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Recent Accounting Pronouncements (Narrative) (Detail) | 9 Months Ended
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Sep. 30, 2015
Disclosure Variable Interest Entities Narrative [Abstract] |
Number of variable interest entities deconsolidated | 1

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- Definition Disclosure - Variable Interest Entities (Narrative) [Abstract] + References No definition available. + Details
Name: | mbi_DisclosureVariableInterestEntitiesNarrativeAbstract
Namespace Prefix: | mbi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the number of VIEs deconsolidated during the period. + References No definition available. + Details
Name: | mbi_NumberOfVariableInterestEntitiesDeconsolidated
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration