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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

X

- 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

X

- Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration