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Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	$ 10,613us-gaap_AssetsFairValueDisclosureRecurring		$ 10,786us-gaap_AssetsFairValueDisclosureRecurring
Fair value financial liabilities measured on recurring basis	3,463us-gaap_LiabilitiesFairValueDisclosureRecurring		3,781us-gaap_LiabilitiesFairValueDisclosureRecurring
Variable Interest Entity Primary Beneficiary [Member] | Residential Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,431us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		1,612us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	379us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbi_LoanRepurchaseCommitmentsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		359us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbi_LoanRepurchaseCommitmentsMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	65us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		89us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	197us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		259us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	86us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		105us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	12us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		36us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	61us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		98us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Money Market Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	428us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_MoneyMarketSecuritiesMember		783us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_MoneyMarketSecuritiesMember
Money Market Securities [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis			136us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_MoneyMarketSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Medium Term Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	197us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_MediumTermNotesMember		203us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_MediumTermNotesMember
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,047us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_VariableInterestEntityNotesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		2,356us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_VariableInterestEntityNotesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	53us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_PerpetualDebtAndEquitySecuritiesMember		51us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_PerpetualDebtAndEquitySecuritiesMember
Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	729us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember		1,161us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember
Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,345us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		5,996us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	691us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		553us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,732us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		1,784us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	290us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		189us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,058us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		1,824us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,162us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		1,173us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	56us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		92us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	22us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		39us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	93us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		154us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	241us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		188us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	2us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeAssetsMember		4us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeAssetsMember
Assets Held For Sale [Member] | Loans Receivable At Fair Value [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	711us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_LoansreceivableatfairvalueMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_AssetsHeldForSaleMember
Assets Held For Sale [Member] | Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	6us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_EquitySecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_AssetsHeldForSaleMember
Assets Held For Sale [Member] | Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	55us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_AssetsHeldForSaleMember
Assets Of Consolidated V I Es [Member] | Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	53us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember		97us-gaap_AssetsFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	246us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByLiabilityClassAxis = mbi_InsuredDerivativesMember / invest_InvestmentAxis = mbi_CreditDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember		1,152us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByLiabilityClassAxis = mbi_InsuredDerivativesMember / invest_InvestmentAxis = mbi_CreditDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	167us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember
Derivative Liabilities [Member] | Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis			11us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_CurrencyDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Derivative Liabilities [Member] | Other Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	24us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_OtherDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember
Other Liabilities [Member] | Warrant [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	28us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_WarrantMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherLiabilitiesMember		59us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = us-gaap_WarrantMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherLiabilitiesMember
Liabilities Held For Sale [Member] | Variable Interest Entity Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	431us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_VariableInterestEntityNotesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_LiabilitiesheldforsaleMember
Liabilities Held For Sale [Member] | Payable For Loans Purchased [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	323us-gaap_LiabilitiesFairValueDisclosureRecurring / invest_InvestmentAxis = mbi_PayableforloanspurchasedMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_LiabilitiesheldforsaleMember
Fair Value Inputs Level 1 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,087us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member		2,713us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Fair value financial liabilities measured on recurring basis	0us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Fair Value Inputs Level 1 [Member] | Money Market Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	428us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = mbi_MoneyMarketSecuritiesMember		783us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = mbi_MoneyMarketSecuritiesMember
Fair Value Inputs Level 1 [Member] | Money Market Securities [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis			136us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = mbi_MoneyMarketSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 1 [Member] | Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	22us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = mbi_PerpetualDebtAndEquitySecuritiesMember		27us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = mbi_PerpetualDebtAndEquitySecuritiesMember
Fair Value Inputs Level 1 [Member] | Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	729us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember		1,161us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	794us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		509us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	573us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		397us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	221us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		112us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 1 [Member] | Assets Held For Sale [Member] | Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	6us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_EquitySecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_AssetsHeldForSaleMember
Fair Value Inputs Level 1 [Member] | Assets Held For Sale [Member] | Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	55us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_AssetsHeldForSaleMember
Fair Value Inputs Level 1 [Member] | Assets Of Consolidated V I Es [Member] | Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	53us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember		97us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Fair Value Inputs Level 2 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,510us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member		5,763us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Fair value financial liabilities measured on recurring basis	2,344us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member		1,645us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Fair Value Inputs Level 2 [Member] | Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	10us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		41us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 2 [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	194us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		255us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 2 [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	86us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		102us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 2 [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	7us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		14us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 2 [Member] | Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	35us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		44us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 2 [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	1,312us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_VariableInterestEntityNotesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		1,416us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_VariableInterestEntityNotesMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 2 [Member] | Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	31us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_PerpetualDebtAndEquitySecuritiesMember		13us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_PerpetualDebtAndEquitySecuritiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	5,353us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		5,248us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	118us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		156us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,724us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		1,765us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	63us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		65us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,048us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		1,776us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,162us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		1,173us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	56us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		86us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	20us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		25us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	6us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		72us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	156us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember		130us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_OtherAssetBackedMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_FixedMaturitiesMember
Fair Value Inputs Level 2 [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	83us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeAssetsMember		46us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeAssetsMember
Fair Value Inputs Level 2 [Member] | Assets Held For Sale [Member] | Loans Receivable At Fair Value [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	711us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_LoansreceivableatfairvalueMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_AssetsHeldForSaleMember
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	2us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = mbi_InsuredDerivativesMember / invest_InvestmentAxis = mbi_CreditDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember		5us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = mbi_InsuredDerivativesMember / invest_InvestmentAxis = mbi_CreditDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	248us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember		165us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByLiabilityClassAxis = mbi_NonInsuredDerivativesMember / invest_InvestmentAxis = mbi_InterestRateDerivativesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_DerivativeLiabilitiesMember
Fair Value Inputs Level 2 [Member] | Other Liabilities [Member] | Warrant [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	28us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_WarrantMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherLiabilitiesMember		59us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = us-gaap_WarrantMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = us-gaap_OtherLiabilitiesMember
Fair Value Inputs Level 2 [Member] | Liabilities Held For Sale [Member] | Variable Interest Entity Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	431us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_VariableInterestEntityNotesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_LiabilitiesheldforsaleMember
Fair Value Inputs Level 2 [Member] | Liabilities Held For Sale [Member] | Payable For Loans Purchased [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	323us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / invest_InvestmentAxis = mbi_PayableforloanspurchasedMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_LiabilitiesheldforsaleMember
Fair Value Inputs Level 3 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,097us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member		2,352us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Fair value financial liabilities measured on recurring basis	1,200us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member		2,301us-gaap_LiabilitiesFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Residential Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,431us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		1,612us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	379us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbi_LoanRepurchaseCommitmentsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		359us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbi_LoanRepurchaseCommitmentsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Fair Value Inputs Level 3 [Member] | Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	55us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	[1]	48us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / invest_InvestmentAxis = mbi_CorporateObligationMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	[1]
Fair Value Inputs Level 3 [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
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