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Business Segments (Summary Of Company's Segment Results) (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Segment Reporting Information [Line Items] |  |  |  |  |  |
Revenues | $ 616 us-gaap_RevenueOtherFinancialServices | [1] | $ 644 us-gaap_RevenueOtherFinancialServices | [1] | $ 880 us-gaap_RevenueOtherFinancialServices | [1]
Net change in fair value of insured derivatives | 459 us-gaap_GainLossOnDerivativeInstrumentsNetPretax |  | 232 us-gaap_GainLossOnDerivativeInstrumentsNetPretax |  | 1,464 us-gaap_GainLossOnDerivativeInstrumentsNetPretax |
Net gains (losses) on financial instruments at fair value and foreign exchange | 78 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange |  | 69 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange |  | 55 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange |
Net investment losses related to other-than-temporary impairments | (15)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet |  |  |  | (105)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet |
Net gains (losses) on extinguishment of debt | 3 us-gaap_GainsLossesOnExtinguishmentOfDebt |  | 60 us-gaap_GainsLossesOnExtinguishmentOfDebt |  |  |
Other net realized gains (losses) | 28 us-gaap_OtherIncome |  | (29)us-gaap_OtherIncome |  | 7 us-gaap_OtherIncome |
Revenues of consolidated VIEs | 101 mbi_RevenuesOfConsolidatedVies |  | 233 mbi_RevenuesOfConsolidatedVies |  | 134 mbi_RevenuesOfConsolidatedVies |
Inter-segment revenues | 0 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity | [2] | 0 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity | [2] | 0 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity | [3]
Total revenues | 1,270 mbi_SegmentRevenue |  | 1,209 mbi_SegmentRevenue |  | 2,435 mbi_SegmentRevenue |
Losses and loss adjustment | 133 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet |  | 117 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet |  | 50 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet |
Operating | 239 us-gaap_SellingGeneralAndAdministrativeExpense |  | 384 us-gaap_SellingGeneralAndAdministrativeExpense |  | 431 us-gaap_SellingGeneralAndAdministrativeExpense |
Interest | 210 us-gaap_InterestExpense |  | 236 us-gaap_InterestExpense |  | 284 us-gaap_InterestExpense |
Expenses of consolidated VIEs | 47 mbi_ExpensesOfConsolidatedVies |  | 56 mbi_ExpensesOfConsolidatedVies |  | 72 mbi_ExpensesOfConsolidatedVies |
Inter-segment expenses | 0 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity | [2] | 0 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity | [2] | 0 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity | [3]
Total expenses | 629 mbi_SegmentExpense |  | 793 mbi_SegmentExpense |  | 837 mbi_SegmentExpense |
Income (loss) before income taxes | 641 mbi_SegmentPretaxIncomeLoss |  | 416 mbi_SegmentPretaxIncomeLoss |  | 1,598 mbi_SegmentPretaxIncomeLoss |
Provision (benefit) for income taxes | 72 us-gaap_IncomeTaxExpenseBenefit |  | 166 us-gaap_IncomeTaxExpenseBenefit |  | 364 us-gaap_IncomeTaxExpenseBenefit |
Net income (loss) | 569 us-gaap_NetIncomeLoss |  | 250 us-gaap_NetIncomeLoss |  | 1,234 us-gaap_NetIncomeLoss |
Identifiable assets | 16,284 us-gaap_Assets |  | 16,953 us-gaap_Assets |  | 21,724 us-gaap_Assets |
U S Public Finance Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Losses and loss adjustment | (10)us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  |  |  |  |
Operating Segments [Member] | U S Public Finance Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Revenues | 373 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [1] | 425 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [1] | 548 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [1]
Net change in fair value of insured derivatives | 1 us-gaap_GainLossOnDerivativeInstrumentsNetPretax / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 3 us-gaap_GainLossOnDerivativeInstrumentsNetPretax / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 1 us-gaap_GainLossOnDerivativeInstrumentsNetPretax / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Net gains (losses) on financial instruments at fair value and foreign exchange | 26 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 29 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 121 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Net investment losses related to other-than-temporary impairments | (15)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  |  |  |  |
Other net realized gains (losses) | 14 us-gaap_OtherIncome / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | (29)us-gaap_OtherIncome / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  |  |
Inter-segment revenues | 44 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [2] | 90 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [2] | 168 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [3]
Total revenues | 443 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 518 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 838 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Losses and loss adjustment | (10)us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 105 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 21 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Operating | 38 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 66 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 124 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Inter-segment expenses | 78 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [2] | 96 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [2] | 124 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember | [3]
Total expenses | 106 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 267 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 269 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Income (loss) before income taxes | 337 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 251 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 569 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Provision (benefit) for income taxes | 115 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 82 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 188 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Net income (loss) | 222 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 169 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 381 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Identifiable assets | 5,887 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 6,056 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |  | 6,887 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_USPublicFinanceInsuranceMember |
Operating Segments [Member] | International And Structured Finance Insurance [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Revenues | 189 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [1] | 148 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [1] | 243 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [1]
Net change in fair value of insured derivatives | 458 us-gaap_GainLossOnDerivativeInstrumentsNetPretax / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 229 us-gaap_GainLossOnDerivativeInstrumentsNetPretax / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 1,463 us-gaap_GainLossOnDerivativeInstrumentsNetPretax / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Net gains (losses) on financial instruments at fair value and foreign exchange | 0 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 24 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 93 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Net investment losses related to other-than-temporary impairments |  |  |  |  | (45)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Other net realized gains (losses) | 12 us-gaap_OtherIncome / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  |  |  | 1 us-gaap_OtherIncome / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Revenues of consolidated VIEs | 105 mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 237 mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 71 mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Inter-segment revenues | 55 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [2] | 78 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [2] | 45 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [3]
Total revenues | 819 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 716 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 1,871 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Losses and loss adjustment | 143 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 12 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 29 us-gaap_PolicyholderBenefitsAndClaimsIncurredNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Operating | 72 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 108 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 147 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Interest | 109 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 112 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 132 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Expenses of consolidated VIEs | 47 mbi_ExpensesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 50 mbi_ExpensesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 59 mbi_ExpensesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Inter-segment expenses | 64 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [2] | 136 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [2] | 208 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember | [3]
Total expenses | 435 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 418 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 575 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Income (loss) before income taxes | 384 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 298 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 1,296 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Provision (benefit) for income taxes | 134 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 101 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 432 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Net income (loss) | 250 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 197 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 864 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Identifiable assets | 10,086 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 11,687 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |  | 17,248 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_StructuredFinanceAndInternationalInsuranceMember |
Operating Segments [Member] | Corporate Operations [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Revenues | 42 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember | [1] | 55 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember | [1] | 68 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Net gains (losses) on financial instruments at fair value and foreign exchange | 55 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 15 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (158)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Net investment losses related to other-than-temporary impairments |  |  |  |  | (60)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Net gains (losses) on extinguishment of debt | 3 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 22 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  |  |
Other net realized gains (losses) | 2 us-gaap_OtherIncome / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  |  |  | 6 us-gaap_OtherIncome / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Revenues of consolidated VIEs |  |  | (14)mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  |  |
Inter-segment revenues | 46 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember | [3] | 85 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember | [3] | 177 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Total revenues | 148 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 163 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 33 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Operating | 87 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 157 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 114 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Interest | 101 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 124 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 152 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Inter-segment expenses | 15 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember | [3] | 7 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember | [3] | 15 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Total expenses | 203 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 288 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 281 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Income (loss) before income taxes | (55)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (125)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (248)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Provision (benefit) for income taxes | (173)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (15)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (179)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Net income (loss) | 118 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (110)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | (69)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Identifiable assets | 2,846 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 2,641 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |  | 2,721 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_CorporateOperationsMember |
Operating Segments [Member] | Advisory Services [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Revenues | 12 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember | [1] | 16 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember | [1] | 21 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Net gains (losses) on financial instruments at fair value and foreign exchange | (3)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 1 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (1)mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Revenues of consolidated VIEs | (8)mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  |  |  |  |
Inter-segment revenues | 22 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember | [3] | 26 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember | [3] | 34 mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Total revenues | 23 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 43 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 54 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Operating | 42 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 53 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 46 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Inter-segment expenses | 6 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember | [3] | 7 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember | [3] | 13 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Total expenses | 48 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 60 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 59 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Income (loss) before income taxes | (25)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (17)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (5)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Provision (benefit) for income taxes | (6)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (5)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (1)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Net income (loss) | (19)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (12)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | (4)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Identifiable assets | 793 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 44 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |  | 44 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_AdvisoryServicesMember |
Operating Segments [Member] | Conduit [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Revenues | 0 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [1] | 0 us-gaap_RevenueOtherFinancialServices / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [1] |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | 0 mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  |  |  |  |
Net gains (losses) on extinguishment of debt | 0 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  |  |  |  |
Revenues of consolidated VIEs | 4 mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 10 mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 63 mbi_RevenuesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Inter-segment revenues | (1)mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [2] | (9)mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [2] | (2)mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [3]
Total revenues | 3 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 1 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 61 mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Operating | 0 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  |  |  |  |
Interest | 0 us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  |  |  |  |
Expenses of consolidated VIEs |  |  | 6 mbi_ExpensesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 13 mbi_ExpensesOfConsolidatedVies / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Inter-segment expenses | 9 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [2] | 26 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [2] | 97 mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember | [3]
Total expenses | 9 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 32 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 110 mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Income (loss) before income taxes | (6)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | (31)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | (49)mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Provision (benefit) for income taxes | 0 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | (10)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | (17)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Net income (loss) | (6)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | (21)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | (32)us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Identifiable assets | 0 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 177 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |  | 694 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_ConduitsMember |
Intersegment Elimination [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Net gains (losses) on extinguishment of debt |  |  | 38 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [4] |  |
Inter-segment revenues | (166)mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [2] | (270)mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [2] | (422)mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [3]
Total revenues | (166)mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | (232)mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | (422)mbi_SegmentRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Inter-segment expenses | (172)mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [2] | (272)mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [2] | (457)mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [3]
Total expenses | (172)mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | (272)mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | (457)mbi_SegmentExpense / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Income (loss) before income taxes | 6 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | 40 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | 35 mbi_SegmentPretaxIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Provision (benefit) for income taxes | 2 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | 13 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | (59)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Net income (loss) | 4 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | 27 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | 94 us-gaap_NetIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Identifiable assets | $ (3,328)us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [5] | $ (3,652)us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [5] | $ (5,870)us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | [6]
[1] | Represents the sum of third-party financial guarantee net premiums earned, net investment income, insurance-related fees and reimbursements, investment management fees and other fees.
[2] | Represents intercompany premium income and expense, intercompany asset management fees and expenses, intercompany interest income and expense pertaining to intercompany receivables and payables and intercompany loans.
[3] | Represents intercompany premium income and expense, intercompany asset management fees and expenses, and intercompany interest income and expense pertaining to intercompany receivables and payables.
[4] | Represents the gain on the debt received as consideration in connection with the settlement with Bank of America.
[5] | Consists of intercompany reinsurance balances, repurchase agreements and deferred income taxes.
[6] | Consists of intercompany reinsurance balances, repurchase agreements and loans.

X
- Definition Intersegmentexpenses in the consolidated group. + References No definition available. + Details
Name: | mbi_ExpenseFromTransactionsWithOtherOperatingSegmentsOfSameEntity
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Total expenses of all Variable Interest Entities consolidated by the reporting entity + References No definition available. + Details
Name: | mbi_ExpensesOfConsolidatedVies
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Change in the fair value of and realized gains and losses on sale of financial instruments and foreign exchange included in earnings. + References No definition available. + Details
Name: | mbi_NetGainsLossesOnFinancialInstrumentsAtFairValueAndForeignExchange
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Intersegment revenues in the consolidated group. + References No definition available. + Details
Name: | mbi_RevenueFromTransactionsWithOtherOperatingSegmentsOfSameEntity
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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