XML 81 R51.htm IDEA: XBRL DOCUMENT v2.4.1.9
Fair Value Of Financial Instruments (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) (Fair Value Inputs Level 3 [Member], USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets $ 2,097us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue $ 2,352us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Realized gains/(losses), assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Unrealized gains/(losses) included in earnings, assets 10us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss (10)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
Unrealized gains/(losses) included in OCI, assets (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
Foreign exchange recognized in OCI or earnings, assets 1mbi_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisInForeignExchangeRecognizedOtherComprehensiveIncomeOrEarningsAssets 0mbi_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisInForeignExchangeRecognizedOtherComprehensiveIncomeOrEarningsAssets
Purchases, assets 112us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Issuances, assets   0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues
Settlements, assets (68)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements (73)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Sales, assets (16)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales (19)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Transfers into level 3, assets 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 [1] 160us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 [1]
Transfers out of level 3, assets (11)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 [1] (14)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 [1]
Ending balance, fair value assets 2,122us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue 2,406us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets 12us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease 4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
Beginning balance, fair value liabilities 1,200us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue 2,301us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Realized gains/(losses), liabilities 9us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings 369us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
Unrealized gains/(losses included in earnings, liabilities (27)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss (813)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
Unrealized gains/(losses) included in OCI, liabilities 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome
Foreign exchange recognized in OCI or earnings, liabilities (22)mbi_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisInForeignExchangeRecognizedOtherComprehensiveIncomeOrEarningsLiabilities 0mbi_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisInForeignExchangeRecognizedOtherComprehensiveIncomeOrEarningsLiabilities
Purchases, liabilities 695us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
Issuances, liabilities 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues
Settlements, liabilities (60)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements (444)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
Sales, liabilities 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySales (41)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySales
Transfers into Level 3, liabilities 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3 [1] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3 [1]
Transfers out of Level 3, liabilities 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3 [1] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3 [1]
Ending balance, fair value liabilities 1,795us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue 1,372us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities (49)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease (7)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 1,431us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
1,612us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Unrealized gains/(losses) included in earnings, assets (3)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(1)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Settlements, assets (56)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(54)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Ending balance, fair value assets 1,372us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
1,557us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets (3)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Other Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Purchases, assets 108us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Ending balance, fair value assets 108us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansReceivableMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 379us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
359us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Unrealized gains/(losses) included in earnings, assets 6us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
5us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Ending balance, fair value assets 385us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
364us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbi_LoanRepurchaseCommitmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
State and municipal bonds [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 8us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
19us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Settlements, assets   (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Transfers into level 3, assets   44us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
[1]
Transfers out of level 3, assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
[1]  
Ending balance, fair value assets 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
62us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Foreign Government Debt [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_ForeignGovernmentDebtMember
12us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_ForeignGovernmentDebtMember
Realized gains/(losses), assets 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_ForeignGovernmentDebtMember
 
Settlements, assets   (5)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_ForeignGovernmentDebtMember
Ending balance, fair value assets 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_ForeignGovernmentDebtMember
7us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_ForeignGovernmentDebtMember
Corporate Obligations [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 10us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
48us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Realized gains/(losses), assets 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
(1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Unrealized gains/(losses) included in earnings, assets   1us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Unrealized gains/(losses) included in OCI, assets   (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Settlements, assets   (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Sales, assets   (19)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Transfers into level 3, assets   3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
[1]
Ending balance, fair value assets 10us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
30us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 55us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
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/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
48us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Settlements, assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Transfers into level 3, assets   17us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
[1]
Ending balance, fair value assets 53us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
64us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets   1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CorporateObligationMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Residential Mortgage Backed Agency [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets   0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedAgencyMember
Transfers into level 3, assets   29us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedAgencyMember
[1]
Ending balance, fair value assets   29us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedAgencyMember
Residential Mortgage Backed Non Agency [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets   6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
Unrealized gains/(losses) included in OCI, assets   (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
Transfers out of level 3, assets   (5)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
[1]
Ending balance, fair value assets   0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
Residential Mortgage Backed Non Agency [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Unrealized gains/(losses) included in earnings, assets 1us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Settlements, assets (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Transfers into level 3, assets   1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
[1]
Ending balance, fair value assets 3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets 1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_ResidentialMortgageBackedNonAgencyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Commercial Mortgage Backed Securities [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 2us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
14us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Settlements, assets   (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Transfers into level 3, assets   1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
[1]
Transfers out of level 3, assets (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
[1]  
Ending balance, fair value assets 1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
14us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets   3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Unrealized gains/(losses) included in earnings, assets   0us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Ending balance, fair value assets   3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Collateralized Debt Obligations [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 87us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
82us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
Unrealized gains/(losses) included in OCI, assets   3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
Purchases, assets   5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
Settlements, assets (5)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
(2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
Sales, assets (8)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
 
Transfers into level 3, assets   33us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
[1]
Transfers out of level 3, assets   (6)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
[1]
Ending balance, fair value assets 74us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
115us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
Collateralized Debt Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
22us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Unrealized gains/(losses) included in earnings, assets (1)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(3)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Settlements, assets   (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Transfers out of level 3, assets   (3)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
[1]
Ending balance, fair value assets 4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
14us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets   (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_CollateralizedDebtObligationsMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Other Asset Backed [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 85us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
58us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
Realized gains/(losses), assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
 
Unrealized gains/(losses) included in OCI, assets (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
Purchases, assets 4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
 
Settlements, assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
(2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
Sales, assets (8)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
 
Transfers into level 3, assets   24us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
[1]
Transfers out of level 3, assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
[1] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
[1]
Ending balance, fair value assets 74us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
85us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
Other Asset Backed [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 26us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
54us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Unrealized gains/(losses) included in earnings, assets 3us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(12)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Settlements, assets (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
(4)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Transfers into level 3, assets   4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
[1]
Transfers out of level 3, assets (6)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
[1]  
Ending balance, fair value assets 21us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
42us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets 3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherAssetBackedMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Medium Term Notes [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value liabilities 197us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
203us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
Unrealized gains/(losses included in earnings, liabilities 5us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
12us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
Foreign exchange recognized in OCI or earnings, liabilities (22)mbi_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisInForeignExchangeRecognizedOtherComprehensiveIncomeOrEarningsLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
 
Ending balance, fair value liabilities 180us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
215us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities (17)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
12us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= us-gaap_MediumTermNotesMember
Credit Derivatives [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value liabilities 244us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
1,147us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
Realized gains/(losses), liabilities 9us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
339us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
Unrealized gains/(losses included in earnings, liabilities (37)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
(838)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
Settlements, liabilities (9)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
(339)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
Ending balance, fair value liabilities 207us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
309us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities (37)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
(30)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CreditDerivativesMember
Other Derivative Liabilities [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value liabilities 24us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
Realized gains/(losses), liabilities   30us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
Unrealized gains/(losses included in earnings, liabilities (3)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
1us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
Ending balance, fair value liabilities 21us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
31us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities (3)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_OtherDerivativeLiabilitiesMember
Variable Interest Entity Notes [Member] | Liabilities Of Consolidated Vies [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value liabilities 735us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
940us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Unrealized gains/(losses included in earnings, liabilities 8us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
18us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Purchases, liabilities 695us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
 
Settlements, liabilities (51)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
(105)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Sales, liabilities   (41)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Ending balance, fair value liabilities 1,387us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
812us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities 8us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
16us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_VariableInterestEntityNotesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Unrealized gains/(losses) included in earnings, assets 4us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Foreign exchange recognized in OCI or earnings, assets 1mbi_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisInForeignExchangeRecognizedOtherComprehensiveIncomeOrEarningsAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Ending balance, fair value assets 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
 
Currency Derivatives [Member] | Liabilities Of Consolidated Vies [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value liabilities   11us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Unrealized gains/(losses included in earnings, liabilities   (6)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Ending balance, fair value liabilities   5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities   (6)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_CurrencyDerivativesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= mbi_LiabilitiesOfConsolidatedViesMember
Perpetual Debt And Equity Securities [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Beginning balance, fair value assets   11us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_PerpetualDebtAndEquitySecuritiesMember
Transfers into level 3, assets   4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_PerpetualDebtAndEquitySecuritiesMember
Ending balance, fair value assets   $ 15us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ invest_InvestmentAxis
= mbi_PerpetualDebtAndEquitySecuritiesMember
[1]
(1) - Transferred in and out at the end of the period.