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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 | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | $ 30 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange |  | $ (55)mbi_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 | 30 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember |  | (55)mbi_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 | (10)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 3 mbi_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 | 6 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbi_LoanRepurchaseCommitmentsMember / dei_LegalEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | [1] | 5 mbi_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 |  |  | 1 mbi_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 | (17)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_FixedMaturitySecuritiesHeldAtFairValueVieMember | [1] | (38)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 | (58)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_ResidentialMortgageLoansMember | [1] | (56)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_ResidentialMortgageLoansMember | [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 | 17 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_MediumTermNotesMember | [2] | (12)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / dei_LegalEntityAxis = us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_MediumTermNotesMember | [2]
Variable Interest Entity Notes [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | $ 89 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_VariableInterestEntityNotesMember | [1] | $ 121 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / 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.

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