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Related Party Transactions (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 Bonds
Related Party Transactions Supervisory And Other Services [Line Items] |
Voting interests of the company | 10.00%
Executed surety bonds to guarantee payment obligations | 5
Outstanding exposure on surety bonds | $ 340

X
- Definition Number of executed surety bonds to guarantee payment obligations. + References No definition available. + Details
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Namespace Prefix: | mbi_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Outstanding exposure on surety bonds. + References No definition available. + Details
Name: | mbi_OutstandingExposureOnSuretyBonds
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Percentage of voting interests of the Company. + References No definition available. + Details
Name: | mbi_PercentageOfVotingInterestsOfCompany
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | mbi_RelatedPartyTransactionsSupervisoryAndOtherServicesLineItems
Namespace Prefix: | mbi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration