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Fair Value Of Financial Instruments (Fair Value Hierarchy Table Presents The Company's Assets And Liabilities At Fair Value Not Recorded On The Company's Consolidated Balance Sheet) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Assets held for sale | $ 802 us-gaap_OtherAssetsHeldForSaleCurrent |  | $ 29 us-gaap_OtherAssetsHeldForSaleCurrent |
Investments held-to-maturity, fair value | 2,632 us-gaap_HeldToMaturitySecuritiesFairValue |  | 2,651 us-gaap_HeldToMaturitySecuritiesFairValue |
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 1 [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Net cash collateral pledged |  |  | 24 mbi_Cashcollateralpledge / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | [1]
Total assets | 0 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |  | 24 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Total liabilities | 0 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |  | 0 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 2 [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Accrued investment income | 43 us-gaap_AccruedInvestmentIncomeReceivable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [1] | 52 us-gaap_AccruedInvestmentIncomeReceivable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [1]
Receivable for investments sold | 69 mbi_ReceivableForInvestmentsSold / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [1] | 22 mbi_ReceivableForInvestmentsSold / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [1]
Total assets | 138 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |  | 103 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Long-term debt | 1,172 us-gaap_LongTermDebtFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |  | 1,412 us-gaap_LongTermDebtFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Payable for investments purchased | 42 mbi_PayableForInvestmentsPurchasedFairValueDisclosure / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [2] | 31 mbi_PayableForInvestmentsPurchasedFairValueDisclosure / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [2]
Total liabilities | 1,214 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |  | 1,443 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 2 [Member] | Facilities [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Assets held for sale | 26 us-gaap_OtherAssetsHeldForSaleCurrent / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorPropertyClassAxis = us-gaap_AssetsHeldForSaleMember |  | 29 us-gaap_OtherAssetsHeldForSaleCurrent / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorPropertyClassAxis = us-gaap_AssetsHeldForSaleMember |
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 3 [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Other investments | 4 us-gaap_OtherInvestments / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 4 us-gaap_OtherInvestments / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Total assets | 2,636 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 2,655 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Investment agreements | 705 mbi_GuaranteedInvestmentAgreementsFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 814 mbi_GuaranteedInvestmentAgreementsFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Medium-term notes | 801 us-gaap_MediumTermNotes / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 927 us-gaap_MediumTermNotes / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Total liabilities | 4,285 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 4,492 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Gross | 4,051 mbi_FinancialGuaranteeGross / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 2,843 mbi_FinancialGuaranteeGross / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Ceded | 109 mbi_FinancialGuaranteeCeded / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 71 mbi_FinancialGuaranteeCeded / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Investments held-to-maturity, fair value | 2,632 us-gaap_HeldToMaturitySecuritiesFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 2,651 us-gaap_HeldToMaturitySecuritiesFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Variable interest entity notes | 2,779 us-gaap_NotesPayable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 2,751 us-gaap_NotesPayable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Carrying Reported Amount Fair Value Disclosure [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Other investments | 4 us-gaap_OtherInvestments / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 5 us-gaap_OtherInvestments / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Accrued investment income | 43 us-gaap_AccruedInvestmentIncomeReceivable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1] | 52 us-gaap_AccruedInvestmentIncomeReceivable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1]
Receivable for investments sold | 69 mbi_ReceivableForInvestmentsSold / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1] | 22 mbi_ReceivableForInvestmentsSold / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1]
Net cash collateral pledged |  |  | 24 mbi_Cashcollateralpledge / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1]
Total assets | 2,899 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 2,933 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Investment agreements | 547 mbi_GuaranteedInvestmentAgreementsFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 700 mbi_GuaranteedInvestmentAgreementsFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Medium-term notes | 1,004 us-gaap_MediumTermNotes / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 1,224 us-gaap_MediumTermNotes / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Long-term debt | 1,810 us-gaap_LongTermDebtFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 1,702 us-gaap_LongTermDebtFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Payable for investments purchased | 42 mbi_PayableForInvestmentsPurchasedFairValueDisclosure / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [2] | 31 mbi_PayableForInvestmentsPurchasedFairValueDisclosure / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [2]
Total liabilities | 6,160 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 6,587 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Gross | 1,959 mbi_FinancialGuaranteeGross / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 2,388 mbi_FinancialGuaranteeGross / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Ceded | 65 mbi_FinancialGuaranteeCeded / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 76 mbi_FinancialGuaranteeCeded / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Carrying Reported Amount Fair Value Disclosure [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Facilities [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Assets held for sale | 26 us-gaap_OtherAssetsHeldForSaleCurrent / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_MajorPropertyClassAxis = us-gaap_AssetsHeldForSaleMember |  | 29 us-gaap_OtherAssetsHeldForSaleCurrent / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_MajorPropertyClassAxis = us-gaap_AssetsHeldForSaleMember |
Carrying Reported Amount Fair Value Disclosure [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Investments held-to-maturity, fair value | 2,757 us-gaap_HeldToMaturitySecuritiesFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 2,801 us-gaap_HeldToMaturitySecuritiesFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Variable interest entity notes | 2,757 us-gaap_NotesPayable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 2,930 us-gaap_NotesPayable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Fair Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Other investments | 4 us-gaap_OtherInvestments / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 4 us-gaap_OtherInvestments / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Accrued investment income | 43 us-gaap_AccruedInvestmentIncomeReceivable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1] | 52 us-gaap_AccruedInvestmentIncomeReceivable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1]
Receivable for investments sold | 69 mbi_ReceivableForInvestmentsSold / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1] | 22 mbi_ReceivableForInvestmentsSold / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1]
Net cash collateral pledged |  |  | 24 mbi_Cashcollateralpledge / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1]
Total assets | 2,774 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 2,782 us-gaap_AssetsFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Investment agreements | 705 mbi_GuaranteedInvestmentAgreementsFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 814 mbi_GuaranteedInvestmentAgreementsFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Medium-term notes | 801 us-gaap_MediumTermNotes / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 927 us-gaap_MediumTermNotes / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Long-term debt | 1,172 us-gaap_LongTermDebtFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 1,412 us-gaap_LongTermDebtFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Payable for investments purchased | 42 mbi_PayableForInvestmentsPurchasedFairValueDisclosure / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [2] | 31 mbi_PayableForInvestmentsPurchasedFairValueDisclosure / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [2]
Total liabilities | 5,499 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 5,935 us-gaap_LiabilitiesFairValueDisclosureNonrecurring / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Gross | 4,051 mbi_FinancialGuaranteeGross / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 2,843 mbi_FinancialGuaranteeGross / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Ceded | 109 mbi_FinancialGuaranteeCeded / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 71 mbi_FinancialGuaranteeCeded / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Fair Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Facilities [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Assets held for sale | 26 us-gaap_OtherAssetsHeldForSaleCurrent / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_MajorPropertyClassAxis = us-gaap_AssetsHeldForSaleMember |  | 29 us-gaap_OtherAssetsHeldForSaleCurrent / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_MajorPropertyClassAxis = us-gaap_AssetsHeldForSaleMember |
Fair Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items] |  |  |  |
Investments held-to-maturity, fair value | 2,632 us-gaap_HeldToMaturitySecuritiesFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 2,651 us-gaap_HeldToMaturitySecuritiesFairValue / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Variable interest entity notes | $ 2,779 us-gaap_NotesPayable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | $ 2,751 us-gaap_NotesPayable / mbi_DisclosedAtFairValueNotRecordedAtFairValueAxis = mbi_ValueDisclosedAtFairValueNotRecordedAtFairValueMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
[1] | Reported within "Other assets" on MBIA's consolidated balance sheets.
[2] | Reported within "Other liabilities" on MBIA's consolidated balance sheets.

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- Definition Cash Collateral Pledge + References No definition available. + Details
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- Definition Represents the Company's balance sheet carrying amount of the financial guarantee insurance contracts ceded to third party reinsurers. The balance sheet carrying amount comprises the prepaid reinsurance premiums and reinsurance recoverable on paid and unpaid losses + References No definition available. + Details
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- Definition Represents the Company's balance sheet carrying amount of the financial guarantee insurance contract obligations with third parties. The gross balance sheet carrying amount comprises the unearned premium revenue and the loss and loss adjustment expense reserves balances + References No definition available. + Details
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- Definition Payable for investments purchased fair value disclosure + References No definition available. + Details
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- Definition Receivable for investments sold. + References No definition available. + Details
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- Definition Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 4 -Article 7 + Details
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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
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- Definition Fair value of investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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- Definition Including the current and noncurrent portions, carrying value at the balance sheet date of a financial instrument used to receive debt funding on a regular basis with original maturities ranging from 5-10 years. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 + Details
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- Definition The lower of the carrying value or fair value less cost to sell of current assets held for sale that are not elsewhere specified in the taxonomy. The carrying value of major classes of assets and liabilities of the disposal group are separately disclosed in the balance sheet in the specific concepts provided. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e1107-107759 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 35 -Paragraph 43 -URI http://asc.fasb.org/extlink&oid=29634951&loc=d3e1739-110224 + Details
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