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Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
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Variable Interest Entity [Line Items] |  |  |  |  |
Premiums receivable | $ 875 us-gaap_PremiumsReceivableAtCarryingValue |  | $ 1,051 us-gaap_PremiumsReceivableAtCarryingValue |  | $ 1,228 us-gaap_PremiumsReceivableAtCarryingValue
Derivative liabilities | 246 us-gaap_DerivativeLiabilities |  | 1,200 us-gaap_DerivativeLiabilities |  |
Collateralized Debt Obligations [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 8,613 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember |  | 12,565 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember |  |
Maximum Exposure to Loss | 5,623 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember |  | 7,693 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember |  |
Investments | 110 us-gaap_Investments / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [1] | 120 us-gaap_Investments / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [1] |
Premiums receivable | 24 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [2] | 43 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [2] |
Unearned premium revenue | 20 us-gaap_UnearnedPremiums / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [3] | 37 us-gaap_UnearnedPremiums / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [3] |
Loss and loss adjustment expense reserves | 70 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember |  | 21 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember |  |
Derivative liabilities | 102 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [4] | 108 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = us-gaap_CollateralizedDebtObligationsMember | [4] |
Residential Mortgage Backed Securities [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 14,136 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  | 21,738 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |
Maximum Exposure to Loss | 7,459 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  | 9,251 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |
Investments | 9 us-gaap_Investments / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [1] | 10 us-gaap_Investments / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [1] |
Premiums receivable | 41 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [2] | 53 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [2] |
Insurance loss recoverable | 518 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [5] | 658 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [5] |
Unearned premium revenue | 39 us-gaap_UnearnedPremiums / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [3] | 51 us-gaap_UnearnedPremiums / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [3] |
Loss and loss adjustment expense reserves | 307 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [6] | 327 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |
Derivative liabilities |  |  | 5 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [4] |
Commercial Mortgage Backed Securities [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 571 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  | 1,367 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Maximum Exposure to Loss | 279 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  | 447 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |
Premiums receivable | 1 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | [2] | 1 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | [2] |
Unearned premium revenue | 1 us-gaap_UnearnedPremiums / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | [3] | 1 us-gaap_UnearnedPremiums / invest_InvestmentAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | [3] |
Consumer Asset Backed [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 6,008 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember |  | 7,830 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember |  |
Maximum Exposure to Loss | 1,989 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember |  | 2,740 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember |  |
Investments |  |  | 9 us-gaap_Investments / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember | [1] |
Premiums receivable | 16 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember | [2] | 19 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember | [2] |
Unearned premium revenue | 14 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember | [3] | 19 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember | [3] |
Loss and loss adjustment expense reserves | 12 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember | [6] | 13 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_ConsumerAssetBackedMember |  |
Corporate Asset Backed [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 6,612 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_CorporateAssetBackedMember |  | 13,028 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_CorporateAssetBackedMember |  |
Maximum Exposure to Loss | 4,608 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_CorporateAssetBackedMember |  | 7,248 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_CorporateAssetBackedMember |  |
Investments |  |  | 2 us-gaap_Investments / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [1] |
Premiums receivable | 41 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [2] | 80 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [2] |
Insurance loss recoverable | 6 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [5] | 18 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [5] |
Unearned premium revenue | 47 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [3] | 96 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_CorporateAssetBackedMember | [3] |
Global Structured Finance [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 35,940 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember |  | 56,528 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember |  |
Maximum Exposure to Loss | 19,958 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember |  | 27,379 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember |  |
Investments | 119 us-gaap_Investments / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [1] | 141 us-gaap_Investments / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [1] |
Premiums receivable | 123 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [2] | 196 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [2] |
Insurance loss recoverable | 524 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [5] | 676 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [5] |
Unearned premium revenue | 121 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [3] | 204 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [3] |
Loss and loss adjustment expense reserves | 389 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [6] | 361 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember |  |
Derivative liabilities | 102 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [4] | 113 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = mbi_GlobalStructuredFinanceMember | [4] |
Global Public Finance [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 49,686 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember |  | 52,317 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember |  |
Maximum Exposure to Loss | 16,698 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember |  | 20,162 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember |  |
Premiums receivable | 179 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember | [2] | 206 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember | [2] |
Unearned premium revenue | 211 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember | [3] | 248 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember | [3] |
Loss and loss adjustment expense reserves |  |  | 5 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_GlobalPublicFinanceMember |  |
Total Insurance [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
VIE Assets | 85,626 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_TotalInsuranceMember |  | 108,845 us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets / invest_InvestmentAxis = mbi_TotalInsuranceMember |  |
Maximum Exposure to Loss | 36,656 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_TotalInsuranceMember |  | 47,541 us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount / invest_InvestmentAxis = mbi_TotalInsuranceMember |  |
Investments | 119 us-gaap_Investments / invest_InvestmentAxis = mbi_TotalInsuranceMember | [1] | 141 us-gaap_Investments / invest_InvestmentAxis = mbi_TotalInsuranceMember | [1] |
Premiums receivable | 302 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_TotalInsuranceMember | [2] | 402 us-gaap_PremiumsReceivableAtCarryingValue / invest_InvestmentAxis = mbi_TotalInsuranceMember | [2] |
Insurance loss recoverable | 524 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = mbi_TotalInsuranceMember | [5] | 676 mbi_InsuranceLossRecoverable / invest_InvestmentAxis = mbi_TotalInsuranceMember | [5] |
Unearned premium revenue | 332 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_TotalInsuranceMember | [3] | 452 us-gaap_UnearnedPremiums / invest_InvestmentAxis = mbi_TotalInsuranceMember | [3] |
Loss and loss adjustment expense reserves | 389 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_TotalInsuranceMember | [6] | 366 us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / invest_InvestmentAxis = mbi_TotalInsuranceMember |  |
Derivative liabilities | $ 102 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = mbi_TotalInsuranceMember | [4] | $ 113 us-gaap_DerivativeLiabilities / invest_InvestmentAxis = mbi_TotalInsuranceMember | [4] |
[1] | Reported within Investments on MBIA's consolidated balance sheets.
[2] | Reported within Premiums receivable on MBIA's consolidated balance sheets.
[3] | Reported within Unearned premium revenue on MBIA's consolidated balance sheets.
[4] | Reported within Derivative liabilities on MBIA's consolidated balance sheets.
[5] | Reported within Insurance loss recoverable on MBIA's consolidated balance sheets.
[6] | Reported within Loss and loss adjustment expense reserves on MBIA's consolidated balance sheets.

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- Definition Carrying amount as of the balance sheet date of paid insurance policy claims and LAE expense expected to be recovered. + References No definition available. + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13495-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226008-175313 + Details
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- Definition Sum of the carrying amounts as of the balance sheet date of all investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(h)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph h -Article 7 + Details
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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a),(b),(c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
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- Definition The carrying amount as of the balance sheet date due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, net of the allowance for doubtful accounts. + References Reference 1: 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.(a),5) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 5 -Article 7 + Details
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