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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
--- | ---
Mar. 31, 2014 | Mar. 31, 2013
Segment Reporting Information [Line Items] |  |
Total premiums earned | $ 93 | $ 131
United States [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 67 | 106
United Kingdom [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 9 | 8
Europe Excluding United Kingdom [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 3 | 3
Internationally Diversified [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 2 | 3
Central And South America [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 9 | 8
Asia [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | 1 | 1
Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Total premiums earned | $ 2 | $ 2

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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