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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	9 Months Ended
	Sep. 30, 2015	Sep. 30, 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	$ 2,555,461	$ 2,214,430	$ 2,523,540	$ 2,206,598
Additional Transactions Reviewed Changes in RMBS Subrogation		24,565
Changes in Estimation Approach In Rmbs Subrogation		53,851
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	(90,000)
Other Changes Rmbs Subrogation	31,921	19,416
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	1,856,754		1,897,426
Subrogation recoveries	2,555,461		2,523,540
Gross loss reserve after subrogation recoveries	(698,707)		(626,114)
Adverse Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	0	0	0	1,252,773
Additional Transactions Reviewed Changes in RMBS Subrogation		0
Changes in Estimation Approach In Rmbs Subrogation		(1,218,681)
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	0
Other Changes Rmbs Subrogation	0	(34,092)
Random Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	2,555,461	2,214,430	$ 2,523,540	$ 953,825
Additional Transactions Reviewed Changes in RMBS Subrogation		24,565
Changes in Estimation Approach In Rmbs Subrogation		1,272,532
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	(90,000)
Other Changes Rmbs Subrogation	$ 31,921	$ 53,508

X

- Definition

This element represents the change in subrogation due to additional transactions reviewed.

+ References

No definition available.

+ Details

Name:	ambc_AdditionalTransactionsReviewedChangesinRMBSSubrogation
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]

+ References

No definition available.

+ 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

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Period Type:

X

- Details

Name:	us-gaap_ValuationTechniqueAxis=ambc_RandomSamplesMember
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X

- Details

Name:	us-gaap_MortgageLoansOnRealEstateWriteDownOrReserveByLoanAxis=ambc_AdverseSamplesMember
Namespace Prefix:
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Period Type:

X

- Details

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