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Business Developments And Risks And Uncertainties (Narrative) (Detail) (USD $) | 12 Months Ended | 0 Months Ended
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jan. 13, 2015
Business Acquisition [Line Items] |  |  |  |
Number of operating segments | 5 us-gaap_NumberOfOperatingSegments |  |  |
Commuted gross insured exposure | $ 7,100,000,000 mbi_CommutedGrossInsuredExposure | $ 20,000,000,000 mbi_CommutedGrossInsuredExposure | $ 13,400,000,000 mbi_CommutedGrossInsuredExposure |
SubsequentEvent [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Cutwater sale effective date | Jan. 01, 2015 |  |  |
Mbia Inc [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Liquid assets | 498,000,000 mbi_LiquidAssets / dei_LegalEntityAxis = mbi_MbiaIncMember | 359,000,000 mbi_LiquidAssets / dei_LegalEntityAxis = mbi_MbiaIncMember |  |
Amount released from tax escrow account | 220,000,000 mbi_ReleaseFromTaxSharingAgreementEscrowAccount / dei_LegalEntityAxis = mbi_MbiaIncMember |  |  |
Mbia Inc [Member] | SubsequentEvent [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Amount released from tax escrow account |  |  |  | 228,000,000 mbi_ReleaseFromTaxSharingAgreementEscrowAccount / dei_LegalEntityAxis = mbi_MbiaIncMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
National [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Impairment of real estate | 3,000,000 us-gaap_ImpairmentOfRealEstate / dei_LegalEntityAxis = mbi_NationalMember | 29,000,000 us-gaap_ImpairmentOfRealEstate / dei_LegalEntityAxis = mbi_NationalMember |  |
Dividends from subsidiaries | 220,000,000 us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries / dei_LegalEntityAxis = mbi_NationalMember |  |  |
Bank Of America [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Commuted gross insured exposure |  | 7,400,000,000 mbi_CommutedGrossInsuredExposure / dei_LegalEntityAxis = mbi_BankOfAmericaMember |  |
Societe Generale [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Commuted gross insured exposure |  | $ 4,200,000,000 mbi_CommutedGrossInsuredExposure / dei_LegalEntityAxis = mbi_SocietegeneraleMember |  |

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