MKL


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

Table of contents



us-gaap:CommonStockValue
us-gaap:ConsolidatedEntities
us-gaap:StatementEquityComponents
us-gaap:SharesOutstanding
us-gaap:StatementEquityComponents
us-gaap:SharesIssued

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareDiluted

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest

us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest
us-gaap:StatementEquityComponents

us-gaap:CostsAndExpenses

us-gaap:DeferredPolicyAcquisitionCostAmortizationExpense
us-gaap:StatementBusinessSegments

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeTaxExpenseBenefit

us-gaap:InterestExpense

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLossAttributableToNoncontrollingInterest

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic

us-gaap:NetInvestmentIncome
us-gaap:StatementBusinessSegments

us-gaap:OperatingIncomeLoss

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTax
us-gaap:StatementEquityComponents
us-gaap:StatementBusinessSegments
us-gaap:PolicyholderBenefitsAndClaimsIncurredNet

us-gaap:PreferredStockDividendsIncomeStatementImpact

us-gaap:PremiumsEarnedNet

us-gaap:ProfitLoss
us-gaap:StatementEquityComponents

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax
us-gaap:ConcentrationRiskByBenchmark
us-gaap:ConcentrationRiskByBenchmark, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService
us-gaap:ProductOrService, us-gaap:ConcentrationRiskByBenchmark
us-gaap:ProductOrService, us-gaap:ConcentrationRiskByBenchmark, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments

us-gaap:Revenues

us-gaap:Assets
us-gaap:ConsolidatedEntities
us-gaap:ConsolidatedEntities, us-gaap:InvestmentsByConsolidatedAndNonconsolidatedEntities
us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments, us-gaap:StatementOperatingActivitiesSegment
us-gaap:StatementOperatingActivitiesSegment

us-gaap:Liabilities
us-gaap:ConsolidatedEntities

us-gaap:LiabilitiesAndStockholdersEquity
us-gaap:ConsolidatedEntities

us-gaap:StockholdersEquity
us-gaap:ConsolidatedEntities

us-gaap:CashAndCashEquivalentsAtCarryingValue
us-gaap:ConsolidatedEntities

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
us-gaap:ConsolidatedEntities

us-gaap:InventoryNet

us-gaap:AmortizationOfIntangibleAssets
us-gaap:StatementBusinessSegments

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:Goodwill
us-gaap:StatementBusinessSegments

us-gaap:IndefiniteLivedIntangibleAssetsExcludingGoodwill

us-gaap:IntangibleAssetsNetExcludingGoodwill
us-gaap:StatementBusinessSegments
us-gaap:BalanceSheetLocation
us-gaap:DeferredTaxAssetsLiabilitiesNet
us-gaap:BalanceSheetLocation
us-gaap:OperatingLeaseRightOfUseAsset

us-gaap:EquitySecuritiesFvNi
us-gaap:ConsolidatedEntities
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency, us-gaap:FinancialInstrument
us-gaap:FairValueByMeasurementFrequency
us-gaap:FairValueByMeasurementFrequency, us-gaap:FinancialInstrument

us-gaap:OtherAssets
us-gaap:ConsolidatedEntities

us-gaap:LongTermDebt
us-gaap:ConsolidatedEntities

us-gaap:DebtAndCapitalLeaseObligations
dei:LegalEntity, us-gaap:LongtermDebtType
us-gaap:LongtermDebtType

us-gaap:MinorityInterest

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive
us-gaap:BalanceSheetLocation
us-gaap:OperatingLeaseLiability

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

us-gaap:StockholdersEquity
us-gaap:ConsolidatedEntities

us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest
us-gaap:StatementEquityComponents

us-gaap:CommonStockValue
us-gaap:ConsolidatedEntities

us-gaap:RetainedEarningsAccumulatedDeficit
us-gaap:ConsolidatedEntities

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax
us-gaap:ConsolidatedEntities
us-gaap:StatementEquityComponents

us-gaap:MinorityInterest
us-gaap:StatementClassOfStock, us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodValueNewIssues

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetIncomeLoss

us-gaap:ProfitLoss
us-gaap:StatementEquityComponents

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:PaymentsToAcquireInvestments

us-gaap:NetCashProvidedByUsedInFinancingActivities

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

us-gaap:DeferredTaxLiabilities
us-gaap:BalanceSheetLocation
us-gaap:ConsolidatedEntities

us-gaap:DeferredTaxAssetsNet

us-gaap:DeferredTaxAssetsValuationAllowance

mkl:AdjustedNetIncomeLoss

mkl:AdjustmenttoLifeandAnnuityBenefits

mkl:CostMethodInvestmentsRealizedGain
us-gaap:LiabilityForCatastropheClaimsByCatastrophicEvent
mkl:IncurredClaimsPropertyCasualtyAndLiabilityNetOfAssumedReinstatementPremium

mkl:NetInvestmentGainsLosses
us-gaap:StatementBusinessSegments

mkl:OtherComprehensiveIncomeSecuritiesAvailableforSaleLifeandAnnuityBenefitsReservesAdjustmentbeforeTax

mkl:OtherInterestAndDividendIncomeExpense
us-gaap:FinancialInstrument
mkl:OtherInvestmentsAvailableForSaleRealizedGainLoss

mkl:PaymentOfContingentConsideration
us-gaap:AwardType
mkl:PotentialIncrementalCommonSharesAttributabletoSharebasedPaymentArrangements

mkl:PremiumsPercentageCededToGross

mkl:ProductsRevenues
us-gaap:StatementBusinessSegments

mkl:Productsexpenses
us-gaap:StatementBusinessSegments

mkl:ReclassificationAdjustmentsForNetGainsLossesIncludedInNetIncomeLoss

mkl:Servicesandotherexpenses
us-gaap:StatementBusinessSegments

mkl:Servicesandotherrevenues
us-gaap:RelatedPartyTransactionsByRelatedParty, us-gaap:StatementOperatingActivitiesSegment
us-gaap:StatementBusinessSegments
us-gaap:StatementOperatingActivitiesSegment
us-gaap:FinancialInstrument
mkl:ShorttermInvestmentsAvailableforsaleRealizedGain
us-gaap:FinancialInstrument
mkl:ShorttermInvestmentsAvailableforsaleRealizedLoss

mkl:SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE
us-gaap:StatementBusinessSegments

mkl:TotalProfitLoss
us-gaap:StatementBusinessSegments

mkl:UnderwritingAcquisitionAndInsuranceExpenses

mkl:UnderwritingProfitLoss
us-gaap:StatementBusinessSegments
us-gaap:StatementEquityComponents
us-gaap:AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition

us-gaap:AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities

us-gaap:AssumedPremiumsEarned
us-gaap:ProductOrService

us-gaap:AssumedPremiumsWritten
us-gaap:ProductOrService

us-gaap:CededPremiumsEarned
us-gaap:ProductOrService

us-gaap:CededPremiumsWritten
us-gaap:ProductOrService
us-gaap:RelatedPartyTransactionsByRelatedParty

us-gaap:CombinedRatio
us-gaap:StatementBusinessSegments
us-gaap:FinancialInstrument
us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded
us-gaap:FinancialInstrument
us-gaap:DebtSecuritiesAvailableForSaleRealizedGain

us-gaap:DebtSecuritiesAvailableForSaleRealizedGainLoss
us-gaap:FinancialInstrument
us-gaap:DebtSecuritiesAvailableForSaleRealizedLoss
us-gaap:StatementBusinessSegments
us-gaap:Depreciation

us-gaap:DirectPremiumsEarned
us-gaap:ProductOrService

us-gaap:DirectPremiumsWritten
us-gaap:ProductOrService
us-gaap:StatementEquityComponents
us-gaap:DividendsPreferredStock

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:EquitySecuritiesFvNiGainLoss

us-gaap:EquitySecuritiesFvNiRealizedGainLoss

us-gaap:EquitySecuritiesFvNiUnrealizedGainLoss

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales

us-gaap:ForeignCurrencyTransactionGainLossRealized

us-gaap:IncomeLossFromEquityMethodInvestments
us-gaap:AwardType
us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements

us-gaap:IncurredClaimsPropertyCasualtyAndLiability

us-gaap:InterestIncomeDepositsWithFinancialInstitutions

us-gaap:InterestIncomeSecuritiesTaxExempt
us-gaap:InvestmentType
us-gaap:InterestIncomeSecuritiesTaxable

us-gaap:InvestmentIncomeDividend

us-gaap:InvestmentIncomeInterestAndDividend

us-gaap:InvestmentIncomeInvestmentExpense

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1

us-gaap:MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments
us-gaap:StatementEquityComponents
us-gaap:MinorityInterestDecreaseFromRedemptions

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax
us-gaap:FinancialInstrument

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax

us-gaap:OtherUnderwritingExpense
us-gaap:StatementBusinessSegments

us-gaap:PaymentsForLossesAndLossAdjustmentExpense

us-gaap:PaymentsForProceedsFromOtherInvestingActivities

us-gaap:PaymentsForProceedsFromShortTermInvestments

us-gaap:PaymentsOfDividendsMinorityInterest

us-gaap:PaymentsToAcquireAdditionalInterestInSubsidiaries

us-gaap:PaymentsToAcquireBusinessesNetOfCashAcquired

us-gaap:PaymentsToAcquireEquityMethodInvestments
us-gaap:StatementBusinessSegments
us-gaap:PolicyholderBenefitsAndClaimsIncurredGross

us-gaap:PremiumsPercentageAssumedToNet

us-gaap:PremiumsWrittenGross
us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:StatementBusinessSegments

us-gaap:PremiumsWrittenNet
us-gaap:ProductOrService
us-gaap:StatementBusinessSegments
us-gaap:DebtInstrument
us-gaap:ProceedsFromDebtNetOfIssuanceCosts

us-gaap:ProceedsFromIssuanceOfDebt

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities

us-gaap:ProceedsFromPaymentsForOtherFinancingActivities

us-gaap:ProceedsFromSaleMaturityAndCollectionsOfInvestments

us-gaap:ProceedsFromSaleOfEquityMethodInvestments

us-gaap:ProceedsFromSaleOfProductiveAssets
us-gaap:LiabilityForCatastropheClaimsByCatastrophicEvent
us-gaap:ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded
us-gaap:StatementBusinessSegments

us-gaap:RepaymentsOfDebtAndCapitalLeaseObligations
us-gaap:BusinessAcquisition, us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodSharesAcquisitions
us-gaap:StatementClassOfStock, us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodSharesNewIssues
us-gaap:StatementEquityComponents
us-gaap:StockRepurchasedDuringPeriodShares
us-gaap:StatementEquityComponents
us-gaap:StockRepurchasedDuringPeriodValue
us-gaap:StatementEquityComponents
us-gaap:StockholdersEquityOther

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
us-gaap:LiabilityForCatastropheClaimsByCatastrophicEvent
us-gaap:StatementBusinessSegments

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
us-gaap:ProductOrService
us-gaap:StatementBusinessSegments
us-gaap:StatementEquityComponents
us-gaap:TemporaryEquityAccretionToRedemptionValue

us-gaap:TemporaryEquityAccretionToRedemptionValueAdjustment

dei:EntityCommonStockSharesOutstanding

mkl:AdjustedLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet

mkl:CumulativeAdjustmentLifeandAnnuityBenefits

mkl:DeferredTaxAssetsTaxDeferredExpenseLeaseLiabilities

mkl:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLifeAndAnnuityBenefits

mkl:DeferredTaxLiabilitiesRightofuseLeaseAssets

mkl:FundsAtLloyds

mkl:FundsatLloydsHoldingCompany

mkl:GrossDeferredTaxAssetsEstimatedAmountRealizedThroughReversalofDeferredTaxLiabilities

mkl:IBNRReservesPercentageOfTotalUnpaidLossesAndLossAdjustmentExpenses
us-gaap:ConsolidatedEntities
mkl:InvestmentInConsolidatedSubsidiaries
us-gaap:SubsequentEventType
mkl:InvestmentInLodgepineFundLimited
us-gaap:ConsolidatedEntities
mkl:Investmentinunconsolidatedvariableinterestentitycarryingamount
us-gaap:InvestmentsByConsolidatedAndNonconsolidatedEntities

mkl:InvestmentsAvailableforSale

mkl:InvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax

mkl:InvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax

mkl:InvestmentsAvailableforSaleAmortizedCostBasis
us-gaap:SubsequentEventType
mkl:InvestorCapitalInLodgepineFundLimited

mkl:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseEffectOfAdoptionOfASC326

mkl:LifeAndAnnuityBenefitsReserveSingleContractConcentration

mkl:LongTermDebtMaturitiesTotalFutureRepaymentsOfPrincipal
dei:LegalEntity
mkl:NetAssetsofUnconsolidatedVariableInterestEntitiesUnderManagement
us-gaap:CededCreditRisk, us-gaap:StatementBusinessSegments
mkl:PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances

mkl:RestrictedInvestmentsAvailableForSale
us-gaap:PlanName
mkl:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance

mkl:ShorttermInvestmentsAvailableforSale

mkl:ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax

mkl:ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax

mkl:ShorttermInvestmentsAvailableforSaleAmortizedCostBasis

mkl:ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12Months

mkl:ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss

mkl:ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionAccumulatedLoss

mkl:ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionTotal

mkl:TradeAccountsReceivableGross
us-gaap:ConcentrationRiskByBenchmark
mkl:TradeAndOtherReceivables

mkl:TraditionalLifeInterestRateAverage

mkl:UnpaidLossesAndLossAdjustmentExpensesUnamortizedFairValueAdjustment

us-gaap:AccountsReceivableGross

us-gaap:AccruedIncomeTaxes

us-gaap:AllowanceForDoubtfulAccountsReceivable

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
us-gaap:FinancialInstrument

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
us-gaap:FinancialInstrument

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis
us-gaap:ConsolidatedEntities
us-gaap:FinancialInstrument

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
us-gaap:FinancialInstrument
us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
us-gaap:FinancialInstrument
us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue

us-gaap:AvailableForSaleSecuritiesDebtSecurities
us-gaap:DebtInstrument
us-gaap:DebtInstrumentFaceAmount

us-gaap:DebtInstrumentFairValue
us-gaap:DebtInstrument
us-gaap:DebtInstrument, us-gaap:LongtermDebtType
us-gaap:DebtInstrumentUnamortizedDiscount

us-gaap:DebtInstrumentUnamortizedDiscountPremiumNet

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPosition
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions

us-gaap:DeferredFinanceCostsNet

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredPolicyAcquisitionCosts
us-gaap:StatementBusinessSegments

us-gaap:DeferredTaxAssetsGross

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards

us-gaap:DeferredTaxAssetsOther

us-gaap:DeferredTaxAssetsTaxCreditCarryforwards

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther

us-gaap:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLossReserves

us-gaap:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsUnearnedPremiumsReserve

us-gaap:DeferredTaxLiabilitiesDeferredExpenseDeferredPolicyAcquisitionCost

us-gaap:DeferredTaxLiabilitiesGoodwillAndIntangibleAssets

us-gaap:DeferredTaxLiabilitiesOther

us-gaap:DeferredTaxLiabilitiesOtherComprehensiveIncome

us-gaap:DefinedBenefitPlanBenefitObligation

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets
us-gaap:ConsolidatedEntities
us-gaap:DueFromAffiliates
us-gaap:ConsolidatedEntities
us-gaap:DueToAffiliateCurrentAndNoncurrent

us-gaap:EquitySecuritiesFvNiCost
us-gaap:ConsolidatedEntities

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue

us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization
mkl:IndefiniteLivedAndFiniteLivedIntangibleAssetsByMajorClass

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseYearFive

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseYearFour

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseYearThree

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo

us-gaap:GoodwillImpairedAccumulatedImpairmentLoss
us-gaap:StatementBusinessSegments

us-gaap:IncomeTaxReceivable
us-gaap:ConsolidatedEntities

us-gaap:IntangibleAssetsGrossExcludingGoodwill
mkl:IndefiniteLivedAndFiniteLivedIntangibleAssetsByMajorClass

us-gaap:Investments
us-gaap:ConsolidatedEntities
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
us-gaap:FairValueByMeasurementFrequency

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths
us-gaap:NoncatastrophicEvent
us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsGross
us-gaap:NoncatastrophicEvent
us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsNet

us-gaap:LiabilityForClaimsAndClaimsAdjustmentExpense
us-gaap:StatementBusinessSegments

us-gaap:LiabilityForFuturePolicyBenefits

us-gaap:LiabilityForFuturePolicyBenefitsDisabilityAndAccidentBenefits

us-gaap:LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContracts

us-gaap:LiabilityForFuturePolicyBenefitsLife

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseOpeningBalanceAdjustments
us-gaap:CreditFacility
us-gaap:LineOfCreditFacilityMaximumBorrowingCapacity

us-gaap:LongTermDebtFairValue

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:LossContingencyEstimateOfPossibleLoss

us-gaap:OperatingLeaseWeightedAverageDiscountRatePercent

us-gaap:OperatingLossCarryforwards
dei:LegalEntity
dei:LegalEntity, us-gaap:TaxPeriod

us-gaap:OtherLiabilities
us-gaap:ConsolidatedEntities

us-gaap:OtherReceivables

us-gaap:OtherShortTermInvestments
us-gaap:ConsolidatedEntities
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
us-gaap:FairValueByMeasurementFrequency

us-gaap:PreferredStockValue
us-gaap:ConsolidatedEntities

us-gaap:PremiumsAndOtherReceivablesNet
us-gaap:ConsolidatedEntities

us-gaap:PremiumsReceivableGross

us-gaap:PrepaidReinsurancePremiums

us-gaap:RedeemableNoncontrollingInterestEquityCommonCarryingAmount
us-gaap:StatementEquityComponents

us-gaap:ReinsurancePayable

us-gaap:ReinsuranceReceivablesIncurredButNotReportedClaims

us-gaap:ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments
us-gaap:StatementBusinessSegments

us-gaap:ReinsuranceRecoverablesAllowance

us-gaap:ReinsuranceRecoverablesGross

us-gaap:ReinsuranceRecoverablesOnPaidAndUnpaidLosses
us-gaap:RelatedPartyTransactionsByRelatedParty

us-gaap:RestrictedCashAndCashEquivalents
us-gaap:ConsolidatedEntities

us-gaap:RestrictedCashAndInvestments
us-gaap:InvestmentType
us-gaap:DebtInstrument, us-gaap:LongtermDebtType
us-gaap:SeniorNotes
us-gaap:ShortdurationInsuranceContractsAccidentYear, us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsCumulativePaidClaimsAndAllocatedClaimAdjustmentExpenseNet
us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearEight
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearFive
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearFour
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearNine
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearOne
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearSeven
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearSix
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearThree
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsHistoricalClaimsDurationYearTwo
us-gaap:ShortdurationInsuranceContractsAccidentYear, us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsLiabilityNet
us-gaap:ShortdurationInsuranceContractsAccidentYear, us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsIncurredClaimsAndAllocatedClaimAdjustmentExpenseNet
us-gaap:StatementBusinessSegments

us-gaap:ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet
us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNetNotSeparatelyPresented

us-gaap:ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndClaimAdjustmentExpenseAggregateReconcilingItems

us-gaap:ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAccumulatedUnallocatedClaimAdjustmentExpense
us-gaap:ProductOrService, us-gaap:ShortdurationInsuranceContractsAccidentYear, us-gaap:StatementBusinessSegments
us-gaap:ShortdurationInsuranceContractsNumberOfReportedClaims
us-gaap:ShortdurationInsuranceContractsAccidentYear, us-gaap:StatementBusinessSegments
us-gaap:StatutoryAccountingPracticesByJurisdiction
us-gaap:StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPayments
us-gaap:StatutoryAccountingPracticesByJurisdiction
us-gaap:StatutoryAccountingPracticesStatutoryCapitalAndSurplusBalance

us-gaap:UnearnedPremiums
us-gaap:StatementBusinessSegments

Plots across concepts


IncomeStatement
Other Comprehensive Income Loss Net Of Tax
Expenses
Interest Expense
Balance Sheet
Intangible Assets Net Excluding Goodwill
Assets
Inventory Net
Current Assets
Inventory Net
NonCurrent Assets
Property Plant And Equipment Net
Liabilities
Other Liabilities
Noncurrent Liabilities
Minority Interest
Stockholders Equity
Accumulated Other Comprehensive Income Loss Net Of Tax
Per Share
Earnings Per Share Diluted
CashFlow
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInOperatingActivities
Foreign Currency Transaction Gain Loss Realized
NetCashProvidedByUsedInInvestingActivities
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInFinancingActivities
Proceeds From Payments For Other Financing Activities
Shares
Weighted Average Number Of Shares Outstanding Basic
LesseeOperatingLeaseLiabilityPaymentsDue
Lessee Operating Lease Liability Payments Due Year Four

