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Business Segments (Summary Of Premiums Earned On Financial Guarantees And Insured Derivatives By Geographic Location Of Risk) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | $ 708 | $ 714 | $ 868
United States [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 545 | 555 | 661
United Kingdom [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 37 | 35 | 29
Europe (Excluding United Kingdom) [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 29 | 23 | 21
Internationally Diversified [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 33 | 41 | 83
Central And South America [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 36 | 40 | 41
Asia [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | 15 | 9 | 17
Other [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Total premiums earned | $ 13 | $ 11 | $ 16

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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