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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 | 3 Months Ended
--- | ---
Mar. 31, 2012 | Mar. 31, 2011
Segment Reporting Information [Line Items] |  |
Total premiums earned | $ 152 | $ 169
United States [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 119 | 122
United Kingdom [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 8 | 7
Europe (Excluding United Kingdom) [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 5 | 12
Internationally Diversified [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 5 | 9
Central And South America [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 11 | 9
Asia [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 1 | 7
Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | $ 3 | $ 3

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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