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Commitments and Contingencies (Narrative) (Detail) (USD $) In Millions, unless otherwise specified | 9 Months Ended
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Sep. 30, 2014 Lawsuits
Commitments and Contingencies [Abstract] |
Other material lawsuits pending | 0
Number of operating lease term extensions | 2
Lease renewal term | 5 years
Operating leases future minimum payments due | $ 42
Lease incentives | $ 6

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- Definition Amount of lease incentives from lessor to fund certain leasehold improvements. + References No definition available. + Details
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Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Number of times lessee can extend the term of the operating lease. + References No definition available. + Details
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Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Other material lawsuits pending + References No definition available. + Details
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Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Definition Term of the lessee's leasing arrangement renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_LesseeLeasingArrangementsOperatingLeasesRenewalTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
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