2.4.0.8 Html 801 737 1 true 172 0 false 4 false false R1.htm 0001000 - Document - Document and Entity Information Document Sheet http://www.cna.com/role/DocumentAndEntityInformationDocument Document and Entity Information Document false false R2.htm 1001000 - Statement - Consolidated Statements of Operations Sheet http://www.cna.com/role/ConsolidatedStatementsOfOperations Consolidated Statements of Operations false false R3.htm 1002500 - Statement - Consolidated Statements of Operations Parenthetical (Parentheticals) Sheet http://www.cna.com/role/ConsolidatedStatementsOfOperationsParentheticalParentheticals Consolidated Statements of Operations Parenthetical (Parentheticals) false false R4.htm 1003000 - Statement - Consolidated Statements of Comprehensive Income (Loss) Sheet http://www.cna.com/role/ConsolidatedStatementsOfComprehensiveIncomeLoss Consolidated Statements of Comprehensive Income (Loss) true false R5.htm 1004000 - Statement - Consolidated Balance Sheets Sheet http://www.cna.com/role/ConsolidatedBalanceSheets Consolidated Balance Sheets false false R6.htm 1005500 - Statement - Consolidated Balance Sheet Parentheticals (Parentheticals) Sheet http://www.cna.com/role/ConsolidatedBalanceSheetParentheticalsParentheticals Consolidated Balance Sheet Parentheticals (Parentheticals) false false R7.htm 1006000 - Statement - Consolidated Statements of Cash Flows Sheet http://www.cna.com/role/ConsolidatedStatementsOfCashFlows Consolidated Statements of Cash Flows false false R8.htm 1007000 - Statement - Consolidated Statements of Stockholders' Equity Sheet http://www.cna.com/role/ConsolidatedStatementsOfStockholdersEquity Consolidated Statements of Stockholders' Equity false false R9.htm 2101100 - Disclosure - Summary of Significant Accounting Policies Sheet http://www.cna.com/role/SummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies false false R10.htm 2113100 - Disclosure - Investments Sheet http://www.cna.com/role/Investments Investments false false R11.htm 2116100 - Disclosure - Derivative Financial Instruments Sheet http://www.cna.com/role/DerivativeFinancialInstruments Derivative Financial Instruments false false R12.htm 2119100 - Disclosure - Fair Value Sheet http://www.cna.com/role/FairValue Fair Value false false R13.htm 2122100 - Disclosure - Income Taxes Sheet http://www.cna.com/role/IncomeTaxes Income Taxes false false R14.htm 2125100 - Disclosure - Claim and Claim Adjustment Expense Reserves Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReserves Claim and Claim Adjustment Expense Reserves false false R15.htm 2128100 - Disclosure - Legal Proceedings and Contingent Liabilities Sheet http://www.cna.com/role/LegalProceedingsAndContingentLiabilities Legal Proceedings and Contingent Liabilities false false R16.htm 2129100 - Disclosure - Reinsurance Sheet http://www.cna.com/role/Reinsurance Reinsurance false false R17.htm 2130100 - Disclosure - Debt Sheet http://www.cna.com/role/Debt Debt false false R18.htm 2131100 - Disclosure - Benefit Plans Sheet http://www.cna.com/role/BenefitPlans Benefit Plans false false R19.htm 2133100 - Disclosure - Other Intangible Assets Sheet http://www.cna.com/role/OtherIntangibleAssets Other Intangible Assets false false R20.htm 2134100 - Disclosure - Operating Leases, Commitments and Contingencies, and Guarantees Sheet http://www.cna.com/role/OperatingLeasesCommitmentsAndContingenciesAndGuarantees Operating Leases, Commitments and Contingencies, and Guarantees false false R21.htm 2136100 - Disclosure - Stockholders' Equity and Statutory Accounting Practices Sheet http://www.cna.com/role/StockholdersEquityAndStatutoryAccountingPractices Stockholders' Equity and Statutory Accounting Practices false false R22.htm 2138100 - Disclosure - Accumulated Other Comprehensive Income (Loss) by Component Sheet http://www.cna.com/role/AccumulatedOtherComprehensiveIncomeLossByComponent Accumulated Other Comprehensive Income (Loss) by Component false false R23.htm 2141100 - Disclosure - Business Segments Sheet http://www.cna.com/role/BusinessSegments Business Segments false false R24.htm 2142100 - Disclosure - Quarterly Financial Data (Unaudited) Sheet http://www.cna.com/role/QuarterlyFinancialDataUnaudited Quarterly