.494410.348-43.6157.26734-2.045-40.295-12.012525.746-18.627-17.004420.988-19.15-19.42736-5.434-25.955-14.63642-10.817-40.808-3.7634512-26.76-0.409346.532-28.581-15.639400.595-38.2081.421446.657-42.296-9.478
Percentage of IncreaseDecreaseInAccountsReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Increase Decrease In Inventories

us-gaap:IncreaseDecreaseInInventories

us-gaap:IncreaseDecreaseInInventories


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value13-4.183-8.0457.8317.988-0.689-1.2433.3874.226-3.26-1.9236.042.984-8.718-4.0955.9288.322-6.929-5.1054.3883.29-6.825-5.2347.633.025-7.057-8.1041014-17.53-8.643158.762-15.313-5.215161.336-17.856-12.5152717-23.848-13.9952213-19.169
Percentage of IncreaseDecreaseInInventories100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value386529103611584210933111359974173231222115631116-1.1421423511463126458012112224117111287725119234741122305526106
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.917.99.437.023.045.713.141.312.430.011.638.60.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value376353292150592147726628435847362156444435384523305137307.746452615143758-3.77211323414103222141128
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.417.216.910.68.114.718.38.217.919.621.610.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Net
Period End2021-06-302021-03-312020-06-302020-03-31
Value39382230
Percentage of NetIncomeLoss105.461.3105.260.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax13.010.58.58.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:ElectricityUsRegulated0.00.00.00.0

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Net
Period End2021-06-302021-03-312020-06-302020-03-31
Value-0.40523-0.08120
Percentage of NetIncomeLoss-1.138.0-0.441.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.16.5-0.06.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:OperatingSegments us-gaap:NaturalGasUsRegulated0.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Net
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value3722303227433444373041233331513819313319332928102316201522470.65102320218.1672217179.397
Percentage of NetIncomeLoss128.6105.260.0151.958.559.4123.0101.063.763.6114.0109.759.771.7115.3106.951.868.9139.162.665.380.593.2139.151.864.9132.0109.758.380.3-17.294.773.059.2144.074.470.577.7124.680.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax13.68.58.812.410.511.613.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:ElectricDomesticRegulated15.210.312.213.913.017.015.20.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwe:GasDomesticRegulated


Net
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value-8.386-0.08120-9.551-1.66633-7.1782.4212219-4.409-0.2122012-6.516-0.891714-7.44-1.639179.143-7.387-0.4192410-3.412-0.2881711-3.486-1.0611010-5.6150.021118.309-2.51-1.325
Percentage of NetIncomeLoss-28.5-0.441.0-44.1-3.545.7-25.55.538.040.3-12.1-1.036.427.7-14.6-2.545.932.0-31.3-5.333.524.6-24.5-5.454.141.7-21.8-2.047.019.092.4-9.333.530.0-37.70.235.236.8-17.5-11.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-3.0-0.06.0-3.6-0.68.9-2.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax nwe:GasDomesticRegulated-28.8-0.221.4-34.1-3.228.4-24.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllOtherSegments


Net
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-1.5890.478-0.049-1.034-0.535-1.06-1.68721-3.704-16.6730.703-2.844-1.001-1.89-0.671-1.9082.1852.097-0.304-1.5820.874-0.408-1.857130.607-1.8779.436-2.606-2.68-1.721-1.593-1.108-1.9920.438-0.936
Percentage of NetIncomeLoss-4.30.8-0.2-4.8-1.1-1.8-7.845.0-5.1-25.12.5-6.5-1.7-3.9-1.8-8.73.94.8-0.7-4.42.3-0.9-7.842.71.2-5.031.3-33.6-5.9-6.6-10.2-7.7-5.30.724.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-0.50.1-0.0-0.4-0.2-0.3-0.68.0-1.0-5.40.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:AllOtherSegments0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value376353292150592147726628435847362156454435384523305137307.7464526
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0104.1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax12.417.216.910.68.114.718.38.217.919.621.610.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Share Based Compensation

us-gaap:ShareBasedCompensation

us-gaap:ShareBasedCompensation


Share
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value1315000.03223000.0-1198000.01152000.01153000.03042000.03229000.01181000.01179000.02418000.02748000.01197000.01242000.02496000.0565000.01172000.01494000.02332000.02257000.01113000.01119000.02242000.01807000.0944000.01085000.01246000.01024000.0707000.0707000.0824000.0578000.0577000.0580000.0669000.0560000.0561000.0563000.01075000.0484000.0583000.0506000.0560000.0358000.0403000.0371000.0490000.0
Percentage of ShareBasedCompensation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-104990000.0-77854000.0-122780000.0-106510000.0-98148000.0-78371000.0-73277000.0-95847000.0-81450000.0-65577000.0-93062000.0-76864000.0-82968000.0-52005000.0-79453000.0-77862000.0-67301000.0-51443000.0-83901000.0-81537000.0-69842000.0-51267000.0-79371000.0-182260000.0-70777000.0-51652000.0-983270000.0-113260000.0-60290000.0-50128000.0-145290000.0-62262000.0-49688000.0-38114000.0-146230000.0-78318000.0-50636000.0-47027000.0-64246000.0-52627000.0-34068000.0-37580000.0-62598000.0-61845000.0-58437000.0-57796000.0
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-34.8-21.2-38.9-38.2-36.9-22.7-22.3-36.2-30.5-17.6-30.3-29.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Payments To Acquire Property Plant And Equipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value10477122106987873958165907664527977675183826951807274568474605176655038616050476452343750615857
Percentage of PaymentsToAcquirePropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Payments To Acquire Investments

us-gaap:PaymentsToAcquireInvestments

us-gaap:PaymentsToAcquireInvestments


Payments
Period End2020-12-312020-09-30
Value05000.0
Percentage of PaymentsToAcquireInvestments0.0100.0

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value6317960.81-11.639-26.71828-11.75949-50.12458-21.24610-122.15257-53.87650-97.97852-39.36370-93.822454527-83.4029403345-59.1831282332-76.7041091025-71.034407.036-9.952-83.554316.40531-45.69
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.24.730.50.3-4.4-7.78.7-4.418.6-13.519.1-8.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Proceeds From Issuance Of Long Term Debt

us-gaap:ProceedsFromIssuanceOfLongTermDebt

us-gaap:ProceedsFromIssuanceOfLongTermDebt


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302019-12-312019-09-302018-12-312018-09-302017-12-312017-09-302016-12-312016-09-302015-12-312015-09-302014-12-312014-09-302013-12-312012-12-312011-12-312011-09-302010-12-312010-09-30
Value0.0990.00.00.01000.00.02500.00.01890.070480251000.00.00.00.00.0
Percentage of ProceedsFromIssuanceOfLongTermDebt0.0100.00.00.00.0100.00.00.0100.00.00.0100.00.0100.0100.0100.0100.00.00.00.00.00.0

Payments Of Dividends Common Stock

us-gaap:PaymentsOfDividendsCommonStock

us-gaap:PaymentsOfDividendsCommonStock


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value31313030303028282828272727262525252523232323222222221815151514141414131313131212121212121212
Percentage of PaymentsOfDividendsCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Debt Instrument Interest Rate Stated Percentage

us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument

us-gaap:DebtInstrumentInterestRateStatedPercentage

nwe:SecuredDebtMontanaDue2030


Debt
Period End2020-09-302020-06-30
Value3.210.0321
Percentage of DebtInstrumentInterestRateStatedPercentage100.0100.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue20300.00.0

nwe:SecuredDebtSouthDakotaDue2030


Debt
Period End2020-09-302020-06-30
Value3.210.0321
Percentage of DebtInstrumentInterestRateStatedPercentage100.0100.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue20300.00.0

us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument, us-gaap:LongtermDebtType

nwe:SecuredDebtMontanaDue2025, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312015-09-302015-06-302014-12-312013-12-312012-12-312011-12-31
Value5.010.05010.05010.05010.05010.05010.03110.03110.05010.05010.05010.0501
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2025 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue20253.11, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312015-06-30
Value3.110.03110.03110.03110.03110.03110.0311
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue20253.11 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2028, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value3.990.03990.03990.03990.03990.03990.03990.0399
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2028 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2030, us-gaap:SecuredDebt


Debt
Period End2020-12-31
Value3.21
Percentage of DebtInstrumentInterestRateStatedPercentage0.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2030 us-gaap:SecuredDebt0.0

nwe:SecuredDebtMontanaDue2039, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value5.710.05710.05710.05710.05710.05710.05710.05710.05710.0571
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2039 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2042, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value4.150.04150.04150.04150.04150.04150.04150.04150.0415
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2042 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2043, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value4.850.04850.04850.04850.04850.04850.04850.0485
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2043 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2044, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value4.180.04180.041760.041760.041760.041760.04176
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2044 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDue2047, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-31
Value4.030.04030.04030.0403
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2047 us-gaap:SecuredDebt0.00.00.00.0

nwe:SecuredDebtMontanaDue2052, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value4.30.0430.0430.0430.0430.0430.0430.0430.043
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDue2052 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtMontanaDueJune2049, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-31
Value3.980.0398
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDueJune2049 us-gaap:SecuredDebt0.00.0

nwe:SecuredDebtMontanaDueSeptember2049, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-31
Value3.980.0398
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtMontanaDueSeptember2049 us-gaap:SecuredDebt0.00.0

nwe:SecuredDebtSouthDakotaDue2025, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value5.010.05010.05010.05010.05010.05010.05010.05010.05010.0501
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2025 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2026, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312016-06-30
Value2.80.0280.0280.0280.0280.028
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2026 us-gaap:SecuredDebt0.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue20262.66, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312016-09-30
Value2.660.02660.02660.02660.02660.0266
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue20262.66 us-gaap:SecuredDebt0.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2030, us-gaap:SecuredDebt


