XML 135 R120.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Related Party Transactions (Narrative) (Detail) - securityloan | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Related Party Transactions [Abstract] |  |
Principal ownership percentage | 10.00% |
Number of loans to executive officers or directors | 0 | 0

X
- Definition Number of loans made to executive officers or directors of teh Company. + References No definition available. + Details
Name: | mbi_LoansToExecutiveOfficersOrDirectors
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

X
- References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration