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Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) (Nondesignated [Member], USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | $ (72)us-gaap_DerivativeGainLossOnDerivativeNet | $ 451 us-gaap_DerivativeGainLossOnDerivativeNet
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | 37 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CreditDefaultSwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_UnrealizedGainsLossesOnInsuredDerivativesMember | 823 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CreditDefaultSwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_UnrealizedGainsLossesOnInsuredDerivativesMember
Unrealized Gains Losses On Insured Derivatives [Member] | All Other [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_UnrealizedGainsLossesOnInsuredDerivativesMember | 15 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_UnrealizedGainsLossesOnInsuredDerivativesMember
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | (9)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CreditDefaultSwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_RealizedGainsLossesAndOtherSettlementsOnInsuredDerivativesMember | (339)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CreditDefaultSwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_RealizedGainsLossesAndOtherSettlementsOnInsuredDerivativesMember
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | All Other [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_RealizedGainsLossesAndOtherSettlementsOnInsuredDerivativesMember | (30)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_RealizedGainsLossesAndOtherSettlementsOnInsuredDerivativesMember
Foreign Exchange And Other Derivative Financial Instruments [Member] | Interest Rate Swap [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | (107)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_ForeignExchangeAndOtherDerivativeFinancialInstrumentsMember | (23)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_ForeignExchangeAndOtherDerivativeFinancialInstrumentsMember
Foreign Exchange And Other Derivative Financial Instruments [Member] | Currency Swap [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income |  | 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CurrencySwapMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_ForeignExchangeAndOtherDerivativeFinancialInstrumentsMember
Foreign Exchange And Other Derivative Financial Instruments [Member] | All Other [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | 3 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_ForeignExchangeAndOtherDerivativeFinancialInstrumentsMember | (1)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_ForeignExchangeAndOtherDerivativeFinancialInstrumentsMember
Foreign Exchange And Other Derivative Financial Instruments Attributable To V I E [Member] | Interest Rate Swaps V I E [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income |  | 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mbi_InterestRateSwapsVIEMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_ForeignExchangeAndOtherDerivativeFinancialInstrumentsAttributableToVIEMember
Foreign Exchange And Other Derivative Financial Instruments Attributable To V I E [Member] | Currency Swaps Vie [Member] |  |
Derivative [Line Items] |  |
Net gain/(loss) recognized in income | $ 4 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mbi_CurrencySwapsVieMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_ForeignExchangeAndOtherDerivativeFinancialInstrumentsAttributableToVIEMember | $ 6 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mbi_CurrencySwapsVieMember / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = mbi_ForeignExchangeAndOtherDerivativeFinancialInstrumentsAttributableToVIEMember

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959 + Details
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Period Type: | duration

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- Details
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- Details
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- Details
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