Debt
Period End2020-12-31
Value3.21
Percentage of DebtInstrumentInterestRateStatedPercentage0.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2030 us-gaap:SecuredDebt0.0

nwe:SecuredDebtSouthDakotaDue2040, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312015-09-30
Value4.260.04260.04260.04260.04260.04260.0426
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2040 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2042, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value4.150.04150.04150.04150.04150.04150.04150.04150.0415
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2042 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2043, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value4.850.04850.04850.04850.04850.04850.04850.0485
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2043 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2044, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value4.220.04220.04220.04220.04220.04220.0422
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2044 us-gaap:SecuredDebt0.00.00.00.00.00.00.0

nwe:SecuredDebtSouthDakotaDue2052, us-gaap:SecuredDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value4.30.0430.0430.0430.0430.0430.0430.0430.043
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations nwe:SecuredDebtSouthDakotaDue2052 us-gaap:SecuredDebt0.00.00.00.00.00.00.00.00.0

Effective Income Tax Rate Continuing Operations

us-gaap:EffectiveIncomeTaxRateContinuingOperations

us-gaap:EffectiveIncomeTaxRateContinuingOperations


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value3.40-2.2-10.1-0.035-0.0370.0560.025-0.8740.021-0.139-0.0130.0660.032-0.0040.0710.0260.1060.086-0.2760.0770.061-0.3540.2120.210.1630.217-1.5690.1350.149-0.2490.1040.1280.117-0.2030.6950.1830.2
Percentage of EffectiveIncomeTaxRateContinuingOperations100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Liabilities

us-gaap:DeferredTaxLiabilities

us-gaap:DeferredTaxLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value471447394340575501611505484440382
Percentage of DeferredTaxLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Unrecognized Tax Benefits

us-gaap:UnrecognizedTaxBenefits

us-gaap:UnrecognizedTaxBenefits


Unrecognized
Period End2021-06-302021-03-312020-12-312020-09-302019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value32333333355657889295113113131120122115
Percentage of UnrecognizedTaxBenefits100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:AmortizationOfDebtIssueCostsDiscountAndDeferredHedgeGain

nwe:AmortizationOfDebtIssueCostsDiscountAndDeferredHedgeGain


Amortization
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-31
Value1334000.01303000.01233000.01204000.01167000.01165000.01160000.01157000.01155000.01162000.01171000.01193000.01191000.01201000.0-1080000.01008000.0979000.0739000.0275000.0287000.01630000.01688000.01538000.097000.0129000.064000.093000.090000.090000.0116000.0400000.0398000.0398000.0499000.0531000.0
Percentage of AmortizationOfDebtIssueCostsDiscountAndDeferredHedgeGain100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:AnnualRiverbedRentExposure us-gaap:LossContingenciesByNatureOfContingency

nwe:AnnualRiverbedRentExposure

nwe:RiverbedRents


Annual
Period End2021-06-302021-03-312020-12-31
Value03800000.00
Percentage of AnnualRiverbedRentExposure0.0100.00.0

nwe:CommonStockAverageSharePrice us-gaap:StatementEquityComponents

nwe:CommonStockAverageSharePrice

nwe:EquityDistributionAgreement


Common
Period End2021-06-302017-12-312014-03-31
Value64.9161.4845.65
Percentage of CommonStockAverageSharePrice100.0100.0100.0

nwe:EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxes

nwe:EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxes


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-143000.0-265000.0-237000.0-222000.0-153000.0-356000.0251000.0-374000.0-189000.0-1376000.0-1686000.0-418000.00-384000.0
Percentage of EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0

nwe:EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxesPercent

nwe:EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxesPercent


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-0.4-0.41.5-0.8-0.007-0.0070.025-0.017-0.007-0.0180.036-0.0150-0.006
Percentage of EffectiveIncomeTaxRateReconciliationAmortizationofExcessDeferredTaxesPercent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0

nwe:IncomeTaxReconciliationAcceleratedTaxDepreciationFlowThroughAdjustment

nwe:IncomeTaxReconciliationAcceleratedTaxDepreciationFlowThroughAdjustment


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value0.50.50.2-0.4-0.003-0.0030.0020.0120.0260.0200.0030.0120.016-0.0050.0020.0310.0230.0160.0070.0060.0230.0080.012-0.01-0.0080.048-0.045-0.045-0.0410.0630.022-0.037-0.034
Percentage of IncomeTaxReconciliationAcceleratedTaxDepreciationFlowThroughAdjustment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:IncomeTaxReconciliationDeductionsAcceleratedTaxDepreciationFlowThroughAdjustment

nwe:IncomeTaxReconciliationDeductionsAcceleratedTaxDepreciationFlowThroughAdjustment


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value184000.0340000.0178000.0-103000.0-59000.0-137000.01503000.0263000.0663000.01523000.0593000.095000.0571000.0916000.05000.077000.0686000.01440000.03177000.0243000.0246000.0938000.01893000.0374000.0-410000.0-2703000.0786000.0745000.01756000.0-878000.0276000.0512000.0-1371000.04716000.0-1170000.0-679000.0-2603000.000
Percentage of IncomeTaxReconciliationDeductionsAcceleratedTaxDepreciationFlowThroughAdjustment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0

nwe:MaximumRatioOfIndebtednessToNetCapitalThresholdPercentage us-gaap:ShortTermDebtType

nwe:MaximumRatioOfIndebtednessToNetCapitalThresholdPercentage

nwe:TermLoanDue2021


Maximum
Period End2020-09-30
Value65.0
Percentage of MaximumRatioOfIndebtednessToNetCapitalThresholdPercentage100.0

nwe:OtherEnergySalesRevenue us-gaap:ProductOrService

nwe:OtherEnergySalesRevenue

nwe:RegulatoryAmortization


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value-3.134-2.51.73.5-10.80.2104.1121.322-3.6-15.26.7
Percentage of OtherEnergySalesRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:OtherEnergySalesRevenue us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

nwe:RegulatoryAmortization, nwe:ElectricDomesticRegulated


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value4.714-2.4-5.7-0.6-4.40.34.55.8182.216-1.7-8.83.3
Percentage of OtherEnergySalesRevenue-151.641.596.0-335.3-17.140.7150.044.6141.5147.2169.274.647.257.949.3

nwe:RegulatoryAmortization, nwe:GasDomesticRegulated


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-30
Value-7.820-0.17.44.1-6.4-0.15.6-1.7-5.8-0.95.7-1.9-6.43.4
Percentage of OtherEnergySalesRevenue251.658.54.0435.3117.159.3-50.055.4-41.5-47.2-69.225.452.842.150.7

nwe:PublicUtilitiesRequestToRecognizePensionContributionOver5Years us-gaap:PublicUtilitiesRegulatoryProceeding

nwe:PublicUtilitiesRequestToRecognizePensionContributionOver5Years

nwe:MontanaAccountingOrder


Public
Period End2020-09-30
Value40
Percentage of PublicUtilitiesRequestToRecognizePensionContributionOver5Years100.0

nwe:ShortTermDebtBasisSpreadOnVariableRate us-gaap:ShortTermDebtType, us-gaap:VariableRate

nwe:ShortTermDebtBasisSpreadOnVariableRate

nwe:TermLoanDue2021, us-gaap:Eurodollar


Short
Period End2020-09-30
Value1.5
Percentage of ShortTermDebtBasisSpreadOnVariableRate100.0

nwe:StockIssuedValueNetOfFees us-gaap:StatementEquityComponents

nwe:StockIssuedValueNetOfFees

nwe:EquityDistributionAgreement


Stock
Period End2021-06-30
Value56
Percentage of StockIssuedValueNetOfFees100.0

us-gaap:AccrualForEnvironmentalLossContingenciesPayments1

us-gaap:AccrualForEnvironmentalLossContingenciesPayments1


Accrual
Period End2021-03-312020-03-31
Value424000.0332000.0
Percentage of AccrualForEnvironmentalLossContingenciesPayments1100.0100.0

us-gaap:AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts

us-gaap:AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts


Adjustments
Period End2021-03-31
Value10000.0
Percentage of AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts100.0

us-gaap:AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Adjustments
Period End2021-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-31
Value10000.000-11000.0591000.00-122000.0
Percentage of AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts100.00.00.00.00.00.00.0

us-gaap:CapitalExpendituresIncurredButNotYetPaid

us-gaap:CapitalExpendituresIncurredButNotYetPaid


Capital
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value7.866185.4442.1513.82710171.9650.9129.7320.6274.1317.1355.8750.1972.9886.7881.980.7495.2495.8053.902-0.2672.8046.3950.5660.6293.3693.9910.782.1642.2716.81-0.156-2.4649.9335.8236.596-0.4263.0451.6952.8481.628-3.1625.95
Percentage of CapitalExpendituresIncurredButNotYetPaid100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonStockDividendsPerShareDeclared

us-gaap:CommonStockDividendsPerShareDeclared


Common
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.620.620.50.60.60.60.5750.5750.5750.5750.550.550.550.550.5250.5250.52500.50.50.50.50.480.480.480.480.40.40.40.40.380.380.380.380.370.370.370.370.360.360.360.360.340.340.340.34
Percentage of CommonStockDividendsPerShareDeclared100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentDecreaseForgiveness us-gaap:StatementScenario, us-gaap:LongtermDebtType

us-gaap:DebtInstrumentDecreaseForgiveness

srt:ScenarioForecast, nwe:NewMarketTaxCreditFinancing


Debt
Period End2021-07-31
Value7900000.0
Percentage of DebtInstrumentDecreaseForgiveness100.0

us-gaap:DefinedBenefitPlanActuarialGainLoss us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanActuarialGainLoss

