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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
	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	$ 2,568,353ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation	$ 2,224,295ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation	$ 2,523,540ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation	$ 2,206,598ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Changes in Estimation Approach In Rmbs Subrogation	0ambc_ChangesinEstimationApproachInRmbsSubrogation	0ambc_ChangesinEstimationApproachInRmbsSubrogation
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation	0ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation
Other Changes Rmbs Subrogation	44,813ambc_OtherChangesRmbsSubrogation	17,697ambc_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	1,899,087ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesBeforeSubrogationRecoveries / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember		1,897,426ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesBeforeSubrogationRecoveries / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember
Subrogation recoveries	2,568,353ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_ValuationTechniqueAxis = ambc_RandomSamplesMember		2,523,540ambc_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	0ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	1,218,681ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	0ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	1,252,773ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Changes in Estimation Approach In Rmbs Subrogation	0ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	0ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	0ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_AdverseSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Other Changes Rmbs Subrogation	0ambc_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	2,568,353ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	1,005,614ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	2,523,540ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	953,825ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Changes in Estimation Approach In Rmbs Subrogation	0ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	0ambc_ChangesinEstimationApproachInRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	0ambc_ImpactOfSponsorActionsInResidentialMortgageBackedSecuritiesSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Other Changes Rmbs Subrogation	$ 44,813ambc_OtherChangesRmbsSubrogation / us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis = ambc_RandomSamplesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember	$ 51,789ambc_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: