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Schedule I- Investments (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014
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Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | $ 6,769 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost
Fair Value | 6,830 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue
Amount at which shown in the balance sheet | 6,830 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount
Assets Of Consolidated VIEs [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 3,055 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Fair Value | 3,053 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Amount at which shown in the balance sheet | 3,178 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Other Aggregated Investments [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 4 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / invest_InvestmentAxis = us-gaap_OtherAggregatedInvestmentsMember
Fair Value | 4 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / invest_InvestmentAxis = us-gaap_OtherAggregatedInvestmentsMember
Amount at which shown in the balance sheet | 4 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / invest_InvestmentAxis = us-gaap_OtherAggregatedInvestmentsMember
Long-Term Available-For-Sale [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 5,162 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember
Fair Value | 5,225 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember
Amount at which shown in the balance sheet | 5,225 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember
Long-Term Available-For-Sale [Member] | U.S. Treasury And Government Agency [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 446 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember
Fair Value | 482 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember
Amount at which shown in the balance sheet | 482 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_USTreasuryAndGovernmentMember
Long-Term Available-For-Sale [Member] | US States And Political Subdivisions [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 1,613 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair Value | 1,699 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Amount at which shown in the balance sheet | 1,699 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Long-Term Available-For-Sale [Member] | Foreign Governments [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 223 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember
Fair Value | 230 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember
Amount at which shown in the balance sheet | 230 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_ForeignGovernmentDebtMember
Long-Term Available-For-Sale [Member] | Corporate Obligations [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 1,434 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CorporateDebtSecuritiesMember
Fair Value | 1,386 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CorporateDebtSecuritiesMember
Amount at which shown in the balance sheet | 1,386 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CorporateDebtSecuritiesMember
Short-Term Available-For-Sale [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 1,335 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_ShortTermAvailableForSaleMember
Fair Value | 1,333 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_ShortTermAvailableForSaleMember
Amount at which shown in the balance sheet | 1,333 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_ShortTermAvailableForSaleMember
Short-Term Available-For-Sale [Member] | Assets Of Consolidated VIEs [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 0 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_ShortTermAvailableForSaleMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Fair Value | 0 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_ShortTermAvailableForSaleMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Amount at which shown in the balance sheet | 0 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_ShortTermAvailableForSaleMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Equity Available For Sale [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 12 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_EquityAvailableForSaleMember
Fair Value | 13 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_EquityAvailableForSaleMember
Amount at which shown in the balance sheet | 13 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_EquityAvailableForSaleMember
AFS Investments [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 6,509 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember
Fair Value | 6,571 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember
Amount at which shown in the balance sheet | 6,571 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember
Investments At Fair Value [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 256 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_InvestmentsAtFairValueMember
Fair Value | 255 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_InvestmentsAtFairValueMember
Amount at which shown in the balance sheet | 255 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_InvestmentsAtFairValueMember
Investments At Fair Value [Member] | Assets Of Consolidated VIEs [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 298 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_InvestmentsAtFairValueMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Fair Value | 421 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_InvestmentsAtFairValueMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Amount at which shown in the balance sheet | 421 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_InvestmentsAtFairValueMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Held-To-Maturity [Member] | Corporate Obligations [Member] | Assets Of Consolidated VIEs [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 2,757 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_HeldtomaturitySecuritiesMember / invest_InvestmentAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Fair Value | 2,632 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_HeldtomaturitySecuritiesMember / invest_InvestmentAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Amount at which shown in the balance sheet | 2,757 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_HeldtomaturitySecuritiesMember / invest_InvestmentAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis = mbi_AssetsOfConsolidatedVIEsMember
Mortgage-backed [Member] | Long-Term Available-For-Sale [Member] | Residential Mortgage Backed Agency [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 1,111 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember
Fair Value | 1,122 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember
Amount at which shown in the balance sheet | 1,122 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_ResidentialMortgageBackedAgencyMember
Mortgage-backed [Member] | Long-Term Available-For-Sale [Member] | Residential Mortgage-Backed Non-Agency [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 50 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember
Fair Value | 49 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember
Amount at which shown in the balance sheet | 49 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_ResidentialMortgageBackedNonAgencyMember
Mortgage-backed [Member] | Long-Term Available-For-Sale [Member] | Commercial Mortgage-Backed [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 17 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Fair Value | 17 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Amount at which shown in the balance sheet | 17 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_DebtSecurityAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Asset-backed [Member] | Long-Term Available-For-Sale [Member] | Collateralized Debt Obligations [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 84 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember
Fair Value | 66 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember
Amount at which shown in the balance sheet | 66 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember
Asset-backed [Member] | Long-Term Available-For-Sale [Member] | Other Asset-Backed [Member] |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |
Cost | 184 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_OtherAssetBackedMember
Fair Value | 174 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesFairValue / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_OtherAssetBackedMember
Amount at which shown in the balance sheet | $ 174 us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCarryingAmount / us-gaap_DebtSecurityAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_InformationByCategoryOfDebtSecurityAxis = mbi_LongTermAvailableForSaleMember / invest_InvestmentAxis = mbi_OtherAssetBackedMember

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- Definition This element represents the carrying (reported) amount of the entity's investments as of the balance sheet date. This amount may represent the individual investment's or group of similar investments' original cost, fair value, or such other amount at which the investment is shown in the entity's balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 15 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 7 -Subparagraph (SX 210.12-15) -URI http://asc.fasb.org/extlink&oid=6955306&loc=d3e611379-123010 + Details
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