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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	3us-gaap_NumberOfOperatingSegments
Cutwater sale effective date	Jan. 01, 2015
Mbia Inc [Member]
Business Acquisition [Line Items]
Gain on sale of subsidiary	$ 24us-gaap_GainOrLossOnSaleOfStockInSubsidiary / dei_LegalEntityAxis = mbi_MbiaIncMember
Liquid assets	567mbi_LiquidAssets / dei_LegalEntityAxis = mbi_MbiaIncMember	498mbi_LiquidAssets / dei_LegalEntityAxis = mbi_MbiaIncMember
Amount released from tax escrow account	228mbi_ReleaseFromTaxSharingAgreementEscrowAccount / dei_LegalEntityAxis = mbi_MbiaIncMember
National [Member]
Business Acquisition [Line Items]
Impairment of real estate	$ 4us-gaap_ImpairmentOfRealEstate / dei_LegalEntityAxis = mbi_NationalMember

X

- Definition

This element represents the liquidity position of the entity

+ References

No definition available.

+ Details

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Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- 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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Date the entity disposed of a business or a group of assets, in CCYY-MM-DD format.

+ References

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
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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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- 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

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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

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- Details

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Period Type:

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