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value0.0040.0110.0150.0120.0180.0240.0240.0240.0190.020.02-0.08-0.081-0.078-0.078-0.071
Percentage of DefinedBenefitPlanActuarialGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-30
Value-2.261-1.22888-1.257-1.234-1.28830.00.00.0-50.226-1.09-1.108-1.07247-1.959-1.944-1.97514-2.472-2.478
Percentage of DefinedBenefitPlanActuarialGainLoss-56525.0-11163.60.0-8380.0-10283.3-7111.10.00.00.00.00.0-5736.8-5540.0-5360.00.02448.82400.02532.10.03169.23490.1

us-gaap:DefinedBenefitPlanAmortizationOfPriorServiceCostCredit us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAmortizationOfPriorServiceCostCredit

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value-459000.0-459000.0-470000.0-471000.0-470000.0-471000.0-470000.0-471000.0-470000.0-471000.0-470000.0-471000.0-470000.0-471000.0-471000.0-470000.0-471000.0-471000.0-470000.0
Percentage of DefinedBenefitPlanAmortizationOfPriorServiceCostCredit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value0.2290.230.2450.2460.2450.2470.2170.2170.2170.2180.2380.2390.2380.2390.2110.2110.2130.2610.26
Percentage of DefinedBenefitPlanExpectedReturnOnPlanAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value6.8416.8436.546.5416.5366.5456.3616.366.366.3627.0527.0517.0447.065.9915.9746.0087.0627.043
Percentage of DefinedBenefitPlanExpectedReturnOnPlanAssets2987.32975.22669.42658.92667.82649.82931.32930.92930.92918.32963.02950.22959.72954.02839.32831.32820.72705.72708.8

us-gaap:DefinedBenefitPlanInterestCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanInterestCost

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value0.0840.0750.1230.1230.1370.1090.1520.1520.150.1550.1440.1450.1420.1470.1780.1780.180.1980.196
Percentage of DefinedBenefitPlanInterestCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-30
Value4.8144.5965.715.715.6945.7266.6226.6226.6156.6296.1056.1056.1026.1086.4086.4086.3886.4296.5526.5536.539
Percentage of DefinedBenefitPlanInterestCost5731.06128.04642.34642.34156.25253.24356.64356.64410.04276.84239.64210.34297.24155.10.03600.03588.83571.70.03309.63336.2

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value-0.504-0.526-0.126-0.516-0.497-0.535-0.086-0.478-0.484-0.469-0.095-0.484-0.499-0.471-0.31-0.322-0.298-0.333-0.347
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value3.522.2443.2063.2053.1043.3073.7895.0224.1974.4163.0883.0892.8513.3255.1264.7255.5284.9644.976
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost-698.4-426.6-2544.4-621.1-624.5-618.1-4405.8-1050.6-867.1-941.6-3250.5-638.2-571.3-705.9-1653.5-1467.4-1855.0-1490.7-1434.0

us-gaap:DefinedBenefitPlanServiceCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanServiceCost

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-30
Value0.1040.0990.0920.0930.0930.0920.0830.0820.0770.0890.0990.10.0870.1120.1140.10.1280.1230.116
Percentage of DefinedBenefitPlanServiceCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-30
Value3.2863.2632.7792.7792.7122.8462.4092.4092.3222.4972.9442.9442.6843.2042.7482.7492.3673.132.942.9392.941
Percentage of DefinedBenefitPlanServiceCost3159.63296.03020.72988.22916.13093.52902.42937.83015.62805.62973.72944.03085.12860.70.02411.42367.02445.30.02389.42535.3

us-gaap:DividendsCommonStock

us-gaap:DividendsCommonStock


Dividends
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value31313030303028282828272727262525252523232323
Percentage of DividendsCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DividendsCommonStock us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Dividends
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value3131303030302828282827272726-176.90325252523232323222222221815151514
Percentage of DividendsCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0-690.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.00.00.00.00.00.0

us-gaap:EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate

us-gaap:EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value21.021.0021.00.210.2100.210.210.2100.210.210.2100.350.350.3500.350.350.3500.350.350.35-0.70.350.350.35-0.70.350.350.35-0.70.350.350.35
Percentage of EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate100.0100.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsOther

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsOther


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value11.012.51.115.70.1540.1520.0040.1170.0850.1070.0110.0860.0870.1090.0080.1790.2120.139-0.0230.5440.1810.1650.0010.0920.1240.1570.0290.290.1990.1810.332-0.177-0.128-0.180.3690.146-0.155-0.139
Percentage of EffectiveIncomeTaxRateReconciliationDeductionsOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value5.96.81.38.20.0850.0740.0040.0630.0550.060.0010.060.0550.0640.0030.0580.0650.0610.0060.0630.060.0680.0120.0240.0170.02100.0260.0360.0270.057-0.028-0.031-0.0270000
Percentage of EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.0

us-gaap:EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost

us-gaap:EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost


Effective
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value0.1-0.4-0.5910.003-0.0120-0.0010.0030.0010.0010.002-0.005-0.001-0.002-0.0010.006-0.003-0.007-0.020.041
Percentage of EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationOtherAdjustments

us-gaap:EffectiveIncomeTaxRateReconciliationOtherAdjustments


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-31
Value-0.4-0.50.5-0.5-0.002-0.0050.006-0.004-0.0080.0010.0190.01-0.007-0.0060.002-0.0010.006-0.00200.0060.004-0.0060.012-0.0160.0020.0060.0010.0230.01-0.007-0.0130-0.013-0.014
Percentage of EffectiveIncomeTaxRateReconciliationOtherAdjustments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent

us-gaap:EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent


Effective
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-30
Value-17.6-21.0-31.1-0.245-0.247-0.185-1.084-0.189-0.223-0.144-0.178-0.279-0.324-0.244-0.626-0.273-0.289-0.138-0.14-0.187-1.919-0.215-0.201-0.246
Percentage of EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes

us-gaap:EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes


Effective
Period End2020-12-312020-09-302019-12-312019-09-302018-12-312018-09-302017-12-312017-09-302017-06-302016-12-312016-09-302016-06-302015-12-312015-09-302015-06-302014-12-312014-09-302014-06-302013-12-312013-09-302013-06-302012-12-312012-09-302012-06-30
Value3.0-6.50.001-0.0250.039-0.107-0.0040.02200.0020-0.003-0.0090.0340-0.0230.440-0.01100.0330.0610.150
Percentage of EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.0100.0100.0100.00.0100.0100.00.0100.00.0100.0100.0100.00.0

us-gaap:EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes

us-gaap:EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes


Effective
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value0.60.11.00.200-0.0170.0030.0090.012-0.0250.0230.0170.0120.035-0.017-0.022-0.0130.048-0.018-0.027-0.0270.002-0.028-0.009-0.0030.0210.00900.0060.0280.004-0.0510.015-0.0340.0230.0250.023
Percentage of EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes100.0100.0100.0100.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ExtinguishmentOfDebtAmount us-gaap:ShortTermDebtType

us-gaap:ExtinguishmentOfDebtAmount

nwe:TermLoanDue2021


Extinguishment
Period End2021-03-31
Value100
Percentage of ExtinguishmentOfDebtAmount100.0

us-gaap:GainLossOnSaleOfOtherAssets

us-gaap:GainLossOnSaleOfOtherAssets


Gain
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-2000.057000.0-63000.029000.04000.0-7000.012000.0012000.0164000.0-142000.066000.04000.0-15000.024000.0-10000.0315000.086000.001069000.0-1109000.055000.0-8000.0-59000.0-1000.088000.0983000.0240000.048000.059000.0-40000.056000.0705000.00100000.0110000.066000.056000.039000.0-863000.013000.00705000.0-88000.0-706000.078000.0
Percentage of GainLossOnSaleOfOtherAssets100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationDeductionsOther

us-gaap:IncomeTaxReconciliationDeductionsOther


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value4.2277.8538.9694.2133.2087.4387.0122.6062.1537.9356.2482.3944.0956.5869.9267.0144.7538.7978.471186.9716.6746.8392.7799.6934.8653.0862.1027.716.8031.8082.168-5.5714.683.2431.52-3.982
Percentage of IncomeTaxReconciliationDeductionsOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationDeductionsQualifiedProductionActivities

us-gaap:IncomeTaxReconciliationDeductionsQualifiedProductionActivities


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value2.2624.3075.552.2051.7373.6114.2311.4141.4064.4322.7871.6562.5593.8883.4882.2541.4593.8313.6242.2182.3242.7753.0760.7330.6511.2611.0820.30.3241.431.0190.4820.5021.1680.00.00.00.0
Percentage of IncomeTaxReconciliationDeductionsQualifiedProductionActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.0

us-gaap:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate

us-gaap:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value8.10713105.6214.36310124.6675.341159.0575.8439.8461217137.844221412131417101321124.1143.13218116.1125.7561526-4.3264.90114125.4353.659146.6874.484
Percentage of IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost

us-gaap:IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost


Income
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value0-261000.000-609000.000186000.0-47000.000275000.036000.000-399000.0000-1646000.0
Percentage of IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost0.0100.00.00.0100.00.00.0100.0100.00.00.0100.0100.00.00.0100.00.00.00.0100.0

us-gaap:IncomeTaxReconciliationOtherAdjustments

us-gaap:IncomeTaxReconciliationOtherAdjustments


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-03-31
Value-148000.0-291000.092000.0-105000.0-47000.0-219000.0398000.0-79000.0-192000.0105000.0-2352000.0284000.0-320000.0-390000.0-179000.0-67000.0126000.0-157000.0-403000.0181000.0160000.0-225000.0-235000.0-458000.0-127000.0-394000.0-245000.0-266000.088000.0-416000.01321000.0-59000.0-563000.0
Percentage of IncomeTaxReconciliationOtherAdjustments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationOtherReconcilingItems

us-gaap:IncomeTaxReconciliationOtherReconcilingItems


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-30
Value-6742000.0-13262000.0-15783000.0-8324000.0-5081000.0-12074000.0-12460000.0-4112000.0-27567000.0-14047000.0-32425000.0-6201000.0-6744000.0-10773000.0-14595000.0-10940000.0-7264000.0-15458000.0-18295000.0-21890000.0-10534000.0-11712000.0-12231000.0-4176000.0-5504000.0-11488000.0-13680000.0-22551000.0-1928000.0-10758000.0-5664000.0-4297000.0
Percentage of IncomeTaxReconciliationOtherReconcilingItems100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationPriorYearIncomeTaxes

us-gaap:IncomeTaxReconciliationPriorYearIncomeTaxes


Income
Period End2020-12-312020-09-302019-12-312019-09-302018-12-312018-09-302017-12-312017-09-302017-06-302016-12-312016-09-302016-06-302015-12-312015-09-302015-06-302014-12-312014-09-302013-12-312013-09-302013-06-302012-12-312012-09-302012-06-302011-12-312011-09-30
Value0-1728000.00559000.00-2978000.0221000.0-850000.0000-128000.0-818000.01025000.000-5172000.01082000.00-541000.0-3758000.01857000.00-1377000.00
Percentage of IncomeTaxReconciliationPriorYearIncomeTaxes0.0100.00.0100.00.0100.0100.0100.00.00.00.0100.0100.0100.00.00.0100.0100.00.0100.0100.0100.00.0100.00.0

us-gaap:IncomeTaxReconciliationStateAndLocalIncomeTaxes

us-gaap:IncomeTaxReconciliationStateAndLocalIncomeTaxes


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value222000.055000.0-1550000.046000.05000.022000.021000.065000.0237000.0928000.0-558000.0638000.0801000.0732000.0-1254000.0-678000.0-492000.0-834000.0-974000.0-615000.0-1025000.0-1100000.0630000.0-857000.0367000.0161000.0-2226000.0-108000.0-6000.0371000.0-2944000.057000.0-842000.0647000.02087000.0270000.0-344000.0935000.0-4484000.0387000.0421000.01996000.0-383000.0-30000.0
Percentage of IncomeTaxReconciliationStateAndLocalIncomeTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInAccruedLiabilities

us-gaap:IncreaseDecreaseInAccruedLiabilities


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-40.34163-61.64458-26.42835-40.96845-48.56227-45.16947-36.53641-41.82351-38.15933-35.72860-37.23738-42.04550-43.53412-17.72739-47.5634-20.40930-32.65724-14.9943-34.54119-35.13529-18.62226-10.04428-9.54621
Percentage of IncreaseDecreaseInAccruedLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction

us-gaap:IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction


Increase
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value2577000.01985000.02185000.01423000.0895000.01800000.01349000.0969000.01206000.0913000.0618000.01800000.01314000.0984000.0
Percentage of IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherCurrentAssets

us-gaap:IncreaseDecreaseInOtherCurrentAssets


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value1539000.0455000.0-717000.04764000.01900000.0-2470000.0-192000.02895000.01421000.0-984000.0-2122000.0-1897000.06059000.0-3258000.0-595000.0-3473000.05627000.0-2386000.0277000.0-5258000.03991000.03374000.0-1508000.0-5046000.02044000.0-1004000.0885000.0-2456000.0137000.0-2767000.0957000.0-5024000.04938000.02069000.01144000.0-373000.02238000.0-1153000.01655000.0-2245000.01376000.02765000.0
Percentage of IncreaseDecreaseInOtherCurrentAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherNoncurrentAssets

us-gaap:IncreaseDecreaseInOtherNoncurrentAssets


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value2.1181.682-0.8292.5312.8920.8026.3142.3071.8431.2161.5024.1232.4031.5052.1555.8443.483.3013.0771.1351.6141.4853.3441.2260.2320.782-37.5039.4130.23924116.9621.84723130.102-0.4191326-0.6611.3612.7515.591-4.864
Percentage of IncreaseDecreaseInOtherNoncurrentAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherNoncurrentLiabilities

us-gaap:IncreaseDecreaseInOtherNoncurrentLiabilities


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value-8.033-20.656-12.964-6.5712.189-2.684-3.8441.308-1.589-2.403-15.823-5.72-12.6917.474-1.0674.6872.6591.1083.827-9.1255.8251.2933.681-7.9739.5341.6484.467-10.9482.774.6982.176-5.154.6786.051-2.567-4.6281.4216.8262.942-9.0853.2645.4621.5796.42
Percentage of IncreaseDecreaseInOtherNoncurrentLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherRegulatoryAssets

us-gaap:IncreaseDecreaseInOtherRegulatoryAssets


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-3.84254-7.377-0.462.933-9.845-1.6344.5561.40611-1.361123.09-13.208-3.2715.0422.861-17.0044.9764.018-0.315-10.551211-3.809-16.770.504-4.6915.5257.614122.21.014-12.5983.0192.247.744-6.7183.8553.552-2.968-6.1235.3283.3465.313-0.412
Percentage of IncreaseDecreaseInOtherRegulatoryAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInRegulatoryLiabilities

us-gaap:IncreaseDecreaseInRegulatoryLiabilities


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-7.007-23.2289.341.0684.1068.259114.387-0.143-23.50918-3.378.122.2050.116-1.444-2.361-7.332.202-1.217-52.643-2.971128.353.5490.843.5560.8323.4251.956.19-8.136-1.3651.2924.66815-3.902-0.794130.552-3.9036.0140.102-3.148-6.684-2.719
Percentage of IncreaseDecreaseInRegulatoryLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInRegulatoryLiabilities us-gaap:PublicUtilitiesRegulatoryProceeding

nwe:MontanaFERCRateFilingSettlement


Increase
Period End2021-06-302021-03-31
Value-4.720
Percentage of IncreaseDecreaseInRegulatoryLiabilities67.1-88.3

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements


Incremental
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value132140.0105350.097529.069280.0198490.0-10704.0335370.0334470.0348520.0113540.0142730.0175370.067622.032399.064598.0130770.0117660.022044.0154540.066787.098065.098991.0245460.0243960.0218460.0134210.0139660.075316.098351.0-99239.0186190.0129350.0101300.0122620.00143910.0171930.043246.0248780.0256900.0221970.0-86148.0116620.0143730.0
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet us-gaap:StatementEquityComponents

us-gaap:InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet

us-gaap:AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedges


Interest
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value113000.0113000.0113000.0114000.0113000.0112000.0113000.0113000.0113000.0
Percentage of InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ComprehensiveIncome


Interest
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value113000.0113000.0113000.0114000.0113000.0112000.0113000.0113000.0113000.0
Percentage of InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions us-gaap:StatementEquityComponents

us-gaap:InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions

nwe:EquityDistributionAgreement


Investment
Period End2021-06-30
Value800000.0
Percentage of InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions100.0

us-gaap:LossContingencyDamagesSoughtValue us-gaap:LossContingenciesByNatureOfContingency

us-gaap:LossContingencyDamagesSoughtValue

nwe:PacificNorthwestSolarLLCPNWS


Loss
Period End2021-06-302021-03-312020-12-312019-06-302019-03-31
Value0.08.00.00.08.0
Percentage of LossContingencyDamagesSoughtValue0.0100.00.00.0100.0

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent


Other
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value21000.0-76000.0-3000.0-8000.0101000.042000.0-87000.063000.0-68000.086000.095000.0-144000.0-104000.051000.026000.08000.0-118000.0233000.0-56000.0268000.0110000.0134000.0-82000.0103000.0
Percentage of OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax

us-gaap:OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax


Other
Period End2021-06-302021-03-312020-06-302020-03-31
Value21000.0-76000.0-8000.0101000.0
Percentage of OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax us-gaap:OtherComprehensiveIncomeLocation

us-gaap:AccumulatedTranslationAdjustment


Other
Period End2021-06-302021-03-312020-06-302020-03-31
Value21000.0-76000.0-8000.0101000.0
Percentage of OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedTranslationAdjustment


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value-3000.0-8000.0101000.042000.0-87000.063000.0-68000.086000.095000.0-144000.0-104000.051000.026000.08000.0-118000.0113000.0233000.0-56000.0268000.0110000.0134000.0-82000.0103000.0
Percentage of OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax0.0100.0100.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ComprehensiveIncome


Other
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-31
Value-3000.0-8000.0101000.042000.0-87000.063000.0-68000.086000.095000.0-144000.0-104000.051000.026000.08000.0-118000.0
Percentage of OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax0.0100.0100.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherComprehensiveIncomeLossBeforeTax

us-gaap:OtherComprehensiveIncomeLossBeforeTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value-38000.0-135000.02615000.0150000.0145000.0254000.0-74000.0196000.066000.0216000.0657000.085000.0240000.0248000.01407000.08000.049000.0204000.0581000.0-2422000.070000.0-56000.0679000.0-668000.0-199000.0125000.0-16719000.0-1807000.0-379000.0-194000.01356000.0-351000.0-211000.0-248000.0-1501000.0-376000.0-251000.0-11000.0-909000.0-465000.0-279000.0
Percentage of OtherComprehensiveIncomeLossBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value21000.0-76000.0-3000.0-3000.0-8000.0101000.0-53000.042000.0-87000.063000.0157000.0-68000.086000.095000.0-5000.0-144000.0-104000.051000.0109000.026000.08000.0-118000.0113000.0233000.0-56000.0268000.0110000.0134000.0-82000.0103000.085000.0-54000.086000.049000.026000.0-79000.046000.0-47000.0124000.0-168000.018000.0
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax


Other
Period End2021-06-302021-03-312013-12-312013-09-302013-06-302012-12-312012-09-302012-06-30
Value212000.0212000.0-1568000.0001230000.000
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax100.0100.0100.00.00.0100.00.00.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax


Other
Period End2021-06-302021-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value159000.0158000.0-963000.0000758000.000-205000.0581000.000
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax100.0100.0100.00.00.00.0100.00.00.0100.0100.00.00.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome


Other
Period End2021-06-302021-03-31
Value159000.0158000.0
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax100.0100.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax


Other
Period End2021-06-302021-03-312013-12-312013-09-302013-06-302012-12-312012-09-302012-06-30
Value53000.054000.0605000.000-472000.000
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax100.0100.0100.00.00.0100.00.00.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-153000.0-153000.0-155000.0-153000.0-153000.0-153000.0-154000.0-154000.0-153000.0-153000.0-154000.0-153000.0-154000.0-153000.0-155000.0-152000.0-153000.0-153000.0-155000.02448000.0-62000.0-62000.0-62000.0901000.0143000.0143000.0219000.0297000.0297000.0297000.0297000.0297000.0297000.0297000.0297000.0297000.0
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-113000.0-113000.0-113000.0-113000.0-113000.0-113000.0-113000.0-114000.0-113000.0-112000.0-159000.0-113000.0-113000.0-113000.0-93000.0-92000.0-93000.0-93000.0-94000.01506000.0-37000.0-37000.0-37000.0555000.091000.089000.0135000.0183000.0183000.0183000.0181000.0183000.0183000.0183000.0180000.0178000.0
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value-113000.0-113000.0-113000.0-113000.0-113000.0-113000.0791000.0-114000.0-113000.0-112000.0-159000.0-113000.0-113000.0-113000.0649000.0-92000.0-93000.0-93000.0-94000.01506000.0-37000.0-37000.0-37000.0555000.091000.089000.0135000.0183000.0183000.0183000.0181000.0
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax100.0100.0100.0100.0100.0100.0-700.0100.0100.0100.0100.0100.0100.0100.0-697.8100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-40000.0-40000.0282000.0-40000.0-40000.040000.041000.040000.040000.041000.0-5000.040000.041000.040000.062000.060000.060000.060000.061000.0-942000.025000.025000.025000.0-346000.0-52000.0-54000.0-84000.0-114000.0-114000.0-114000.0-116000.0-114000.0-114000.0-114000.0-117000.0-119000.0
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossTax

us-gaap:OtherComprehensiveIncomeLossTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value-13000.0-14000.0-905000.040000.040000.0-40000.03000.0-40000.0-40000.0-41000.0-128000.0-40000.0-41000.0-40000.0-546000.0-60000.0-60000.0-60000.0-183000.0942000.0-25000.0-25000.0-219000.0346000.052000.054000.06642000.0747000.0114000.0114000.0-489000.0114000.0114000.0114000.0589000.0119000.0106000.0-14000.0-3073000.0114000.000
Percentage of OtherComprehensiveIncomeLossTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0

us-gaap:PaymentsOfFinancingCosts

us-gaap:PaymentsOfFinancingCosts


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.1730.4420.0141.4550.9680.1410.0410.1990.7350.140.0-0.009-0.1250.225160.0140.140.0021.8241.2595.1980.151-0.0420.436101.0924.4160.6880.0750.0697.5930.00.00.00.0330.1560.0150.0751.0410.00.0011.4086.5230.088
Percentage of PaymentsOfFinancingCosts100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0

us-gaap:PensionContributions

us-gaap:PensionContributions


Pension
Period End2021-06-302021-03-312020-09-30
Value3.11.46.6
Percentage of PensionContributions100.0100.0100.0

us-gaap:PensionContributions us-gaap:RetirementPlanName

nwe:NorthWesternEnergyPensionPlanMT


Pension
Period End2020-12-31
Value0.0
Percentage of PensionContributions0.0

us-gaap:ProceedsFromRepaymentsOfLinesOfCredit

us-gaap:ProceedsFromRepaymentsOfLinesOfCredit


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value394912632-231.06.057-83.029-22.03080.00.00.0
Percentage of ProceedsFromRepaymentsOfLinesOfCredit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.0

us-gaap:ProceedsFromRepurchaseOfEquity

us-gaap:ProceedsFromRepurchaseOfEquity


Proceeds
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value332000.0-300000.0353000.0416000.0-2492000.0212000.0221000.0202000.0797000.0193000.0283000.0199000.01574000.0184000.0488000.01283000.0-872000.0166000.0887000.0174000.0-1788000.0165000.0179000.0983000.0-1991000.067000.076000.055000.0-1012000.065000.072000.070000.0-1249000.0128000.067000.0-699000.075000.0
Percentage of ProceedsFromRepurchaseOfEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromShortTermDebt

us-gaap:ProceedsFromShortTermDebt


Proceeds
Period End2020-09-30
Value0.0
Percentage of ProceedsFromShortTermDebt0.0

us-gaap:PropertyPlantAndEquipmentAdditions

us-gaap:PropertyPlantAndEquipmentAdditions


Property
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value104771221069878739581659076645279776751838269518072745684746051766550384278
Percentage of PropertyPlantAndEquipmentAdditions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PropertyPlantAndEquipmentAdditions us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Property
Period End2021-06-302021-03-312020-06-302020-03-31
Value82687963
Percentage of PropertyPlantAndEquipmentAdditions79.088.681.380.8

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Property
Period End2021-06-302021-03-312020-06-302020-03-31
Value218.9141815
Percentage of PropertyPlantAndEquipmentAdditions21.011.418.719.2

us-gaap:PropertyPlantAndEquipmentAdditions us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Property
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value87796370635260524266625541706657416257635071625445675541334745
Percentage of PropertyPlantAndEquipmentAdditions82.181.380.873.178.379.878.182.082.583.480.782.879.783.680.182.981.177.980.185.788.585.283.890.387.488.285.082.787.4110.758.6

nwe:GasDomesticRegulated


Property
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value19181525171316119.107131511101316119.6931714106.47712125.8366.529.0569.8238.7444.799-4.61132
Percentage of PropertyPlantAndEquipmentAdditions17.918.719.226.921.720.221.918.017.516.619.317.220.316.419.917.118.922.119.914.311.514.816.29.712.611.815.017.312.6-10.741.4

us-gaap:ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax

us-gaap:ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax


Reclassification
Period End2021-06-302021-03-31
Value-159000.0-158000.0
Percentage of ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax100.0100.0

us-gaap:ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax us-gaap:OtherComprehensiveIncomeLocation

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


Reclassification
Period End2021-06-302021-03-31
Value-159000.0-158000.0
Percentage of ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax100.0100.0

us-gaap:RegulatedOperatingRevenueElectricNonNuclear

us-gaap:RegulatedOperatingRevenueElectricNonNuclear


Regulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value241270234244217244247241219273227245209238262274
Percentage of RegulatedOperatingRevenueElectricNonNuclear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RegulatedOperatingRevenueGas

us-gaap:RegulatedOperatingRevenueGas


Regulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value56130793651908033511118034521038235
Percentage of RegulatedOperatingRevenueGas100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RepaymentsOfShortTermDebt

us-gaap:RepaymentsOfShortTermDebt


Repayments
Period End2021-03-31
Value100
Percentage of RepaymentsOfShortTermDebt100.0

us-gaap:StockIssuedDuringPeriodSharesNewIssues us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodSharesNewIssues

us-gaap:CommonStock


Stock
Period End2021-06-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value880000.00000021000.000836000.00805000.000001100000.00007767000.000296000.0278000.0
Percentage of StockIssuedDuringPeriodSharesNewIssues100.00.00.00.00.00.0100.00.00.0100.00.0100.00.00.00.00.0100.00.00.00.0100.00.00.0100.0100.0

us-gaap:StockIssuedDuringPeriodSharesShareBasedCompensation us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodSharesShareBasedCompensation

us-gaap:CommonStock


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value093000.0000146000.03000.00086000.0001000.071000.001000.06000.0127000.01000.01000.01000.0166000.01000.02000.03000.0161000.01000.02000.01000.0115000.02000.0
Percentage of StockIssuedDuringPeriodSharesShareBasedCompensation0.0100.00.00.00.0100.0100.00.00.0100.00.00.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:TreasuryStock


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value017000.000035000.000025000.0042000.00-30000.014000.0-8000.0-21000.015000.0-4000.0-15000.0-3000.031000.010000.0-17000.0-21000.038000.012000.0-18000.0-3000.021000.03000.0
Percentage of StockIssuedDuringPeriodSharesShareBasedCompensation0.018.30.00.00.024.00.00.00.029.10.00.00.0-42.30.0-800.0-350.011.8-400.0-1500.0-300.018.71000.0-850.0-700.023.61200.0-900.0-300.018.3150.0

us-gaap:StockIssuedDuringPeriodSharesTreasuryStockReissued us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodSharesTreasuryStockReissued

us-gaap:TreasuryStock


Stock
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value5000.012000.0-7000.0-7000.0-4000.0-3000.0-3000.0-3000.0-35000.0-3000.0-47000.0-5000.00-17000.00000-13000.013000.000-15000.015000.00017000.0
Percentage of StockIssuedDuringPeriodSharesTreasuryStockReissued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.00.00.00.0100.0100.00.00.0100.0100.00.00.0100.0

us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation

us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value1299000.02242000.0-1211000.01140000.01139000.0290000.03211000.01169000.01169000.0760000.02739000.01129000.01289000.01817000.0-2356000.01661000.02777000.01459000.070000.01998000.01293000.0455000.0
Percentage of StockIssuedDuringPeriodValueShareBasedCompensation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value1299000.03211000.0-1210000.01140000.01139000.03031000.03220000.01169000.01169000.02406000.02739000.01186000.01232000.02485000.0-1068000.01433000.02226000.02929000.01040000.01585000.01212000.02853000.01041000.0416000.01550000.01338000.01561000.0662000.0819000.01246000.01178000.0
Percentage of StockIssuedDuringPeriodValueShareBasedCompensation100.0143.299.9100.0100.01045.2100.3100.0100.0316.6100.0105.095.6136.845.386.380.2200.81485.779.393.7627.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stock
Period End2021-06-302021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value01000.0002000.00000-1000.001000.0-2000.01000.001000.00000000000001000.0
Percentage of StockIssuedDuringPeriodValueShareBasedCompensation0.00.00.00.00.10.00.00.00.0-0.10.00.10.10.10.00.10.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:TreasuryStock


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value0-970000.0-1000.000-2741000.0-11000.000-1646000.00-56000.057000.0-669000.0-1286000.0227000.0551000.0-1471000.0-970000.0413000.081000.0-2398000.070000.0-359000.0518000.0-2085000.057000.035000.055000.0-1012000.0-31000.0
Percentage of StockIssuedDuringPeriodValueShareBasedCompensation0.0-43.30.10.00.0-945.2-0.30.00.0-216.60.0-5.04.4-36.854.613.719.8-100.8-1385.720.76.3-527.00.00.00.00.00.00.00.00.00.0

us-gaap:StockIssuedDuringPeriodValueTreasuryStockReissued

us-gaap:StockIssuedDuringPeriodValueTreasuryStockReissued


Stock
Period End2021-03-312020-03-31
Value682000.0259000.0
Percentage of StockIssuedDuringPeriodValueTreasuryStockReissued100.0100.0

us-gaap:StockIssuedDuringPeriodValueTreasuryStockReissued us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2021-03-312020-03-31
Value367000.0147000.0
Percentage of StockIssuedDuringPeriodValueTreasuryStockReissued53.856.8

us-gaap:TreasuryStock


Stock
Period End2021-06-302021-03-312020-06-302020-03-312016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value152000.0315000.0206000.0112000.00013000.0453000.00010000.041000.00096000.0
Percentage of StockIssuedDuringPeriodValueTreasuryStockReissued0.046.20.043.20.00.00.00.00.00.00.00.00.00.00.0

us-gaap:TaxesExcludingIncomeAndExciseTaxes

us-gaap:TaxesExcludingIncomeAndExciseTaxes


Taxes
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value47474245464438444444424243424439393936403535323532323027272828252525232425232022202519202422
Percentage of TaxesExcludingIncomeAndExciseTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:TaxesExcludingIncomeAndExciseTaxes us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Taxes
Period End2021-06-302021-03-312020-06-302020-03-31
Value36373634
Percentage of TaxesExcludingIncomeAndExciseTaxes78.278.078.478.1

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Taxes
Period End2021-06-302021-03-312020-06-302020-03-31
Value1010109.761
Percentage of TaxesExcludingIncomeAndExciseTaxes21.822.021.621.9

us-gaap:TaxesExcludingIncomeAndExciseTaxes us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Taxes
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value35363434343533333334303031283227272528252523202020201919191718191715161518141518
Percentage of TaxesExcludingIncomeAndExciseTaxes78.478.478.178.878.678.278.878.778.278.478.678.378.077.479.577.677.477.880.277.377.077.373.572.772.174.974.773.774.473.675.175.174.175.374.774.573.873.175.873.2

nwe:GasDomesticRegulated


Taxes
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value9.772109.7619.3559.4749.748.9979.169.3189.5268.3558.5698.7648.3058.3287.8837.9897.217.0627.3717.5256.867.3577.6457.9597.0256.5726.7926.6046.1486.1726.4636.1245.085.7085.2466.6525.3065.0416.659
Percentage of TaxesExcludingIncomeAndExciseTaxes21.621.621.921.221.421.721.221.321.821.621.421.721.922.620.522.422.622.219.822.723.022.626.527.327.925.125.326.325.626.424.924.925.924.725.325.526.226.924.526.7

us-gaap:AllOtherSegments


Taxes
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value0.0020.0020.0020.0030.0020.0030.0030.0020.0020.0030.0020.0020.0020.0010.0020.0030.0030.0020.0020.0030.0030.0020.0020.0030.0030.0030.0030.0030.0030.0030.0030.0020.0030.0040.003
Percentage of TaxesExcludingIncomeAndExciseTaxes0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses

us-gaap:UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses


Utilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value778073737179797680818573737478707580826872797579618191687472767267687463676563666967
Percentage of UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses us-gaap:ConsolidationItems, us-gaap:ProductOrService

us-gaap:OperatingSegments, us-gaap:ElectricityUsRegulated


Utilities
Period End2021-06-302021-03-312020-06-302020-03-31
Value58575358
Percentage of UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses75.371.474.774.5

us-gaap:OperatingSegments, us-gaap:NaturalGasUsRegulated


Utilities
Period End2021-06-302021-03-312020-06-302020-03-31
Value19211822
Percentage of UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses25.026.226.528.2

us-gaap:UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses us-gaap:StatementBusinessSegments

nwe:ElectricDomesticRegulated


Utilities
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-30
Value5453585759575452545753545859505155545860605548494752494745494447454345
Percentage of UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses74.174.774.574.673.471.373.271.673.572.776.271.972.472.173.971.169.472.073.598.674.060.571.366.365.468.367.870.866.467.170.971.169.267.768.8

nwe:GasDomesticRegulated


Utilities
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-30
Value2018221820211919212019202125192021201921212521222221181819201718191919
Percentage of UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses27.426.528.224.525.925.925.926.628.526.027.426.926.730.528.028.427.427.425.035.327.027.630.830.531.328.525.527.428.927.727.727.829.431.030.1

us-gaap:AllOtherSegments


Utilities
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-0.1871.918-1.104-0.872-2.184-0.4960.7350.5332.3010.2570.6321.29-1.5221.004-2.5710.8960.714-2.177-1.3110.4262.5060.4461.155-20.918-0.84310-1.4252.4452.352.3994.8641.163.2243.8210.893
Percentage of UtilitiesOperatingExpenseMaintenanceOperationsAndOtherCostsAndExpenses-0.22.4-1.5-1.2-2.8-0.61.00.72.80.30.91.7-2.01.3-3.71.20.9-2.6-1.90.63.10.61.5-33.9-1.011.9-2.13.33.33.16.71.74.75.11.4

dei:EntityCommonStockSharesOutstanding

dei:EntityCommonStockSharesOutstanding


Entity
Period End2021-07-232021-04-162021-02-052020-10-16
Value51505050
Percentage of EntityCommonStockSharesOutstanding100.0100.0100.0100.0

nwe:AssetDefinedBenefitPlanNoncurrent us-gaap:RetirementPlanType

nwe:AssetDefinedBenefitPlanNoncurrent

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Asset
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value8436000.07783000.04565000.05061000.00
Percentage of AssetDefinedBenefitPlanNoncurrent100.0100.0100.0100.00.0

us-gaap:PensionPlansDefinedBenefit


Asset
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value7001000.04333000.02672000.02535000.00
Percentage of AssetDefinedBenefitPlanNoncurrent83.055.758.550.10.0

nwe:CommonStockAggregateGrossSalesPriceMaximum us-gaap:StatementEquityComponents

nwe:CommonStockAggregateGrossSalesPriceMaximum

nwe:EquityDistributionAgreement


Common
Period End2021-06-30
Value200
Percentage of CommonStockAggregateGrossSalesPriceMaximum100.0

nwe:CreditFacilityBorrowingsandLetterofCreditAmountOutstanding

nwe:CreditFacilityBorrowingsandLetterofCreditAmountOutstanding


Credit
Period End2020-12-312019-12-312018-12-312017-12-31
Value222289308319
Percentage of CreditFacilityBorrowingsandLetterofCreditAmountOutstanding100.0100.0100.0100.0

nwe:CustomerAdvances

nwe:CustomerAdvances


Customer
Period End2020-12-312019-12-31
Value6556
Percentage of CustomerAdvances100.0100.0

nwe:DeferredTaxAssetsCustomerAdvances

nwe:DeferredTaxAssetsCustomerAdvances


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value1714131115141110131617
Percentage of DeferredTaxAssetsCustomerAdvances100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:DeferredTaxAssetsEnvironmentalLiability

nwe:DeferredTaxAssetsEnvironmentalLiability


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value6039000.05938000.05810000.05821000.09698000.09410000.08968000.09026000.09701000.09670000.08425000.0
Percentage of DeferredTaxAssetsEnvironmentalLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:DeferredTaxAssetsUnbilledRevenue

nwe:DeferredTaxAssetsUnbilledRevenue


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value149.82125.94412281918156.57710
Percentage of DeferredTaxAssetsUnbilledRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:DeferredTaxLiabilitiesExcessTaxDepreciation

nwe:DeferredTaxLiabilitiesExcessTaxDepreciation


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value412393371356459392349304278280223
Percentage of DeferredTaxLiabilitiesExcessTaxDepreciation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:DeferredTaxLiabilitiesFlowThroughDepreciation

nwe:DeferredTaxLiabilitiesFlowThroughDepreciation


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value8371574516012510379634928
Percentage of DeferredTaxLiabilitiesFlowThroughDepreciation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:Deferredtaxassetsproductiontaxcredits

nwe:Deferredtaxassetsproductiontaxcredits


Deferredtaxassetsproductiontaxcredits
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value63503828176.556.4523.1710.0
Percentage of Deferredtaxassetsproductiontaxcredits100.0100.0100.0100.0100.0100.0100.0100.00.0

nwe:DefinedBenefitPlanActuarialNetGainsLossesInRegulatoryAssets us-gaap:RegulatoryAsset, us-gaap:RetirementPlanType

nwe:DefinedBenefitPlanActuarialNetGainsLossesInRegulatoryAssets

us-gaap:PensionCosts, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-497000.0259000.0-1910000.0-1735000.0-4739000.0
Percentage of DefinedBenefitPlanActuarialNetGainsLossesInRegulatoryAssets100.0100.0100.0100.0100.0

us-gaap:PensionCosts, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-115990000.0-111450000.0-116420000.0-105540000.0-127950000.0
Percentage of DefinedBenefitPlanActuarialNetGainsLossesInRegulatoryAssets23337.4-43030.56095.56083.32700.0

nwe:DefinedBenefitPlanAmortizationOfPriorServiceCostCreditRegulatoryAssets us-gaap:RegulatoryAsset, us-gaap:RetirementPlanType

nwe:DefinedBenefitPlanAmortizationOfPriorServiceCostCreditRegulatoryAssets

us-gaap:PensionCosts, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value3.8575.897.9229.95511
Percentage of DefinedBenefitPlanAmortizationOfPriorServiceCostCreditRegulatoryAssets100.0100.0100.0100.0100.0

nwe:EnvironmentalRemediationObligationMaximum us-gaap:EnvironmentalRemediationContingency

nwe:EnvironmentalRemediationObligationMaximum

nwe:EnvironmentalRemediationObligations


Environmental
Period End2021-06-302021-03-312020-12-312020-09-30
Value31313230
Percentage of EnvironmentalRemediationObligationMaximum100.0100.0100.0100.0

nwe:EnvironmentalRemediationObligationMinimum us-gaap:EnvironmentalRemediationContingency

nwe:EnvironmentalRemediationObligationMinimum

nwe:EnvironmentalRemediationObligations


Environmental
Period End2021-06-302021-03-312020-12-312020-09-30
Value25262627
Percentage of EnvironmentalRemediationObligationMinimum100.0100.0100.0100.0

nwe:EnvironmentalRemediationObligationToBeIncurredDuringNext5Years us-gaap:EnvironmentalRemediationContingency, us-gaap:EnvironmentalRemediationSite

nwe:EnvironmentalRemediationObligationToBeIncurredDuringNext5Years

nwe:ManufacturedGasPlants, nwe:AberdeenSouthDakotaSite


Environmental
Period End2021-06-302021-03-312020-12-312020-09-30
Value2900000.03000000.03100000.02400000.0
Percentage of EnvironmentalRemediationObligationToBeIncurredDuringNext5Years100.0100.0100.0100.0

nwe:LineOfCreditFacilityMaximumPercentageOfTotalAvailabilityProvidedByASingleLender us-gaap:CreditFacility

nwe:LineOfCreditFacilityMaximumPercentageOfTotalAvailabilityProvidedByASingleLender

nwe:UnsecuredRevolvingLineOfCredit


Line
Period End2020-09-30
Value13.0
Percentage of LineOfCreditFacilityMaximumPercentageOfTotalAvailabilityProvidedByASingleLender100.0

nwe:MinimumExpectedFutureEmployerPensionContributionsRemainderofFiscalYear

nwe:MinimumExpectedFutureEmployerPensionContributionsRemainderofFiscalYear


Minimum
Period End2021-06-302021-03-31
Value6700000.09800000.0
Percentage of MinimumExpectedFutureEmployerPensionContributionsRemainderofFiscalYear100.0100.0

nwe:NumberOfCustomers

nwe:NumberOfCustomers


Number
Period End2020-12-312019-12-31
Value743000.0734800.0
Percentage of NumberOfCustomers100.0100.0

nwe:QualifyingFacilityLiability

nwe:QualifyingFacilityLiability


Qualifying
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value8192102132134138136136136184177
Percentage of QualifyingFacilityLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:QualifyingFacilityLiability us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased

nwe:QualifyingFacilityContracts


Qualifying
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-31
Value8192102132134138136136136184177165
Percentage of QualifyingFacilityLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

nwe:RabbiTrustInvestmentFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

nwe:RabbiTrustInvestmentFairValueDisclosure

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring


Rabbi
Period End2020-12-312019-12-312018-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value2729222827292725252729242321232119222016161414101010108.0497.0037.1365.495
Percentage of RabbiTrustInvestmentFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:RabbiTrustInvestmentFairValueDisclosure us-gaap:FairValueByMeasurementBasis, us-gaap:FairValueByMeasurementFrequency

us-gaap:EstimateOfFairValueFairValueDisclosure, us-gaap:FairValueMeasurementsRecurring


Rabbi
Period End2020-12-312019-12-312018-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302015-12-312014-12-312013-12-31
Value27292228272927252527242116
Percentage of RabbiTrustInvestmentFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:RegulatoryAssetForCOVIDUncollectableAccounts us-gaap:PublicUtilitiesRegulatoryProceeding

nwe:RegulatoryAssetForCOVIDUncollectableAccounts

nwe:SouthDakotaAccountingOrder


Regulatory
Period End2020-12-312020-09-30
Value200000.0400000.0
Percentage of RegulatoryAssetForCOVIDUncollectableAccounts100.0100.0

nwe:RestrictedCashFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

nwe:RestrictedCashFairValueDisclosure

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring


Restricted
Period End2020-12-312019-12-312018-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value105.6996.6692.6486.7995.3544.594.1646.356.2326.4376.241313121317158.8736.657.9877.7638.3816.3927.6717.528.64512111312
Percentage of RestrictedCashFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwe:RestrictedCashFairValueDisclosure us-gaap:FairValueByMeasurementBasis, us-gaap:FairValueByMeasurementFrequency

us-gaap:EstimateOfFairValueFairValueDisclosure, us-gaap:FairValueMeasurementsRecurring


Restricted
Period End2020-12-312019-12-312018-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302015-12-312014-12-312013-12-31
Value105.6996.6692.6486.7995.3544.594.1646.356.2326.24136.65
Percentage of RestrictedCashFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccrualForEnvironmentalLossContingencies us-gaap:EnvironmentalRemediationContingency

us-gaap:AccrualForEnvironmentalLossContingencies

nwe:EnvironmentalRemediationObligations


Accrual
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-31
Value282828292930282929292829303030303131303031312828292929
Percentage of AccrualForEnvironmentalLossContingencies100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccrualForEnvironmentalLossContingencies us-gaap:EnvironmentalRemediationContingency, us-gaap:EnvironmentalRemediationSite

nwe:ManufacturedGasPlants, nwe:AberdeenSouthDakotaSite


Accrual
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302014-09-302014-06-302014-03-312013-09-30
Value8.18.27.88.08.18.28.08.08.38.48.89.39.49.610101010111111111111
Percentage of AccrualForEnvironmentalLossContingencies28.428.427.127.127.127.127.927.628.128.330.631.431.331.734.234.033.734.336.636.90.00.00.00.0

nwe:ManufacturedGasPlants, nwe:CombinedManufacturingSites


Accrual
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-30
Value2222222324242122222222222323232324242324
Percentage of AccrualForEnvironmentalLossContingencies78.278.578.579.380.380.975.676.276.375.876.777.077.377.677.777.878.578.478.278.6

us-gaap:AccrualForEnvironmentalLossContingenciesGross

us-gaap:AccrualForEnvironmentalLossContingenciesGross


Accrual
Period End2021-03-312020-12-312020-03-312019-12-31
Value28282930
Percentage of AccrualForEnvironmentalLossContingenciesGross100.0100.0100.0100.0

us-gaap:AccrualForEnvironmentalLossContingenciesGross us-gaap:EnvironmentalRemediationContingency

nwe:EnvironmentalRemediationObligations


Accrual
Period End2021-06-30
Value27
Percentage of AccrualForEnvironmentalLossContingenciesGross0.0

us-gaap:AccrualForEnvironmentalLossContingenciesGross us-gaap:EnvironmentalRemediationContingency, us-gaap:EnvironmentalRemediationSite

nwe:ManufacturedGasPlants, nwe:AberdeenSouthDakotaSite


Accrual
Period End2021-06-30
Value8.0
Percentage of AccrualForEnvironmentalLossContingenciesGross0.0

nwe:ManufacturedGasPlants, nwe:CombinedManufacturingSites


Accrual
Period End2021-06-30
Value21
Percentage of AccrualForEnvironmentalLossContingenciesGross0.0

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent


Accrual
Period End2020-12-312019-12-31
Value8985
Percentage of AccrualForTaxesOtherThanIncomeTaxesCurrent100.0100.0

us-gaap:AccruedEnvironmentalLossContingenciesNoncurrent

us-gaap:AccruedEnvironmentalLossContingenciesNoncurrent


Accrued
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value2527282930302828303029
Percentage of AccruedEnvironmentalLossContingenciesNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax


Accumulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-31
Value-10503000.0-10616000.0-10729000.0-10842000.0-10955000.0-11068000.0-11181000.0-11294000.0-11408000.0-11521000.0-11633000.0-9642000.0-9755000.0-9868000.0-9981000.0-10074000.0-10166000.0-10259000.0-10352000.0-10446000.0-8940000.0-8977000.0-9014000.0-9051000.0-8496000.0-8405000.0-8316000.01953000.03147000.03330000.03513000.03694000.03877000.04060000.04243000.04423000.04601000.04792000.04975000.0
Percentage of AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax


Accumulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-31
Value-1643000.0-1802000.0-1960000.0-120000.0-120000.0-120000.0-120000.0-251000.0-251000.0-251000.0-251000.0-31000.0-31000.0-31000.0-31000.0742000.0742000.0742000.0742000.0937000.0937000.0937000.0937000.01247000.01247000.01247000.01247000.01329000.01329000.01329000.01329000.02292000.02292000.02292000.02292000.01534000.01534000.01534000.01739000.0
Percentage of AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax


Accumulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-31
Value1445000.01424000.01500000.01503000.01506000.01514000.01413000.01466000.01424000.01511000.01448000.01291000.01359000.01273000.01178000.01183000.01327000.01431000.01380000.01271000.01245000.01237000.01355000.01242000.01009000.01065000.0797000.0687000.0553000.0635000.0532000.0447000.0501000.0415000.0366000.0340000.0419000.0373000.0420000.0
Percentage of AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivableCurrent

us-gaap:AllowanceForDoubtfulAccountsReceivableCurrent


Allowance
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value5600000.02300000.02300000.02900000.02900000.04000000.04300000.04500000.03200000.02900000.02900000.0
Percentage of AllowanceForDoubtfulAccountsReceivableCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssetRetirementObligation

us-gaap:AssetRetirementObligation


Asset
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-31
Value45424039393521209.2836.2927.1816.688
Percentage of AssetRetirementObligation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssetRetirementObligationsNoncurrent

us-gaap:AssetRetirementObligationsNoncurrent


Asset
Period End2020-12-312019-12-31
Value4542
Percentage of AssetRetirementObligationsNoncurrent100.0100.0

us-gaap:BuildingsAndImprovementsGross

us-gaap:BuildingsAndImprovementsGross


Buildings
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value303278264242225219168163145137105
Percentage of BuildingsAndImprovementsGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalLeaseObligationsCurrent

us-gaap:CapitalLeaseObligationsCurrent


Capital
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value2618000.02569000.02522000.02476000.02430000.02384000.02341000.02298000.02255000.02212000.02173000.02133000.02093000.02053000.02016000.01979000.01942000.01905000.01871000.01837000.01803000.01777000.01754000.01730000.01707000.01684000.01661000.01662000.01659000.01656000.01638000.01612000.01585000.01561000.01538000.01370000.01348000.01323000.01300000.01276000.01197000.0
Percentage of CapitalLeaseObligationsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalLeaseObligationsNoncurrent

us-gaap:CapitalLeaseObligationsNoncurrent


Capital
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value1516161718181919202121222223232424252526262727282829292930303131313232323333333435
Percentage of CapitalLeaseObligationsNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ContractualObligation

us-gaap:ContractualObligation


Contractual
Period End2020-09-30
Value123
Percentage of ContractualObligation100.0

us-gaap:ContractualObligation us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased

nwe:QualifyingFacilityContracts


Contractual
Period End2021-06-302021-03-312020-12-31
Value80109115
Percentage of ContractualObligation0.00.00.0

us-gaap:DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet us-gaap:LongtermDebtType

us-gaap:DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet

nwe:DebtInstrumentUnamortizedDiscountPremiumandDebtIssuanceCostsNet


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value-13376000.0-12356000.0-12292000.0-13221000.0-13299000.0-13999000.0
Percentage of DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet100.0100.0100.0100.0100.0100.0

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredIncomeTaxLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-31
Value628598549521800689611
Percentage of DeferredIncomeTaxLiabilities100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsGross

us-gaap:DeferredTaxAssetsGross


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value157150154180225187185124157164173
Percentage of DeferredTaxAssetsGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsHedgingTransactions

us-gaap:DeferredTaxAssetsHedgingTransactions


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value3171000.03956000.04074000.04323000.07192000.06483000.06251000.00
Percentage of DeferredTaxAssetsHedgingTransactions100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value0.393102868723.67742160.05186
Percentage of DeferredTaxAssetsOperatingLossCarryforwards100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0

us-gaap:DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration us-gaap:IncomeTaxAuthority, us-gaap:TaxPeriod

us-gaap:DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration

us-gaap:DomesticCountry, nwe:Year2036


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value0.4103174174173
Percentage of DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration100.0100.0100.0100.0100.0

us-gaap:DomesticCountry, nwe:Year2037


Deferred
Period End2020-12-312019-12-312018-12-312017-12-31
Value78787854
Percentage of DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration19550.075.444.831.2

us-gaap:StateAndLocalJurisdiction, nwe:Year2024


Deferred
Period End2020-12-312019-12-312018-12-312017-12-31
Value38616144
Percentage of DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration9525.058.935.025.2

us-gaap:DeferredTaxAssetsOther

us-gaap:DeferredTaxAssetsOther


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value2490000.01801000.0196000.01138000.03173000.03696000.04415000.02827000.03539000.02300000.00
Percentage of DeferredTaxAssetsOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value1113111218171710117.2694.267
Percentage of DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value313030264554512059410.0
Percentage of DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals

us-gaap:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value6.2667.0691.11.1261.1210.01.77212124.3780.0
Percentage of DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals100.0100.0100.0100.0100.00.0100.0100.0100.0100.00.0

us-gaap:DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill

us-gaap:DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value83821191171681521371221189677
Percentage of DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxLiabilitiesRegulatoryAssetsAndLiabilities

us-gaap:DeferredTaxLiabilitiesRegulatoryAssetsAndLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value48510.9240.4091214210.024-1.0980.0
Percentage of DeferredTaxLiabilitiesRegulatoryAssetsAndLiabilities100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value6.366.6866.7248.6016.438
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-115.987-111.449-116.425-105.549-127.962
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax-1823.7-1666.9-1731.5-1227.2-1987.6

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-3246000.0-934000.0-1260000.0-1079000.0-38000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-246000.0-397000.0-548000.0-698000.0-849000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanAmountsRecognizedInBalanceSheet us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAmountsRecognizedInBalanceSheet

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value3950000.01207000.0-1941000.0-2541000.0-7612000.0
Percentage of DefinedBenefitPlanAmountsRecognizedInBalanceSheet100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-132520000.0-126560000.0-124320000.0-110290000.0-121400000.0
Percentage of DefinedBenefitPlanAmountsRecognizedInBalanceSheet-3355.0-10485.86404.74340.31594.8

us-gaap:DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value8436000.07783000.04565000.05061000.00
Percentage of DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent100.0100.0100.0100.00.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value7001000.04333000.02672000.02535000.00
Percentage of DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent83.055.758.550.10.0

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate us-gaap:Range, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate

srt:Maximum, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1.80.0280.03950.0330.0355
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate100.0100.0100.0100.0100.0

srt:Maximum, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.30.0320.0420.0360.041
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate127.8114.3106.3109.1115.5

srt:Minimum, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1.80.0280.0390.0320.034
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate100.0100.098.797.095.8

srt:Minimum, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.20.0310.04150.0350.0395
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate122.2110.7105.1106.1111.3

us-gaap:DefinedBenefitPlanBenefitObligation us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanBenefitObligation

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value192020222628
Percentage of DefinedBenefitPlanBenefitObligation100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value820735649696646628
Percentage of DefinedBenefitPlanBenefitObligation4288.03628.53151.83040.02464.22194.9

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value5.6995.8516.6067.607
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value209207206200
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter3677.13550.93119.52639.9

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value2.7293.0253.2083.353
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value35333230
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths1289.81101.21016.8904.4

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value1.4571.8432.1862.254
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value40393835
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive2759.82120.71744.01597.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value1.6152.3372.4322.502
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value39373634
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour2426.61609.11510.11387.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value2.3312.5012.7312.714
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value37363533
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree1623.61445.61295.91232.6

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo

us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value2.4692.9342.7852.927
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value36343331
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo1479.71186.91216.51083.7

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets us-gaap:FairValueByMeasurementBasis, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets

us-gaap:ChangeDuringPeriodFairValueDisclosure, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value232118201817
Percentage of DefinedBenefitPlanFairValueOfPlanAssets100.0100.0100.0100.0100.0100.0

us-gaap:ChangeDuringPeriodFairValueDisclosure, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value688609525586524500
Percentage of DefinedBenefitPlanFairValueOfPlanAssets2980.82835.32813.72877.92819.92782.4

us-gaap:DefinedBenefitPlanFundedStatusOfPlan us-gaap:FairValueByMeasurementBasis, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanFundedStatusOfPlan

us-gaap:ChangeDuringPeriodFairValueDisclosure, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value3.95-1.2071.9412.5417.612
Percentage of DefinedBenefitPlanFundedStatusOfPlan100.0100.0100.0100.0100.0

us-gaap:ChangeDuringPeriodFairValueDisclosure, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-132.523126124110121
Percentage of DefinedBenefitPlanFundedStatusOfPlan-3355.0-10485.86404.74340.31594.8

us-gaap:DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-31
Value5.0
Percentage of DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear100.0

us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value757675592634643
Percentage of DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value619545466522524
Percentage of DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value757675592634646
Percentage of DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanPlanAssetsTargetAllocationPercentage

us-gaap:DefinedBenefitPlanPlanAssetsTargetAllocationPercentage


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value5.00.050.050.05
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanWeightedAverageAssetAllocations us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:RetirementPlanSponsorLocation, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanWeightedAverageAssetAllocations

nwe:DefinedBenefitPlanEquitySecuritiesGlobal, stpr:MT, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-31
Value61.161.2
Percentage of DefinedBenefitPlanWeightedAverageAssetAllocations100.0100.0

nwe:DefinedBenefitPlanEquitySecuritiesGlobal, stpr:MT, us-gaap:PensionPlansDefinedBenefit