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Derivative Instruments (Credit Derivatives Sold) (Detail) (Insurance Operations [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Derivative [Line Items] |  |
Derivative notional amount | $ 13,525 invest_DerivativeNotionalAmount | $ 28,935 invest_DerivativeNotionalAmount
Total fair value of credit derivatives | (246)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue | (1,152)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue
Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 1 year 7 months 6 days | 2 years 7 months 6 days
Derivative notional amount | 9,481 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 23,954 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | (244)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (1,132)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 16 years 8 months 12 days | 18 years 6 months 0 days
Derivative notional amount | 4,044 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 4,945 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | (2)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (5)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity |  | 28 years 0 months 0 days
Derivative notional amount | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 36 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | 0 us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (15)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aaa [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 6,914 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 7,406 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | (2)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (2)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aaa [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 6,914 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 7,406 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aaa [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aaa [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aa [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 363 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 2,049 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | 0 us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aa [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 246 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 1,972 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aa [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 117 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 77 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Aa [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingAaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating A [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 3,903 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 4,350 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | (2)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (3)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating A [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 968 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 1,068 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating A [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 2,935 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 3,282 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating A [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingaMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Bbb [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,163 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 9,138 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | (2)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (78)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Bbb [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 193 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 7,552 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Bbb [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 970 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 1,586 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Bbb [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBbbMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Below Investment Grade [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,182 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 5,992 invest_DerivativeNotionalAmount / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Total fair value of credit derivatives | (240)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | (1,069)us-gaap_CreditRiskDerivativeLiabilitiesAtFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Below Investment Grade [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,160 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 5,956 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_CreditDefaultSwapMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Below Investment Grade [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 22 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = mbi_InsuredSwapsMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember
Credit Rating Below Investment Grade [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | $ 0 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember | $ 36 invest_DerivativeNotionalAmount / us-gaap_CreditDerivativesByContractTypeAxis = us-gaap_OtherCreditDerivativesMember / us-gaap_ExternalCreditRatingByGroupingAxis = mbi_CreditRatingBelowInvestmentGradeMember / us-gaap_StatementBusinessSegmentsAxis = mbi_InsuranceOperationsMember

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Weighted Average Remaining Maturity Credit Derivatives In Years + References No definition available. + Details
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- Definition Fair value of credit risk derivative liability. + 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 50 -Paragraph 4K -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5708775-113959 + Details
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