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Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified | 3 Months Ended |  |
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Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2013
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |  |  |
Subrogation recoveries | $ 2,568,353 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation | $ 2,224,295 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation | $ 2,523,540 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation | $ 2,206,598 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Changes in Estimation Approach In Rmbs Subrogation | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation |  |
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation |  |
Other Changes Rmbs Subrogation | 44,813 ambc_OtherChangesRmbsSubrogation | 17,697 ambc_OtherChangesRmbsSubrogation |  |
Random Samples [Member] |  |  |  |
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |  |  |
Gross loss reserve before subrogation recoveries | 1,899,087 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesBeforeSubrogationRecoveries / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember |  | 1,897,426 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesBeforeSubrogationRecoveries / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember |
Subrogation recoveries | 2,568,353 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember |  | 2,523,540 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember |
Gross loss reserve after subrogation recoveries | (669,266)ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesAfterSubrogationRecoveries / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember |  | (626,114)ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesAfterSubrogationRecoveries / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember |
Adverse Samples [Member] |  |  |  |
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |  |  |
Subrogation recoveries | 0 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 1,218,681 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 1,252,773 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Changes in Estimation Approach In Rmbs Subrogation | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |
Other Changes Rmbs Subrogation | 0 ambc_OtherChangesRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | (34,092)ambc_OtherChangesRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |
Random Samples [Member] |  |  |  |
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |  |  |
Subrogation recoveries | 2,568,353 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 1,005,614 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 2,523,540 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 953,825 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Changes in Estimation Approach In Rmbs Subrogation | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |
Other Changes Rmbs Subrogation | $ 44,813 ambc_OtherChangesRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | $ 51,789 ambc_OtherChangesRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |

X
- Definition This element represents the change in subrogation due to changes in estimation approach. + References No definition available. + Details
Name: | ambc_ChangesinEstimationApproachInRmbsSubrogation
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The change in RMBS subrogation due to the impact of sponsor actions which includes loan repurchases, direct payments, and other contributions from sponsors. + References No definition available. + Details
Name: | ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents the changes in RMBS subrogation for reasons other than additional transactions being reviewed, adverse loans being reviewed or due to adverse loans being repurchased by the sponsor. + References No definition available. + Details
Name: | ambc_OtherChangesRmbsSubrogation
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | ambc_ScheduleOfBalanceOfRmbsSubrogationRecoveriesAndRelatedClaimLiabilitiesByEstimationApproachLineItems
Namespace Prefix: | ambc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration. + References No definition available. + Details
Name: | ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This element represents the related gross claim liability net of subrogation recoveries for RMBS financial guarantee insurance contracts with credit deterioration that have estimated subrogation recoveries. + References No definition available. + Details
Name: | ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesAfterSubrogationRecoveries
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This element represents the related gross claim liability for RMBS financial guarantee insurance contracts with credit deterioration that have estimated subrogation recoveries. + References No definition available. + Details
Name: | ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesBeforeSubrogationRecoveries
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis=ambc_AdverseSamplesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis=ambc_RandomSamplesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |