XML 14 R48.htm IDEA: XBRL DOCUMENT v2.4.1.9
Fair Value Of Financial Instruments (Quantitative Information Regarding The Significant Unobservable Inputs For Certain Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Other Derivative Liabilities [Member] | Discounted cash flow [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair value, liabilities $ 21us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_DiscountedCashFlowMember		 $ 24us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_DiscountedCashFlowMember
Discounted Cash Flows [Member] | Other Derivative Liabilities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range dollars 0mbi_FairValueMeasurementRangeDollars
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_DiscountedCashFlowsMember		 0mbi_FairValueMeasurementRangeDollars
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_DiscountedCashFlowsMember
Discounted Cash Flows [Member] | Other Derivative Liabilities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range dollars 83mbi_FairValueMeasurementRangeDollars
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_DiscountedCashFlowsMember		 83mbi_FairValueMeasurementRangeDollars
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_DiscountedCashFlowsMember
Discounted Cash Flows [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range dollars 42mbi_FairValueMeasurementRangeDollars
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_DiscountedCashFlowsMember		 [1] 42mbi_FairValueMeasurementRangeDollars
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_DiscountedCashFlowsMember
Credit Derivatives [Member] | Commercial Mortgage Backed Securities [Member] | BET Model [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair value, liabilities 191us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_BETValuationModelMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 224us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_BETValuationModelMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Multi Sector C D O [Member] | Direct Price Model [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair value, liabilities 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_ValuationTechniqueAxis
= mbi_DirectPriceModelMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 9us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_ValuationTechniqueAxis
= mbi_DirectPriceModelMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Other Derivative Liabilities [Member] | BET And Dual Default Valuation Models [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair value, liabilities 10us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_BetanddualdefaultvaluationmodelsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 11us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_BetanddualdefaultvaluationmodelsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Recovery Rates [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 25.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 25.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Recovery Rates [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 90.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 90.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Recovery Rates [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 61.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 59.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Recovery Rates [Member] | Other Derivative Liabilities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 42.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 42.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Recovery Rates [Member] | Other Derivative Liabilities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 45.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 45.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Recovery Rates [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 45.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 45.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_RecoveryRatesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 19.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 12.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 32.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 29.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 28.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 25.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Multi Sector C D O [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 53.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Multi Sector C D O [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 53.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Multi Sector C D O [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 53.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_MultiSectorCDOMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Other Derivative Liabilities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 41.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Other Derivative Liabilities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 51.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Nonperformance Risk [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 50.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_NonperformanceRiskMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Weighted Average Life [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Weighted Average (in years) 1mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 1.3mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Weighted Average Life [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Weighted Average (in years) 2mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 3.2mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Weighted Average Life [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Weighted Average (in years) 1.6mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 2.3mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Weighted Average Life [Member] | Other Derivative Liabilities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Weighted Average (in years) 0.5mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 0.2mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Weighted Average Life [Member] | Other Derivative Liabilities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Weighted Average (in years) 7.8mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 7.9mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Weighted Average Life [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Weighted Average (in years) 1mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 1.1mbi_FairValueDisclosureWeightedAverageInYears
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_WeightedAverageLifeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Commercial Mortgage Backed Securities Spreads [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 0.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_CommercialMortgageBackedSecuritiesSpreadsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 0.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_CommercialMortgageBackedSecuritiesSpreadsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Commercial Mortgage Backed Securities Spreads [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 57.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_CommercialMortgageBackedSecuritiesSpreadsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 41.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_CommercialMortgageBackedSecuritiesSpreadsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Credit Derivatives [Member] | Commercial Mortgage Backed Securities Spreads [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 22.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_CommercialMortgageBackedSecuritiesSpreadsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember		 19.00%mbi_FairValueMeasurementRangePercentage
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_CommercialMortgageBackedSecuritiesSpreadsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_CreditDerivativesMember
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Quoted market prices adjusted for financial guarantees provided to VIE obligations [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair Value, assets 1,480us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_ValuationTechniqueAxis
= mbi_QuotedMarketPricesAdjustedForFinancialGuaranteesProvidedToVieObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 1,431us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_ValuationTechniqueAxis
= mbi_QuotedMarketPricesAdjustedForFinancialGuaranteesProvidedToVieObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 0.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 0.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 6.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 10.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 2.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 2.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] | Discounted cash flow [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair Value, assets 385us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_ValuationTechniqueAxis
= mbi_DiscountedCashFlowMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 379us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_ValuationTechniqueAxis
= mbi_DiscountedCashFlowMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Quoted market prices of VIE assets adjusted for financial guarantees provided [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Fair value, liabilities $ 1,387us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_QuotedMarketPricesOfVieAssetsAdjustedForFinancialGuaranteesProvidedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 $ 735us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_ValuationTechniqueAxis
= mbi_QuotedMarketPricesOfVieAssetsAdjustedForFinancialGuaranteesProvidedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 0.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 0.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 39.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 35.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Range percentage 9.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		 16.00%mbi_FairValueMeasurementRangePercentage
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ mbi_UnobservableInputAxis
= mbi_ImpactOfFinancialGuaranteeMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
[1]
Midpoint of cash flows are used for the weighted average.