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Business Segments (Summary Of Premiums Earned On Financial Guarantees And Insured Derivatives By Geographic Location Of Risk) (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | $ 661 | $ 708 | $ 714
United States [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 530 | 545 | 555
United Kingdom [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 36 | 37 | 35
Europe (Excluding United Kingdom) [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 15 | 29 | 23
Internationally Diversified [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 16 | 33 | 41
Central And South America [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 48 | 36 | 40
Asia [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 5 | 15 | 9
Other [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | $ 11 | $ 13 | $ 11

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- Definition Premiums Earned Net Financial Guarantee Insurance Contracts And Insured Derivatives + References No definition available. + Details
Name: | mbi_PremiumsEarnedNetFinancialGuaranteeInsuranceContractsAndInsuredDerivatives
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration