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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, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | $ 134 | $ 186 | $ 265 | $ 338
United States [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 109 | 142 | 215 | 261
United Kingdom [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 9 | 10 | 17 | 18
Europe Excluding United Kingdom [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 3 | 4 | 6 | 9
Internationally Diversified [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 3 | 5 | 6 | 10
Central And South America [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 7 | 21 | 15 | 32
Asia [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | 1 | 1 | 2 | 2
Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total premiums earned | $ 2 | $ 3 | $ 4 | $ 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