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Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Subrogation By Estimation Approach [Roll Forward] |  |
Discounted RMBS subrogation (gross of reinsurance), beginning balance | $ 2,523,540 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation | $ 2,206,598 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Changes recognized |  |
Changes in Estimation Approach In Rmbs Subrogation | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation | 0 ambc_ChangesinEstimationApproachInRmbsSubrogation
Impact of sponsor actions | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation | 0 ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation
Other Changes Rmbs Subrogation | 44,813 ambc_OtherChangesRmbsSubrogation | 17,697 ambc_OtherChangesRmbsSubrogation
Discounted RMBS subrogation (gross of reinsurance), ending balance | 2,568,353 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation | 2,224,295 ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Random Samples [Member] |  |
Subrogation By Estimation Approach [Roll Forward] |  |
Discounted RMBS subrogation (gross of reinsurance), beginning balance | 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 recognized |  |
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 | 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
Discounted RMBS subrogation (gross of reinsurance), ending balance | 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
Adverse Samples [Member] |  |
Subrogation By Estimation Approach [Roll Forward] |  |
Discounted RMBS subrogation (gross of reinsurance), beginning balance | 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 recognized |  |
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 | 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
Discounted RMBS subrogation (gross of reinsurance), ending balance | $ 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

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

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: |