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Fair Value Of Financial Instruments (Gains And Losses On Fair Value Option Included In The Company's Consolidated Statements Of Operations) (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange $ 78mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange $ 69mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange $ 55mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
Non Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange 78mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember		 69mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember		 55mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange 50mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 175mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 18mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Variable Interest Entity [Member] | Loan Repurchase Commitments [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange 20mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 [1] 172mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 [1] 9mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 [1]
Investments Carried At Fair Value [Member] | Non Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange 2mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_InvestmentsCarriedAtFairValueMember		 [2] 8mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_InvestmentsCarriedAtFairValueMember		 [2] 10mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_InvestmentsCarriedAtFairValueMember		 [2]
Fixed Maturity Securities Held At Fair Value - VIE [Member] | Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange (104)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_FixedMaturitySecuritiesHeldAtFairValueVieMember		 [1] (74)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_FixedMaturitySecuritiesHeldAtFairValueVieMember		 [1] (55)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_FixedMaturitySecuritiesHeldAtFairValueVieMember		 [1]
Residential Mortgage Loans [Member] | Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange (182)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_ResidentialMortgageLoansMember		 [1] (107)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_ResidentialMortgageLoansMember		 [1] (107)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_ResidentialMortgageLoansMember		 [1]
Other Loans [Member] | Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange 10mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_OtherLoansMember		 [1] 13mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_OtherLoansMember		 [1] (56)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_OtherLoansMember		 [1]
Medium Term Notes [Member] | Non Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange 6mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= us-gaap_MediumTermNotesMember		 [2] 38mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= us-gaap_MediumTermNotesMember		 [2]  
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Net gains (losses) on financial instruments at fair value and foreign exchange $ 269mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_VariableInterestEntityNotesMember		 [1] $ 155mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_VariableInterestEntityNotesMember		 [1] $ 107mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis
= mbi_VariableInterestEntityNotesMember		 [1]
[1]
Reported within Net gains (losses) of financial instruments at fair value and foreign exchange-VIE on MBIA's consolidated statements of operations.
[2]
Reported within Net gains (losses) of financial instruments at fair value and foreign exchange on MBIA's consolidated statements of operations.