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Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) (USD $)
In Millions, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2013

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

$ 2,071us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue

$ 3,457us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue

Gross unrealized losses

(147)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments

(229)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments

Wrapped Securities [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

147us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember

Gross unrealized losses

(37)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember

Loss and loss adjustment expense reserves

39mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember

^[1]

Asset-backed [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

195us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

Gross unrealized losses

(33)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

Asset-backed [Member] | Wrapped Securities [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

121us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

Gross unrealized losses

(33)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

Loss and loss adjustment expense reserves

38mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

^[1]

Asset-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

113us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

^[2]

Gross unrealized losses

(31)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

^[2]

Loss and loss adjustment expense reserves

38mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

^[1],[2]

Asset-backed [Member] | Wrapped Securities [Member] | Other Insurers [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

8us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

Gross unrealized losses

(2)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

Loss and loss adjustment expense reserves

0mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember

^[1]

Mortgage-backed [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

442us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

Gross unrealized losses

(11)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

Mortgage-backed [Member] | Wrapped Securities [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

5us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

Gross unrealized losses

0mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

Loss and loss adjustment expense reserves

1mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

^[1]

Mortgage-backed [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

4us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

^[2]

Gross unrealized losses

0mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

^[2]

Loss and loss adjustment expense reserves

1mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

^[1],[2]

Mortgage-backed [Member] | Wrapped Securities [Member] | Other Insurers [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

1us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

Gross unrealized losses

0mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

Loss and loss adjustment expense reserves

0mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember

^[1]

Corporate Obligations [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

719us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember

Gross unrealized losses

(92)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember

All Other Securities [Member] | Wrapped Securities [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

21us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

Gross unrealized losses

(4)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

Loss and loss adjustment expense reserves

0mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

^[1]

All Other Securities [Member] | Wrapped Securities [Member] | Mbia Corp And National [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

21us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

^[2]

Gross unrealized losses

(4)mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

^[2]

Loss and loss adjustment expense reserves

0mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_MbiaCorpAndNationalMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

^[1],[2]

All Other Securities [Member] | Wrapped Securities [Member] | Other Insurers [Member]

Schedule Of Investments [Line Items]

Total Available-For-Sale, Fair Value

0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

Gross unrealized losses

0mbi_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

Loss and loss adjustment expense reserves

$ 0mbi_LiabilityForClaimsAndClaimsAdjustmentExpenseInsuredByFinancialGuarantor
/ us-gaap_FinancialInstrumentAxis
= mbi_WrappedSecuritiesMember
/ dei_LegalEntityAxis
= mbi_OtherInsurersMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= mbi_AllOtherSecuritiesMember

^[1]

[1]	Insurance loss reserve estimates are based on the proportion of par value owned to the total amount of par value insured.
[2]	Includes investments insured by MBIA Corp. and National.

X

- Definition

Amount of accumulated pre-tax unrealized losses before deducting pre-tax unrealized gains on investments in available-for-sale securities impacting investments.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbi_
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Balance Type:	credit
Period Type:	instant

X

- Definition

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events by financial guarantor that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

No definition available.

+ Details

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

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

+ Details

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X

- Details

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- Details

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X

- Details

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X

- Details

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