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Business Developments And Risks And Uncertainties (Narrative) (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014
Business Acquisition [Line Items] |  |
Number of operating segments | 3 us-gaap_NumberOfOperatingSegments |
Cutwater sale effective date | Jan. 01, 2015 |
Mbia Inc [Member] |  |
Business Acquisition [Line Items] |  |
Gain on sale of subsidiary | $ 24 us-gaap_GainOrLossOnSaleOfStockInSubsidiary / dei_LegalEntityAxis = mbi_MbiaIncMember |
Liquid assets | 567 mbi_LiquidAssets / dei_LegalEntityAxis = mbi_MbiaIncMember | 498 mbi_LiquidAssets / dei_LegalEntityAxis = mbi_MbiaIncMember
Amount released from tax escrow account | 228 mbi_ReleaseFromTaxSharingAgreementEscrowAccount / dei_LegalEntityAxis = mbi_MbiaIncMember |
National [Member] |  |
Business Acquisition [Line Items] |  |
Impairment of real estate | $ 4 us-gaap_ImpairmentOfRealEstate / dei_LegalEntityAxis = mbi_NationalMember |

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- Definition This element represents the amount released from the escrow account related to the tax sharing agreement during the period + References No definition available. + Details
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- Details
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Period Type: | duration

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- Definition Date the entity disposed of a business or a group of assets, in CCYY-MM-DD format. + References No definition available. + Details
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- Definition Amount of gain (loss) on sale or disposal of equity in securities of subsidiaries. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph ((13)(g)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 13 -Subparagraph g -Article 9 + Details
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Period Type: | duration

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- Definition The charge against earnings in the period to reduce the carrying amount of real property to fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
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- Details
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Period Type: |