XML 122 R85.htm IDEA: XBRL DOCUMENT v2.4.1.9

Investments (Average Credit Ratings For Securities Rated Below Investment Grade Without The Effect Of Financial Guarantees) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Asset-backed [Member]
Schedule Of Investments [Line Items]
Fair Value Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	$ 67mbi_FairValueOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Percentage Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	56.00%mbi_PercentageOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Fair Value Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	5mbi_FairValueOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember
Percentage Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	100.00%mbi_PercentageOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Fair Value Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	$ 0mbi_FairValueOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Percentage Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	0.00%mbi_PercentageOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember

X

- Definition

Fair Value of Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors.

+ References

No definition available.

+ Details

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

X

- Definition

Percentage of securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors.

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfSecuritiesRatedBelowInvestmentGradeWithoutGivingEffectToBenefitOfGuaranteesProvidedByFinancialGuarantors
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_ScheduleOfInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: