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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 | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 | Jun. 30, 2011
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | $ 186 | $ 176 | $ 338 | $ 345
United States [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 142 | 130 | 261 | 252
United Kingdom [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 10 | 10 | 18 | 17
Europe (Excluding United Kingdom) [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 4 | 9 | 9 | 21
Internationally Diversified [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 5 | 9 | 10 | 18
Central And South America [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 21 | 10 | 32 | 19
Asia [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 1 | 5 | 2 | 12
Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | $ 3 | $ 3 | $ 6 | $ 6

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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