Tables

  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:CommonStockValue █████████████████████████████████▁▁▁▁▁▁▁▁▁▁3451.9683447.6143428.343425.2473421.8453419.5283404.9193402.9343400.9643395.943392.9933392.3223387.1213383.6683381.8343379.1563376.233376.0373368.6663365.753360.833354.6173342.3573335.2083327.4893320.3233308.3953302.8683297.4623302.3013288.8633277.4883269.355911.33908.98905.841904.047902.441891.507890.393888.616886.574884.457NANANA872.876NANANA
 us-gaap:SharesOutstanding us-gaap:StatementEquityComponents us-gaap:CommonStock▁▁█13.76513.76513.783NA13.77513.77513.794NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:SharesIssued us-gaap:StatementEquityComponents us-gaap:CommonStock▁▂▂▂▂▂▃▃▄▄▅▅▅▅▆▅▆▇▇██▇▇▇▇13.73413.76513.78313.77813.77613.77513.79413.81513.82613.85613.88813.88413.88613.89513.90413.89413.91813.9513.95513.99113.99113.96813.95913.9513.95NA13.962NANANA13.986NANANANANANANA9.621NANANA9.718NANANA9.819NANANA
 us-gaap:SharesIssued us-gaap:StatementEquityComponents us-gaap:PreferredStockNANANA0.60.60.00.0NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding ▁█13.81713.841NA13.82713.82113.815NA13.86413.87813.911NA13.94313.9513.959NA13.9914.01914.046NA14.08514.08814.074NA14.06214.05214.063NA14.05714.05514.058NA14.05612.5149.666NA9.6599.6769.671NA9.7189.7579.757NA9.769.807NANANANANA
us-gaap:WeightedAverageNumberOfSharesOutstandingBasic ▁█13.79313.819NA13.80913.80813.815NA13.84913.86613.895NA13.91713.92513.932NA13.94713.97713.998NA14.03314.01213.994NA13.98313.97513.972NA13.98113.98413.995NA14.00112.4649.636NA9.6329.6519.642NA9.689.7179.717NA9.7489.794NANANANANA
us-gaap:EarningsPerShareBasic █▇█▇█▁▇▆▇▇▃▆▆▅▇▄▆▅▆▅▅▆▆▆▆▆▆▅▅▅▆▅▅▆▅▅▆▅▅▅▅▅▆▆▅▅▆▅▅▅57.1242.0959.4431.0765.81-100.636.3413.9736.142.81-53.8828.5620.01-4.2530.48-18.8210.343.919.145.625.4411.2114.237.436.7613.578.15.332.676.286.984.692.249.536.255.338.445.945.215.53.120.8514.426.492.134.349.516.023.341.67
us-gaap:EarningsPerShareDiluted █▇█▇█▁▇▆▇▇▃▆▆▅▇▄▆▅▆▅▅▆▆▆▆▆▆▅▅▅▆▅▅▆▅▅▆▅▅▅▅▅▆▆▅▅▆▅▅▅57.0242.0259.3331.0365.75-100.636.2613.9536.0742.76-53.8828.519.97-4.2530.39-18.8210.313.99.115.65.4111.1514.147.396.7213.498.055.32.666.256.954.672.249.56.235.328.425.925.195.483.110.8514.376.482.124.339.496.023.341.67
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:ComprehensiveIncomeNetOfTax ▇▆█▆█▁▆▆▇▇▃▆▅▄▇▅▆▆▅▅▅▆▅▅▄▆▆▅▆▆▅▅▄▆▅▅▅▅▅▅▅▅▅▆▅▅▅▆▅▅849.654358.997931.961520.0891092.393-1352.809488.244250.069623.33732.245-680.373315.106164.336-174.839629.247-19.869342.357223.239-29.0589.161209.942396.994134.984-51.143-132.925281.807418.57136.502250.588230.273206.45144.409-149.054257.68476.987147.45473.416205.945183.696-52.62696.04524.738104.599225.328-33.903134.53981.263339.859171.869-1.996
us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest █▅▂▃▇▄▂▁▇▃▁▂▃▁▄▁▃▃▂▂▃▄▂▃▃▄▂▃▃▂▂▃▂▂▃▃▃▂▃▃▃▃▂▂▂▂11.2416.0040.1241.33510.0334.2630.437-1.7429.1891.091-1.831-0.4691.333-1.2464.471-1.891.7811.173-0.035-0.3761.8873.2840.3551.91.0582.9840.621.021.078-0.2080.2031.3680.920.3611.3382.0261.0340.462.0951.4051.3351.5890.306-0.0930.0410.868NANANANA
us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest ▇▆█▆█▁▆▆▇▇▃▆▅▄▇▅▆▅▅▅▅▆▅▅▄▆▆▅▆▆▅▅▄▆▅▅▅▅▅▅▅▅▅▅▅▅860.895365.001932.085521.4241102.426-1348.546488.681248.327632.519733.336-682.204314.637165.669-176.085633.718-21.759344.138224.412-29.08588.785211.829400.278135.339-49.243-131.867284.791419.19137.522251.666230.065206.653145.777-148.134258.04578.325149.4874.45206.405185.791-51.22197.3826.327104.905225.235-33.862135.407NANANANA
us-gaap:CostsAndExpenses █▇▇▇▆▇▆▆▆▅▆▅▅▅▅▆▄▄▄▄▄▃▃▄▄▃▃▄▄▃▃▃▃▂▂▂▁▂▁▁▁▁▁▁▁▁2421.5012154.8372211.0882219.3431889.7552140.9961827.7071770.811772.671677.6581974.9891680.3441675.7321470.4611483.1751834.2821240.1511284.3051216.2071278.6491182.2491131.0051141.2061160.0191175.0311033.3211140.8921166.1571174.8231093.9751142.3711068.912957.552678.501718.364688.598551.912636.426588.492585.273588.556591.181481.403451.457467.166456.193NANANANA
us-gaap:DeferredPolicyAcquisitionCostAmortizationExpense █▇█▆▆▆▆▅▅▅▅▄▄▄▄▃▂▂▂▂▁▁332.809322.587335.062296.093302.195295.811294.969280.635263.065261.827276.3241.848249.25241.905245.508230.823213.474204.548202.013201.873188.366189.969NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest █▇█▇█▁▇▆▇▇▃▆▆▅▆▄▆▅▆▅▅▆▆▆▅▆▆▅▅▅▅▅▅▅▅▅▅▅▅▅▅▅1020.446728.0521013.064584.0711175.373-1772.059641.01261.928650.194732.676-930.456519.027360.73742.837143.654-359.948209.54594.044180.212119.481115.891214.336249.617152.681100.286239.521166.557103.48154.359115.981106.16492.13445.656117.78965.89752.485119.12674.54274.87267.15936.71411.451NANANANANANANANA
us-gaap:IncomeTaxExpenseBenefit █▇▇▇█▁▇▆▇▇▃▆▆▆▂▄▆▅▆▆▆▆▆▆▅▆▆▆▅▆▅▆▅▆▅▅▆▅▅▅▅▅▅▆▅▅217.112148.371165.635130.028243.702-370.683129.49757.975143.711155.163-177.082109.99981.15108.431-295.672-98.91358.11823.00447.50936.0635.21850.6951.34448.2717.83345.51548.33526.65713.21828.487.22525.16716.9828.5267.8040.81128.35816.82922.56512.495.0651.59-28.71828.1428.99719.361NANANANA
us-gaap:InterestExpense █▇▇▇█▇▇█▇▆▆▆▅▆▅▄▄▅▄▅▅▄▄▄▄▄▃▄▄▄▄▄▄▂▂▃▂▂▂▂▂▁▁▁▁▁46.56842.38944.38142.74445.42745.0342.66547.46541.26740.2939.4937.96136.70240.05935.43831.81431.79733.40232.20633.15233.69730.84129.63730.06429.28829.31228.30629.64829.78929.69931.2530.61928.56123.57423.69424.69222.20922.16721.73623.65621.89818.96218.77218.59818.33417.959NANANANA
us-gaap:NetIncomeLoss █▇█▇█▁▇▆▇▇▃▆▆▅▇▄▆▅▆▅▅▆▆▆▆▆▆▅▅▅▆▅▅▅▅▅▅▅▅▅▅▅▆▅▅▅▆▅▅▅792.11573.694847.299452.726921.768-1405.763511.104205.637497.298576.427-751.543409.438278.231-64.306434.881-259.141149.6669.869132.72683.79678.797160.37197.892102.51991.369190.992117.59575.80340.06887.71698.76465.59927.75688.90256.79249.65389.68757.25350.17653.26430.3148.272140.14363.2520.83142.56993.35659.12632.79816.358
us-gaap:NetIncomeLossAttributableToNoncontrollingInterest █▅▂▃▇▄▂▁▇▃▁▂▃▁▄▁▃▃▂▂▃▄▂▃▃▄▂▃▃▂▂▃▃▂▃▃▃▂▃▃▃▃▂▂▂▂11.2245.9870.131.3179.9034.3870.409-1.6849.1851.086-1.831-0.411.356-1.2884.445-1.8941.7671.171-0.023-0.3751.8763.2760.3811.8911.0843.0140.6271.0211.073-0.2150.1751.3680.920.3611.3012.0211.0810.462.1311.4051.3351.5890.306-0.0930.0860.637NANANANA
us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic █▇█▇█▁▇▆▇▇▃▆▆▅774.11573.694828.899452.726921.768-1405.763511.104205.637497.298576.427-751.543409.438278.231-64.306NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:NetInvestmentIncome ▆▆▆▅▅▄█████▇▇▇▆▇▆▆▅▅▅▅▄▄▅▅▅▅▅▄▅▄▃▁▃▁▁▃▂▁▁▂▂▂▁▂96.26196.5797.58890.38495.61588.243112.493113.382111.831114.182114.505106.307105.387108.016101.553104.48999.299100.36893.79393.14794.99691.29482.69287.0690.58692.87593.2591.09692.16986.71588.58586.19277.97964.61774.27364.43863.60279.79467.12562.19964.25370.09971.09268.65264.38468.402NANANANA
us-gaap:OperatingIncomeLoss █▇█▇█▁▇▆▇▇▃▆▆▅▆▄▆▅▆▅▆▆▆▆▅▆▆▅▅▅▅▅▅▅▅▅▅▅▅▅▅▅▅▅▅▅1079.271745.3571144.562692.3921242.26-1805.33753.822262.248666.446794.83-932.137555.605311.281105.01179.092-328.134241.342127.446212.418152.633193.688245.177279.254182.745129.574268.833194.863133.12984.148145.68137.414122.75374.217141.36389.59177.177141.33596.70996.60890.81558.61230.413130.503109.89748.24880.526NANANANA
us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax ▄▄█▅▄▃▅▃▄▄▄▂▃▄▃▆▄▄▃▃▃▅▃▃▅▂▃▁▅▄▄▄▃▄▄▄▄▄▄▃▄4.915-0.80838.235.756-1.405-12.7346.36-4.606-3.7492.3773.473-14.471-10.454.953-9.32116.2631.9621.545-5.563-8.349-8.12110.329-6.995-10.85410.385-21.814-12.602-27.2236.6710.913-0.2121.709-10.459-1.181-1.3933.266-3.1622.8231.347-8.1330.156NANANANANANANANANA
us-gaap:OtherComprehensiveIncomeLossNetOfTax ▅▁▅▅▆▅▄▅▆▆▅▃▂▃▇▇▇▆▂▄▆▇▃▂▁▅█▃▇▆▅▅▂▆▄▅▄▆▆▃▅57.561-214.6884.65667.381170.75552.83-22.83244.374126.036155.82371.17-94.391-113.918-110.491194.392239.276192.711153.372-161.7885.364131.156236.632-62.934-153.653-224.3290.785300.969-39.302210.525142.564107.71478.81-176.81168.78220.23297.806-16.318148.692133.484-105.8965.731NANANANANANANANANA
 us-gaap:PolicyholderBenefitsAndClaimsIncurredNet us-gaap:StatementBusinessSegments mkl:UnderwritingOperations▃▅▃▄▂█▃▂▁▁815.464881.952814.098863.092713.7621076.377772.763752.187677.887687.731NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:PreferredStockDividendsIncomeStatementImpact 18.0NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:PremiumsEarnedNet ███▇▇▇▇▆▆▆▆▆▅▅▅▅▅▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▃▂▂▂▂▂▂▂▁▁▁▁▁▁1568.0371497.6951526.8941394.4281360.1741330.7091346.3231300.0321199.4611203.9771227.5321185.3231148.1841151.0211131.941099.8621033.574982.602983.081974.244950.859957.686958.65963.675957.557943.65971.931954.007965.599949.375962.487919.723784.819564.587573.939530.537513.056529.596516.825509.203490.201463.111466.743435.355416.688412.135NANANANA
us-gaap:ProfitLoss █▇█▇█▁▇▆▇▇▃▆▆▅▇▄▆▅▆▅▅▆▆▆▅▆▆▅▅▅▆▅▅▅▅▅▅▅▅▅▅▅▆▅▅▅▅▅▅▅803.334579.681847.429454.043931.671-1401.376511.513203.953506.483577.513-753.374409.028279.587-65.594439.326-261.035151.42771.04132.70383.42180.673163.646198.273104.4192.453194.006118.22276.82441.14187.50198.93966.96728.67689.26358.09351.67490.76857.71352.30754.66931.6499.861140.44963.15720.91743.20693.74259.21133.0316.436
us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax ▃▂█▂▂▂▆▂▂▁▃▁▂▁▄▁▁▄▄▄▃▃▄▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▁▁▂▁▁▁1161.721779.0583355.65887.621764.983598.1552581.529587.5702.171542.1381042.852518.244628.193439.4321662.267341.804330.9931411.7511428.6251431.2821375.9371376.1821420.461342.7641304.6051302.1541335.7551299.2861258.9711239.6551279.7851191.6651031.769819.864807.955765.775693.247733.135685.1676.088647.168621.594611.906561.354515.414536.719551.368500.349522.432495.177
us-gaap:Revenues █▇█▇▇▁▆▅▆▆▃▅▅▄▄▄▄▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▁▁▁▁▁▁▁3500.7722900.1943355.652911.7353132.015335.6662581.5292033.0582439.1162472.4881042.8522235.9491987.0131575.4711662.2671506.1481481.4931411.7511428.6251431.2821375.9371376.1821420.461342.7641304.6051302.1541335.7551299.2861258.9711239.6551279.7851191.6651031.769819.864807.955765.775693.247733.135685.1676.088647.168621.594611.906561.354515.414536.719551.368500.349522.432495.177
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:Assets █▇▇▇▇▆▆▆▆▆▆▆▆▅▅▅▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▁▁▁▁▁▁▁▁▁▁45641.51343043.02941710.05440170.01939067.62636048.78737473.81537036.19636421.58434736.72633306.26333958.30533247.03132866.47132805.01628519.41127203.34126400.67925875.29926403.64526335.62825685.2324941.27125181.57325366.1425253.38925200.35725076.43525166.27424452.99223955.51123808.57723499.9813117.99112556.58812383.41711965.23311859.28411532.10311371.75411464.53711041.53610825.589NANANA10241.896NANANA
us-gaap:Liabilities █▇▇▇▇▆▆▆▆▆▆▆▆▆▆▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▁▁▁▁▁▁▁▁▁▁31415.06329623.21128649.73128021.24127442.72526161.0426217.83726235.72425857.20624770.37824031.89924019.41223613.61923389.60123137.16619459.25718164.13417661.49417334.2117798.7117823.85417370.99917037.70417427.48217564.37217320.88317537.30717835.81717959.13617491.89117205.31817274.74917099.2738887.0698581.3468489.768222.3298183.3168069.7578093.6628116.4587778.4677637.897NANANA7450.182NANANA
us-gaap:LiabilitiesAndStockholdersEquity █▇▇▇▇▆▆▆▆▆▆▆▆▅▅▅▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▁▁▁▁▁▁▁▁▁▁45641.51343043.02941710.05440170.01939067.62636048.78737473.81537036.19636421.58434736.72633306.26333958.30533247.03132866.47132805.01628519.41127203.34126400.67925875.29926403.64526335.62825685.2324941.27125181.57325366.1425253.38925200.35725076.43525166.27424452.99223955.51123808.57723499.9813117.99112556.58812383.41711965.23311859.28411532.10311371.75411464.53711041.53610825.589NANANA10241.896NANANA
us-gaap:StockholdersEquity █▇▇▇▆▅▆▆▆▅▅▅▅▅▅▅▅▅▄▄▄▄▄▄▄▄▄▄▄▃▃▃▃▂▁▁▁▁▁▁▁▁▁13974.97113163.94412799.78911893.94711394.5539720.72811070.86710623.45410396.3659795.9829080.6539783.9929480.869324.2119504.1488908.8858954.4098653.28460.9278527.2838438.3698239.1167834.157695.237741.877869.6587594.8187175.1937143.0576900.1326673.5776457.4236320.9044151.5093888.6573806.1163655.1663602.0933387.5133212.183282.9733198.3783171.523NANANA2774.36NANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:CashAndCashEquivalentsAtCarryingValue ▆▆▇██▆▅▄▄▄▃▄▃▃▄▃▄▃▃▄▃▄▄▄▃▃▃▃▃▄▃▃▃▁▂▁▁▁▁▁▁▁▁▁▁▁▁3679.4333882.3794341.7364593.0254833.6893834.6643072.8072715.4552220.7932415.4212014.1682347.041945.372048.9762198.4592076.2662315.2121852.7351738.7472156.3982007.9382284.1652630.0092261.2011852.9441958.0871960.1691765.5911944.1342151.421978.5262115.3221702.622899.075973.181834.828837.208691.797775.032920.193767.954649.947745.259817.954686.675637.672850.494NANANA
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents ▅▆▇▇█▆▄▃▂▂▂▂▁▂▂▂▂▁▁▂▂4351.8184497.9045216.6495262.5535627.3724458.3243500.3533199.7692641.4662764.4052396.4322626.9422244.3962441.6522500.8462355.6652586.2432114.6912085.1642540.3692361.838NA3070.141NANANA2482.394NANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:InventoryNet NANA412.6NANANA303.1NANANA298.7NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:AmortizationOfIntangibleAssets ▇▇▇█▇▇▇▆▇▇▅▅▅▅▅▄▃▃▃▃▃▃▄▄▃▃▃▃▃▃▃▃▂▂▂▂▂▂▁▁▁▁▁▁▁▁39.72939.55339.03944.66437.75437.85835.97535.69536.340.66829.67127.79529.64128.82327.30818.65418.02616.7717.05917.0117.20417.2618.44418.91416.94914.6416.63513.50513.48813.99917.46816.84811.2929.6158.4347.9598.3158.8046.7056.0235.5556.0085.1073.9033.8563.958NANANANA
us-gaap:PropertyPlantAndEquipmentNet NANA632.0NANANA588.6NANANA551.542NANANA501.617NANANA412.402NANANA430.835NANANA421.39NANANA347.909NANANA330.229NANANA244.849NANANA159.567NANANANANANANA
us-gaap:Goodwill █████▇▇▆▆▆▆▄▄▅▄▃▂▂▂▂▂▂▂▁▁▁▁▁▁▁▁▁▁2606.1382604.822604.6242604.5752606.5072309.5762308.5482187.5852189.3672215.8182237.9751783.7841784.6671789.0351777.4641425.7891216.4031142.5351142.2481165.8921167.8611171.8091167.8441043.7131044.2321039.9111049.1151067.4571022.3151019.77967.7171008.2051041.9NA674.93NANANA607.561NANANA470.58NANANA402.519NANANA
us-gaap:IndefiniteLivedIntangibleAssetsExcludingGoodwill NANA92.4NANANA92.4NANANA92.4NANANA88.2NANANA48.2NANANA48.2NANANA58.0NANANA58.0NANANA10.1NANANA4.1NANANANANANANANANANANA
us-gaap:IntangibleAssetsNetExcludingGoodwill ▇▇███▇▇▇▇▇▇▅▅▅▅▃▂▂▂▂▂▂▂▁▂▂▂▂▂▂▁▁▁1696.7481736.1481782.7181820.4531865.6661692.2481738.4741659.1291695.5881712.6181726.1961241.1081269.521317.8281355.681990.008806.585711.999722.542733.415753.191775.254792.372652.667669.664680.357702.747727.456677.877687.982565.083560.836576.688NA374.295NANANANANANANANANANANANANANANA
 us-gaap:DeferredTaxAssetsLiabilitiesNet us-gaap:BalanceSheetLocation us-gaap:OtherAssetsNANA3.9NANANA22.3NANANA35.9NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:OperatingLeaseRightOfUseAsset us-gaap:BalanceSheetLocation us-gaap:OtherAssetsNANA528.418NANANA232.717NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:EquitySecuritiesFvNi █▆▅▂▁▁▆▅▄▃▁▃▂8205.7087528.8176994.116183.9445664.2475684.0877590.7556978.8746875.9336381.1735720.9456549.8486069.245NA0.0NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:LongTermDebt NANA3484.023NANANA3534.183NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:ConsolidatedEntities srt:ParentCompanyNANA3441.355NANANA3438.91NANANA2539.389NANANA2537.331NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:DebtAndCapitalLeaseObligations █▇▆▇▇▇▇▇▇▆▅▅▅▆▆▄▄▄▄▅▅▄▄▄▄▄▄▄▄▄▄▄▄▃▂▂▂▂▂▂▂▁▁4160.1753564.9493484.0233498.3113606.1093593.9543534.1833896.9623625.7443058.9683009.5772993.2433024.3063048.0963099.232471.4192485.6712581.6052574.5292589.352602.4322299.7562241.4272240.5172246.8752249.5542253.5942273.7952258.5222255.8242256.2272250.4792249.8191732.251492.551510.5981309.531305.5731293.521271.811268.4441027.7111015.947NANANA963.648NANANA
us-gaap:MinorityInterest ▃▃▃▃▃▂▂▂▃▃▃▁▁▁▁▁▁▁▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▁▁██▇▇▇▃23.07821.2214.89213.81115.69511.6027.54911.41616.71622.36419.649-3.838-3.446-3.061-2.567-2.041-1.893-1.956.4846.9927.2047.4476.4598.2778.0067.747.1848.1768.5978.0544.4334.9174.9454.9120.36-0.1970.12573.87574.83365.91265.10664.69116.169NANANA17.354NANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo NANA78.953NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree NANA68.871NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour NANA59.137NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive NANA48.738NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive NANA286.035NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:StockholdersEquity █▇▇▇▆▅▆▆▆▅▅▅▅▅▅▅▅▅▄▄▄▄▄▄▄▄▄▄▄▃▃▃▃▂▁▁▁▁▁▁▁▁▁13974.97113163.94412799.78911893.94711394.5539720.72811070.86710623.45410396.3659795.9829080.6539783.9929480.869324.2119504.1488908.8858954.4098653.28460.9278527.2838438.3698239.1167834.157695.237741.877869.6587594.8187175.1937143.0576900.1326673.5776457.4236320.9044151.5093888.6573806.1163655.1663602.0933387.5133212.183282.9733198.3783171.523NANANA2774.36NANANA
us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest █▇▇▇▆▅▆▆▆▅▅▅▅▅▅▅▅▅▅▅▅▄▄▄▄▄▄▄▄▄▃▃▃▂▂▂▂▂▁▁▁▁▁▁▁▁▁13998.04913185.16412814.68111907.75811410.2489732.3311078.41610634.8710413.0819818.3469100.3029780.1549477.4149321.159501.5818906.8448952.5168651.258467.4118534.2758445.5738246.5637840.6097703.5077749.8767877.3987602.0027183.3697151.6546908.1866678.016462.346325.8494156.4213889.0173805.9193655.2913675.9683462.3463278.0923348.0793263.0693187.6923074.162866.4432922.4592791.714NANANA
us-gaap:CommonStockValue █████████████████████████████████▁▁▁▁▁▁▁▁▁▁3451.9683447.6143428.343425.2473421.8453419.5283404.9193402.9343400.9643395.943392.9933392.3223387.1213383.6683381.8343379.1563376.233376.0373368.6663365.753360.833354.6173342.3573335.2083327.4893320.3233308.3953302.8683297.4623302.3013288.8633277.4883269.355911.33908.98905.841904.047902.441891.507890.393888.616886.574884.457NANANA872.876NANANA
us-gaap:RetainedEarningsAccumulatedDeficit █▇▇▆▆▅▆▆▆▅▅▅▅▅▃▂▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▁▁▁▁▁▁▁▁▁▁▁▁9503.8898754.768195.1827377.0956948.4666039.4747457.1766988.8886808.2016338.8745782.316576.5626184.2995927.7393776.7433378.5243666.2463557.9273526.3953433.8913355.2623293.3673137.2852942.6062843.3032753.9632581.8662468.7442402.7132365.4692294.9092197.8162148.242160.062068.342009.1331957.7781890.041835.0861794.3871761.0671744.2451735.973NANANA1514.398NANANA
us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax ▃▃▃▃▃▂▂▂▂▂▁▁▁▂█▇▇▆▆▆▆▆▅▅▆▆▆▅▆▅▅▄▄▄▄▄▄▄▃▃▃▃▃427.223369.679584.376499.714432.351261.726208.772231.632187.261.168-94.65-184.892-90.5612.8042345.5712151.2051911.9331719.2361565.8661727.6421722.2771591.1321354.5081417.4161571.0781795.3721704.5571403.5811442.8821232.3621089.805982.119903.3091080.119911.337891.142793.341809.612660.92527.4633.29567.559551.093NANANA387.086NANANA
us-gaap:MinorityInterest ▃▃▃▃▃▂▂▂▃▃▃▁▁▁▁▁▁▁▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▁▁██▇▇▇▃23.07821.2214.89213.81115.69511.6027.54911.41616.71622.36419.649-3.838-3.446-3.061-2.567-2.041-1.893-1.956.4846.9927.2047.4476.4598.2778.0067.747.1848.1768.5978.0544.4334.9174.9454.9120.36-0.1970.12573.87574.83365.91265.10664.69116.169NANANA17.354NANANA
 us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementClassOfStock,us-gaap:StatementEquityComponents us-gaap:PreferredStock,mkl:TotalEquityNANA0.00.0591.891NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementClassOfStock,us-gaap:StatementEquityComponents us-gaap:PreferredStock,us-gaap:ParentNANA0.00.0591.891NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementClassOfStock,us-gaap:StatementEquityComponents us-gaap:PreferredStock,us-gaap:PreferredStockNANA0.00.0591.891NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:NetCashProvidedByUsedInOperatingActivities ▆▄▆█▅▂▆▆▄▂▃▅▄▂▄▅▄▂▄▄▃▁▃▄▄▂▃▄▄▂▃▄▃▂▃▃▃▁▂▃▃▂▂▃▂▂495.048318.124475.999772.847423.06365.678562.162462.8230.43518.723129.681455.642249.86257.672259.826360.758225.99911.946210.266254.143174.783-104.569100.766312.35215.20322.832180.164299.563214.64822.417203.064302.486184.41755.554152.988134.798169.139-64.39250.21160.765109.546-9.20350.467109.25859.2474.319NANANANA
us-gaap:NetCashProvidedByUsedInInvestingActivities ▁▁▃▁▅█▅▄▂▆▄▅▄▅▃▃▆▅▃▅▃▄▆▅▄▅▅▃▃▆▄▅▇▄▅▄▅▅▄▅▄▅▅▅▅▄-1159.752-1077.587-534.239-1031.165147.037906.619121.999-135.512-863.766342.12-344.024-7.576-377.395-68.244-650.232-531.001399.11937.657-550.544-74.231-676.429-243.907293.941120.155-318.98530.66259.135-437.823-423.965180.448-326.09114.779752.001-353.30314.501-337.20813.869-30.65-179.82816.157-219.112-91.528-110.84636.80421.252-230.553NANANANA
us-gaap:NetCashProvidedByUsedInFinancingActivities ▇▄▄▃█▄▁▆█▄▄▃▄▃█▃▃▄▄▄▆▄▄▄▄▄▄▄▄▄▄▄▄▆▄▅▄▄▄▄▅▄▄▄▄▄510.57453.707-41.065-131.909586.62320.907-411.327250.488520.225-0.069-7.216-60.306-36.767-74.696555.63-100.696-172.077-26.542-50.974-26.917238.712-8.802-17.53-8.388-14.845-33.448-20.385-7.942-7.855-30.942-14.172-19.44-22.21231.189-28.665195.758-34.2349.103-16.227-16.989226.0641.741-11.981-24.231-27.16917.771NANANANA
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect ▃▁▃▂█▇▅▆▃▅▃▅▃▃▄▃▅▄▂▄-146.086-718.745-45.904-364.8191169.048957.971300.584558.303-122.939367.973-230.51382.546-197.256-59.194145.181-230.578471.55229.527-455.205178.531NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:NetCashProvidedByUsedInOperatingActivities ▆▄▆█▅▂▆▆▄▂▃▅▄▂▄▅▄▂▄▄▃▁▃▄▄▂▃▄▄▂▃▄▃▂▃▃▃▁▂▃▃▂▂▃▂▂495.048318.124475.999772.847423.06365.678562.162462.8230.43518.723129.681455.642249.86257.672259.826360.758225.99911.946210.266254.143174.783-104.569100.766312.35215.20322.832180.164299.563214.64822.417203.064302.486184.41755.554152.988134.798169.139-64.39250.21160.765109.546-9.20350.467109.25859.2474.319NANANANA
us-gaap:NetIncomeLoss █▇█▇█▁▇▆▇▇▃▆▆▅▇▄▆▅▆▅▅▆▆▆▆▆▆▅▅▅▆▅▅▅▅▅▅▅▅▅▅▅▆▅▅▅▆▅▅▅792.11573.694847.299452.726921.768-1405.763511.104205.637497.298576.427-751.543409.438278.231-64.306434.881-259.141149.6669.869132.72683.79678.797160.37197.892102.51991.369190.992117.59575.80340.06887.71698.76465.59927.75688.90256.79249.65389.68757.25350.17653.26430.3148.272140.14363.2520.83142.56993.35659.12632.79816.358
us-gaap:ProfitLoss █▇█▇█▁▇▆▇▇▃▆▆▅▇▄▆▅▆▅▅▆▆▆▅▆▆▅▅▅▆▅▅▅▅▅▅▅▅▅▅▅▆▅▅▅▅▅▅▅803.334579.681847.429454.043931.671-1401.376511.513203.953506.483577.513-753.374409.028279.587-65.594439.326-261.035151.42771.04132.70383.42180.673163.646198.273104.4192.453194.006118.22276.82441.14187.50198.93966.96728.67689.26358.09351.67490.76857.71352.30754.66931.6499.861140.44963.15720.91743.20693.74259.21133.0316.436
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:NetCashProvidedByUsedInInvestingActivities ▁▁▃▁▅█▅▄▂▆▄▅▄▅▃▃▆▅▃▅▃▄▆▅▄▅▅▃▃▆▄▅▇▄▅▄▅▅▄▅▄▅▅▅▅▄-1159.752-1077.587-534.239-1031.165147.037906.619121.999-135.512-863.766342.12-344.024-7.576-377.395-68.244-650.232-531.001399.11937.657-550.544-74.231-676.429-243.907293.941120.155-318.98530.66259.135-437.823-423.965180.448-326.09114.779752.001-353.30314.501-337.20813.869-30.65-179.82816.157-219.112-91.528-110.84636.80421.252-230.553NANANANA
us-gaap:PaymentsToAcquirePropertyPlantAndEquipment ▄▅▅▄▃▅▅█▄▄▅▄▅▄▄▂▃▃▂▂▃▂▃▄▂▄▅▆▁▂▂▂▂▂▂▂▁▂▃▃▂▂▂25.08830.6528.5322.10320.76129.90727.91946.22524.47624.75627.70726.49829.02623.36224.55314.52119.71415.86414.10914.93119.73414.917.723.11315.33623.60629.78234.3967.22910.72511.04810.25911.97614.44212.0310.6049.96812.91716.62116.35314.31912.83913.355NANANANANANANA
us-gaap:PaymentsToAcquireInvestments █▆▆▄▁▄▃▂▃▃▂▃▇▅▁▃814.613595.695557.395315.82666.582382.415298.407169.892260.115227.556136.65223.888687.998497.37713.843223.124NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
us-gaap:NetCashProvidedByUsedInFinancingActivities ▇▄▄▃█▄▁▆█▄▄▃▄▃█▃▃▄▄▄▆▄▄▄▄▄▄▄▄▄▄▄▄▆▄▅▄▄▄▄▅▄▄▄▄▄510.57453.707-41.065-131.909586.62320.907-411.327250.488520.225-0.069-7.216-60.306-36.767-74.696555.63-100.696-172.077-26.542-50.974-26.917238.712-8.802-17.53-8.388-14.845-33.448-20.385-7.942-7.855-30.942-14.172-19.44-22.21231.189-28.665195.758-34.2349.103-16.227-16.989226.0641.741-11.981-24.231-27.16917.771NANANANA
us-gaap:PaymentsForRepurchaseOfCommonStock █▅▁▁▁▅▇▃▆▇▅▂▃▃▆▅▇▅▇▁▃▁▂▂▂▄▁▂▁▄▁▄█▁▁▁▃▁▃▄▃▁▂▄▄▂38.80322.0232.8890.00.07823.86534.30912.73231.61737.64923.1786.57211.96812.28926.40225.24235.68223.51235.6390.29714.4860.724.2294.5925.12217.5480.1318.5150.12517.2820.52616.00440.6890.1690.8110.013.7632.2999.47719.94413.4920.03.13817.82919.8644.387NANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument mkl:FourPointNinePercentUnsecuredSeniorNotesDueJuly20224.9000000000000005e-06NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument mkl:ThreePointFourFivePercentUnsecuredSeniorNotesDueMay2052NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument,us-gaap:LongtermDebtType mkl:FivePointZeroPercentUnsecuredSeniorNotesDueMarch302043,us-gaap:SeniorNotesNANA5e-06NANANA5.0000000000000004e-08NANANA5.0000000000000004e-08NANANA5.0000000000000004e-08NANANA5.0000000000000004e-08NANANA5.0000000000000004e-08NANANANANANANANANANANANANANANANANANANANANANANANANANANA

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
Value345134473428342534213419340434023400339533923392338733833381337933763376336833653360335433423335332733203308330232973302328832773269911908905904902891890888886884872
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 Assets7.68.08.28.58.89.59.19.29.39.810.210.010.210.310.311.812.412.813.012.712.813.113.413.213.113.113.113.213.113.513.713.813.96.97.27.37.67.67.77.87.88.08.28.5

us-gaap:CommonStockValue us-gaap:ConsolidatedEntities

srt:ParentCompany


Common
Period End2020-12-312019-12-31
Value34283404
Percentage of CommonStockValue100.0100.0
Percentage of Assets8.29.1
Percentage of Assets srt:ParentCompany20.420.5

Shares Outstanding

us-gaap:SharesOutstanding us-gaap:StatementEquityComponents

us-gaap:SharesOutstanding

us-gaap:CommonStock


Shares
Period End2021-06-302021-03-312020-12-312020-06-302020-03-312019-12-31
Value131313131313
Percentage of SharesOutstanding100.0100.0100.0100.0100.0100.0

Shares Issued

us-gaap:SharesIssued us-gaap:StatementEquityComponents

us-gaap:SharesIssued

us-gaap:CommonStock


Shares
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-312011-12-312010-12-312009-12-312008-12-312007-12-31
Value1313131313131313131313131313131313131313131313131313139.6219.7189.8199.8149.957
Percentage of SharesIssued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PreferredStock


Shares
Period End2020-09-302020-06-302020-03-312019-12-31
Value0.60.60.00.0
Percentage of SharesIssued4.44.40.00.0

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
Value131313131313131313131313141414141414141414141414129.6669.6599.6769.6719.7189.7579.7579.769.807
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 End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value131313131313131313131313131314141313131313131314129.6369.6329.6519.6429.689.7179.7179.7489.794
Percentage of WeightedAverageNumberOfSharesOutstandingBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareBasic


Earnings
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value57.1242.0959.4431.0765.81-100.636.3413.9736.142.81-53.8828.5620.01-4.2530.48-18.8210.343.919.145.625.4411.2114.237.436.7613.578.15.332.676.286.984.692.249.536.255.338.445.945.215.53.120.8514.426.492.134.349.516.023.341.67
Percentage of EarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted

us-gaap:EarningsPerShareDiluted


Earnings
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value57.0242.0259.3331.0365.75-100.636.2613.9536.0742.76-53.8828.519.97-4.2530.39-18.8210.313.99.115.65.4111.1514.147.396.7213.498.055.32.666.256.954.672.249.56.235.328.425.925.195.483.110.8514.376.482.124.339.496.023.341.67
Percentage of EarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Comprehensive Income Net Of Tax

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTax


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value8493589315201092-1352.809488250623732-680.373315164-174.839629-19.869342223-29.0589209396134-51.143-132.92528141836250230206144-149.0542577614773205183-52.6269624104225-33.90313481339171-1.996
Percentage of ComprehensiveIncomeNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax73.146.127.858.6142.8-226.218.942.688.8135.1-65.260.826.2-39.837.9-5.8103.415.8-2.06.215.328.89.5-3.8-10.221.631.32.819.918.616.112.1-14.431.49.519.310.628.126.8-7.814.84.017.140.1-6.625.114.767.932.9-0.4

Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest

us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest

us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value116.0040.1241.335104.2630.437-1.7429.1891.091-1.831-0.4691.333-1.2464.471-1.891.7811.173-0.035-0.3761.8873.2840.3551.91.0582.9840.621.021.078-0.2080.2031.3680.920.3611.3382.0261.0340.462.0951.4051.3351.5890.306-0.0930.0410.868
Percentage of ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.00.80.00.21.30.70.0-0.31.30.2-0.2-0.10.2-0.30.3-0.60.50.1-0.0-0.00.10.20.00.10.10.20.00.10.1-0.00.00.10.10.00.20.30.10.10.30.20.20.30.1-0.00.00.2

Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest

us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest

us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value8603659325211102-1348.546488248632733-682.204314165-176.085633-21.759344224-29.08588211400135-49.243-131.86728441937251230206145-148.1342587814974206185-51.2219726104225-33.862135
Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax74.146.927.858.7144.1-225.518.942.390.1135.3-65.460.726.4-40.138.1-6.4104.015.9-2.06.215.429.19.5-3.7-10.121.931.42.920.018.616.112.2-14.431.59.719.510.728.227.1-7.615.04.217.140.1-6.625.2

us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest us-gaap:StatementEquityComponents

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value10-0.6711.0993.7286.740.9624.0723.8488.5420.333-1.925-0.111.75-0.7534.873-1.7041.8041.4570.471-0.1912.132.2512.0881.932
Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest1.2-0.20.10.70.6-0.10.81.51.40.00.3-0.01.10.40.87.80.50.6-1.6-0.21.00.61.5-3.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.9-0.10.00.40.90.20.20.71.20.1-0.2-0.00.3-0.20.3-0.50.50.10.0-0.00.20.20.10.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:RedeemableNoncontrollingInterestsTemporaryEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:TotalEquity


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value8503659305171095-1349.508484244623733-680.604314163-175.007628-20.055342222-29.55688209398133-51.175
Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest98.8100.299.999.399.4100.199.298.598.6100.099.8100.098.999.499.292.299.599.4101.6100.299.099.498.5103.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax73.246.927.758.3143.2-225.618.841.688.9135.2-65.360.726.1-39.837.8-5.9103.415.8-2.16.215.228.99.4-3.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:TotalEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NoncontrollingInterest


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.7276.675-0.975-2.3933.2933.301-3.635-5.590.6470.7580.094-0.359-0.417-0.493-0.402-0.186-0.023-0.284-0.506-0.185-0.2431.033-1.733-0.0320.462.0951.4051.3351.5890.306-0.0930.0410.868
Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest0.11.8-0.1-0.50.3-0.2-0.7-2.30.10.1-0.0-0.1-0.30.3-0.10.9-0.0-0.11.7-0.2-0.10.3-1.30.10.21.1-2.71.46.00.3-0.0-0.10.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.10.9-0.0-0.30.40.6-0.1-1.00.10.10.0-0.1-0.1-0.1-0.0-0.1-0.0-0.0-0.0-0.0-0.00.1-0.1-0.00.10.30.20.20.30.1-0.00.00.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:NoncontrollingInterest0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Parent


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value8493589315201092-1352.809488250623732-680.698315164-174.514629-19.869342223-29.0589209396134-51.143
Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest98.798.4100.099.799.1100.399.9100.798.599.999.8100.199.299.199.391.399.599.599.9100.499.199.299.7103.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax73.146.127.858.6142.8-226.218.942.688.8135.1-65.360.826.2-39.737.9-5.8103.415.8-2.06.215.328.89.5-3.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:Parent0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Costs And Expenses

us-gaap:CostsAndExpenses

us-gaap:CostsAndExpenses


Costs
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value24212154221122191889214018271770177216771974168016751470148318341240128412161278118211311141116011751033114011661174109311421068957678718688551636588585588591481451467456
Percentage of CostsAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax208.4276.665.9250.0247.0357.970.8301.4252.5309.5189.4324.2266.8334.689.2536.6374.791.085.189.385.982.280.386.490.179.485.489.893.388.289.389.792.882.888.989.979.686.885.986.690.995.178.780.490.685.0

Deferred Policy Acquisition Cost Amortization Expense

us-gaap:DeferredPolicyAcquisitionCostAmortizationExpense

us-gaap:DeferredPolicyAcquisitionCostAmortizationExpense


Deferred
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value332322335296302295294280263261276241249241245230213204202201188189
Percentage of DeferredPolicyAcquisitionCostAmortizationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax28.641.410.033.439.549.511.447.837.548.326.546.739.755.014.867.564.514.514.114.113.713.8

us-gaap:DeferredPolicyAcquisitionCostAmortizationExpense us-gaap:StatementBusinessSegments

mkl:Insurance


Deferred
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value264260271239238239233218208199215182191179190177160147
Percentage of DeferredPolicyAcquisitionCostAmortizationExpense79.680.881.080.879.080.979.277.979.376.478.275.677.074.277.476.875.172.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax22.833.58.126.931.240.09.037.229.736.920.735.330.540.811.451.948.510.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Insurance0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:Reinsurance


Deferred
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value67616356635661615461605857625553535650484247
Percentage of DeferredPolicyAcquisitionCostAmortizationExpense20.419.219.019.221.019.120.822.120.723.621.824.423.025.822.623.224.927.825.023.922.825.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax5.98.01.96.48.39.42.410.57.811.45.811.49.114.23.315.616.04.03.53.43.13.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Reinsurance0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value102072810135841175-1772.059641261650732-930.45651936042143-359.9482099418011911521424915210023916610354115106924511765521197474673611
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax87.893.530.265.8153.6-296.324.844.692.6135.1-89.2100.257.49.78.6-105.363.36.712.68.38.415.617.611.47.718.412.58.04.39.48.37.74.414.48.26.917.210.210.99.95.71.8

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
Value217148165130243-370.68312957143155-177.08210981108-295.672-98.91358234736355051487.83345482613287.2252516287.8040.811281622125.0651.59-28.718288.99719
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 RevenueFromContractWithCustomerExcludingAssessedTax18.719.04.914.631.9-62.05.09.920.528.6-17.021.212.924.7-17.8-28.917.61.63.32.52.63.73.63.60.63.53.62.11.02.30.62.11.63.51.00.14.12.33.31.80.80.3-4.75.01.73.6

Interest Expense

us-gaap:InterestExpense

us-gaap:InterestExpense


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
Value46424442454542474140393736403531313332333330293029292829292931302823232422222123211818181817
Percentage of InterestExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax4.05.41.34.85.97.51.78.15.97.43.87.35.89.12.19.39.62.42.32.32.42.22.12.22.22.32.12.32.42.42.42.62.82.92.93.23.23.03.23.53.43.13.13.33.63.3

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value792573847452921-1405.763511205497576-751.543409278-64.306434-259.1411496913283781601971029119011775408798652788564989575053308.27214063204293593216
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.273.625.251.0120.5-235.019.835.070.8106.3-72.179.044.3-14.626.2-75.845.24.99.35.95.711.713.97.67.014.78.85.83.27.17.75.52.710.87.06.512.97.87.37.94.71.322.911.34.07.916.911.86.33.3

Net Income Loss Attributable To Noncontrolling Interest

us-gaap:NetIncomeLossAttributableToNoncontrollingInterest

us-gaap:NetIncomeLossAttributableToNoncontrollingInterest


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
Value115.9870.131.3179.9034.3870.409-1.6849.1851.086-1.831-0.411.356-1.2884.445-1.8941.7671.171-0.023-0.3751.8763.2760.3811.8911.0843.0140.6271.0211.073-0.2150.1751.3680.920.3611.3012.0211.0810.462.1311.4051.3351.5890.306-0.0930.0860.637
Percentage of NetIncomeLossAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.00.80.00.11.30.70.0-0.31.30.2-0.2-0.10.2-0.30.3-0.60.50.1-0.0-0.00.10.20.00.10.10.20.00.10.1-0.00.00.10.10.00.20.30.20.10.30.20.20.30.1-0.00.00.1

Net Income Loss Available To Common Stockholders Basic

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value774573828452921-1405.763511205497576-751.543409278-64.306
Percentage of NetIncomeLossAvailableToCommonStockholdersBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax66.673.624.751.0120.5-235.019.835.070.8106.3-72.179.044.3-14.6

Net Investment Income

us-gaap:NetInvestmentIncome

us-gaap:NetInvestmentIncome


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
Value9696979095881121131111141141061051081011049910093939491828790929391928688867764746463796762647071686468
Percentage of NetInvestmentIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax8.312.42.910.212.514.84.419.315.921.111.020.516.824.66.130.630.07.16.66.56.96.65.86.56.97.17.07.07.37.06.97.27.67.99.28.49.210.99.89.29.911.311.612.212.512.7

us-gaap:NetInvestmentIncome us-gaap:StatementBusinessSegments

mkl:Investing


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value96969790958811211311111311410610510710110499100939394918287909293919286888677647464637967626470716864
Percentage of NetInvestmentIncome100.0100.0100.0100.099.999.899.999.999.899.8100.099.999.899.9100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax8.312.42.910.212.514.74.419.315.921.011.020.516.724.66.130.630.07.16.66.56.96.65.86.56.97.17.07.07.37.06.97.27.67.99.28.49.210.99.89.29.911.311.612.212.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Investing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:MarkelVenturesOperations


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value0.0020.0030.0030.0040.0540.1840.1240.1620.1980.2520.0560.1430.1920.1220.1270.1020.060.043
Percentage of NetInvestmentIncome0.00.00.00.00.10.20.10.10.20.20.00.10.20.10.10.10.10.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:MarkelVenturesOperations0.00.00.00.00.00.00.00.00.00.10.00.00.00.00.00.00.00.0

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
Value107974511446921242-1805.33753262666794-932.137555311105179-328.1342411272121521932452791821292681941338414513712274141897714196969058301301094880
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 RevenueFromContractWithCustomerExcludingAssessedTax92.995.734.178.0162.4-301.829.244.694.9146.6-89.4107.249.623.910.8-96.072.99.014.910.714.117.819.713.69.920.614.610.26.711.810.710.37.217.211.110.120.413.214.113.49.14.921.319.69.415.0

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
Value4.915-0.808385.756-1.405-12.7346.36-4.606-3.7492.3773.473-14.471-10.454.953-9.321161.9621.545-5.563-8.349-8.12110-6.995-10.85410-21.814-12.602-27.2236.6710.913-0.2121.709-10.459-1.181-1.3933.266-3.1622.8231.347-8.1330.156
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 RevenueFromContractWithCustomerExcludingAssessedTax0.4-0.11.10.6-0.2-2.10.2-0.8-0.50.40.3-2.8-1.71.1-0.64.80.60.1-0.4-0.6-0.60.8-0.5-0.80.8-1.7-0.9-2.10.50.1-0.00.1-1.0-0.1-0.20.4-0.50.40.2-1.20.0

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
Value57-214.68846717052-22.8324412615571-94.391-113.918-110.491194239192153-161.7885.364131236-62.934-153.653-224.3290300-39.30221014210778-176.811682097-16.318148133-105.8965
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 RevenueFromContractWithCustomerExcludingAssessedTax5.0-27.62.57.622.38.8-0.97.617.928.76.8-18.2-18.1-25.111.770.058.210.9-11.30.49.517.2-4.4-11.4-17.27.022.5-3.016.711.58.46.6-17.120.62.512.8-2.420.319.5-15.710.2

us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value0.0170.017-0.0060.0180.13-0.1240.028-0.0580.0040.0050.0-0.059-0.0230.0420.0260.0040.0140.002-0.012-0.0010.0110.008-0.0260.009
Percentage of OtherComprehensiveIncomeLossNetOfTax0.0-0.0-0.00.00.1-0.2-0.1-0.10.00.00.00.10.0-0.00.00.00.00.00.0-0.00.00.00.0-0.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.0-0.00.00.0-0.00.0-0.00.00.00.0-0.0-0.00.00.00.00.00.0-0.0-0.00.00.0-0.00.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:RedeemableNoncontrollingInterestsTemporaryEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:TotalEquity


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value57-214.697846717052-22.864412615571-94.332-113.895-110.533194239192153-161.7765.365131236-62.908-153.662
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.099.9100.2100.1100.1100.0100.0100.099.9100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax5.0-27.62.57.622.38.9-0.97.617.928.76.8-18.2-18.1-25.211.770.058.210.9-11.30.49.517.2-4.4-11.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:TotalEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value57-214.697846717052-22.864412615571-94.332-113.895-110.533194239192153-161.7765.365131236-62.908-153.662
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.099.9100.2100.1100.1100.0100.0100.099.9100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax5.0-27.62.57.622.38.9-0.97.617.928.76.8-18.2-18.1-25.211.770.058.210.9-11.30.49.517.2-4.4-11.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Parent


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value57-214.697846717052-22.864412615571-94.332-113.895-110.533194239192153-161.7765.365131236-62.908-153.662
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.099.9100.2100.1100.1100.0100.0100.099.9100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax5.0-27.62.57.622.38.9-0.97.617.928.76.8-18.2-18.1-25.211.770.058.210.9-11.30.49.517.2-4.4-11.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:Parent0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Policyholder Benefits And Claims Incurred Net

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet us-gaap:StatementBusinessSegments

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet

mkl:UnderwritingOperations


Policyholder
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value8158818148637131076772752677687
Percentage of PolicyholderBenefitsAndClaimsIncurredNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax70.2113.224.397.293.3179.929.9128.096.5126.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:UnderwritingOperations0.00.00.00.00.00.00.00.00.00.0

Preferred Stock Dividends Income Statement Impact

us-gaap:PreferredStockDividendsIncomeStatementImpact

us-gaap:PreferredStockDividendsIncomeStatementImpact


Preferred
Period End2021-06-30
Value18
Percentage of PreferredStockDividendsIncomeStatementImpact100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.5

Premiums Earned Net

us-gaap:PremiumsEarnedNet

us-gaap:PremiumsEarnedNet


Premiums
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
Value15681497152613941360133013461300119912031227118511481151113110991033982983974950957958963957943971954965949962919784564573530513529516509490463466435416412
Percentage of PremiumsEarnedNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax135.0192.245.5157.1177.8222.552.2221.3170.8222.1117.7228.7182.8261.968.1321.8312.369.668.868.169.169.667.571.873.472.572.873.476.776.675.277.276.168.971.069.374.072.275.475.375.774.576.377.680.876.8

Profit Loss

us-gaap:ProfitLoss

us-gaap:ProfitLoss


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value803579847454931-1401.376511203506577-753.374409279-65.594439-261.0351517113283801631981049219411876418798662889585190575254319.86114063204393593316
Percentage of ProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax69.274.425.351.2121.8-234.319.834.772.1106.5-72.278.944.5-14.926.4-76.445.75.09.35.85.911.914.07.87.114.98.95.93.37.17.75.62.810.97.26.713.17.97.68.14.91.623.011.34.18.117.011.86.33.3

us-gaap:ProfitLoss us-gaap:StatementEquityComponents

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value10-0.6881.1053.716.611.0864.0443.9068.5380.328-1.925-0.0511.773-0.7954.847-1.7081.791.4550.483-0.192.1192.2432.1141.923
Percentage of ProfitLoss1.3-0.10.10.80.7-0.10.81.91.70.10.3-0.00.61.21.10.71.22.00.4-0.22.61.41.11.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.9-0.10.00.40.90.20.20.71.20.1-0.2-0.00.3-0.20.3-0.50.50.10.0-0.00.20.20.10.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:RedeemableNoncontrollingInterestsTemporaryEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:TotalEquity


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value792580846450925-1402.462507200497577-751.449409277-64.799434-259.327149691328378161196102
Percentage of ProfitLoss98.7100.199.999.299.3100.199.298.198.399.999.7100.099.498.898.999.398.898.099.6100.297.498.698.998.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.274.525.250.7120.9-234.519.734.170.9106.5-72.178.944.2-14.726.1-75.945.24.99.35.85.711.713.87.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:TotalEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NoncontrollingInterest


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.7276.675-0.975-2.3933.2933.301-3.635-5.590.6470.7580.094-0.359-0.417-0.493-0.402-0.186-0.023-0.284-0.506-0.185-0.2431.033-1.733-0.0320.462.1311.4051.3351.5890.306-0.0930.0860.637
Percentage of ProfitLoss0.11.2-0.1-0.50.4-0.2-0.7-2.70.10.1-0.0-0.1-0.10.8-0.10.1-0.0-0.4-0.4-0.2-0.30.6-0.9-0.00.84.12.64.216.10.2-0.10.41.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.10.9-0.0-0.30.40.6-0.1-1.00.10.10.0-0.1-0.1-0.1-0.0-0.1-0.0-0.0-0.0-0.0-0.00.1-0.1-0.00.10.30.20.20.30.1-0.00.00.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:NoncontrollingInterest0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Parent


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value792573847452921-1405.763511205497576-751.543409278-64.306434-259.141149691328378160197102
Percentage of ProfitLoss98.699.0100.099.798.9100.399.9100.898.299.899.8100.199.598.099.099.398.898.4100.0100.497.798.099.898.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.273.625.251.0120.5-235.019.835.070.8106.3-72.179.044.3-14.626.2-75.845.24.99.35.95.711.713.97.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:Parent0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value792573847452921-1405.763511205497576-751.543409278-64.306434-259.141149691328378160197102575053308.272140632042
Percentage of ProfitLoss98.699.0100.099.798.9100.399.9100.898.299.899.8100.199.598.099.099.398.898.4100.0100.497.798.099.898.299.295.997.495.883.999.8100.199.698.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.273.625.251.0120.5-235.019.835.070.8106.3-72.179.044.3-14.626.2-75.845.24.99.35.95.711.713.97.67.87.37.94.71.322.911.34.07.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Revenue From Contract With Customer Excluding Assessed Tax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value116177933558877645982581587702542104251862843916623413301411142814311375137614201342130413021335129912581239127911911031819807765693733685676647621611561515536551500522495
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConcentrationRiskByBenchmark

us-gaap:RevenueFromContractWithCustomer


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1100719800839716542500535645486493472581397394318307
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax94.792.423.894.593.790.619.491.291.989.847.491.192.690.423.793.392.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax94.792.423.894.593.790.619.491.291.989.847.491.192.690.423.793.392.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RevenueFromContractWithCustomer100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConcentrationRiskByBenchmark, us-gaap:StatementBusinessSegments

us-gaap:RevenueFromContractWithCustomer, mkl:MarkelVenturesOperations


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1049675756799654481461475588426447446555370377310290
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax90.486.722.590.185.680.517.980.983.878.642.986.188.484.422.790.887.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax90.486.722.590.185.680.517.980.983.878.642.986.188.484.422.790.887.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RevenueFromContractWithCustomer mkl:MarkelVenturesOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomer, mkl:Other


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value58447139626070605660
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax5.15.72.14.48.110.12.710.38.111.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax5.15.72.14.48.110.12.710.38.111.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RevenueFromContractWithCustomer mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService

mkl:OtherRevenues


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value2531252523302720293124232421232223
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.24.10.82.83.05.11.13.64.25.82.34.63.84.91.46.77.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.24.10.82.83.05.11.13.64.25.82.34.63.84.91.46.77.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:OtherRevenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ProgramServicesAndOtherFronting


Revenue
Period End2021-06-302021-03-312020-06-302020-03-31
Value27272425
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.43.53.24.3
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.43.53.24.3
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:ProgramServicesAndOtherFronting100.0100.0100.0100.0

mkl:ProgramServicesandOther


Revenue
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value2923242531302724
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.92.63.24.31.25.24.04.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.92.63.24.31.25.24.04.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:ProgramServicesandOther100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService, us-gaap:ConcentrationRiskByBenchmark

mkl:InvestmentManagement, us-gaap:RevenueFromContractWithCustomer


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value20164121252937423040381817178.8561.2489.277
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.82.11.22.43.35.01.47.34.37.53.73.52.83.90.50.42.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.82.11.22.43.35.01.47.34.37.53.73.52.83.90.50.42.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:InvestmentManagement us-gaap:RevenueFromContractWithCustomer100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Services, us-gaap:RevenueFromContractWithCustomer


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value5063844754852771741341141281129810210396949592
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax43.649.414.254.736.329.15.219.518.320.79.419.916.421.95.727.928.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax43.649.414.254.736.329.15.219.518.320.79.419.916.421.95.727.928.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Services us-gaap:RevenueFromContractWithCustomer100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Product, us-gaap:RevenueFromContractWithCustomer


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value581318311332414338360378486333356350461283290222204
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax50.040.99.337.554.256.514.064.469.261.534.267.773.464.517.565.061.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax50.040.99.337.554.256.514.064.469.261.534.267.773.464.517.565.061.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:Product us-gaap:RevenueFromContractWithCustomer100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService, us-gaap:ConcentrationRiskByBenchmark, us-gaap:StatementBusinessSegments

mkl:InvestmentManagement, us-gaap:RevenueFromContractWithCustomer, mkl:Other


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value20164121252937423040
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.82.11.22.43.35.01.47.34.37.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.82.11.22.43.35.01.47.34.37.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:InvestmentManagement us-gaap:RevenueFromContractWithCustomer mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Services, us-gaap:RevenueFromContractWithCustomer, mkl:MarkelVenturesOperations


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value468356444467240143101971019291959487868885
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax40.345.813.352.731.424.03.916.514.517.18.718.315.019.95.225.825.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax40.345.813.352.731.424.03.916.514.517.18.718.315.019.95.225.825.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Services us-gaap:RevenueFromContractWithCustomer mkl:MarkelVenturesOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Services, us-gaap:RevenueFromContractWithCustomer, mkl:Other


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value37273018373033172619
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.33.60.92.04.95.21.33.03.83.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.33.60.92.04.95.21.33.03.83.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Services us-gaap:RevenueFromContractWithCustomer mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Product, us-gaap:RevenueFromContractWithCustomer, mkl:MarkelVenturesOperations


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value581318311332414338360378486333356350461283290222204
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax50.040.99.337.554.256.514.064.469.261.534.267.773.464.517.565.061.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax50.040.99.337.554.256.514.064.469.261.534.267.773.464.517.565.061.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:Product us-gaap:RevenueFromContractWithCustomer mkl:MarkelVenturesOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

mkl:OtherRevenues, mkl:MarkelVenturesOperations


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value2531252423292520282824232321222223
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.24.00.82.73.14.91.03.54.15.32.34.53.84.81.46.57.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.24.00.82.73.14.91.03.54.15.32.34.53.84.81.46.57.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:OtherRevenues mkl:MarkelVenturesOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:OtherRevenues, mkl:Other


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.1310.5260.1010.896-0.0230.7062.6720.3780.3462.628
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.10.00.1-0.00.10.10.10.00.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.10.00.1-0.00.10.10.10.00.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:OtherRevenues mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ProgramServicesAndOtherFronting, mkl:Other


Revenue
Period End2021-06-302021-03-312020-06-302020-03-31
Value27272425
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.43.53.24.3
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.43.53.24.3
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:ProgramServicesAndOtherFronting mkl:Other100.0100.0100.0100.0

mkl:ProgramServicesandOther, mkl:Other


Revenue
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value2923242531302724
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.92.63.24.31.25.24.04.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.92.63.24.31.25.24.04.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:ProgramServicesandOther mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1075706781824678511486496616454471469578392400332313
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax92.690.723.392.888.685.418.884.487.983.945.390.692.189.224.197.494.7
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax92.690.723.392.888.685.418.884.487.983.945.390.692.189.224.197.494.7
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:MarkelVenturesOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Other


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value8672100638687104918587
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax7.49.33.07.211.414.64.015.612.116.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax7.49.33.07.211.414.64.015.612.116.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Revenues

us-gaap:Revenues

us-gaap:Revenues


Revenues
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value35002900335529113132335258120332439247210422235198715751662150614811411142814311375137614201342130413021335129912581239127911911031819807765693733685676647621611561515536551500522495
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax301.3372.3100.0328.0409.456.1100.0346.1347.4456.1100.0431.4316.3358.5100.0440.6447.6100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Assets

us-gaap:Assets

us-gaap:Assets


Assets
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value4564143043417104017039067360483747337036364213473633306339583324732866328052851927203264002587526403263352568524941251812536625253252002507625166244522395523808234991311712556123831196511859115321137111464110411082510241
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
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

us-gaap:Assets us-gaap:ConsolidatedEntities

srt:ParentCompany


Assetsus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-31
Value16826166381364412484
Percentage of Assets40.344.441.038.1
Percentage of Assets40.344.441.038.1
Percentage of Assets srt:ParentCompany100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidatedEntities, us-gaap:InvestmentsByConsolidatedAndNonconsolidatedEntities

us-gaap:VariableInterestEntityPrimaryBeneficiary, mkl:MarkelDiversifiedFund


Assetsus-gaap:
Period End2020-09-302019-12-31
Value1119
Percentage of Assets0.00.1
Percentage of Assets0.00.1
Percentage of Assets us-gaap:VariableInterestEntityPrimaryBeneficiary mkl:MarkelDiversifiedFund100.0100.0

us-gaap:Assets us-gaap:StatementBusinessSegments

mkl:Investing


Assetsus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2478122129191002031719029
Percentage of Assets59.459.157.361.973.5
Percentage of Assets59.459.157.361.973.5
Percentage of Assets mkl:Investing100.0100.0100.0100.0100.0

mkl:MarkelVenturesOperations


Assetsus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312013-12-312012-12-312011-12-31
Value36362550212419001206936891630
Percentage of Assets8.76.86.45.84.73.97.15.5
Percentage of Assets8.76.86.45.84.73.97.15.5
Percentage of Assets mkl:MarkelVenturesOperations100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Other


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312016-12-31
Value659061626063579559995932617159885711570656283759241
Percentage of Assets14.414.314.514.415.416.516.516.215.716.416.911.50.9
Percentage of Assets14.414.314.514.415.416.516.516.215.716.416.911.50.9
Percentage of Assets mkl:Other100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:UnderwritingOperations


Assetsus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value72286621645168285397
Percentage of Assets17.317.719.420.820.9
Percentage of Assets17.317.719.420.820.9
Percentage of Assets mkl:UnderwritingOperations100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:StatementBusinessSegments, us-gaap:StatementOperatingActivitiesSegment

mkl:Investing, us-gaap:SegmentContinuingOperations


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-31
Value2720825470247812341222097203482212921893212141991419100209562030320194203171988419635192991902919235189761841318056183421833518450185311812218183177091755017125165289749927791378766879586928572867281987844
Percentage of Assets59.659.259.458.356.656.459.159.158.257.357.361.761.161.461.969.772.273.173.572.972.171.772.472.872.373.173.572.372.372.473.371.970.374.373.973.873.374.275.475.475.675.776.6
Percentage of Assets59.659.259.458.356.656.459.159.158.257.357.361.761.161.461.969.772.273.173.572.972.171.772.472.872.373.173.572.372.372.473.371.970.374.373.973.873.374.275.475.475.675.776.6
Percentage of Assets mkl:Investing us-gaap:SegmentContinuingOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:MarkelVenturesOperations, us-gaap:SegmentContinuingOperations


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value379337063636365737412612255022572308224621242027193618911900
Percentage of Assets8.38.68.79.19.67.26.86.16.36.56.46.05.85.85.8
Percentage of Assets8.38.68.79.19.67.26.86.16.36.56.46.05.85.85.8
Percentage of Assets mkl:MarkelVenturesOperations us-gaap:SegmentContinuingOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:UnderwritingOperations, us-gaap:SegmentContinuingOperations


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-31
Value80497704722873047229715566216896718668696451650169556972682853975385
Percentage of Assets17.617.917.318.218.519.817.718.619.719.819.419.120.921.220.820.921.6
Percentage of Assets17.617.917.318.218.519.817.718.619.719.819.419.120.921.220.820.921.6
Percentage of Assets mkl:UnderwritingOperations us-gaap:SegmentContinuingOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:StatementOperatingActivitiesSegment

us-gaap:SegmentContinuingOperations


Assetsus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-31
Value39050368803564634374330683011531302310473070929030276772948529195290582714526412257152494024427249162479824200234432396224135240352395323832241772348123019229042261012250116651152911218112221090110902110251047210059
Percentage of Assets85.685.785.585.684.683.583.583.884.383.683.186.887.888.482.792.694.594.594.494.494.294.294.095.295.195.295.195.096.196.096.196.296.293.492.993.193.894.694.595.996.296.798.2
Percentage of Assets85.685.785.585.684.683.583.583.884.383.683.186.887.888.482.792.694.594.594.494.494.294.294.095.295.195.295.195.096.196.096.196.296.293.492.993.193.894.694.595.996.296.798.2
Percentage of Assets us-gaap:SegmentContinuingOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

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
Value31415296232864928021274422616126217262352585724770240312401923613233892313719459181641766117334177981782317370170371742717564173201753717835179591749117205172741709988878581848982228183806980938116777876377450
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 Assets68.868.868.769.870.272.670.070.871.071.372.270.771.071.270.568.266.866.967.067.467.767.668.369.269.268.669.671.171.471.571.872.672.867.768.368.668.769.070.071.270.870.470.672.7

us-gaap:Liabilities us-gaap:ConsolidatedEntities

srt:ParentCompany


Liabilitiesus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-31
Value4026556745632980
Percentage of Liabilities14.121.219.012.9
Percentage of Assets9.714.913.79.1
Percentage of Assets srt:ParentCompany23.933.533.423.9

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
Value4564143043417104017039067360483747337036364213473633306339583324732866328052851927203264002587526403263352568524941251812536625253252002507625166244522395523808234991311712556123831196511859115321137111464110411082510241
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

us-gaap:LiabilitiesAndStockholdersEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Liabilities
Period End2020-12-312019-12-312018-12-312017-12-31
Value16826166381364412484
Percentage of LiabilitiesAndStockholdersEquity40.344.441.038.1
Percentage of Assets40.344.441.038.1
Percentage of Assets srt:ParentCompany100.0100.0100.0100.0

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value1397413163127991189311394972011070106231039697959080978394809324950489088954865384608527843882397834769577417869759471757143690066736457632041513888380636553602338732123282319831712774
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets30.630.630.729.629.227.029.528.728.528.227.328.828.528.429.031.232.932.832.732.332.032.131.430.630.531.230.128.628.428.227.927.126.931.631.030.730.530.429.428.228.629.029.327.1

us-gaap:StockholdersEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Stockholders
Period End2020-12-312019-12-312018-12-312017-12-31
Value127991107090809504
Percentage of StockholdersEquity100.0100.0100.0100.0
Percentage of Assets30.729.527.329.0
Percentage of Assets srt:ParentCompany76.166.566.676.1

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
Value367938824341459348333834307227152220241520142347194520482198207623151852173821562007228426302261185219581960176519442151197821151702899973834837691775920767649745817686637850640478
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 Assets8.19.010.411.412.410.68.27.36.17.06.06.95.96.26.77.38.57.06.78.27.68.910.59.07.37.87.87.07.78.88.38.97.26.97.86.77.05.86.78.16.75.96.90.00.00.08.30.00.0

us-gaap:CashAndCashEquivalentsAtCarryingValue us-gaap:ConsolidatedEntities

srt:ParentCompany


Cash
Period End2020-12-312019-12-312018-12-312017-12-31
Value657737263349
Percentage of CashAndCashEquivalentsAtCarryingValue15.124.013.115.9
Percentage of Assets1.62.00.81.1
Percentage of Assets srt:ParentCompany3.94.41.92.8

Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents


Cash
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302015-12-312014-12-31
Value43514497521652625627445835003199264127642396262622442441250023552586211420852540236130702482
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets9.510.412.513.114.412.49.38.67.38.07.27.76.87.47.68.39.58.08.19.69.012.39.9

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents us-gaap:ConsolidatedEntities

srt:ParentCompany


Cash
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value723738266350370460
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents13.921.111.114.017.815.0
Percentage of Assets1.72.00.81.11.41.8
Percentage of Assets srt:ParentCompany4.34.42.02.80.00.0

Inventory Net

us-gaap:InventoryNet

us-gaap:InventoryNet


Inventory
Period End2020-12-312019-12-312018-12-31
Value412303298
Percentage of InventoryNet100.0100.0100.0
Percentage of Assets1.00.80.9

Amortization Of Intangible Assets

us-gaap:AmortizationOfIntangibleAssets

us-gaap:AmortizationOfIntangibleAssets


Amortization
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
Value3939394437373535364029272928271818161717171718181614161313131716119.6158.4347.9598.3158.8046.7056.0235.5556.0085.1073.9033.8563.958
Percentage of AmortizationOfIntangibleAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AmortizationOfIntangibleAssets us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Amortization
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value13131315111110101010109.1391010106.9176.9566.904
Percentage of AmortizationOfIntangibleAssets34.934.634.035.530.731.328.629.029.026.636.732.934.135.039.037.138.641.2
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets mkl:MarkelVenturesOperations0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:Other


Amortization
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
Value2525252826262525252918181918
Percentage of AmortizationOfIntangibleAssets65.165.466.064.569.368.771.471.071.073.463.367.165.965.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets mkl:Other0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:UnderwritingSegments


Amortization
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value-10.4-10.4-10.4-10.4-10.7-10.569-9.8-9.8-9.8
Percentage of AmortizationOfIntangibleAssets-26.2-26.3-26.6-23.3-28.3-27.7192.3-27.5-27.0-24.1
Percentage of Assets0.00.00.00.00.00.00.00.00.00.0
Percentage of Assets mkl:UnderwritingSegments0.00.00.00.00.00.00.00.00.00.0

Property Plant And Equipment Net

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:PropertyPlantAndEquipmentNet


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
Value632588551501412430421347330244159
Percentage of PropertyPlantAndEquipmentNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.51.61.71.51.61.71.71.52.62.11.5

Goodwill

us-gaap:Goodwill

us-gaap:Goodwill


Goodwill
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302012-12-312011-12-312010-12-312009-12-31
Value26062604260426042606230923082187218922152237178317841789177714251216114211421165116711711167104310441039104910671022101996710081041674607470402
Percentage of Goodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.76.16.26.56.76.46.25.96.06.46.75.35.45.45.45.04.54.34.44.44.44.64.74.14.14.14.24.34.14.24.04.24.45.45.34.33.9

us-gaap:Goodwill us-gaap:StatementBusinessSegments

mkl:Insurance


Goodwillus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value772771770771672
Percentage of Goodwill29.733.434.443.458.9
Percentage of Assets1.92.12.32.42.6
Percentage of Assets mkl:Insurance0.00.00.00.00.0

mkl:MarkelVenturesOperations


Goodwillus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312013-12-312012-12-312011-12-31
Value901606497424237191192151
Percentage of Goodwill34.626.322.223.920.819.828.525.0
Percentage of Assets2.21.61.51.30.90.81.51.3
Percentage of Assets mkl:MarkelVenturesOperations24.823.823.422.419.720.521.624.1

mkl:OtherOperations


Goodwillus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-31
Value808807847457
Percentage of Goodwill31.035.037.925.8
Percentage of Assets1.92.22.51.4
Percentage of Assets mkl:OtherOperations0.00.00.00.0

mkl:Reinsurance


Goodwillus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value1221221221221221221221221221221220.0
Percentage of Goodwill4.75.35.56.910.710.511.711.512.012.012.70.0
Percentage of Assets0.30.30.40.40.50.50.50.50.50.50.50.0
Percentage of Assets mkl:Reinsurance0.00.00.00.00.00.00.00.00.00.00.00.0

Indefinite Lived Intangible Assets Excluding Goodwill

us-gaap:IndefiniteLivedIntangibleAssetsExcludingGoodwill

us-gaap:IndefiniteLivedIntangibleAssetsExcludingGoodwill


Indefinite
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value9292928848485858104.1
Percentage of IndefiniteLivedIntangibleAssetsExcludingGoodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.20.20.30.30.20.20.20.20.10.0

Intangible Assets Net Excluding Goodwill

us-gaap:IntangibleAssetsNetExcludingGoodwill

us-gaap:IntangibleAssetsNetExcludingGoodwill


Intangible
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302012-12-31
Value169617361782182018651692173816591695171217261241126913171355990806711722733753775792652669680702727677687565560576374
Percentage of IntangibleAssetsNetExcludingGoodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets3.74.04.34.54.84.74.64.54.74.95.23.73.84.04.13.53.02.72.82.82.93.03.22.62.62.72.82.92.72.82.42.42.53.0

us-gaap:IntangibleAssetsNetExcludingGoodwill us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Intangible
Period End2020-12-312019-12-312018-12-312017-12-31
Value623473431400
Percentage of IntangibleAssetsNetExcludingGoodwill35.027.225.029.5
Percentage of Assets1.51.31.31.2
Percentage of Assets mkl:MarkelVenturesOperations17.118.520.321.1

mkl:OtherOperations


Intangible
Period End2020-12-312019-12-312018-12-312017-12-31
Value716781805417
Percentage of IntangibleAssetsNetExcludingGoodwill40.244.946.730.8
Percentage of Assets1.72.12.41.3
Percentage of Assets mkl:OtherOperations0.00.00.00.0

mkl:UnderwritingSegments


Intangible
Period End2020-12-312019-12-312018-12-312017-12-31
Value442484489537
Percentage of IntangibleAssetsNetExcludingGoodwill24.827.828.339.7
Percentage of Assets1.11.31.51.6
Percentage of Assets mkl:UnderwritingSegments0.00.00.00.0

Deferred Tax Assets Liabilities Net

us-gaap:DeferredTaxAssetsLiabilitiesNet us-gaap:BalanceSheetLocation

us-gaap:DeferredTaxAssetsLiabilitiesNet

us-gaap:OtherAssets


Deferred
Period End2020-12-312019-12-312018-12-31
Value3.92235
Percentage of DeferredTaxAssetsLiabilitiesNet100.0100.0100.0
Percentage of Assets0.00.10.1
Percentage of Assets us-gaap:OtherAssets0.00.00.0

Operating Lease Right Of Use Asset

us-gaap:OperatingLeaseRightOfUseAsset us-gaap:BalanceSheetLocation

us-gaap:OperatingLeaseRightOfUseAsset

us-gaap:OtherAssets


Operating
Period End2020-12-312019-12-31
Value528232
Percentage of OperatingLeaseRightOfUseAsset100.0100.0
Percentage of Assets1.30.6
Percentage of Assets us-gaap:OtherAssets0.00.0

Equity Securities Fv Ni

us-gaap:EquitySecuritiesFvNi

us-gaap:EquitySecuritiesFvNi


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value82057528699461835664568475906978687563815720654960690.0
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0
Percentage of Assets18.017.516.815.414.515.820.318.818.918.417.219.318.30.0

us-gaap:EquitySecuritiesFvNi us-gaap:ConsolidatedEntities

srt:ParentCompany


Equity
Period End2020-12-312019-12-312018-12-312017-12-31
Value1817183111750.0
Percentage of EquitySecuritiesFvNi26.024.120.50.0
Percentage of Assets4.44.93.50.0
Percentage of Assets srt:ParentCompany10.811.08.60.0

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value81647472693560815548555275446934683763365667642759495799
Percentage of EquitySecuritiesFvNi99.599.399.298.398.097.799.499.499.499.399.198.198.00.0
Percentage of Assets17.917.416.615.114.215.420.118.718.818.217.018.917.917.7
Percentage of Assets us-gaap:FairValueInputsLevel1 us-gaap:FairValueMeasurementsRecurring0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:FairValueInputsLevel3, us-gaap:FairValueMeasurementsRecurring


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value4156581021151314544374453122119168
Percentage of EquitySecuritiesFvNi0.50.70.81.72.02.30.60.60.60.70.91.92.00.0
Percentage of Assets0.10.10.10.30.30.40.10.10.10.10.20.40.40.5
Percentage of Assets us-gaap:FairValueInputsLevel3 us-gaap:FairValueMeasurementsRecurring0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency, us-gaap:FinancialInstrument

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring, us-gaap:BanksTrustAndInsuranceEquities


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value30492738251621612014194024632247221920531876211019811934
Percentage of EquitySecuritiesFvNi37.236.436.035.035.634.132.432.232.332.232.832.232.60.0
Percentage of Assets6.76.46.05.45.25.46.66.16.15.95.66.26.05.9
Percentage of Assets us-gaap:FairValueInputsLevel1 us-gaap:FairValueMeasurementsRecurring us-gaap:BanksTrustAndInsuranceEquities0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring, us-gaap:IndustrialMiscellaneousAndAllOthers


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value51154734441939203534361250814686461842833790431639683864
Percentage of EquitySecuritiesFvNi62.362.963.263.462.463.566.967.267.267.166.365.965.40.0
Percentage of Assets11.211.010.69.89.010.013.612.712.712.311.412.711.911.8
Percentage of Assets us-gaap:FairValueInputsLevel1 us-gaap:FairValueMeasurementsRecurring us-gaap:IndustrialMiscellaneousAndAllOthers0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:FairValueInputsLevel3, us-gaap:FairValueMeasurementsRecurring, us-gaap:BanksTrustAndInsuranceEquities


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value4156581021151314544374453122119168
Percentage of EquitySecuritiesFvNi0.50.70.81.72.02.30.60.60.60.70.91.92.00.0
Percentage of Assets0.10.10.10.30.30.40.10.10.10.10.20.40.40.5
Percentage of Assets us-gaap:FairValueInputsLevel3 us-gaap:FairValueMeasurementsRecurring us-gaap:BanksTrustAndInsuranceEquities0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByMeasurementFrequency

us-gaap:FairValueMeasurementsRecurring


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value82057528699461835664568475906978687563815720654960695967
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0
Percentage of Assets18.017.516.815.414.515.820.318.818.918.417.219.318.318.2
Percentage of Assets us-gaap:FairValueMeasurementsRecurring0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByMeasurementFrequency, us-gaap:FinancialInstrument

us-gaap:FairValueMeasurementsRecurring, us-gaap:BanksTrustAndInsuranceEquities


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value30902794257422632130207225092292225720981930223321012103
Percentage of EquitySecuritiesFvNi37.737.136.836.637.636.533.132.832.832.933.734.134.60.0
Percentage of Assets6.86.56.25.65.55.76.76.26.26.05.86.66.36.4
Percentage of Assets us-gaap:FairValueMeasurementsRecurring us-gaap:BanksTrustAndInsuranceEquities0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:FairValueMeasurementsRecurring, us-gaap:IndustrialMiscellaneousAndAllOthers


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value51154734441939203534361250814686461842833790431639683864
Percentage of EquitySecuritiesFvNi62.362.963.263.462.463.566.967.267.267.166.365.965.40.0
Percentage of Assets11.211.010.69.89.010.013.612.712.712.311.412.711.911.8
Percentage of Assets us-gaap:FairValueMeasurementsRecurring us-gaap:IndustrialMiscellaneousAndAllOthers0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Other Assets

us-gaap:OtherAssets

us-gaap:OtherAssets


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
Value249124662393239124622110190618791798161913831214124712831223113610109659469659599329449611000987985994921909106710961210666663680592486465483435455506433
Percentage of OtherAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.55.75.76.06.35.95.15.14.94.74.23.63.83.93.74.03.73.73.73.73.63.63.83.83.93.93.94.03.73.74.54.65.25.15.35.55.04.14.04.33.84.14.74.2

us-gaap:OtherAssets us-gaap:ConsolidatedEntities

srt:ParentCompany


Other
Period End2020-12-312019-12-312018-12-312017-12-31
Value364347135121
Percentage of OtherAssets15.218.29.89.9
Percentage of Assets0.90.90.40.4
Percentage of Assets srt:ParentCompany2.22.11.01.0

Long Term Debt

us-gaap:LongTermDebt

us-gaap:LongTermDebt


Long
Period End2020-12-312019-12-31
Value34843534
Percentage of LongTermDebt100.0100.0
Percentage of Assets8.49.4

us-gaap:LongTermDebt us-gaap:ConsolidatedEntities

srt:ParentCompany


Long
Period End2020-12-312019-12-312018-12-312017-12-31
Value3441343825392537
Percentage of LongTermDebt98.897.30.00.0
Percentage of Assets8.39.27.67.7
Percentage of Assets srt:ParentCompany20.520.718.620.3

Debt And Capital Lease Obligations

us-gaap:DebtAndCapitalLeaseObligations

us-gaap:DebtAndCapitalLeaseObligations


Debt
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
Value4160356434843498360635933534389636253058300929933024304830992471248525812574258926022299224122402246224922532273225822552256225022491732149215101309130512931271126810271015963
Percentage of DebtAndCapitalLeaseObligations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets9.18.38.48.79.210.09.410.510.08.89.08.89.19.39.48.79.19.89.99.89.99.09.08.98.98.98.99.19.09.29.49.59.613.211.912.210.911.011.211.211.19.39.49.4

us-gaap:DebtAndCapitalLeaseObligations dei:LegalEntity, us-gaap:LongtermDebtType

mkl:MarkelVenturesOperations, mkl:OtherDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-31
Value42707878
Percentage of DebtAndCapitalLeaseObligations1.22.02.62.5
Percentage of Assets0.10.20.20.2
Percentage of Assets mkl:MarkelVenturesOperations mkl:OtherDebt0.00.00.00.0

us-gaap:DebtAndCapitalLeaseObligations us-gaap:LongtermDebtType

mkl:OtherDebt


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value4295102185153119
Percentage of DebtAndCapitalLeaseObligations1.22.73.46.06.05.3
Percentage of Assets0.10.30.30.60.60.5
Percentage of Assets mkl:OtherDebt0.00.00.00.00.00.0

Minority Interest

us-gaap:MinorityInterest

us-gaap:MinorityInterest


Minority
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
Value2321141315117.54911162219-3.838-3.446-3.061-2.567-2.041-1.893-1.956.4846.9927.2047.4476.4598.2778.0067.747.1848.1768.5978.0544.4334.9174.9454.9120.36-0.1970.12573746565641617
Percentage of MinorityInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.00.00.00.00.00.00.00.00.10.1-0.0-0.0-0.0-0.0-0.0-0.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0-0.00.00.60.60.60.60.60.10.2

Lessee Operating Lease Liability Payments Due Year Two

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo


Lessee
Period End2020-12-31
Value78
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearTwo100.0
Percentage of Assets0.2

Lessee Operating Lease Liability Payments Due Year Three

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree


Lessee
Period End2020-12-31
Value68
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearThree100.0
Percentage of Assets0.2

Lessee Operating Lease Liability Payments Due Year Four

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour


Lessee
Period End2020-12-31
Value59
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFour100.0
Percentage of Assets0.1

Lessee Operating Lease Liability Payments Due Year Five

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive


Lessee
Period End2020-12-31
Value48
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFive100.0
Percentage of Assets0.1

Lessee Operating Lease Liability Payments Due After Year Five

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive


Lessee
Period End2020-12-31
Value286
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive100.0
Percentage of Assets0.7

Operating Lease Liability

us-gaap:OperatingLeaseLiability us-gaap:BalanceSheetLocation

us-gaap:OperatingLeaseLiability

us-gaap:OtherLiabilities


Operating
Period End2020-12-312019-12-31
Value565262
Percentage of OperatingLeaseLiability100.0100.0
Percentage of Assets1.40.7
Percentage of Assets us-gaap:OtherLiabilities0.00.0

Lessee Operating Lease Liability Payments Due

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue


Lessee
Period End2020-12-31
Value632
Percentage of LesseeOperatingLeaseLiabilityPaymentsDue100.0
Percentage of Assets1.5

Lessee Operating Lease Liability Undiscounted Excess Amount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount


Lessee
Period End2020-12-31
Value66
Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount100.0
Percentage of Assets0.2

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value1397413163127991189311394972011070106231039697959080978394809324950489088954865384608527843882397834769577417869759471757143690066736457632041513888380636553602338732123282319831712774
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets30.630.630.729.629.227.029.528.728.528.227.328.828.528.429.031.232.932.832.732.332.032.131.430.630.531.230.128.628.428.227.927.126.931.631.030.730.530.429.428.228.629.029.327.1

us-gaap:StockholdersEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Stockholders
Period End2020-12-312019-12-312018-12-312017-12-31
Value127991107090809504
Percentage of StockholdersEquity100.0100.0100.0100.0
Percentage of Assets30.729.527.329.0
Percentage of Assets srt:ParentCompany76.166.566.676.1

Stockholders Equity Including Portion Attributable To Noncontrolling Interest

us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest

us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312008-12-312007-12-31
Value139981318512814119071141097321107810634104139818910097809477932195018906895286518467853484458246784077037749787776027183715169086678646263254156388938053655367534623278334832633187307428662922279121802641
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets30.730.630.729.629.227.029.628.728.628.327.328.828.528.429.031.232.932.832.732.332.132.131.430.630.631.230.228.628.428.327.927.126.931.731.030.730.531.030.028.829.229.629.40.00.00.027.30.00.0

us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap:StatementEquityComponents

mkl:TotalEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-31
Value13998131851281411907114109732110781063410413981891009780947793219501890689528651846785348445824678407703774976026678
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets30.730.630.729.629.227.029.628.728.628.327.328.828.528.429.031.232.932.832.732.332.132.131.430.630.630.227.9
Percentage of Assets mkl:TotalEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-312012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312008-12-312007-12-31
Value42736958449943226120823118761-94.65-184.892-90.5612234521511911171915651727172215911354141715711704108980966052763356755158642447938713357
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest3.12.84.64.23.82.71.92.21.80.6-1.0-1.9-1.00.124.724.221.419.918.520.220.419.317.318.420.322.416.322.019.116.118.917.417.319.114.816.413.90.613.5
Percentage of Assets0.90.91.41.21.10.70.60.60.50.2-0.3-0.5-0.30.07.27.57.06.56.16.56.56.25.45.66.26.84.56.85.74.65.55.15.10.00.00.03.80.00.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-312012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312008-12-312007-12-31
Value345134473428342534213419340434023400339533923392338733833381337933763376336833653360335433423335332733083288902891890888886884872871872872869866
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest24.726.126.828.830.035.130.732.032.734.637.334.735.736.335.637.937.739.039.839.439.840.742.643.342.943.549.224.525.727.226.527.227.728.430.429.931.339.932.8
Percentage of Assets7.68.08.28.58.89.59.19.29.39.810.210.010.210.310.311.812.412.813.012.712.813.113.413.213.113.113.77.67.77.87.88.08.20.00.00.08.50.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NoncontrollingInterest


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-312012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312008-12-312007-12-31
Value2321141315117.54911162219-3.838-3.446-3.061-2.567-2.041-1.893-1.956.4846.9927.2047.4476.4598.2778.0067.1844.433737465656416161618170.261-0.136
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest0.20.20.10.10.10.10.10.10.20.20.2-0.0-0.0-0.0-0.0-0.0-0.0-0.00.10.10.10.10.10.10.10.10.12.02.22.01.92.00.50.50.60.60.60.0-0.0
Percentage of Assets0.10.00.00.00.00.00.00.00.00.10.1-0.0-0.0-0.0-0.0-0.0-0.0-0.00.00.00.00.00.00.00.00.00.00.60.60.60.60.60.10.00.00.00.20.00.0
Percentage of Assets us-gaap:NoncontrollingInterest0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Parent


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-31
Value13974131631279911893113949720110701062310396979590809783948093249504890889548653846085278438823978347695774175946673
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest99.899.899.999.999.999.999.999.999.899.899.8100.0100.0100.0100.0100.0100.0100.099.999.999.999.999.999.999.999.999.9
Percentage of Assets30.630.630.729.629.227.029.528.728.528.227.328.828.528.429.031.232.932.832.732.332.032.131.430.630.530.127.9
Percentage of Assets us-gaap:Parent0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:PreferredStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-31
Value5915915915915910.00.0
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest4.24.54.65.05.20.00.0
Percentage of Assets1.31.41.41.51.50.00.0
Percentage of Assets us-gaap:PreferredStock0.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-12-312013-12-312012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312008-12-312007-12-31
Value950387548195737769486039745769886808633857826576618459273776337836663557352634333355329331372942284325812294189018351794176117441735159815531552151412971417
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest67.966.464.062.060.962.167.365.765.464.663.567.265.363.639.737.941.041.141.640.239.739.940.038.236.734.034.451.453.054.752.653.554.552.054.253.154.259.553.7
Percentage of Assets20.820.319.618.417.816.819.918.918.718.217.419.418.618.011.511.813.513.513.613.012.712.812.611.711.210.29.615.915.915.815.415.816.00.00.00.014.80.00.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

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
Value345134473428342534213419340434023400339533923392338733833381337933763376336833653360335433423335332733203308330232973302328832773269911908905904902891890888886884872
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 Assets7.68.08.28.58.89.59.19.29.39.810.210.010.210.310.311.812.412.813.012.712.813.113.413.213.113.113.113.213.113.513.713.813.96.97.27.37.67.67.77.87.88.08.28.5

us-gaap:CommonStockValue us-gaap:ConsolidatedEntities

srt:ParentCompany


Common
Period End2020-12-312019-12-31
Value34283404
Percentage of CommonStockValue100.0100.0
Percentage of Assets8.29.1
Percentage of Assets srt:ParentCompany20.420.5

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
Value95038754819573776948603974576988680863385782657661845927377633783666355735263433335532933137294228432753258124682402236522942197214821602068200919571890183517941761174417351514
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 Assets20.820.319.618.417.816.819.918.918.718.217.419.418.618.011.511.813.513.513.613.012.712.812.611.711.210.910.29.89.59.79.69.29.116.516.516.216.415.915.915.815.415.816.014.8

us-gaap:RetainedEarningsAccumulatedDeficit us-gaap:ConsolidatedEntities

srt:ParentCompany


Retained
Period End2020-12-312019-12-31
Value81957457
Percentage of RetainedEarningsAccumulatedDeficit100.0100.0
Percentage of Assets19.619.9
Percentage of Assets srt:ParentCompany48.744.8

Accumulated Other Comprehensive Income Loss Net Of Tax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax


Accumulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312009-12-31
Value42736958449943226120823118761-94.65-184.892-90.5612234521511911171915651727172215911354141715711795170414031442123210899829031080911891793809660527633567551387
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.90.91.41.21.10.70.60.60.50.2-0.3-0.5-0.30.07.27.57.06.56.16.56.56.25.45.66.27.16.85.65.75.04.54.13.88.27.37.26.66.85.74.65.55.15.13.8

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:ConsolidatedEntities

srt:ParentCompany


Accumulated
Period End2020-12-312019-12-31
Value584208
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0
Percentage of Assets1.40.6
Percentage of Assets srt:ParentCompany3.51.3

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


Accumulated
Period End2020-12-312020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312010-12-31
Value-58.014-51.016-51.016-53.72-54.182-54.697-56.058-56.658-57.167-57.735-58.399-62.267-63.04-63.942-64.658-44.311-44.701-45.095-45.558-43.799-44.274-44.743-45.206-29.492-29.812-30.137-30.456-33.375-33.785-34.151-34.521-39.698-40.22-40.702-41.185-31.726
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax-9.9-19.5-24.4-23.2-28.9-89.459.230.663.1-450.9-2.5-2.9-3.3-3.7-4.1-2.6-2.6-2.8-3.4-3.1-2.8-2.5-2.7-2.1-2.1-2.4-2.8-3.4-3.7-3.2-3.8-4.5-5.1-5.0-6.2-5.8
Percentage of Assets-0.1-0.1-0.1-0.1-0.1-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.1-0.1-0.1-0.1-0.1-0.1-0.3-0.3-0.3-0.3-0.3-0.4-0.3
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:AccumulatedNetUnrealizedInvestmentGainLoss


Accumulated
Period End2020-12-312020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312010-12-31
Value69841134637732920048-36.795431372477227820551866171418501837169814721526167019051793146314761272113110269491116946930836850704581
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax119.6157.3165.7163.2176.0327.2-50.819.9-48.21071.1105.6105.9107.5108.5109.5107.1106.7106.8108.7107.7106.3106.1105.2104.3102.3103.3103.8104.5105.1103.4103.9104.4105.4105.0106.6105.5
Percentage of Assets1.71.10.91.00.90.60.1-0.10.10.47.68.07.67.16.67.07.06.65.96.16.67.57.15.85.95.24.74.34.08.57.57.57.07.26.15.4
Percentage of Assets us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


Accumulated
Period End2020-12-312019-12-312018-12-312017-12-31
Value584208-94.652345
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0
Percentage of Assets1.40.6-0.37.2
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment


Accumulated
Period End2020-12-312020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312010-12-31
Value-56.42-98.859-86.249-92.581-88.033-84.28-86.652-91.439-77.027-66.6-74.003-64.656-80.915-82.863-84.406-78.855-70.507-62.375-72.696-65.727-54.864-65.275-43.491-30.896-3.674-10.34-11.246-11.006-12.715-2.256-1.0750.355-2.9060.209-2.6141.541
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax-9.7-37.8-41.3-40.0-47.0-137.891.549.585.1-520.1-3.2-3.0-4.2-4.8-5.4-4.6-4.1-3.9-5.4-4.6-3.5-3.6-2.6-2.2-0.3-0.8-1.0-1.1-1.4-0.2-0.10.0-0.40.0-0.40.3
Percentage of Assets-0.1-0.3-0.2-0.2-0.2-0.2-0.3-0.3-0.2-0.2-0.2-0.2-0.3-0.3-0.3-0.3-0.3-0.2-0.3-0.3-0.2-0.3-0.2-0.1-0.0-0.0-0.0-0.0-0.1-0.0-0.00.0-0.00.0-0.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Minority Interest

us-gaap:MinorityInterest

us-gaap:MinorityInterest


Minority
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
Value2321141315117.54911162219-3.838-3.446-3.061-2.567-2.041-1.893-1.956.4846.9927.2047.4476.4598.2778.0067.747.1848.1768.5978.0544.4334.9174.9454.9120.36-0.1970.12573746565641617
Percentage of MinorityInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.00.00.00.00.00.00.00.00.10.1-0.0-0.0-0.0-0.0-0.0-0.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0-0.00.00.60.60.60.60.60.10.2

Stock Issued During Period Value New Issues

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementClassOfStock, us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodValueNewIssues

us-gaap:PreferredStock, mkl:TotalEquity


Stock
Period End2020-12-312020-09-302020-06-30
Value0.00.0591
Percentage of StockIssuedDuringPeriodValueNewIssues0.00.0100.0
Percentage of Assets0.00.00.0
Percentage of Assets us-gaap:PreferredStock mkl:TotalEquity0.00.00.0

us-gaap:PreferredStock, us-gaap:Parent


Stock
Period End2020-12-312020-09-302020-06-30
Value0.00.0591
Percentage of StockIssuedDuringPeriodValueNewIssues0.00.0100.0
Percentage of Assets0.00.00.0
Percentage of Assets us-gaap:PreferredStock us-gaap:Parent0.00.00.0

us-gaap:PreferredStock, us-gaap:PreferredStock


Stock
Period End2020-12-312020-09-302020-06-30
Value0.00.0591
Percentage of StockIssuedDuringPeriodValueNewIssues0.00.0100.0
Percentage of Assets0.00.00.0
Percentage of Assets us-gaap:PreferredStock us-gaap:PreferredStock0.00.00.0

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
Value49531847577242365562462230181294552495725936022511210254174-104.569100312215221802992142220330218455152134169-64.39250160109-9.20350109594.319
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 RevenueFromContractWithCustomerExcludingAssessedTax42.640.814.287.155.311.021.878.832.83.512.487.939.813.115.6105.568.30.814.717.812.7-7.67.123.316.51.813.523.117.01.815.925.417.96.818.917.624.4-8.87.323.816.9-1.58.219.511.50.8

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-1159.752-1077.587-534.239-1031.165147906121-135.512-863.766342-344.024-7.576-377.395-68.244-650.232-531.00139937-550.544-74.231-676.429-243.907293120-318.9853059-437.823-423.965180-326.09114752-353.30314-337.20813-30.65-179.82816-219.112-91.528-110.8463621-230.553
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 RevenueFromContractWithCustomerExcludingAssessedTax-99.8-138.3-15.9-116.219.2151.64.7-23.1-123.063.1-33.0-1.5-60.1-15.5-39.1-155.4120.62.7-38.5-5.2-49.2-17.720.78.9-24.52.44.4-33.7-33.714.6-25.59.672.9-43.11.8-44.02.0-4.2-26.22.4-33.9-14.7-18.16.64.1-43.0

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
Value51053-41.065-131.90958620-411.327250520-0.069-7.216-60.306-36.767-74.696555-100.696-172.077-26.542-50.974-26.917238-8.802-17.53-8.388-14.845-33.448-20.385-7.942-7.855-30.942-14.172-19.44-22.21231-28.665195-34.2349.103-16.227-16.9892261.741-11.981-24.231-27.16917
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 RevenueFromContractWithCustomerExcludingAssessedTax43.96.9-1.2-14.976.73.5-15.942.674.1-0.0-0.7-11.6-5.9-17.033.4-29.5-52.0-1.9-3.6-1.917.3-0.6-1.2-0.6-1.1-2.6-1.5-0.6-0.6-2.5-1.1-1.6-2.228.2-3.525.6-4.91.2-2.4-2.534.90.3-2.0-4.3-5.33.3

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

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect


Cash
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-146.086-718.745-45.904-364.8191169957300558-122.939367-230.51382-197.256-59.194145-230.57847129-455.205178
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax-12.6-92.3-1.4-41.1152.8160.211.695.0-17.567.9-22.173.8-31.4-13.58.7-67.5142.52.1-31.912.5

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
Value49531847577242365562462230181294552495725936022511210254174-104.569100312215221802992142220330218455152134169-64.39250160109-9.20350109594.319
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 RevenueFromContractWithCustomerExcludingAssessedTax42.640.814.287.155.311.021.878.832.83.512.487.939.813.115.6105.568.30.814.717.812.7-7.67.123.316.51.813.523.117.01.815.925.417.96.818.917.624.4-8.87.323.816.9-1.58.219.511.50.8

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value792573847452921-1405.763511205497576-751.543409278-64.306434-259.1411496913283781601971029119011775408798652788564989575053308.27214063204293593216
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.273.625.251.0120.5-235.019.835.070.8106.3-72.179.044.3-14.626.2-75.845.24.99.35.95.711.713.97.67.014.78.85.83.27.17.75.52.710.87.06.512.97.87.37.94.71.322.911.34.07.916.911.86.33.3

Profit Loss

us-gaap:ProfitLoss

us-gaap:ProfitLoss


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302009-03-31
Value803579847454931-1401.376511203506577-753.374409279-65.594439-261.0351517113283801631981049219411876418798662889585190575254319.86114063204393593316
Percentage of ProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax69.274.425.351.2121.8-234.319.834.772.1106.5-72.278.944.5-14.926.4-76.445.75.09.35.85.911.914.07.87.114.98.95.93.37.17.75.62.810.97.26.713.17.97.68.14.91.623.011.34.18.117.011.86.33.3

us-gaap:ProfitLoss us-gaap:StatementEquityComponents

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value10-0.6881.1053.716.611.0864.0443.9068.5380.328-1.925-0.0511.773-0.7954.847-1.7081.791.4550.483-0.192.1192.2432.1141.923
Percentage of ProfitLoss1.3-0.10.10.80.7-0.10.81.91.70.10.3-0.00.61.21.10.71.22.00.4-0.22.61.41.11.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.9-0.10.00.40.90.20.20.71.20.1-0.2-0.00.3-0.20.3-0.50.50.10.0-0.00.20.20.10.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:RedeemableNoncontrollingInterestsTemporaryEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

mkl:TotalEquity


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value792580846450925-1402.462507200497577-751.449409277-64.799434-259.327149691328378161196102
Percentage of ProfitLoss98.7100.199.999.299.3100.199.298.198.399.999.7100.099.498.898.999.398.898.099.6100.297.498.698.998.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.274.525.250.7120.9-234.519.734.170.9106.5-72.178.944.2-14.726.1-75.945.24.99.35.85.711.713.87.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax mkl:TotalEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NoncontrollingInterest


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value0.7276.675-0.975-2.3933.2933.301-3.635-5.590.6470.7580.094-0.359-0.417-0.493-0.402-0.186-0.023-0.284-0.506-0.185-0.2431.033-1.733-0.0320.462.1311.4051.3351.5890.306-0.0930.0860.637
Percentage of ProfitLoss0.11.2-0.1-0.50.4-0.2-0.7-2.70.10.1-0.0-0.1-0.10.8-0.10.1-0.0-0.4-0.4-0.2-0.30.6-0.9-0.00.84.12.64.216.10.2-0.10.41.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.10.9-0.0-0.30.40.6-0.1-1.00.10.10.0-0.1-0.1-0.1-0.0-0.1-0.0-0.0-0.0-0.0-0.00.1-0.1-0.00.10.30.20.20.30.1-0.00.00.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:NoncontrollingInterest0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Parent


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value792573847452921-1405.763511205497576-751.543409278-64.306434-259.141149691328378160197102
Percentage of ProfitLoss98.699.0100.099.798.9100.399.9100.898.299.899.8100.199.598.099.099.398.898.4100.0100.497.798.099.898.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.273.625.251.0120.5-235.019.835.070.8106.3-72.179.044.3-14.626.2-75.845.24.99.35.95.711.713.97.6
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:Parent0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value792573847452921-1405.763511205497576-751.543409278-64.306434-259.141149691328378160197102575053308.272140632042
Percentage of ProfitLoss98.699.0100.099.798.9100.399.9100.898.299.899.8100.199.598.099.099.398.898.4100.0100.497.798.099.898.299.295.997.495.883.999.8100.199.698.5
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax68.273.625.251.0120.5-235.019.835.070.8106.3-72.179.044.3-14.626.2-75.845.24.99.35.95.711.713.97.67.87.37.94.71.322.911.34.07.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

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-1159.752-1077.587-534.239-1031.165147906121-135.512-863.766342-344.024-7.576-377.395-68.244-650.232-531.00139937-550.544-74.231-676.429-243.907293120-318.9853059-437.823-423.965180-326.09114752-353.30314-337.20813-30.65-179.82816-219.112-91.528-110.8463621-230.553
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 RevenueFromContractWithCustomerExcludingAssessedTax-99.8-138.3-15.9-116.219.2151.64.7-23.1-123.063.1-33.0-1.5-60.1-15.5-39.1-155.4120.62.7-38.5-5.2-49.2-17.720.78.9-24.52.44.4-33.7-33.714.6-25.59.672.9-43.11.8-44.02.0-4.2-26.22.4-33.9-14.7-18.16.64.1-43.0

Payments To Acquire Property Plant And Equipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-31
Value253028222029274624242726292324141915141419141723152329347.229101110111412109.968121616141213
Percentage of PaymentsToAcquirePropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Payments To Acquire Investments

us-gaap:PaymentsToAcquireInvestments

us-gaap:PaymentsToAcquireInvestments


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value8145955573156638229816926022713622368749713223
Percentage of PaymentsToAcquireInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

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
Value51053-41.065-131.90958620-411.327250520-0.069-7.216-60.306-36.767-74.696555-100.696-172.077-26.542-50.974-26.917238-8.802-17.53-8.388-14.845-33.448-20.385-7.942-7.855-30.942-14.172-19.44-22.21231-28.665195-34.2349.103-16.227-16.9892261.741-11.981-24.231-27.16917
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 RevenueFromContractWithCustomerExcludingAssessedTax43.96.9-1.2-14.976.73.5-15.942.674.1-0.0-0.7-11.6-5.9-17.033.4-29.5-52.0-1.9-3.6-1.917.3-0.6-1.2-0.6-1.1-2.6-1.5-0.6-0.6-2.5-1.1-1.6-2.228.2-3.525.6-4.91.2-2.4-2.534.90.3-2.0-4.3-5.33.3

Payments For Repurchase Of Common Stock

us-gaap:PaymentsForRepurchaseOfCommonStock

us-gaap:PaymentsForRepurchaseOfCommonStock


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
Value38222.8890.00.0782334123137236.572111226253523350.297140.724.2294.5925.122170.1318.5150.125170.52616400.1690.8110.0132.2999.47719130.03.13817194.387
Percentage of PaymentsForRepurchaseOfCommonStock100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0

Debt Instrument Interest Rate Stated Percentage

us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:DebtInstrument

us-gaap:DebtInstrumentInterestRateStatedPercentage

mkl:FourPointNinePercentUnsecuredSeniorNotesDueJuly2022


Debt
Period End2021-06-30
Value4.9
Percentage of DebtInstrumentInterestRateStatedPercentage100.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.0
Percentage of LongTermDebtAndCapitalLeaseObligations mkl:FourPointNinePercentUnsecuredSeniorNotesDueJuly20220.0

mkl:ThreePointFourFivePercentUnsecuredSeniorNotesDueMay2052


Debt
Period End2021-05-04
Value3.45
Percentage of DebtInstrumentInterestRateStatedPercentage0.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.0
Percentage of LongTermDebtAndCapitalLeaseObligations mkl:ThreePointFourFivePercentUnsecuredSeniorNotesDueMay20520.0

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

mkl:FivePointZeroPercentUnsecuredSeniorNotesDueMarch302043, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value5.00.050.050.050.050.05
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations mkl:FivePointZeroPercentUnsecuredSeniorNotesDueMarch302043 us-gaap:SeniorNotes0.00.00.00.00.00.0

Deferred Tax Liabilities

us-gaap:DeferredTaxLiabilities

us-gaap:DeferredTaxLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312012-12-312011-12-312010-12-31
Value986860446505330176310168410344
Percentage of DeferredTaxLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxLiabilities us-gaap:BalanceSheetLocation

us-gaap:OtherLiabilities


Deferred
Period End2020-12-312019-12-312018-12-31
Value990883481
Percentage of DeferredTaxLiabilities100.4102.6108.0

us-gaap:DeferredTaxLiabilities us-gaap:ConsolidatedEntities

srt:ParentCompany


Deferred
Period End2020-12-312019-12-312018-12-312017-12-31
Value1701296484
Percentage of DeferredTaxLiabilities17.315.114.516.7

Deferred Tax Assets Net

us-gaap:DeferredTaxAssetsNet

us-gaap:DeferredTaxAssetsNet


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value666534449434659684716772
Percentage of DeferredTaxAssetsNet100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Assets Valuation Allowance

us-gaap:DeferredTaxAssetsValuationAllowance

us-gaap:DeferredTaxAssetsValuationAllowance


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value24453625185.1314.8010.0
Percentage of DeferredTaxAssetsValuationAllowance100.0100.0100.0100.0100.0100.0100.00.0

mkl:AdjustedNetIncomeLoss

mkl:AdjustedNetIncomeLoss


Adjusted
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
Value787581820429908-1389.75502193500594-749.75397278-59.255424-262.439144541287876156198103941891137437879765279160518157505330
Percentage of AdjustedNetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:AdjustmenttoLifeandAnnuityBenefits

mkl:AdjustmenttoLifeandAnnuityBenefits


Adjustmentto
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-0.9-49.312202212-41.73136250.00.00.00.0
Percentage of AdjustmenttoLifeandAnnuityBenefits100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.0

mkl:CostMethodInvestmentsRealizedGain

mkl:CostMethodInvestmentsRealizedGain


Cost
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-06-302019-03-31
Value0.04.7220.00.0110.00.0
Percentage of CostMethodInvestmentsRealizedGain0.0100.00.00.0100.00.00.0

mkl:IncurredClaimsPropertyCasualtyAndLiabilityNetOfAssumedReinstatementPremium us-gaap:LiabilityForCatastropheClaimsByCatastrophicEvent

mkl:IncurredClaimsPropertyCasualtyAndLiabilityNetOfAssumedReinstatementPremium

mkl:COVID19PandemicIndirectEffect


Incurred
Period End2020-12-31
Value0.0
Percentage of IncurredClaimsPropertyCasualtyAndLiabilityNetOfAssumedReinstatementPremium0.0

mkl:NetInvestmentGainsLosses

mkl:NetInvestmentGainsLosses


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value674526848539911-1681.44153132425612-845.922426105-122.998-3.788-40.0071720
Percentage of NetInvestmentGainsLosses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:NetInvestmentGainsLosses us-gaap:StatementBusinessSegments

mkl:Investing


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value674526848539911-1681.44153132425612-845.922426105-122.998-3.788-40.0071720
Percentage of NetInvestmentGainsLosses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:OtherComprehensiveIncomeSecuritiesAvailableforSaleLifeandAnnuityBenefitsReservesAdjustmentbeforeTax

mkl:OtherComprehensiveIncomeSecuritiesAvailableforSaleLifeandAnnuityBenefitsReservesAdjustmentbeforeTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.92949-11.921-20.625-22.74-12.87241-31.314-35.938-25.813
Percentage of OtherComprehensiveIncomeSecuritiesAvailableforSaleLifeandAnnuityBenefitsReservesAdjustmentbeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:OtherInterestAndDividendIncomeExpense

mkl:OtherInterestAndDividendIncomeExpense


Other
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-30
Value417000.0-195000.0365000.046000.0757000.0797000.0
Percentage of OtherInterestAndDividendIncomeExpense100.0100.0100.0100.0100.0100.0

mkl:OtherInvestmentsAvailableForSaleRealizedGainLoss us-gaap:FinancialInstrument

mkl:OtherInvestmentsAvailableForSaleRealizedGainLoss

mkl:SalesOfOtherInvestments


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-30
Value46000.0-1332000.066000.038000.0-5389000.0144000.0-4527000.0124000.0452000.0
Percentage of OtherInvestmentsAvailableForSaleRealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:PaymentOfContingentConsideration

mkl:PaymentOfContingentConsideration


Payment
Period End2020-09-302019-09-302017-12-312016-12-312015-12-31
Value210.00.00.00.0
Percentage of PaymentOfContingentConsideration100.00.00.00.00.0

mkl:PotentialIncrementalCommonSharesAttributabletoSharebasedPaymentArrangements us-gaap:AwardType

mkl:PotentialIncrementalCommonSharesAttributabletoSharebasedPaymentArrangements

us-gaap:RestrictedStockUnitsRSU


Potential
Period End2020-12-312020-09-302020-06-302020-03-31
Value12000.02000.0-2000.013000.0
Percentage of PotentialIncrementalCommonSharesAttributabletoSharebasedPaymentArrangements100.0100.0100.0100.0

mkl:PremiumsPercentageCededToGross

mkl:PremiumsPercentageCededToGross


Premiums
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value37.037.0036.00.370.38-0.010.390.410.3800.380.380.360.050.170.160.16-0.010.170.180.1700.180.190.1800.190.190.1900.20.180.120.010.120.12
Percentage of PremiumsPercentageCededToGross100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0

mkl:ProductsRevenues

mkl:ProductsRevenues


Products
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
Value592328321342423352372386501348368362472294
Percentage of ProductsRevenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ProductsRevenues us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Products
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
Value592328321342423352372386501348368362472294
Percentage of ProductsRevenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Productsexpenses

mkl:Productsexpenses


Productsexpenses
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
Value502296281296364314356354425319351341450269
Percentage of Productsexpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Productsexpenses us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Productsexpensesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value502296281296364314356354425319351341450269
Percentage of Productsexpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ReclassificationAdjustmentsForNetGainsLossesIncludedInNetIncomeLoss

mkl:ReclassificationAdjustmentsForNetGainsLossesIncludedInNetIncomeLoss


Reclassification
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
Value3.9430.088-0.1743.3621.385-1.1871.908-0.203-0.8030.246-2.353-10.5735.891-0.8149.6985.2070.2229.1690.229.758101272-6.04.9849.053104.994.8185.944127.6547.957123.8976.4845.7397.9317.0557.9950.8276.464135.7443.09910
Percentage of ReclassificationAdjustmentsForNetGainsLossesIncludedInNetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Servicesandotherexpenses

mkl:Servicesandotherexpenses


Servicesandotherexpenses
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
Value51641253652228421717615317017480132129132
Percentage of Servicesandotherexpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Servicesandotherexpenses us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Servicesandotherexpensesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value4503444334322221439896999492949088
Percentage of Servicesandotherexpenses87.383.780.882.878.166.055.862.658.554.3115.271.969.666.9

mkl:Other


Servicesandotherexpensesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value65676189627478577079-12.25373943
Percentage of Servicesandotherexpenses12.716.311.417.221.934.044.237.441.545.7-15.228.130.433.1

mkl:Reinsurance


Servicesandotherexpensesus-gaap:
Period End2021-06-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-0.1090.00.00.00.00.00.00.00.00.00.0
Percentage of Servicesandotherexpenses-0.00.00.00.00.00.00.00.00.00.00.0

mkl:Servicesandotherrevenues

mkl:Servicesandotherrevenues


Servicesandotherrevenues
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
Value569450560545341245218200200193178155155145
Percentage of Servicesandotherrevenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:Servicesandotherrevenues us-gaap:RelatedPartyTransactionsByRelatedParty, us-gaap:StatementOperatingActivitiesSegment

mkl:UnconsolidatedEntitiesManagedByNephila, mkl:InsurancelinkedSecuritiesOperations


Servicesandotherrevenuesus-gaap:
Period End2021-06-302021-03-312020-06-302020-03-31
Value42284241
Percentage of Servicesandotherrevenues7.46.412.416.9

mkl:UnconsolidatedentitiesmanagedbyNephilaandMCIM, mkl:InsurancelinkedSecuritiesOperations


Servicesandotherrevenuesus-gaap:
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value5532464348524752
Percentage of Servicesandotherrevenues9.86.013.517.822.026.223.627.3

mkl:Servicesandotherrevenues us-gaap:StatementBusinessSegments

mkl:MarkelVenturesOperations


Servicesandotherrevenuesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value48237745948225415811410911510510310610697
Percentage of Servicesandotherrevenues84.983.982.088.474.564.652.254.557.554.858.168.568.367.4

mkl:Other


Servicesandotherrevenuesus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value867210063868710491858774484947
Percentage of Servicesandotherrevenues15.116.118.011.625.535.447.845.542.545.241.931.531.732.6

mkl:Servicesandotherrevenues us-gaap:StatementOperatingActivitiesSegment

mkl:InsurancelinkedSecuritiesOperations


Servicesandotherrevenuesus-gaap:
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value6638545367545053
Percentage of Servicesandotherrevenues11.87.116.021.630.727.325.027.6

mkl:ShorttermInvestmentsAvailableforsaleRealizedGain us-gaap:FinancialInstrument

mkl:ShorttermInvestmentsAvailableforsaleRealizedGain

mkl:SalesOfShortTermInvestments


Shortterm
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
Value278000.030000.0281000.0655000.01002000.098000.0169000.01540000.0499000.01591000.0-20000.01447000.0
Percentage of ShorttermInvestmentsAvailableforsaleRealizedGain100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforsaleRealizedLoss us-gaap:FinancialInstrument

mkl:ShorttermInvestmentsAvailableforsaleRealizedLoss

mkl:SalesOfShortTermInvestments


Shortterm
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
Value0.6330.0940.0640.0430.1840.1720.342.1722.0490.7820.5013.997
Percentage of ShorttermInvestmentsAvailableforsaleRealizedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE

mkl:SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value-135.204-90.83-170.947-167.252-164.148-104.017-198.339-148.096-118.592-70.224
Percentage of SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE us-gaap:StatementBusinessSegments

mkl:Insurance


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value-154.526-119.064-149.937-137.312-151.205-116.132-152.8-135.029-101.721-72.574
Percentage of SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE114.3131.187.782.192.1111.677.091.285.8103.3

mkl:Other


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value-2.419-0.4211.6960.741-0.663-1.797-1.4660.7331.319-8.945
Percentage of SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE1.80.5-1.0-0.40.41.70.7-0.5-1.112.7

mkl:Reinsurance


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value2128-22.706-30.681-12.2813-44.073-13.8-18.1911
Percentage of SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE-16.1-31.513.318.37.5-13.422.29.315.3-16.1

mkl:TotalProfitLoss

mkl:TotalProfitLoss


Total
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value107974511446921242-1805.33753262666794-932.137555311105262-329.906240127
Percentage of TotalProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:TotalProfitLoss us-gaap:StatementBusinessSegments

mkl:Insurance


Total
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value20511616574135-206.3741288147529.5054274102107-159.5017462
Percentage of TotalProfitLoss19.015.714.410.810.911.417.131.07.16.6-1.07.623.997.640.848.331.049.4

mkl:Investing


Total
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value7716239466291006-1593.382644145537726-731.473532210-15.1049764116121
Percentage of TotalProfitLoss71.483.682.790.981.088.385.455.480.691.478.595.867.6-14.437.3-19.548.695.2

mkl:MarkelVenturesOperations


Total
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value10851537979412135812917231323446.6163528
Percentage of TotalProfitLoss10.16.94.711.56.4-2.32.813.512.33.8-1.84.34.222.616.8-2.014.822.6

mkl:Other


Total
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-0.84-23.27410-56.974-3.776-13.3725.2216.607-8.91-16.642-111.872-9.057-10.017-13.366
Percentage of TotalProfitLoss-0.1-3.10.9-8.2-0.30.70.72.5-1.3-2.112.0-1.6-3.2-12.7

mkl:Reinsurance


Total
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value-4.903-23.218-31.385-34.88124-33.959-45.696-6.4758.8163.356-115.347-33.663237.162-48.04-214.37434-70.564
Percentage of TotalProfitLoss-0.5-3.1-2.7-5.02.01.9-6.1-2.51.30.412.4-6.17.66.8-18.365.014.2-55.4

mkl:UnderwritingAcquisitionAndInsuranceExpenses

mkl:UnderwritingAcquisitionAndInsuranceExpenses


Underwriting
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
Value548526540492489495485475462455459441451424418395400373385372375364369365379340388350365355368352363228234231224238208202196202207181179156
Percentage of UnderwritingAcquisitionAndInsuranceExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:UnderwritingProfitLoss

mkl:UnderwritingProfitLoss


Underwriting
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
Value2049117238157-240.80287725961-101.6316.5169711158-371.479110-2.34811122631191181134115510432-10.794514134-20.68248-1.205-4.763672.378250.255-13.327-53.5674928-13.653
Percentage of UnderwritingProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:UnderwritingProfitLoss us-gaap:StatementBusinessSegments

mkl:Insurance


Underwriting
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value20511616574135-206.3741288147529.5054274102107-159.5017462
Percentage of UnderwritingProfitLoss100.3128.595.9195.485.785.7146.8111.880.685.4-9.4651.576.292.0184.742.967.3-2679.4

mkl:Other


Underwriting
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
Value4.393-2.696-2.952-1.722-2.232-0.4694.65-2.1312.6325.584.211-2.274-0.3991.81
Percentage of UnderwritingProfitLoss2.1-3.0-1.7-4.5-1.40.25.3-2.94.59.1-4.1-34.9-0.41.6

mkl:Reinsurance


Underwriting
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-5.012-23.21810-34.88124-33.959-45.696-6.4758.8163.356-115.347-33.663237.162-47.916-214.85734-71.2642612303633280.46523157.708-0.08715-27.5184.086-42.3954.845
Percentage of UnderwritingProfitLoss-2.4-25.55.8-90.915.714.1-52.1-8.914.95.5113.5-516.624.26.4-82.557.831.53035.124.057.347.631.128.524.91.115.315.023.70.830.3-66.411.9205.010.1

us-gaap:AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition us-gaap:StatementEquityComponents

us-gaap:AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition

mkl:TotalEquity


Adjustments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value4.442193.3933.4023.615191.7182.415.0246.8480.673.2925.0177.2122.4922.8212.6787.892.8245.0395.5177.9564.1465.015
Percentage of AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonStock


Adjustments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-03-31
Value4.442193.3933.4023.615191.7182.415.0246.8480.673.2925.0177.2122.4922.8212.6787.892.8245.0395.5177.9564.1465.0152.3661.902
Percentage of AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0

us-gaap:Parent


Adjustments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value4.442193.3933.4023.615191.7182.415.0246.8480.673.2925.0177.2122.4922.8212.6787.892.8245.0395.5177.9564.1465.015
Percentage of AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities

us-gaap:AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities


Adjustments
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
Value-308.286-261.557318-508.6081467258-276.048-558.7946-29.72512362174-59.09417094-268.215207122-171.174222173-65.084235155-33.7098378-122.10510677-19.0644638-38.887
Percentage of AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssumedPremiumsEarned

us-gaap:AssumedPremiumsEarned


Assumed
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
Value37538037837737234037134734430333732631933631035631230729729229529028429330431231230133634734133124110210694
Percentage of AssumedPremiumsEarned100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssumedPremiumsEarned us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Assumed
Period End2021-06-302021-03-312020-06-302020-03-31
Value23142613
Percentage of AssumedPremiumsEarned6.33.97.14.0

mkl:ProgramServicesandOther


Assumed
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value142613201216
Percentage of AssumedPremiumsEarned3.87.14.05.93.75.4

mkl:UnderwritingOperations


Assumed
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value351365362346326327331287313316335356312
Percentage of AssumedPremiumsEarned93.796.196.292.996.094.196.394.696.099.399.6100.0100.0

us-gaap:AssumedPremiumsWritten

us-gaap:AssumedPremiumsWritten


Assumed
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
Value3906472493333455842353222716091583062655491202923106111602413205131132803134501402543665641662402231456091116130448289117517768
Percentage of AssumedPremiumsWritten100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssumedPremiumsWritten us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Assumed
Period End2021-06-302021-03-312020-06-302020-03-31
Value4525286.003
Percentage of AssumedPremiumsWritten11.84.08.21.0

mkl:ProgramServicesandOther


Assumed
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value17286.003392.46631
Percentage of AssumedPremiumsWritten5.48.21.012.30.95.2

mkl:UnderwritingOperations


Assumed
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value344621315316578282268578274259546292310
Percentage of AssumedPremiumsWritten88.296.094.691.899.087.799.194.889.898.199.4100.0100.0

us-gaap:CededPremiumsEarned

us-gaap:CededPremiumsEarned


Ceded
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
Value901897873797798830848843842746748735711646503223193187203202210199204211222213228222223226250230176758469
Percentage of CededPremiumsEarned100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CededPremiumsEarned us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Ceded
Period End2021-06-302021-03-312020-06-302020-03-31
Value607598525561
Percentage of CededPremiumsEarned67.366.765.967.6

mkl:ProgramServicesandOther


Ceded
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value507525561596550531
Percentage of CededPremiumsEarned63.665.967.670.765.371.2

mkl:UnderwritingOperations


Ceded
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value294299290272269246292215242239222223193
Percentage of CededPremiumsEarned32.733.336.434.132.429.334.728.832.933.634.4100.0100.0

us-gaap:CededPremiumsWritten

us-gaap:CededPremiumsWritten


Ceded
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
Value1132923865875916676754894941777720827816712438230219200157200227210159205231217194214259220196233173808071806751596671535462
Percentage of CededPremiumsWritten100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CededPremiumsWritten us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Ceded
Period End2021-06-302021-03-312020-06-302020-03-31
Value783634597396
Percentage of CededPremiumsWritten69.268.765.158.7

mkl:ProgramServicesandOther


Ceded
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value538597396623654549
Percentage of CededPremiumsWritten61.565.158.769.769.570.6

mkl:UnderwritingOperations


Ceded
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value349289337319279271286228266262251230219
Percentage of CededPremiumsWritten30.831.338.534.941.330.330.529.432.232.235.3100.0100.0

us-gaap:CededPremiumsWritten us-gaap:RelatedPartyTransactionsByRelatedParty

mkl:HagertyGroupLLC


Ceded
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value100675068724742576240
Percentage of CededPremiumsWritten8.97.45.87.87.97.15.66.56.65.2

mkl:Syndicate2357andcertainotherNephilaReinsurers


Ceded
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value18611779119122906412614193
Percentage of CededPremiumsWritten16.512.79.213.613.413.48.514.115.012.0

us-gaap:CombinedRatio

us-gaap:CombinedRatio


Combined
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
Value87.094.0-3.097.00.881.18-0.010.940.950.950.040.990.920.9-0.031.340.891.0-0.010.980.930.8800.880.960.83-0.020.971.010.9500.961.030.910.011.01
Percentage of CombinedRatio100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0

us-gaap:CombinedRatio us-gaap:StatementBusinessSegments

mkl:Insurance


Combined
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value84.091.0-4.094.00.881.19-0.010.920.950.950.020.960.920.89-0.041.190.910.92
Percentage of CombinedRatio96.696.8133.396.9100.0100.8100.097.9100.0100.050.097.0100.098.9133.388.8102.292.0

mkl:Reinsurance


Combined
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
Value102.0109.0-2.0116.00.91.150.051.030.960.990.131.150.90.97-0.031.830.851.3200.940.860.82-0.020.861.00.89-0.010.971.00.940.010.981.250.84
Percentage of CombinedRatio117.2116.066.7119.6102.397.5-500.0109.6101.1104.2325.0116.297.8107.8100.0136.695.5132.0-0.095.992.593.20.097.7104.2107.250.0100.099.098.90.0102.1121.492.3

us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded

mkl:SalesOfFixedMaturities


Debt
Period End2020-09-302020-06-302019-06-30
Value-202000.0-1537000.00
Percentage of DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded100.0100.00.0

us-gaap:DebtSecuritiesAvailableForSaleRealizedGain us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleRealizedGain

mkl:SalesOfFixedMaturities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-06-30
Value4.7920.0830.5575.2925.3481.3854.1910.8561.6610.1440.4732.9160.2420.1410.554
Percentage of DebtSecuritiesAvailableForSaleRealizedGain100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleRealizedGainLoss

us-gaap:DebtSecuritiesAvailableForSaleRealizedGainLoss


Debt
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
Value4.4023.4092.9194.935-2.8129.738-2.2460.15-0.0670.681-2.89-0.496-7.642-0.946
Percentage of DebtSecuritiesAvailableForSaleRealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleRealizedLoss us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleRealizedLoss

mkl:SalesOfFixedMaturities


Debt
Period End2021-06-302020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-06-30
Value0.0810.9931.2095.1262.8841.7390.1980.630.283.1161.0037.7060.9520.412
Percentage of DebtSecuritiesAvailableForSaleRealizedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Depreciation us-gaap:StatementBusinessSegments

us-gaap:Depreciation

mkl:MarkelVenturesOperations


Depreciationus-gaap:
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value1516161514131312131413131212139.79.69.4
Percentage of Depreciation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DirectPremiumsEarned

us-gaap:DirectPremiumsEarned


Direct
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
Value209420142021181417851821182217951697164616381594154114601324966914862889883865867878881875844887875852828871818719538552505
Percentage of DirectPremiumsEarned100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DirectPremiumsEarned us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Direct
Period End2021-06-302021-03-312020-06-302020-03-31
Value582583498545
Percentage of DirectPremiumsEarned27.828.927.929.9

mkl:ProgramServicesandOther


Direct
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value491498545576538514
Percentage of DirectPremiumsEarned27.127.929.932.131.731.3

mkl:UnderwritingOperations


Direct
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value15111431132312871275121911591131111310701037966914
Percentage of DirectPremiumsEarned72.271.172.972.170.167.968.368.769.969.471.0100.0100.0

us-gaap:DirectPremiumsWritten

us-gaap:DirectPremiumsWritten


Direct
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
Value24932157204819382027173817781942197516451617173717321497124010351046849836888957879842878951801864841976795832836877597547519530518474501508473402444448
Percentage of DirectPremiumsWritten100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DirectPremiumsWritten us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Direct
Period End2021-06-302021-03-312020-06-302020-03-31
Value737608567388
Percentage of DirectPremiumsWritten29.628.228.022.4

mkl:ProgramServicesandOther


Direct
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value518567388584652517
Percentage of DirectPremiumsWritten26.828.022.430.133.031.5

mkl:UnderwritingOperations


Direct
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value1756154914201460134913581323112712071182103910351046
Percentage of DirectPremiumsWritten70.471.873.272.077.669.967.068.569.568.369.4100.0100.0

us-gaap:DividendsPreferredStock us-gaap:StatementEquityComponents

us-gaap:DividendsPreferredStock

mkl:TotalEquity


Dividends
Period End2021-06-30
Value-18.0
Percentage of DividendsPreferredStock100.0

us-gaap:Parent


Dividends
Period End2021-06-30
Value-18.0
Percentage of DividendsPreferredStock100.0

us-gaap:RetainedEarnings


Dividends
Period End2021-06-30
Value-18.0
Percentage of DividendsPreferredStock100.0

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents


Effect
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value8.044-12.989532512-35.23327-19.473-9.8337.199-8.951-5.214-32.95626-20.04340186.466-31.654-3.396
Percentage of EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EquitySecuritiesFvNiGainLoss

us-gaap:EquitySecuritiesFvNiGainLoss


Equity
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
Value670523845534914-1691.17953331425611-843.032426112-122.052
Percentage of EquitySecuritiesFvNiGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EquitySecuritiesFvNiRealizedGainLoss

us-gaap:EquitySecuritiesFvNiRealizedGainLoss


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value1.3453.117-16.751682-39.0652.505-0.345
Percentage of EquitySecuritiesFvNiRealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EquitySecuritiesFvNiUnrealizedGainLoss

us-gaap:EquitySecuritiesFvNiUnrealizedGainLoss


Equity
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value669520862518831-1652.11453132
Percentage of EquitySecuritiesFvNiUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1


Fair
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value-0.057-2.355-1.02-0.1260.87-3.3213.2257.358-7.3242.047-67.6832.418-25.322-18.059-12.465-51.6395.9236.2110.7996.8816.5816.6920.00.00.00.0
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases


Fair
Period End2020-12-312020-09-302020-06-302020-03-312020-01-012019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value0.00.00.090900.00.00.50.00.00.00.0280.0491.256.00.00.0251700.00.00.00.0
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases0.00.00.0100.0100.00.00.0100.00.00.00.00.0100.00.0100.0100.0100.00.00.0100.0100.00.00.00.00.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales


Fair
Period End2021-06-302020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-30
Value154213161.3641.7220.8570.06.8690.6820.06.401280.00.01.303250.00.0250.00.00.00.0
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0100.0100.00.00.0100.0100.00.00.0100.00.00.00.00.0

us-gaap:ForeignCurrencyTransactionGainLossRealized

us-gaap:ForeignCurrencyTransactionGainLossRealized


Foreign
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value-12.25725-87.117-65.577-21.4678-59.2665325-21.864411.38386-22.1140.3941.7720.8790.095
Percentage of ForeignCurrencyTransactionGainLossRealized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeLossFromEquityMethodInvestments

us-gaap:IncomeLossFromEquityMethodInvestments


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-31
Value9.0183.9257.4192.4835.647-19.9790.9320.3661.1741.8961.344-3.556-1.491.7780.4424.2391.8024.5931.9521.2323.921-0.253-3.314-0.0041.7121.344-2.5282.2531.4583.5836.1878.8284.8931.99
Percentage of IncomeLossFromEquityMethodInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements us-gaap:AwardType

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements

us-gaap:RestrictedStockUnitsRSU


Incremental
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value24000.022000.018000.013000.008000.015000.012000.016000.0-24000.026000.025000.027000.0-1000.042000.040000.046000.0-1000.049000.072000.075000.04000.071000.068000.081000.04000.065000.061000.052000.04000.039000.034000.027000.01000.023000.021000.0
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncurredClaimsPropertyCasualtyAndLiability

us-gaap:IncurredClaimsPropertyCasualtyAndLiability


Incurred
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
Value81487981486371310767737526786878697365996156551075522611485579511473470484536446478570610542552533442287340303221288282306306314209224251260
Percentage of IncurredClaimsPropertyCasualtyAndLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestIncomeDepositsWithFinancialInstitutions

us-gaap:InterestIncomeDepositsWithFinancialInstitutions


Interest
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value0.8740.6720.8050.8942.3791012141310121311108.217.7795.8344.9493.3542.8782.6542.2911.5691.2871.1161.2511.3471.531.6081.4741.2571.0420.6040.670.760.7210.679
Percentage of InterestIncomeDepositsWithFinancialInstitutions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestIncomeSecuritiesTaxExempt

us-gaap:InterestIncomeSecuritiesTaxExempt


Interest
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value14151515161617171718191920202121222222222221212124252524252320202021222222
Percentage of InterestIncomeSecuritiesTaxExempt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestIncomeSecuritiesTaxable us-gaap:InvestmentType

us-gaap:InterestIncomeSecuritiesTaxable

mkl:OtherTaxableBonds


Interest
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value40393938393940404140414039373736363435363635353434353838403540383321242526
Percentage of InterestIncomeSecuritiesTaxable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:TaxableMunicipalBonds


Interest
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value16161616161617181818181818171717171716161615141414141413128.9968.5747.4526.6135.7035.6085.675.685
Percentage of InterestIncomeSecuritiesTaxable40.441.941.742.442.542.342.745.545.145.644.945.546.147.147.248.849.050.247.345.543.945.041.542.741.640.137.234.931.425.221.019.519.826.723.022.421.1

us-gaap:InvestmentIncomeDividend

us-gaap:InvestmentIncomeDividend


Investment
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value1925222018282625222524212024212119201817161719171819181414161312101219109.512
Percentage of InvestmentIncomeDividend100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InvestmentIncomeInterestAndDividend

us-gaap:InvestmentIncomeInterestAndDividend


Investment
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value10010010294989311511711511811811110911210510810310498969995889094969694969091898167776665
Percentage of InvestmentIncomeInterestAndDividend100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InvestmentIncomeInvestmentExpense

us-gaap:InvestmentIncomeInvestmentExpense


Investment
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-30
Value4.1534.3434.4283.8473.0844.863.3544.0263.9164.1993.8144.9863.6644.2864.2544.2364.2254.3165.1733.7544.2714.0096.1313.1613.813.8953.3333.8683.8384.2212.9173.5833.1222.6593.532.2791.968
Percentage of InvestmentIncomeInvestmentExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1


Liability
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
Value145522802511585826020415055276194133623291551285721316311836
Percentage of LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1


Liability
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
Value557633372374445587381423537635396365496576327356342486309345381493
Percentage of LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss


Liability
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
Value-0.9510.4751.4151.777-1.509-0.4881.736-1.4290.782-0.022-0.8680.4690.193-0.294-6.838.2492.944-0.6112.022-1.3360.4170.957
Percentage of LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1

us-gaap:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1


Liability
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
Value81487981486371310767737526776878697365996156551075522615485579511485
Percentage of LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments

us-gaap:MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments


Marketable
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302012-12-312012-09-302012-06-302011-12-312011-09-302011-06-30
Value4.935-2.8129.738-2.2460.15-0.0670.681-2.89-0.496-7.642-0.946-3.46-36.56318245.5862720291303.5746.10510187.0468.12717221116148.399.20815226.219
Percentage of MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:MinorityInterestDecreaseFromRedemptions us-gaap:StatementEquityComponents

us-gaap:MinorityInterestDecreaseFromRedemptions

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Minority
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302015-12-312015-09-30
Value0.00.1470.00.01.7775.2520.0-0.4830.05.0250.07.0650.00.0390.00.06.1790.00.0-0.460.00.0
Percentage of MinorityInterestDecreaseFromRedemptions0.0100.00.00.0100.0100.00.0100.00.0100.00.0100.00.0100.00.00.0100.00.00.0100.00.00.0

mkl:TotalEquity


Minority
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302015-12-312015-09-30
Value0.00.5310.00.01.2984.8330.00.4830.03.7360.0-0.60.1955.3910.2660.02.0498.970.00.5490.00.0
Percentage of MinorityInterestDecreaseFromRedemptions0.0361.20.00.073.092.00.0-100.00.074.30.0-8.50.013823.10.00.033.20.00.0-119.30.00.0

us-gaap:CommonStock


Minority
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302015-12-312015-09-302010-12-312010-09-30
Value0.00.5310.00.01.2984.8330.00.4830.03.7360.0-0.60.1955.3910.0450.02.0490.8610.00.5490.00.0-16.690.0
Percentage of MinorityInterestDecreaseFromRedemptions0.0361.20.00.073.092.00.0-100.00.074.30.0-8.50.013823.10.00.033.20.00.0-119.30.00.00.00.0

us-gaap:Parent


Minority
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302015-12-312015-09-30
Value0.00.5310.00.01.2984.8330.00.4830.03.7360.0-0.60.1955.3910.0450.02.0490.8610.00.5490.00.0
Percentage of MinorityInterestDecreaseFromRedemptions0.0361.20.00.073.092.00.0-100.00.074.30.0-8.50.013823.10.00.033.20.00.0-119.30.00.0

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value64-271.215687721678-129.4179219921884-101.666-138.094-144.121289328283
Percentage of OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax us-gaap:FinancialInstrument

us-gaap:FixedMaturities


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value62-321.232769623698-80.0589519721787-103.083-143.593-144.168-14.7472079
Percentage of OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax96.9118.4110.8124.8109.0124.861.9102.498.799.4103.0101.4104.0100.0-5.16.228.0

us-gaap:ShortTermInvestments


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1.0950.6844.4971.4253.128-6.7062.031-2.2662.5061.355-2.5271.4175.4990.047-0.1160.0160.133
Percentage of OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax1.7-0.36.51.81.4-8.5-1.6-2.41.30.6-3.0-1.4-4.0-0.0-0.00.00.0

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value51-214.464546117165-31.8964812915267-80.429-104.036-116.108199222189
Percentage of OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax


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-0.654-0.5928.42-0.538-0.8840.0-2.704-0.462-0.515-1.361-0.6-0.509-0.568-0.664-3.868-0.773-0.902-0.71620-0.39-0.394-0.4631.759-0.475-0.469-0.46315-0.32-0.325-0.319-2.919-0.41-0.366-0.37-5.177-0.522-0.482-0.48310-0.379-0.355
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax


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
Value55-214.376546417264-29.9884812815264-91.002-98.145-116.922209227190160-135.7332314923818-149.266-230.142121339-7.53220814711884-158.6918120100-8.029153147-90.336420-19.504167-49.92797
Percentage of OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherUnderwritingExpense

us-gaap:OtherUnderwritingExpense


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value215204205196187199190194199193183200202182172165186168183170187174
Percentage of OtherUnderwritingExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherUnderwritingExpense us-gaap:StatementBusinessSegments

mkl:Insurance


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value204187181179167183177171179175167172180169159142163146
Percentage of OtherUnderwritingExpense94.991.788.691.489.491.993.388.390.190.991.686.189.493.192.286.487.686.8

mkl:Other


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-2.4812.698-0.002-0.7182.3630.164-2.2742.417-3.4873.105-0.3051.6480.2140.384
Percentage of OtherUnderwritingExpense-1.21.3-0.0-0.41.30.1-1.21.2-1.81.6-0.20.80.10.2

mkl:Reinsurance


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value13142317171515202314152621121123232230342330
Percentage of OtherUnderwritingExpense6.26.911.49.09.48.07.910.511.77.58.513.110.56.66.614.512.613.616.720.012.417.6

us-gaap:PaymentsForLossesAndLossAdjustmentExpense

us-gaap:PaymentsForLossesAndLossAdjustmentExpense


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value702685652626604646642627688691673559629639656512471543522508499530
Percentage of PaymentsForLossesAndLossAdjustmentExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsForProceedsFromOtherInvestingActivities

us-gaap:PaymentsForProceedsFromOtherInvestingActivities


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
Value-3.85-42.637-55.09513-46.2469.949-15.97-3.3160.8071.6849.842.664280.716-13.3722.113-0.1665.8550.956-0.2130.4120.1930.0361.25-0.930.4410.8811.6890.182-0.3841.809-5.3960.0462.438-6.8387.4872.985-1.476-1.759-29.4786.165201.908-17.614-1.59414
Percentage of PaymentsForProceedsFromOtherInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsForProceedsFromShortTermInvestments

us-gaap:PaymentsForProceedsFromShortTermInvestments


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
Value564663131965674-942.695-355.541157623-329.659-844.348-36.86-91.396-129.032171271-515.644-162.324348-7.593671-322.887-625.54991449146-84.454-54.757398-130.557293158-391.74102442593.694-79.23348-107.181167107-30.37-47.11523-148.411
Percentage of PaymentsForProceedsFromShortTermInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsOfDividendsMinorityInterest

us-gaap:PaymentsOfDividendsMinorityInterest


Payments
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-31
Value1117000.02366000.01842000.01845000.02246000.02093000.02808000.01200000.02149000.01109000.04706000.01970000.01584000.02004000.02341000.02018000.0744000.02149000.01038000.02563000.01234000.01331000.01159000.01782000.0931000.01364000.01168000.01141000.01204000.0747000.02032000.02863000.0470000.02736000.01615000.06840000.0
Percentage of PaymentsOfDividendsMinorityInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireAdditionalInterestInSubsidiaries

us-gaap:PaymentsToAcquireAdditionalInterestInSubsidiaries


Payments
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-312010-09-30
Value0.03.075110.00.00.09.7540.06.4650.1956.8630.2660.09.0988.970.00.0893.0780.00.00.02.16100.00.08.16170.03.4120.08.441.8230.00.320.00.00.00.00.0
Percentage of PaymentsToAcquireAdditionalInterestInSubsidiaries0.0100.0100.00.00.00.0100.00.0100.0100.0100.0100.00.0100.0100.00.0100.0100.00.00.00.0100.0100.00.00.0100.0100.00.0100.00.0100.0100.00.0100.00.00.00.00.00.0

us-gaap:PaymentsToAcquireBusinessesNetOfCashAcquired

us-gaap:PaymentsToAcquireBusinessesNetOfCashAcquired


Payments
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
Value6.280.05470.02190.397159.411633.51-0.0057.8098393901983.811.7650.01.1624.62610.00.00.02.77914715153-1.15621-44.28736-2.507102628099141.9553.8861734.9671223
Percentage of PaymentsToAcquireBusinessesNetOfCashAcquired100.00.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.00.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireEquityMethodInvestments

us-gaap:PaymentsToAcquireEquityMethodInvestments


Payments
Period End2020-12-312019-12-312018-12-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302011-12-312011-09-30
Value0.0405.2174.353.11.1260.00.3852.04180.66.640.3581.0338.0513195.7910.02.00.4-0.720.0
Percentage of PaymentsToAcquireEquityMethodInvestments0.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.00.0

us-gaap:PolicyholderBenefitsAndClaimsIncurredGross us-gaap:StatementBusinessSegments

us-gaap:PolicyholderBenefitsAndClaimsIncurredGross

mkl:ProgramServicesAndOtherFronting


Policyholder
Period End2021-06-302020-06-30
Value636394
Percentage of PolicyholderBenefitsAndClaimsIncurredGross100.0100.0

mkl:UnderwritingOperations


Policyholder
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value9931073105410238681243885846893821
Percentage of PolicyholderBenefitsAndClaimsIncurredGross156.00.00.00.0220.00.00.00.00.00.0

us-gaap:PremiumsPercentageAssumedToNet

us-gaap:PremiumsPercentageAssumedToNet


Premiums
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value24.025.0-1.027.00.270.2600.270.290.2500.280.280.29-0.010.320.30.3100.30.310.3-0.010.30.320.3300.320.350.37
Percentage of PremiumsPercentageAssumedToNet100.0100.0100.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0

us-gaap:PremiumsWrittenGross

us-gaap:PremiumsWrittenGross


Premiums
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
Value288428042297227223732322201322642247225517762043199720461360132813571460996112912771392956115812651252100510961343135999910761100743607610
Percentage of PremiumsWrittenGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PremiumsWrittenGross us-gaap:RelatedPartyTransactionsByRelatedParty

mkl:HagertyGroupLLC


Premiums
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value1761191071441541008812012884
Percentage of PremiumsWrittenGross6.14.34.76.46.54.34.45.35.73.7

mkl:Syndicate2357andcertainotherNephilaReinsurers


Premiums
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value18611779119122906412614193
Percentage of PremiumsWrittenGross6.54.23.55.25.23.93.25.66.34.1

us-gaap:PremiumsWrittenGross us-gaap:StatementBusinessSegments

mkl:Insurance


Premiums
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value18211638154615141553141413401418136811921173124812331093102010981109912
Percentage of PremiumsWrittenGross63.258.467.366.665.560.966.662.660.952.966.161.161.853.475.082.781.762.5

mkl:Other


Premiums
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
Value783634578536596394521619655548487561554461
Percentage of PremiumsWrittenGross27.222.625.223.625.117.025.927.429.224.327.427.527.822.5

mkl:Reinsurance


Premiums
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
Value279532172222223513151226223513115234208492862302475471211962694538923925837711320630248912320117962
Percentage of PremiumsWrittenGross9.719.07.59.89.422.17.510.09.922.86.511.510.524.16.317.318.337.512.117.421.132.69.420.620.430.211.318.822.636.012.418.716.38.4

us-gaap:PremiumsWrittenNet

us-gaap:PremiumsWrittenNet


Premiums
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
Value17511881143213971456164612581370130514771055121611801334922109711371260839929105011817969531034103581188110841139803842927662526539566581467524530519401467454
Percentage of PremiumsWrittenNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PremiumsWrittenNet us-gaap:ProductOrService

mkl:ProgramServicesAndOtherFronting


Premiums
Period End2021-06-302021-03-312020-06-302020-03-31
Value-0.471-0.462-0.828-2.03
Percentage of PremiumsWrittenNet-0.0-0.0-0.1-0.1

mkl:ProgramServicesandOther


Premiums
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value-1.384-0.828-2.030.7290.6510.24
Percentage of PremiumsWrittenNet-0.1-0.1-0.10.10.00.0

mkl:UnderwritingOperations


Premiums
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value1751188113981457164813691304147612151179133410971137
Percentage of PremiumsWrittenNet100.0100.0100.1100.1100.199.9100.0100.0100.099.999.9100.0100.0

us-gaap:PremiumsWrittenNet us-gaap:StatementBusinessSegments

mkl:Insurance


Premiums
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value14941387129312201267119511381181112699896810211001912843908917770
Percentage of PremiumsWrittenNet85.373.890.487.387.172.690.486.286.367.691.884.084.868.491.582.780.661.1

mkl:Other


Premiums
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-0.347-0.445-1.356-1.772-0.411-2.0080.7031.2850.666-0.232-0.234-0.7620.7510.765
Percentage of PremiumsWrittenNet-0.0-0.0-0.1-0.1-0.0-0.10.10.10.1-0.0-0.0-0.10.10.1

mkl:Reinsurance


Premiums
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
Value25749413917818845211918717847887195178421781892204891121572264028820421531610016625343511715115259
Percentage of PremiumsWrittenNet14.726.39.712.813.027.59.513.713.732.48.316.115.131.58.517.319.438.813.416.921.634.111.121.420.830.512.418.923.338.314.617.916.59.0

us-gaap:ProceedsFromDebtNetOfIssuanceCosts us-gaap:DebtInstrument

us-gaap:ProceedsFromDebtNetOfIssuanceCosts

mkl:ThreePointFourFivePercentUnsecuredSeniorNotesDueMay2052


Proceeds
Period End2021-05-04
Value591
Percentage of ProceedsFromDebtNetOfIssuanceCosts100.0

us-gaap:ProceedsFromIssuanceOfDebt

us-gaap:ProceedsFromIssuanceOfDebt


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value741152332673896684464787613656526221210195.7632051616208.541132725341910-16.699468.965507313874132337.47725935
Percentage of ProceedsFromIssuanceOfDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value1711001341482541043251401771289284183191181272274401229262255216341351422388310326342440624360370120156971371198753891121176012679
Percentage of ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromPaymentsForOtherFinancingActivities

us-gaap:ProceedsFromPaymentsForOtherFinancingActivities


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-28.081-5.039-56.118-1.056-1.059-1.057-1.387-1.745-1.706-1.11415-15.929-2.05-1.238-2.4883.36-6.242-1.463-0.895-1.05-3.333-10.0950.7321.234-9.047-3.407-1.283-16.219-3.246-0.6090.2230.008-2.6372.383-3.614.515-18.1986.953-6.938-0.167-0.914-0.1031.281-0.254-11.2940.0
Percentage of ProceedsFromPaymentsForOtherFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:ProceedsFromSaleMaturityAndCollectionsOfInvestments

us-gaap:ProceedsFromSaleMaturityAndCollectionsOfInvestments


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value6969351171160266279398133571279314021797
Percentage of ProceedsFromSaleMaturityAndCollectionsOfInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromSaleOfEquityMethodInvestments

us-gaap:ProceedsFromSaleOfEquityMethodInvestments


Proceeds
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value0.00.015220-215.4970.0550.4150.0570.4742.407-0.5352.8460.9995.480.9510.8396.362155.354117.718285152750.00.00.0
Percentage of ProceedsFromSaleOfEquityMethodInvestments0.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.0

us-gaap:ProceedsFromSaleOfProductiveAssets

us-gaap:ProceedsFromSaleOfProductiveAssets


Proceeds
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value190.2080.3812.168-0.174131.2370.1910.1
Percentage of ProceedsFromSaleOfProductiveAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded us-gaap:LiabilityForCatastropheClaimsByCatastrophicEvent

us-gaap:ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded

mkl:COVID19Pandemic


Reinsurance
Period End2020-12-31
Value13
Percentage of ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded100.0

us-gaap:ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded us-gaap:StatementBusinessSegments

mkl:ProgramServicesAndOtherFronting


Reinsurance
Period End2021-06-302021-03-312020-06-302020-03-31
Value-637.3443-395.0308
Percentage of ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded0.00.00.00.0

mkl:ProgramServicesandOther


Reinsurance
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value500412394308500412338365
Percentage of ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded3676.50.00.00.00.00.00.00.0

mkl:UnderwritingOperations


Reinsurance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value177191-240.745-160.387-154.307-167.18-112.844-94.362-215.389-134.023
Percentage of ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded0.00.0-1770.20.00.00.00.00.00.00.0

us-gaap:RepaymentsOfDebtAndCapitalLeaseObligations

us-gaap:RepaymentsOfDebtAndCapitalLeaseObligations


Repayments
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value145711356230566773643657710235841299.917183121216321213294317148.6081.884483.037268501914327334.3551933
Percentage of RepaymentsOfDebtAndCapitalLeaseObligations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StockIssuedDuringPeriodSharesAcquisitions us-gaap:BusinessAcquisition, us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodSharesAcquisitions

mkl:LansingBuildingProductsLLC, mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Stock
Period End2020-09-302020-06-30
Value0.043
Percentage of StockIssuedDuringPeriodSharesAcquisitions0.0100.0

us-gaap:StockIssuedDuringPeriodSharesNewIssues us-gaap:StatementClassOfStock, us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodSharesNewIssues

us-gaap:CommonStock, us-gaap:CommonStock


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-31
Value2000.01000.08000.02000.01000.02000.0
Percentage of StockIssuedDuringPeriodSharesNewIssues100.0100.0100.0100.0100.0100.0

us-gaap:PreferredStock, us-gaap:PreferredStock


Stock
Period End2020-09-302020-06-30
Value0600000.0
Percentage of StockIssuedDuringPeriodSharesNewIssues0.060000.0

us-gaap:StockRepurchasedDuringPeriodShares us-gaap:StatementEquityComponents

us-gaap:StockRepurchasedDuringPeriodShares

us-gaap:CommonStock


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value33000.019000.03000.00021000.030000.012000.031000.037000.020000.06000.011000.011000.024000.024000.037000.024000.042000.0015000.01000.05000.05000.0
Percentage of StockRepurchasedDuringPeriodShares100.0100.0100.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0

us-gaap:StockRepurchasedDuringPeriodValue us-gaap:StatementEquityComponents

us-gaap:StockRepurchasedDuringPeriodValue

mkl:TotalEquity


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value38222.8890.00.0782334123137236.572111226253523350.297140.724.2294.592
Percentage of StockRepurchasedDuringPeriodValue100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Parent


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value38222.8890.00.0782334123137236.572111226253523350.297140.724.2294.592
Percentage of StockRepurchasedDuringPeriodValue100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RetainedEarnings


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302010-12-312010-09-302010-06-302010-03-31
Value38222.8890.00.0782334123137236.572111226253523350.297140.724.2294.5922.2999.47719-87.2981728-4.387
Percentage of StockRepurchasedDuringPeriodValue100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.00.00.00.0

us-gaap:StockholdersEquityOther us-gaap:StatementEquityComponents

us-gaap:StockholdersEquityOther

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value3050000.02264000.04501000.0982000.02366000.01842000.0420000.02247000.01974000.03007000.0629000.02119000.01109000.04706000.02070000.01575000.02010000.02343000.02016000.0738000.02149000.0993000.02478000.01864000.0
Percentage of StockholdersEquityOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:TotalEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value-1148000.0-299000.0-1914000.0-33000.0-1175000.0-508000.0113000.0-293000.0-2277000.0-1217000.02250000.0-2708000.0872000.09000.0-31000.0-102000.0874000.0-260000.022000.0-31000.01158000.0-1110000.0-2100000.0-2645000.0
Percentage of StockholdersEquityOther-37.6-13.2-42.5-3.4-49.7-27.626.9-13.0-115.3-40.5357.7-127.878.60.2-1.5-6.543.5-11.11.1-4.253.9-111.8-84.7-141.9

us-gaap:CommonStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value88000.0-645000.0243000.000-16000.0-267000.000165000.0-1000.0-1309000.01369000.0-11000.0-38000.0-105000.0436000.017000.0001271000.0-1271000.0-2222000.0-2342000.0-294000.098000.034000.0-234000.052000.065000.0000
Percentage of StockholdersEquityOther2.9-28.55.40.00.0-0.9-63.60.00.05.5-0.2-61.8123.4-0.2-1.8-6.721.70.70.00.059.1-128.0-89.7-125.60.00.00.00.00.00.00.00.00.0

us-gaap:NoncontrollingInterest


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-1131000.0347000.0-2056000.0-509000.0-800000.0-752000.0232000.0-290000.0-1955000.0-1957000.0-1000.033000.0-32000.01000.0-97000.0-38000.0-80000.041000.02000.027000.0045000.085000.0-303000.01418000.08076000.0594000.01638000.0-359000.0-1260000.0254000.0242000.014000.0
Percentage of StockholdersEquityOther-37.115.3-45.7-51.8-33.8-40.855.2-12.9-99.0-65.1-0.21.6-2.90.0-4.7-2.4-4.01.70.13.70.04.53.4-16.30.00.00.00.00.00.00.00.00.0

us-gaap:Parent


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value-17000.0-646000.0142000.0476000.0-375000.0244000.0-119000.0-3000.0-322000.0740000.02251000.0-2741000.0904000.08000.066000.0-64000.0954000.0-301000.020000.0-58000.01158000.0-1155000.0-2185000.0-2342000.0
Percentage of StockholdersEquityOther-0.6-28.53.248.5-15.813.2-28.3-0.1-16.324.6357.9-129.481.50.23.2-4.147.5-12.81.0-7.953.9-116.3-88.2-125.6

us-gaap:RetainedEarnings


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-31
Value-105000.0-1000.0-101000.0476000.0-375000.0260000.0148000.0-3000.0-322000.0575000.02252000.0-1432000.0-465000.019000.0104000.041000.0518000.0-318000.020000.0-58000.0-113000.0116000.037000.00000000000
Percentage of StockholdersEquityOther-3.4-0.0-2.248.5-15.814.135.2-0.1-16.319.1358.0-67.6-41.90.45.02.625.8-13.61.0-7.9-5.311.71.50.00.00.00.00.00.00.00.00.00.0

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value9509709851030877118097190079675710308607567238171226684638652660651592639647
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense us-gaap:LiabilityForCatastropheClaimsByCatastrophicEvent

mkl:A2021Catastrophes


Supplemental
Period End2021-06-302021-03-31
Value3.664
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense0.46.6

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense us-gaap:StatementBusinessSegments

mkl:Insurance


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value7837988198177301006732722657618740674610570602808538492
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense82.482.283.179.383.285.375.480.282.581.671.978.380.778.873.765.978.677.2

mkl:Reinsurance


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value166172166213147173238178139139289186145153214418146145133129152130129128
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense17.617.816.920.716.814.724.619.817.518.428.121.719.321.226.334.121.422.820.519.723.422.020.219.8

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense


Supplemental
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value-135.189-90.87-170.947-167.247-164.148-104.072-198.365-147.993-118.739-70.21-161.26-124.127-157.546-108.067-162.133-151.127-161.628-22.739-154.775-80.717-139.719-106.595-168.679-163.115
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense us-gaap:ProductOrService

mkl:MarineAndEnergyGeneralLiabWorkersCompAndPropertyInsuranceSegment


Supplemental
Period End2021-03-31
Value-89.1
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense98.1

us-gaap:SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense us-gaap:StatementBusinessSegments

mkl:Reinsurance


Supplemental
Period End2021-03-312020-03-312016-09-302015-09-30
Value-18.613-19.135-24.241
Percentage of SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense20.5-13.423.714.9

us-gaap:TemporaryEquityAccretionToRedemptionValue us-gaap:StatementEquityComponents

us-gaap:TemporaryEquityAccretionToRedemptionValue

mkl:RedeemableNoncontrollingInterestsTemporaryEquity


Temporary
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value-13.717-7.9068.0242313-16.0138.35912-3.324-18.361-1.79312-0.363-5.051103.2985.141154.5634.9282.5293.452-1.053-1.376
Percentage of TemporaryEquityAccretionToRedemptionValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:TotalEquity


Temporary
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value137.906-8.024-23.621-13.07316-8.359-12.2213.324181.793-12.0350.3635.051-10.156-3.298-5.141-15.143-4.563-4.928-2.529-3.4521.0531.376
Percentage of TemporaryEquityAccretionToRedemptionValue-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0

us-gaap:Parent


Temporary
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value137.906-8.024-23.621-13.07316-8.359-12.2213.324181.793-12.0350.3635.051-10.156-3.298-5.141-15.143-4.563-4.928-2.529-3.4521.0531.376
Percentage of TemporaryEquityAccretionToRedemptionValue-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0

us-gaap:RetainedEarnings


Temporary
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value137.906-8.024-23.621-13.07316-8.359-12.2213.324181.793-12.0350.3635.051-10.156-3.298-5.141-15.143-4.563-4.928-2.529-3.4521.0531.376
Percentage of TemporaryEquityAccretionToRedemptionValue-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0-100.0

us-gaap:TemporaryEquityAccretionToRedemptionValueAdjustment

us-gaap:TemporaryEquityAccretionToRedemptionValueAdjustment


Temporary
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-13.717-7.9068.0242313-16.0138.35912-3.324-18.361-1.79312-0.363-5.051103.2985.141154.5634.9282.5293.452-1.053-1.376-3.0621.3474.3431.2592.701-0.1171.1380.0-0.215-2.886-3.383-1.7028.1860.00.00.00.0
Percentage of TemporaryEquityAccretionToRedemptionValueAdjustment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.00.00.00.00.0

dei:EntityCommonStockSharesOutstanding

dei:EntityCommonStockSharesOutstanding


Entity
Period End2021-07-272021-04-212021-02-022020-10-20
Value13131313
Percentage of EntityCommonStockSharesOutstanding100.0100.0100.0100.0

mkl:AdjustedLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet

mkl:AdjustedLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet


Adjusted
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value9547937892439015811981058401827045914638459245354551
Percentage of AdjustedLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:CumulativeAdjustmentLifeandAnnuityBenefits

mkl:CumulativeAdjustmentLifeandAnnuityBenefits


Cumulative
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-31
Value6970119107876451
Percentage of CumulativeAdjustmentLifeandAnnuityBenefits100.0100.0100.0100.0100.0100.0100.0

mkl:DeferredTaxAssetsTaxDeferredExpenseLeaseLiabilities

mkl:DeferredTaxAssetsTaxDeferredExpenseLeaseLiabilities


Deferred
Period End2020-12-312019-12-312018-12-31
Value135550.0
Percentage of DeferredTaxAssetsTaxDeferredExpenseLeaseLiabilities100.0100.00.0

mkl:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLifeAndAnnuityBenefits

mkl:DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLifeAndAnnuityBenefits


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value1088478771351561431610.0
Percentage of DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLifeAndAnnuityBenefits100.0100.0100.0100.0100.0100.0100.0100.00.0

mkl:DeferredTaxLiabilitiesRightofuseLeaseAssets

mkl:DeferredTaxLiabilitiesRightofuseLeaseAssets


Deferred
Period End2020-12-312019-12-312018-12-31
Value127490.0
Percentage of DeferredTaxLiabilitiesRightofuseLeaseAssets100.0100.00.0

mkl:FundsAtLloyds

mkl:FundsAtLloyds


Funds
Period End2020-12-31
Value1100
Percentage of FundsAtLloyds100.0

mkl:FundsatLloydsHoldingCompany

mkl:FundsatLloydsHoldingCompany


Fundsat
Period End2020-12-31
Value374
Percentage of FundsatLloydsHoldingCompany100.0

mkl:GrossDeferredTaxAssetsEstimatedAmountRealizedThroughReversalofDeferredTaxLiabilities

mkl:GrossDeferredTaxAssetsEstimatedAmountRealizedThroughReversalofDeferredTaxLiabilities


Gross
Period End2020-12-31
Value666
Percentage of GrossDeferredTaxAssetsEstimatedAmountRealizedThroughReversalofDeferredTaxLiabilities100.0

mkl:IBNRReservesPercentageOfTotalUnpaidLossesAndLossAdjustmentExpenses

mkl:IBNRReservesPercentageOfTotalUnpaidLossesAndLossAdjustmentExpenses


I
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value66.00.650.640.640.670.65
Percentage of IBNRReservesPercentageOfTotalUnpaidLossesAndLossAdjustmentExpenses100.0100.0100.0100.0100.0100.0

mkl:InvestmentInConsolidatedSubsidiaries us-gaap:ConsolidatedEntities

mkl:InvestmentInConsolidatedSubsidiaries

srt:ParentCompany


Investment
Period End2020-12-312019-12-312018-12-312017-12-31
Value1225912239106979510
Percentage of InvestmentInConsolidatedSubsidiaries100.0100.0100.0100.0

mkl:InvestmentInLodgepineFundLimited us-gaap:SubsequentEventType

mkl:InvestmentInLodgepineFundLimited

us-gaap:SubsequentEvent


Investment
Period End2021-07-01
Value18
Percentage of InvestmentInLodgepineFundLimited100.0

mkl:Investmentinunconsolidatedvariableinterestentitycarryingamount us-gaap:ConsolidatedEntities

mkl:Investmentinunconsolidatedvariableinterestentitycarryingamount

mkl:UnconsolidatedMarkelCATCoFund2


Investmentinunconsolidatedvariableinterestentitycarryingamountus-gaap:
Period End2021-06-302021-03-312020-12-312019-12-31
Value41565826
Percentage of Investmentinunconsolidatedvariableinterestentitycarryingamount100.0100.0100.0100.0

mkl:Investmentinunconsolidatedvariableinterestentitycarryingamount us-gaap:InvestmentsByConsolidatedAndNonconsolidatedEntities

mkl:UnconsolidatedMarkelCATCoFund2


Investmentinunconsolidatedvariableinterestentitycarryingamountus-gaap:
Period End2020-09-302019-12-31
Value9226
Percentage of Investmentinunconsolidatedvariableinterestentitycarryingamount0.0100.0

mkl:InvestmentsAvailableforSale

mkl:InvestmentsAvailableforSale


Investments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value147021356512715121411098910374111671174911120
Percentage of InvestmentsAvailableforSale100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:InvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax

mkl:InvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax


Investments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value7947461031957871661537625224
Percentage of InvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:InvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax

mkl:InvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax


Investments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value17330.9634.97416461423133
Percentage of InvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:InvestmentsAvailableforSaleAmortizedCostBasis

mkl:InvestmentsAvailableforSaleAmortizedCostBasis


Investments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value13925128521168511188101359761106431114811030
Percentage of InvestmentsAvailableforSaleAmortizedCostBasis100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:InvestorCapitalInLodgepineFundLimited us-gaap:SubsequentEventType

mkl:InvestorCapitalInLodgepineFundLimited

us-gaap:SubsequentEvent


Investor
Period End2021-07-01
Value98
Percentage of InvestorCapitalInLodgepineFundLimited100.0

mkl:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseEffectOfAdoptionOfASC326

mkl:LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseEffectOfAdoptionOfASC326


Liability
Period End2020-12-312020-09-302020-06-302020-03-312019-06-30
Value3849000.03849000.03849000.03849000.00
Percentage of LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseEffectOfAdoptionOfASC326100.0100.0100.0100.00.0

mkl:LifeAndAnnuityBenefitsReserveSingleContractConcentration

mkl:LifeAndAnnuityBenefitsReserveSingleContractConcentration


Life
Period End2020-12-31
Value33.9
Percentage of LifeAndAnnuityBenefitsReserveSingleContractConcentration100.0

mkl:LongTermDebtMaturitiesTotalFutureRepaymentsOfPrincipal

mkl:LongTermDebtMaturitiesTotalFutureRepaymentsOfPrincipal


Long
Period End2020-12-31
Value3522
Percentage of LongTermDebtMaturitiesTotalFutureRepaymentsOfPrincipal100.0

mkl:NetAssetsofUnconsolidatedVariableInterestEntitiesUnderManagement dei:LegalEntity

mkl:NetAssetsofUnconsolidatedVariableInterestEntitiesUnderManagement

mkl:UnconsolidatedMarkelCATCoFunds


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312018-12-31
Value72681792911002000260027003400
Percentage of NetAssetsofUnconsolidatedVariableInterestEntitiesUnderManagement100.0100.0100.0100.0100.0100.0100.0100.0

mkl:PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances us-gaap:CededCreditRisk, us-gaap:StatementBusinessSegments

mkl:PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances

mkl:FairfaxFinancialGroup, mkl:UnderwritingOperations


Percentage
Period End2020-12-312019-12-312018-12-312017-12-31
Value9.00.10.090.1
Percentage of PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances100.0100.0100.0100.0

mkl:FosunInternationalHoldingsLtd, mkl:ProgramServices


Percentage
Period End2020-12-312019-12-312018-12-312017-12-31
Value18.00.210.240.25
Percentage of PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances200.0210.0266.7250.0

mkl:TenLargestReinsurers, mkl:ProgramServices


Percentage
Period End2020-12-312019-12-312018-12-312017-12-31
Value70.00.710.750.79
Percentage of PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances777.8710.0833.3790.0

mkl:TenLargestReinsurers, mkl:UnderwritingOperations


Percentage
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value60.00.620.610.610.67
Percentage of PercentageOfReinsuranceRecoverableOnPaidAndUnpaidLossesBeforeConsideringReinsuranceAllowances666.7620.0677.8610.00.0

mkl:RestrictedInvestmentsAvailableForSale

mkl:RestrictedInvestmentsAvailableForSale


Restricted
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312015-09-302014-12-312013-12-31
Value421741344781467240684343501650405225
Percentage of RestrictedInvestmentsAvailableForSale100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance us-gaap:PlanName

mkl:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance

mkl:A2016CompensationPlan


Share
Period End2020-12-31
Value179560.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance100.0

mkl:ShorttermInvestmentsAvailableforSale

mkl:ShorttermInvestmentsAvailableforSale


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value3263273620341897929250119615451077
Percentage of ShorttermInvestmentsAvailableforSale100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax

mkl:ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value5551000.04327000.03645000.0682000.0489000.0429000.01355000.0364000.0443000.0
Percentage of ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedGainBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax

mkl:ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value133000.04000.06000.01540000.02772000.05840000.060000.01100000.02774000.0
Percentage of ShorttermInvestmentsAvailableforSaleAccumulatedGrossUnrealizedLossBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforSaleAmortizedCostBasis

mkl:ShorttermInvestmentsAvailableforSaleAmortizedCostBasis


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value3257273220301898931256119415461080
Percentage of ShorttermInvestmentsAvailableforSaleAmortizedCostBasis100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12Months

mkl:ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12Months


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value30959683491706566703.316115197
Percentage of ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12Months100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss

mkl:ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value133000.04000.06000.01540000.02772000.05840000.060000.01100000.02774000.0
Percentage of ShorttermInvestmentsAvailableforsaleContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionAccumulatedLoss

mkl:ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionAccumulatedLoss


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value133000.04000.06000.01540000.02772000.05840000.060000.01100000.02774000.0
Percentage of ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionTotal

mkl:ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionTotal


Shortterm
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302018-12-31
Value30959683491706566703.316115197
Percentage of ShorttermInvestmentsAvailableforsaleUnrealizedLossPositionTotal100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:TradeAccountsReceivableGross

mkl:TradeAccountsReceivableGross


Trade
Period End2020-09-302020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value3304292592592261811239397857351
Percentage of TradeAccountsReceivableGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

mkl:TradeAndOtherReceivables us-gaap:ConcentrationRiskByBenchmark

mkl:TradeAndOtherReceivables

mkl:CustomerswithContracts


Trade
Period End2021-06-302021-03-312020-12-312020-09-302019-12-31
Value615406406378263
Percentage of TradeAndOtherReceivables100.0100.0100.0100.0100.0

mkl:TraditionalLifeInterestRateAverage

mkl:TraditionalLifeInterestRateAverage


Traditional
Period End2020-12-31
Value2.3
Percentage of TraditionalLifeInterestRateAverage100.0

mkl:UnpaidLossesAndLossAdjustmentExpensesUnamortizedFairValueAdjustment

mkl:UnpaidLossesAndLossAdjustmentExpensesUnamortizedFairValueAdjustment


Unpaid
Period End2020-12-312016-12-312015-12-31
Value-56.4956891
Percentage of UnpaidLossesAndLossAdjustmentExpensesUnamortizedFairValueAdjustment100.0100.0100.0

us-gaap:AccountsReceivableGross

us-gaap:AccountsReceivableGross


Accounts
Period End2020-09-302020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value2030238621111866170815811253112611521161430365331
Percentage of AccountsReceivableGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccruedIncomeTaxes

us-gaap:AccruedIncomeTaxes


Accrued
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value17648351466337842.212
Percentage of AccruedIncomeTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivable

us-gaap:AllowanceForDoubtfulAccountsReceivable


Allowance
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value2426232218151311121719161513
Percentage of AllowanceForDoubtfulAccountsReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302018-12-31
Value7887411027957871660536624525224
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value7765967562344737302613202551
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax9.88.99.47.97.25.28.96.15.80.05.90.00.00.0

us-gaap:AssetBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0990.1130.1540.1680.1590.0010.0280.0460.0560.0090.0070.00.0010.008
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommercialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value10799149150148104578152173.1540.0130.6686.108
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax13.713.414.515.817.015.810.713.110.00.01.40.00.00.0

us-gaap:ForeignGovernmentDebtSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value19419627521017214113515816013398105113150
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax24.726.426.822.019.821.425.325.430.60.043.90.00.00.0

us-gaap:ResidentialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value434858677171324234156.171.0582.56414
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax5.56.65.77.18.210.86.16.76.50.02.80.00.00.0

us-gaap:USGovernmentSponsoredEnterprisesDebtSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value383151535048232819125.6713.6125.71911
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax4.94.35.05.65.87.44.54.63.80.02.50.00.00.0

us-gaap:USStatesAndPoliticalSubdivisions


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value3212943863883542482352722221569673107193
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax40.839.737.640.640.737.744.043.642.40.043.20.00.00.0

us-gaap:USTreasurySecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value5.0635.4679.0911011112.8833.2012.8941.0480.3080.020.0230.054
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax0.60.70.91.11.31.80.50.50.60.00.10.00.00.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302018-12-31
Value16330.9573.4341440142216133
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1.5372.9830.0030.6712.966.4511.6867.2492.6896.6461717132.737
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax9.19.00.319.521.116.011.731.915.90.013.00.00.00.0

us-gaap:CommercialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1.7783.0090.0340.0220.0350.4511.3820.233.9992444705816
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax10.59.13.60.60.21.19.61.023.70.033.20.00.00.0

us-gaap:ForeignGovernmentDebtSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value2.271.9670.0572.3729.943299.398147.0288.6932117122.41
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax13.45.96.069.170.971.965.262.741.60.016.10.00.00.0

us-gaap:ResidentialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0940.0130.0290.0280.0350.2650.5170.6631.4284.5441231204.863
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax0.60.03.00.80.20.73.62.98.40.09.30.00.00.0

us-gaap:USGovernmentSponsoredEnterprisesDebtSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value3.0759.110.0920.0240.00.00.20.0110.1040.8434.1148.0815.5440.818
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax18.227.49.60.70.00.01.40.00.60.03.10.00.00.0

us-gaap:USStatesAndPoliticalSubdivisions


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value3.565100.2350.281.0324.090.8120.1120.8476.1912850337.916
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax21.132.124.68.27.410.15.60.55.00.021.50.00.00.0

us-gaap:USTreasurySecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value4.6135.4690.5070.0370.0190.0290.4020.1990.4221.1131.9523.362.7971.819
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax27.216.553.01.10.10.12.80.92.50.01.50.00.00.0

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value106671011996559290920395049448960111133985299509946100259681955195159669970295919563959095569038893792099371992910123998310074101291024210599442445624833491651255172522352415256
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis us-gaap:ConsolidatedEntities

srt:ParentCompany


Available
Period End2020-12-312019-12-312018-12-312017-12-31
Value248658717533
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis2.67.07.25.6

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value73976176472075580684887190295297999710371186
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis6.97.57.97.88.28.59.09.18.19.79.810.010.412.4

us-gaap:AssetBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value3.5055.7135.8126.1658.1228.648119.881111319243034
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis0.00.10.10.10.10.10.10.10.10.10.20.20.30.4

us-gaap:CommercialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value17361761173616821730182017611708170916901691167216681244
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis16.317.418.018.118.819.218.617.815.417.217.016.816.613.0

us-gaap:ForeignGovernmentDebtSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value14231354135213331352140514151471147814811482146314541341
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis13.313.414.014.414.714.815.015.313.315.014.914.714.514.0

us-gaap:ResidentialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value776790811825836849855868877879886898910846
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis7.37.88.48.99.18.99.19.07.98.98.99.09.18.9

us-gaap:USGovernmentSponsoredEnterprisesDebtSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value725591500471323324318331337356357359360352
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis6.85.85.25.13.53.43.43.53.03.63.63.63.63.7

us-gaap:USStatesAndPoliticalSubdivisions


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value38623928390338983852396939544047414042064285428943794381
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis36.238.840.442.041.941.841.942.237.242.743.143.143.745.9

us-gaap:USTreasurySecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1400924580352343320282293295272248241184162
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis13.19.16.03.83.73.43.03.12.72.82.52.41.81.7

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value2570252223482169
Percentage of AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value2748268625922385
Percentage of AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value2849229818611512
Percentage of AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value2972241719941608
Percentage of AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value2311236925072746
Percentage of AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value2627264629423168
Percentage of AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value8773812479197510
Percentage of AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value8151756071016775
Percentage of AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value419370383346
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue


Available
Period End2021-06-302021-03-312020-12-312020-09-30
Value425373390348
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost us-gaap:FinancialInstrument

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost

us-gaap:AssetBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.5055.7135.8126.1658.1228.648119.8811113192430
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommercialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value1736176117361682173018201761170817091690169116721668
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost49556.230839.629873.727295.821310.021048.015955.217291.915331.412821.18624.36738.55519.7

us-gaap:ResidentialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value776790811825836849855868877879886898910
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost22143.213844.713966.513393.510293.89819.37749.08787.77868.06668.54519.73618.93011.9

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue us-gaap:FinancialInstrument

us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue

us-gaap:AssetBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.6045.8265.9666.3338.2818.609119.9241113192429
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommercialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value1843185818851833187819241817179017581683165016011610
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue51140.231896.931605.528954.622690.222350.616454.118037.915702.212862.88502.76535.55410.2

us-gaap:ResidentialMortgageBackedSecurities


Available
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value819839870893907920888909909889880868892
Percentage of AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue22728.714415.914590.114106.310956.810687.68038.39166.48127.66798.74535.13541.82996.3

us-gaap:AvailableForSaleSecuritiesDebtSecurities

us-gaap:AvailableForSaleSecuritiesDebtSecurities


Available
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
Value1143910828106811024410060101239970102041164210162100439952101349904994099191005310006989110318103991015293949353952399711042210474102931023610142103121067848094979528053265507553855765479539454315112
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentFaceAmount us-gaap:DebtInstrument

us-gaap:DebtInstrumentFaceAmount

mkl:ThreePointFourFivePercentUnsecuredSeniorNotesDueMay2052


Debt
Period End2021-05-04
Value600
Percentage of DebtInstrumentFaceAmount100.0

us-gaap:DebtInstrumentFairValue

us-gaap:DebtInstrumentFairValue


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-31
Value486840964400427041753587390742573845311330303037308831823351268627122755272128472842250424032441242725252493249024842428237223611688
Percentage of DebtInstrumentFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentFairValue us-gaap:DebtInstrument

mkl:FourPointNinePercentUnsecuredSeniorNotesDueJuly2022


Debt
Period End2021-06-30
Value350
Percentage of DebtInstrumentFairValue7.2

us-gaap:DebtInstrumentUnamortizedDiscount us-gaap:DebtInstrument, us-gaap:LongtermDebtType

us-gaap:DebtInstrumentUnamortizedDiscount

mkl:FivePointZeroPercentUnsecuredSeniorNotesDueApril52046, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value6.1776.4216.6646.9097.154
Percentage of DebtInstrumentUnamortizedDiscount100.0100.0100.0100.0100.0

mkl:FivePointZeroPercentUnsecuredSeniorNotesDueMarch302043, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value4.9835.2075.4315.6555.8796.103
Percentage of DebtInstrumentUnamortizedDiscount80.781.181.581.882.20.0

mkl:FivePointZeroPercentUnsecuredSeniorNotesDueMay202049MemberDomain, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-31
Value7.4227.6840.0
Percentage of DebtInstrumentUnamortizedDiscount120.2119.70.0

mkl:FourPointNineZeroPercentUnsecuredSeniorNotesDueJuly12022, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value0.4320.7050.9781.2571.5361.815
Percentage of DebtInstrumentUnamortizedDiscount7.011.014.718.221.50.0

mkl:FourPointOneFivePercentUnsecuredSeniorNotesDueSeptember172050, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-31
Value5.2725.4490.0
Percentage of DebtInstrumentUnamortizedDiscount85.384.90.0

mkl:FourPointThreePercentUnsecuredSeniorNotesDueNovember12047, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-31
Value3.9734.1264.2784.451
Percentage of DebtInstrumentUnamortizedDiscount64.364.364.264.4

mkl:SevenPointThreeFivePercentUnsecuredSeniorNotesDueAugust152034, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value0.9371.0051.0741.1431.2121.972
Percentage of DebtInstrumentUnamortizedDiscount15.215.716.116.516.90.0

mkl:ThreePointFivePercentUnsecuredSeniorNotesDueNovember12027, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-31
Value1.7292.0132.2982.558
Percentage of DebtInstrumentUnamortizedDiscount28.031.434.537.0

mkl:ThreePointSixTwoFivePercentUnsecuredSeniorNotesDueMarch302023, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value0.4520.6530.8551.0561.2571.458
Percentage of DebtInstrumentUnamortizedDiscount7.310.212.815.317.60.0

mkl:ThreePointThreeFivePercentUnsecuredSeniorNotesDueSeptember172029, us-gaap:SeniorNotes


Debt
Period End2020-12-312019-12-312018-12-31
Value2.1632.410.0
Percentage of DebtInstrumentUnamortizedDiscount35.037.50.0

us-gaap:DebtInstrumentUnamortizedDiscountPremiumNet

us-gaap:DebtInstrumentUnamortizedDiscountPremiumNet


Debt
Period End2020-12-31
Value33
Percentage of DebtInstrumentUnamortizedDiscountPremiumNet100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.0223.3565.4861501872423524959732032198315331442
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1017404078161312222134153187
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger7.09.216.611.415.816.615.411.28.810.60.0

us-gaap:CommercialMortgageBackedSecurities


Debt
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value2.5265.3897.425223334310724709550497481
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger46.03.64.09.39.66.931.935.635.835.934.50.0

us-gaap:FixedMaturities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value3.0223.3565.48615018724235249597220321983153314421468
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger100.0100.0100.0100.0100.0100.0100.0100.099.8100.0100.0100.0100.00.0

us-gaap:ForeignGovernmentDebtSecurities


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value13116016615916616114784847563
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger87.485.268.745.433.716.57.34.35.55.30.0

us-gaap:ResidentialMortgageBackedSecurities


Debt
Period End2021-06-302021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.130.430.08.0855871103245242128126148
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger4.312.80.03.316.514.410.612.112.28.48.80.0

us-gaap:USStatesAndPoliticalSubdivisions


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value2.8922.9262.962.9943.0253.0216.832590370453411402404
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger95.787.254.02.01.61.21.95.19.318.222.926.827.90.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.0080.0130.022.6166.981197.287111247779173
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.3011.2891.9040.3991.3871.3945.2616.4994.9834.4911.874
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss11.518.59.85.512.511.311.18.45.56.10.0

us-gaap:CommercialMortgageBackedSecurities


Debt
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0080.0130.0210.1520.2560.233.9992334413314
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss40.00.50.30.83.52.132.550.244.445.045.80.0

us-gaap:FixedMaturities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0080.0130.022.6166.981197.28711124777917331
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.099.5100.0100.0100.0100.00.0

us-gaap:ForeignGovernmentDebtSecurities


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value2.2875.648176.0058.4884.0725.6457.1177.6225.4741.958
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss87.480.988.082.476.733.111.99.28.47.50.0

us-gaap:ResidentialMortgageBackedSecurities


Debt
Period End2021-06-302021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0030.0040.00.1630.4510.6541.4274.5328.8148.3766.6943.518
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss37.530.80.00.86.25.911.69.511.49.29.10.0

us-gaap:USStatesAndPoliticalSubdivisions


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0050.0090.0120.0150.0230.1020.110.0990.8296.1581623187.127
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss62.569.260.00.60.30.51.50.96.713.021.225.725.50.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value25.035.064.0122.0162.0267.0560.0541.0
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value483523244961858885761611452155283261060053549
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value77790.0921185205411684556313411401149
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months1.63.40.00.69.626.96.837.329.219.912.06.811.30.0

us-gaap:CommercialMortgageBackedSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value84105137.3722.033312020.00.08.8656531049962253
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months1.84.52.70.40.24.233.10.00.03.125.017.527.10.0

us-gaap:FixedMaturities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value17391355146152318690607337138209241342123371777
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months36.058.329.58.236.090.799.574.589.073.892.470.295.00.0

us-gaap:ForeignGovernmentDebtSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value146101206.1051733151621577913741945532831
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months3.04.44.20.319.641.426.734.851.448.416.17.69.20.0

us-gaap:ResidentialMortgageBackedSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value8.5821.0843.3453.3033.7563.441112.1052.4231.874276665590157
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months0.20.00.70.20.40.51.90.51.60.710.611.116.60.0

us-gaap:USGovernmentSponsoredEnterprisesDebtSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1762791414240.00.00.08811711511
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months3.612.03.00.84.00.00.00.03.42.03.30.0

us-gaap:USStatesAndPoliticalSubdivisions


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value2302582857461251271.0533.254.781656138485580
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months4.811.15.63.15.216.420.90.22.11.725.123.024.10.0

us-gaap:USTreasurySecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value101452966517.6753.299367.4817.4670.02.92212010278
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months21.022.813.32.80.90.46.01.74.80.00.12.02.90.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value17330.9432.3589.815267.192124.6015.7415610775
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:AllOtherCorporateBonds


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1.5372.9830.0030.371.6714.5471.2875.8621.2951.38510129.3660.863
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss9.09.00.315.717.017.017.946.028.124.119.411.612.30.0

us-gaap:CommercialMortgageBackedSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1.7783.0090.0260.0090.0140.2991.1260.00.00.1571029241.98
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss10.49.12.80.40.11.115.70.00.02.717.927.532.60.0

us-gaap:FixedMaturities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value16330.9370.8187.043207.132114.2854.63553107746.29
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss99.2100.099.434.771.878.299.291.493.180.795.199.698.10.0

us-gaap:ForeignGovernmentDebtSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value2.271.9670.0570.0854.295113.3935.7642.9563.048149.4256.7140.452
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss13.35.96.03.643.844.547.245.264.253.125.68.88.80.0

us-gaap:ResidentialMortgageBackedSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.0910.0090.0290.0280.0350.1020.0660.0090.0010.0123.68522141.345
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.50.03.11.20.40.40.90.10.00.26.521.218.70.0

us-gaap:USGovernmentSponsoredEnterprisesDebtSecurities


Debt
Period End2021-06-302021-03-312020-12-312020-09-302019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value3.0759.110.0920.0240.1970.00.00.01.9234.5452.7140.079
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss18.027.49.81.02.70.00.00.03.44.23.60.0

us-gaap:USStatesAndPoliticalSubdivisi