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Insurance In Force (Summary Of Company's Reinsurance Agreements For U.S. Public Finance And Structured Finance And International Insurance Operations) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers	$ 6,087mbi_AggregateAmountOfInsuredParOutstandingCededToReinsurers		$ 7,100mbi_AggregateAmountOfInsuredParOutstandingCededToReinsurers
Reinsurance Recoverables Secured By Letters Of Credit Amount	34mbi_ReinsuranceRecoverablesSecuredByLettersOfCreditAmount
Reinsurance Recoverable	7us-gaap_ReinsuranceRecoverables	[1]
Moody's Aaa [Member] | S&P AA+ [Member] | Overseas Private Investment Corporation [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers	289mbi_AggregateAmountOfInsuredParOutstandingCededToReinsurers / us-gaap_CededCreditRiskAxis = mbi_OverseasPrivateInvestmentCorporationMember / us-gaap_CreditRatingMoodysAxis = us-gaap_MoodysAaaRatingMember / us-gaap_CreditRatingStandardPoorsAxis = us-gaap_StandardPoorsAAPlusRatingMember
Moody's A2 or above [Member] | S&P A- or above [Member] | Others [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers	145mbi_AggregateAmountOfInsuredParOutstandingCededToReinsurers / us-gaap_CededCreditRiskAxis = mbi_OtherReinsurersMember / us-gaap_CreditRatingMoodysAxis = mbi_Moodysa2OrAboveRatingMember / us-gaap_CreditRatingStandardPoorsAxis = mbi_StandardpoorsaminusoraboveratingmemberMember
Reinsurance Recoverables Secured By Letters Of Credit Amount	2mbi_ReinsuranceRecoverablesSecuredByLettersOfCreditAmount / us-gaap_CededCreditRiskAxis = mbi_OtherReinsurersMember / us-gaap_CreditRatingMoodysAxis = mbi_Moodysa2OrAboveRatingMember / us-gaap_CreditRatingStandardPoorsAxis = mbi_StandardpoorsaminusoraboveratingmemberMember
Mood'ys A3 Rating [Member] | S&P AA [Member] | Assured Guaranty Corp [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers	2,019mbi_AggregateAmountOfInsuredParOutstandingCededToReinsurers / us-gaap_CededCreditRiskAxis = mbi_AssuredGuarantyCorpMember / us-gaap_CreditRatingMoodysAxis = us-gaap_MoodysA3RatingMember / us-gaap_CreditRatingStandardPoorsAxis = us-gaap_StandardPoorsAARatingMember
Reinsurance Recoverable	6us-gaap_ReinsuranceRecoverables / us-gaap_CededCreditRiskAxis = mbi_AssuredGuarantyCorpMember / us-gaap_CreditRatingMoodysAxis = us-gaap_MoodysA3RatingMember / us-gaap_CreditRatingStandardPoorsAxis = us-gaap_StandardPoorsAARatingMember	[1]
Moody's Baa 1 Rating [Member] | S&P AA [Member] | Assured Guaranty Re Ltd [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers	3,634mbi_AggregateAmountOfInsuredParOutstandingCededToReinsurers / us-gaap_CededCreditRiskAxis = mbi_AssuredGuarantyReLtdMember / us-gaap_CreditRatingMoodysAxis = us-gaap_MoodysBaa1RatingMember / us-gaap_CreditRatingStandardPoorsAxis = us-gaap_StandardPoorsAARatingMember
Reinsurance Recoverables Secured By Letters Of Credit Amount	32mbi_ReinsuranceRecoverablesSecuredByLettersOfCreditAmount / us-gaap_CededCreditRiskAxis = mbi_AssuredGuarantyReLtdMember / us-gaap_CreditRatingMoodysAxis = us-gaap_MoodysBaa1RatingMember / us-gaap_CreditRatingStandardPoorsAxis = us-gaap_StandardPoorsAARatingMember
Reinsurance Recoverable	$ 1us-gaap_ReinsuranceRecoverables / us-gaap_CededCreditRiskAxis = mbi_AssuredGuarantyReLtdMember / us-gaap_CreditRatingMoodysAxis = us-gaap_MoodysBaa1RatingMember / us-gaap_CreditRatingStandardPoorsAxis = us-gaap_StandardPoorsAARatingMember	[1]
[1] Total reinsurance recoverable is primarily related to recoverables on unpaid losses.

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Aggregate amount of insured par outstanding ceded to reinsurers.

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- Definition

Amount after valuation allowance recoverable including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 6

-Article 7



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.(a),6)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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