Financial Data (Unaudited) false false R25.htm 2143100 - Disclosure - Related Party Transactions Sheet http://www.cna.com/role/RelatedPartyTransactions Related Party Transactions false false R26.htm 2144100 - Disclosure - Subsequent Events Sheet http://www.cna.com/role/SubsequentEvents Subsequent Events false false R27.htm 2145100 - Disclosure - Schedule I. Summary of Investments - Other Than Investments in Related Parties Sheet http://www.cna.com/role/ScheduleISummaryOfInvestmentsOtherThanInvestmentsInRelatedParties Schedule I. Summary of Investments - Other Than Investments in Related Parties false false R28.htm 2146100 - Disclosure - Schedule II. Condensed Financial Information of Registrant (Parent Company) Sheet http://www.cna.com/role/ScheduleIiCondensedFinancialInformationOfRegistrantParentCompany Schedule II. Condensed Financial Information of Registrant (Parent Company) false false R29.htm 2147100 - Disclosure - Schedule III. Supplementary Insurance Information Sheet http://www.cna.com/role/ScheduleIiiSupplementaryInsuranceInformation Schedule III. Supplementary Insurance Information false false R30.htm 2148100 - Disclosure - Schedule IV. Reinsurance Sheet http://www.cna.com/role/ScheduleIvReinsurance Schedule IV. Reinsurance false false R31.htm 2149100 - Disclosure - Schedule V. Valuation and Qualifying Accounts Sheet http://www.cna.com/role/ScheduleVValuationAndQualifyingAccounts Schedule V. Valuation and Qualifying Accounts false false R32.htm 2150100 - Disclosure - Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations Sheet http://www.cna.com/role/ScheduleViSupplementalInformationConcerningPropertyAndCasualtyInsuranceOperations Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations false false R33.htm 2201201 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://www.cna.com/role/SummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) false false R34.htm 2301302 - Disclosure - Summary of Significant Accounting Policies (Life Settlement Contracts) (Tables) Sheet http://www.cna.com/role/SummaryOfSignificantAccountingPoliciesLifeSettlementContractsTables Summary of Significant Accounting Policies (Life Settlement Contracts) (Tables) false false R35.htm 2313301 - Disclosure - Investments (Tables) Sheet http://www.cna.com/role/InvestmentsTables Investments (Tables) false false R36.htm 2316301 - Disclosure - Derivative Financial Instruments (Tables) Sheet http://www.cna.com/role/DerivativeFinancialInstrumentsTables Derivative Financial Instruments (Tables) false false R37.htm 2319301 - Disclosure - Fair Value (Tables) Sheet http://www.cna.com/role/FairValueTables Fair Value (Tables) false false R38.htm 2322301 - Disclosure - Income Taxes (Tables) Sheet http://www.cna.com/role/IncomeTaxesTables Income Taxes (Tables) false false R39.htm 2325301 - Disclosure - Claim and Claim Adjustment Expense Reserves (Tables) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesTables Claim and Claim Adjustment Expense Reserves (Tables) false false R40.htm 2329301 - Disclosure - Reinsurance (Tables) Sheet http://www.cna.com/role/ReinsuranceTables Reinsurance (Tables) false false R41.htm 2330301 - Disclosure - Debt (Tables) Sheet http://www.cna.com/role/DebtTables Debt (Tables) false false R42.htm 2331301 - Disclosure - Benefit Plans (Tables) Sheet http://www.cna.com/role/BenefitPlansTables Benefit Plans (Tables) false false R43.htm 2333301 - Disclosure - Other Intangible Assets (Tables) Sheet http://www.cna.com/role/OtherIntangibleAssetsTables Other Intangible Assets (Tables) false false R44.htm 2334301 - Disclosure - Operating Leases, Commitments and Contingencies, and Guarantees (Tables) Sheet http://www.cna.com/role/OperatingLeasesCommitmentsAndContingenciesAndGuaranteesTables Operating Leases, Commitments and Contingencies, and Guarantees (Tables) false false R45.htm 2336301 - Disclosure - Stockholders' Equity and Statutory Accounting Practices (Tables) Sheet http://www.cna.com/role/StockholdersEquityAndStatutoryAccountingPracticesTables Stockholders' Equity and Statutory Accounting Practices (Tables) false false R46.htm 2338301 - Disclosure - Accumulated Other Comprehensive Income (Loss) by Component (Tables) Sheet http://www.cna.com/role/AccumulatedOtherComprehensiveIncomeLossByComponentTables Accumulated Other Comprehensive Income (Loss) by Component (Tables) false false R47.htm 2341301 - Disclosure - Business Segments (Tables) Sheet http://www.cna.com/role/BusinessSegmentsTables Business Segments (Tables) false false R48.htm 2342301 - Disclosure - Quarterly Financial Data (Unaudited) (Tables) Sheet http://www.cna.com/role/QuarterlyFinancialDataUnauditedTables Quarterly Financial Data (Unaudited) (Tables) false false R49.htm 2349301 - Disclosure - Schedule V. Valuation and Qualifying Accounts (Tables) Sheet http://www.cna.com/role/ScheduleVValuationAndQualifyingAccountsTables Schedule V. Valuation and Qualifying Accounts (Tables) false false R50.htm 2350301 - Disclosure - Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Tables) Sheet http://www.cna.com/role/ScheduleViSupplementalInformationConcerningPropertyAndCasualtyInsuranceOperationsTables Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Tables) false false R51.htm 2401403 - Disclosure - Summary of Significant Accounting Policies (Narrative) (Details) Sheet http://www.cna.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails Summary of Significant Accounting Policies (Narrative) (Details) false false R52.htm 2401404 - Disclosure - Summary of Significant Accounting Policies (Life Settlement Contracts) (Details) Sheet http://www.cna.com/role/SummaryOfSignificantAccountingPoliciesLifeSettlementContractsDetails Summary of Significant Accounting Policies (Life Settlement Contracts) (Details) false false R53.htm 2413402 - Disclosure - Investments (Narrative) (Details) Sheet http://www.cna.com/role/InvestmentsNarrativeDetails Investments (Narrative) (Details) false false R54.htm 2413403 - Disclosure - Investments (Net investment income) (Details) Sheet http://www.cna.com/role/InvestmentsNetInvestmentIncomeDetails Investments (Net investment income) (Details) false false R55.htm 2413404 - Disclosure - Investments (Net realized investment gains (losses)) (Details) Sheet http://www.cna.com/role/InvestmentsNetRealizedInvestmentGainsLossesDetails Investments (Net realized investment gains (losses)) (Details) false false R56.htm 2413405 - Disclosure - Investments (Net change in unrealized gains (losses) on investments) (Details) Sheet http://www.cna.com/role/InvestmentsNetChangeInUnrealizedGainsLossesOnInvestmentsDetails Investments (Net change in unrealized gains (losses) on investments) (Details) false false R57.htm 2413406 - Disclosure - Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) Sheet http://www.cna.com/role/InvestmentsComponentsOfOtherThanTemporaryImpairmentLossesRecognizedInEarningsDetails Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) false false R58.htm 2413407 - Disclosure - Investments (Summary of fixed maturity and equity securities) (Details) Sheet http://www.cna.com/role/InvestmentsSummaryOfFixedMaturityAndEquitySecuritiesDetails Investments (Summary of fixed maturity and equity securities) (Details) false false R59.htm 2413408 - Disclosure - Investments (Securities in a gross unrealized loss position) (Details) Sheet http://www.cna.com/role/InvestmentsSecuritiesInGrossUnrealizedLossPositionDetails Investments (Securities in a gross unrealized loss position) (Details) false false R60.htm 2413409 - Disclosure - Investments (Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI) (Details) Sheet http://www.cna.com/role/InvestmentsActivityRelatedToPretaxFixedMaturityCreditLossComponentReflectedWithinRetainedEarningsForSecuritiesStillHeldForWhichPortionOfOttiLossWasRecognizedInOciDetails Investments (Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI) (Details) false false R61.htm 2413410 - Disclosure - Investments (Contractual maturity) (Details) Sheet http://www.cna.com/role/InvestmentsContractualMaturityDetails Investments (Contractual maturity) (Details) false false R62.htm 2416402 - Disclosure - Derivative Financial Instruments (Narrative) (Details) Sheet http://www.cna.com/role/DerivativeFinancialInstrumentsNarrativeDetails Derivative Financial Instruments (Narrative) (Details) false false R63.htm 2416403 - Disclosure - Derivative Financial Instruments (Summary of aggregate contractual or notional amounts and gross estimated fair values related to derivative financial instruments) (Details) Sheet http://www.cna.com/role/DerivativeFinancialInstrumentsSummaryOfAggregateContractualOrNotionalAmountsAndGrossEstimatedFairValuesRelatedToDerivativeFinancialInstrumentsDetails Derivative Financial Instruments (Summary of aggregate contractual or notional amounts and gross estimated fair values related to derivative financial instruments) (Details) false false R64.htm 2419402 - Disclosure - Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) Sheet http://www.cna.com/role/FairValueAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) false false R65.htm 2419403 - Disclosure - Fair Value (Table of reconciliation for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs) (Details) Sheet http://www.cna.com/role/FairValueTableOfReconciliationForAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisUsingSignificantUnobservableInputsDetails Fair Value (Table of reconciliation for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs) (Details) false false R66.htm 2419404 - Disclosure - Fair Value (Narrative) (Details) Sheet http://www.cna.com/role/FairValueNarrativeDetails Fair Value (Narrative) (Details) false false R67.htm 2419405 - Disclosure - Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) Sheet http://www.cna.com/role/FairValueQuantitativeInformationAboutSignificantUnobservableInputsInFairValueMeasurementOfLevel3AssetsDetails Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) false false R68.htm 2419406 - Disclosure - Fair Value (Carrying amount and estimated fair value of financial instrument assets and liabilities which are not measured at fair value) (Details) Sheet http://www.cna.com/role/FairValueCarryingAmountAndEstimatedFairValueOfFinancialInstrumentAssetsAndLiabilitiesWhichAreNotMeasuredAtFairValueDetails Fair Value (Carrying amount and estimated fair value of financial instrument assets and liabilities which are not measured at fair value) (Details) false false R69.htm 2422402 - Disclosure - Income Taxes (Narrative) (Details) Sheet http://www.cna.com/role/IncomeTaxesNarrativeDetails Income Taxes (Narrative) (Details) false false R70.htm 2422403 - Disclosure - Income Taxes (Reconciliation between the Company's federal income tax (expense) benefit at statutory rates and the recorded income tax (expense) benefit) (Details) Sheet http://www.cna.com/role/IncomeTaxesReconciliationBetweenCompanysFederalIncomeTaxExpenseBenefitAtStatutoryRatesAndRecordedIncomeTaxExpenseBenefitDetails Income Taxes (Reconciliation between the Company's federal income tax (expense) benefit at statutory rates and the recorded income tax (expense) benefit) (Details) false false R71.htm 2422404 - Disclosure - Income Taxes (Current and deferred components of the Company's income tax (expense) benefit) (Details) Sheet http://www.cna.com/role/IncomeTaxesCurrentAndDeferredComponentsOfCompanysIncomeTaxExpenseBenefitDetails Income Taxes (Current and deferred components of the Company's income tax (expense) benefit) (Details) false false R72.htm 2422405 - Disclosure - Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) Sheet http://www.cna.com/role/IncomeTaxesSignificantComponentsOfCompanysDeferredTaxAssetsAndLiabilitiesDetails Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) false false R73.htm 2425402 - Disclosure - Claim and Claim Adjustment Expense Reserves (Narrative) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesNarrativeDetails Claim and Claim Adjustment Expense Reserves (Narrative) (Details) false false R74.htm 2425403 - Disclosure - Claim and Claim Adjustment Expense Reserves (Reconcilliation of claim and claim adjustment expense reserves) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesReconcilliationOfClaimAndClaimAdjustmentExpenseReservesDetails Claim and Claim Adjustment Expense Reserves (Reconcilliation of claim and claim adjustment expense reserves) (Details) false false R75.htm 2425404 - Disclosure - Claim and Claim Adjustment Expense Reserves (Net prior year claim and claim adjustment expense reserve development) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesNetPriorYearClaimAndClaimAdjustmentExpenseReserveDevelopmentDetails Claim and Claim Adjustment Expense Reserves (Net prior year claim and claim adjustment expense reserve development) (Details) false false R76.htm 2425405 - Disclosure - Claim and Claim Adjustment Expense Reserves (Gross and net carried claim and claim adjustment expense reserves) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesGrossAndNetCarriedClaimAndClaimAdjustmentExpenseReservesDetails Claim and Claim Adjustment Expense Reserves (Gross and net carried claim and claim adjustment expense reserves) (Details) false false R77.htm 2425406 - Disclosure - Claim and Claim Adjustment Expense Reserves (Net prior year development) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesNetPriorYearDevelopmentDetails Claim and Claim Adjustment Expense Reserves (Net prior year development) (Details) false false R78.htm 2425407 - Disclosure - Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for CNA Specialty segment) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesNetPriorYearClaimAndAllocatedClaimAdjustmentExpenseReserveDevelopmentForCnaSpecialtySegmentDetails Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for CNA Specialty segment) (Details) false false R79.htm 2425408 - Disclosure - Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for CNA Commercial segment) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesNetPriorYearClaimAndAllocatedClaimAdjustmentExpenseReserveDevelopmentForCnaCommercialSegmentDetails Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for CNA Commercial segment) (Details) false false R80.htm 2425409 - Disclosure - Claim and Claim Adjustment Expense Reserves Net prior year claim and allocated claim adjustment expense reserve development for Hardy segment (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesNetPriorYearClaimAndAllocatedClaimAdjustmentExpenseReserveDevelopmentForHardySegmentDetails Claim and Claim Adjustment Expense Reserves Net prior year claim and allocated claim adjustment expense reserve development for Hardy segment (Details) false false R81.htm 2425410 - Disclosure - Claim and Claim Adjustment Expense Reserves (Impact of Loss Portfolio Transfer on the Consolidated Statement of Operations) (Details) Sheet http://www.cna.com/role/ClaimAndClaimAdjustmentExpenseReservesImpactOfLossPortfolioTransferOnConsolidatedStatementOfOperationsDetails Claim and Claim Adjustment Expense Reserves (Impact of Loss Portfolio Transfer on the Consolidated Statement of Operations) (Details) false false R82.htm 2429402 - Disclosure - Reinsurance (Narrative) (Details) Sheet http://www.cna.com/role/ReinsuranceNarrativeDetails Reinsurance (Narrative) (Details) false false R83.htm 2429403 - Disclosure - Reinsurance (Components of Reinsurance Receivables) (Details) Sheet http://www.cna.com/role/ReinsuranceComponentsOfReinsuranceReceivablesDetails Reinsurance (Components of Reinsurance Receivables) (Details) false false R84.htm 2429404 - Disclosure - Reinsurance (Components of Earned Premiums) (Details) Sheet http://www.cna.com/role/ReinsuranceComponentsOfEarnedPremiumsDetails Reinsurance (Components of Earned Premiums) (Details) false false R85.htm 2429405 - Disclosure - Reinsurance (Components of Written Premiums) (Details) Sheet http://www.cna.com/role/ReinsuranceComponentsOfWrittenPremiumsDetails Reinsurance (Components of Written Premiums) (Details) false false R86.htm 2429406 - Disclosure - Reinsurance (Components of Life Insurance Inforce) (Details) Sheet http://www.cna.com/role/ReinsuranceComponentsOfLifeInsuranceInforceDetails Reinsurance (Components of Life Insurance Inforce) (Details) false false R87.htm 2430402 - Disclosure - Debt (Narrative) (Details) Sheet http://www.cna.com/role/DebtNarrativeDetails Debt (Narrative) (Details) false false R88.htm 2430403 - Disclosure - Debt (Schedule of debt instruments) (Details) Sheet http://www.cna.com/role/DebtScheduleOfDebtInstrumentsDetails Debt (Schedule of debt instruments) (Details) false false R89.htm 2430404 - Disclosure - Debt (Maturity of debt) (Details) Sheet http://www.cna.com/role/DebtMaturityOfDebtDetails Debt (Maturity of debt) (Details) false false R90.htm 2431402 - Disclosure - Benefit Plans (Narrative) (details) Sheet http://www.cna.com/role/BenefitPlansNarrativeDetails Benefit Plans (Narrative) (details) false false R91.htm 2431403 - Disclosure - Benefit Plans (Funded Status) (Details) Sheet http://www.cna.com/role/BenefitPlansFundedStatusDetails Benefit Plans (Funded Status) (Details) false false R92.htm 2431404 - Disclosure - Benefit Plans (Components of net periodic cost (benefit)) (Details) Sheet http://www.cna.com/role/BenefitPlansComponentsOfNetPeriodicCostBenefitDetails Benefit Plans (Components of net periodic cost (benefit)) (Details) false false R93.htm 2431405 - Disclosure - Benefit Plans (Schedule of amounts recognized in Other comprehensive income) (Details) Sheet http://www.cna.com/role/BenefitPlansScheduleOfAmountsRecognizedInOtherComprehensiveIncomeDetails Benefit Plans (Schedule of amounts recognized in Other comprehensive income) (Details) false false R94.htm 2431406 - Disclosure - Benefit Plans (Schedule of estimated amounts to be recognized from Accumulated other comprehensive income into net periodic cost (benefit) during next fiscal year) (Details) Sheet http://www.cna.com/role/BenefitPlansScheduleOfEstimatedAmountsToBeRecognizedFromAccumulatedOtherComprehensiveIncomeIntoNetPeriodicCostBenefitDuringNextFiscalYearDetails Benefit Plans (Schedule of estimated amounts to be recognized from Accumulated other comprehensive income into net periodic cost (benefit) during next fiscal year) (Details) false false R95.htm 2431407 - Disclosure - Benefit Plans (Actuarial Assumptions for Benefit Obligations) (Details) Sheet http://www.cna.com/role/BenefitPlansActuarialAssumptionsForBenefitObligationsDetails Benefit Plans (Actuarial Assumptions for Benefit Obligations) (Details) false false R96.htm 2431408 - Disclosure - Benefit Plans (Actuarial Assumptions for Net Cost or Benefit) (Details) Sheet http://www.cna.com/role/BenefitPlansActuarialAssumptionsForNetCostOrBenefitDetails Benefit Plans (Actuarial Assumptions for Net Cost or Benefit) (Details) false false R97.htm 2431409 - Disclosure - Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) Sheet http://www.cna.com/role/BenefitPlansFairValueOfPlanAssetsMeasuredOnRecurringBasisDetails Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) false false R98.htm 2431410 - Disclosure - Benefit Plans (Reconciliation of Level 3 Plan Assets) (Details) Sheet http://www.cna.com/role/BenefitPlansReconciliationOfLevel3PlanAssetsDetails Benefit Plans (Reconciliation of Level 3 Plan Assets) (Details) false false R99.htm 2431411 - Disclosure - Benefit Plans (Estimated Future Minimum Benefit Payments to Participants) (Details) Sheet http://www.cna.com/role/BenefitPlansEstimatedFutureMinimumBenefitPaymentsToParticipantsDetails Benefit Plans (Estimated Future Minimum Benefit Payments to Participants) (Details) false false R100.htm 2431412 - Disclosure - Benefit Plans (Significant Assumptions Used to Estimate Fair Value of Stock Options and SARS) (Details) Sheet http://www.cna.com/role/BenefitPlansSignificantAssumptionsUsedToEstimateFairValueOfStockOptionsAndSarsDetails Benefit Plans (Significant Assumptions Used to Estimate Fair Value of Stock Options and SARS) (Details) false false R101.htm 2431413 - Disclosure - Benefit Plans (Stock Option and SARs Activity) (Details) Sheet http://www.cna.com/role/BenefitPlansStockOptionAndSarsActivityDetails Benefit Plans (Stock Option and SARs Activity) (Details) false false R102.htm 2431414 - Disclosure - Benefit Plans (Weighted-average grant date fair value for awards granted, total intrinsic value for awards exercised and total fair value for awards vested) (Details) Sheet http://www.cna.com/role/BenefitPlansWeightedAverageGrantDateFairValueForAwardsGrantedTotalIntrinsicValueForAwardsExercisedAndTotalFairValueForAwardsVestedDetails Benefit Plans (Weighted-average grant date fair value for awards granted, total intrinsic value for awards exercised and total fair value for awards vested) (Details) false false R103.htm 2431415 - Disclosure - Benefit Plans (Restricted Shares, Performance-Based Restricted Stock Units and Performance Share Unit Activity) (Details) Sheet http://www.cna.com/role/BenefitPlansRestrictedSharesPerformanceBasedRestrictedStockUnitsAndPerformanceShareUnitActivityDetails Benefit Plans (Restricted Shares, Performance-Based Restricted Stock Units and Performance Share Unit Activity) (Details) false false R104.htm 2433402 - Disclosure - Schedule of Other Intangible Assets (Narrative) (Details) Sheet http://www.cna.com/role/ScheduleOfOtherIntangibleAssetsNarrativeDetails Schedule of Other Intangible Assets (Narrative) (Details) false false R105.htm 2433403 - Disclosure - Schedule of Other Intangible Assets (Details) Sheet http://www.cna.com/role/ScheduleOfOtherIntangibleAssetsDetails Schedule of Other Intangible Assets (Details) false false R106.htm 2434402 - Disclosure - Operating Leases, Commitments and Contingencies, and Guarantees (Narrative) (Detail) Sheet http://www.cna.com/role/OperatingLeasesCommitmentsAndContingenciesAndGuaranteesNarrativeDetail Operating Leases, Commitments and Contingencies, and Guarantees (Narrative) (Detail) false false R107.htm 2434403 - Disclosure - Operating Leases, Commitments and Contingencies, and Guarantees (Future Minimum Lease Payments and Sublease Receipts) (Details) Sheet http://www.cna.com/role/OperatingLeasesCommitmentsAndContingenciesAndGuaranteesFutureMinimumLeasePaymentsAndSubleaseReceiptsDetails Operating Leases, Commitments and Contingencies, and Guarantees (Future Minimum Lease Payments and Sublease Receipts) (Details) false false R108.htm 2436402 - Disclosure - Stockholders' Equity and Statutory Accounting Practices (Narrative) (Details) Sheet http://www.cna.com/role/StockholdersEquityAndStatutoryAccountingPracticesNarrativeDetails Stockholders' Equity and Statutory Accounting Practices (Narrative) (Details) false false R109.htm 2436403 - Disclosure - Stockholders' Equity and Statutory Accounting Practices Combined statutory capital and surplus and net income (loss) (Details) Sheet http://www.cna.com/role/StockholdersEquityAndStatutoryAccountingPracticesCombinedStatutoryCapitalAndSurplusAndNetIncomeLossDetails Stockholders' Equity and Statutory Accounting Practices Combined statutory capital and surplus and net income (loss) (Details) false false R110.htm 2438402 - Disclosure - Accumulated Other Comprehensive Income (Loss) Narrative (Details) Sheet http://www.cna.com/role/AccumulatedOtherComprehensiveIncomeLossNarrativeDetails Accumulated Other Comprehensive Income (Loss) Narrative (Details) false false R111.htm 2438403 - Disclosure - Accumulated Other Comprehensive Income (Loss) by Component (Details) Sheet http://www.cna.com/role/AccumulatedOtherComprehensiveIncomeLossByComponentDetails Accumulated Other Comprehensive Income (Loss) by Component (Details) false false R112.htm 2441402 - Disclosure - Business Segments (Narrative) (Details) Sheet http://www.cna.com/role/BusinessSegmentsNarrativeDetails Business Segments (Narrative) (Details) false false R113.htm 2441403 - Disclosure - Business Segments (Income Statement Information) (Details) Sheet http://www.cna.com/role/BusinessSegmentsIncomeStatementInformationDetails Business Segments (Income Statement Information) (Details) false false R114.htm 2441404 - Disclosure - Business Segments (Balance Sheet Information) (Details) Sheet http://www.cna.com/role/BusinessSegmentsBalanceSheetInformationDetails Business Segments (Balance Sheet Information) (Details) false false R115.htm 2441405 - Disclosure - Business Segments (Revenues by Line of Business) (Details) Sheet http://www.cna.com/role/BusinessSegmentsRevenuesByLineOfBusinessDetails Business Segments (Revenues by Line of Business) (Details) false false R116.htm 2442402 - Disclosure - Quarterly Financial Data (Unaudited) (Details) Sheet http://www.cna.com/role/QuarterlyFinancialDataUnauditedDetails Quarterly Financial Data (Unaudited) (Details) false false R117.htm 2443401 - Disclosure - Related Party Transactions Narrative (Details) Sheet http://www.cna.com/role/RelatedPartyTransactionsNarrativeDetails Related Party Transactions Narrative (Details) false false R118.htm 2444401 - Disclosure - Subsequent Events (Narrative) (Details) Sheet http://www.cna.com/role/SubsequentEventsNarrativeDetails Subsequent Events (Narrative) (Details) false false R119.htm 2446401 - Disclosure - Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Operations and Comprehensive Income) (Details) Sheet http://www.cna.com/role/ScheduleIiCondensedFinancialInformationOfRegistrantParentCompanyScheduleOfCondensedFinancialInformationOfRegistrantStatementsOfOperationsAndComprehensiveIncomeDetails Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Operations and Comprehensive Income) (Details) false false R120.htm 2446402 - Disclosure - Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Balance Sheets) (Details) Sheet http://www.cna.com/role/ScheduleIiCondensedFinancialInformationOfRegistrantParentCompanyScheduleOfCondensedFinancialInformationOfRegistrantBalanceSheetsDetails Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Balance Sheets) (Details) false false R121.htm 2446403 - Disclosure - Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Cash Flows) (Details) Sheet http://www.cna.com/role/ScheduleIiCondensedFinancialInformationOfRegistrantParentCompanyScheduleOfCondensedFinancialInformationOfRegistrantStatementsOfCashFlowsDetails Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Cash Flows) (Details) false false R122.htm 2446404 - Disclosure - Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule II. Condensed Financial Information of Registrant (Narrative)) (Details) Sheet http://www.cna.com/role/ScheduleIiCondensedFinancialInformationOfRegistrantParentCompanyScheduleIiCondensedFinancialInformationOfRegistrantNarrativeDetails Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule II. Condensed Financial Information of Registrant (Narrative)) (Details) false false R123.htm 2449402 - Disclosure - Schedule V. Valuation and Qualifying Accounts (Schedule of valuation and qualifying accounts) (Details) Sheet http://www.cna.com/role/ScheduleVValuationAndQualifyingAccountsScheduleOfValuationAndQualifyingAccountsDetails Schedule V. Valuation and Qualifying Accounts (Schedule of valuation and qualifying accounts) (Details) false false R124.htm 2450402 - Disclosure - Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Details) Sheet http://www.cna.com/role/ScheduleViSupplementalInformationConcerningPropertyAndCasualtyInsuranceOperationsDetails Schedule VI. Supplemental Information Concerning Property and Casualty Insurance Operations (Details) false false All Reports Book All Reports Element cna_DiscountedReservesForUnfundedStructureSettlementsDiscountAmount had a mix of decimals attribute values: -8 -6. Element cna_MortalityAssumption had a mix of decimals attribute values: 2 4. 'Monetary' elements on report '2401403 - Disclosure - Summary of Significant Accounting Policies (Narrative) (Details)' had a mix of different decimal attribute values. 'Monetary' elements on report '2425402 - Disclosure - Claim and Claim Adjustment Expense Reserves (Narrative) (Details)' had a mix of different decimal attribute values. 'Monetary' elements on report '2431414 - Disclosure - Benefit Plans (Weighted-average grant date fair value for awards granted, total intrinsic value for awards exercised and total fair value for awards vested) (Details)' had a mix of different decimal attribute values. Process Flow-Through: 1001000 - Statement - Consolidated Statements of Operations Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2013' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2013' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2013' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2013' Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2012' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2012' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2012' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2012' Process Flow-Through: 1002500 - Statement - Consolidated Statements of Operations Parenthetical (Parentheticals) Process Flow-Through: 1003000 - Statement - Consolidated Statements of Comprehensive Income (Loss) Process Flow-Through: 1004000 - Statement - Consolidated Balance Sheets Process Flow-Through: Removing column 'Dec. 31, 2011' Process Flow-Through: Removing column 'Dec. 31, 2010' Process Flow-Through: 1005500 - Statement - Consolidated Balance Sheet Parentheticals (Parentheticals) Process Flow-Through: 1006000 - Statement - Consolidated Statements of Cash Flows cna-20131231.xml cna-20131231.xsd cna-20131231_cal.xml cna-20131231_def.xml cna-20131231_lab.xml cna-20131231_pre.xml true true