Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified	4 Months Ended	8 Months Ended	12 Months Ended
Apr. 30, 2013	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 2,523,225	$ 2,482,918	$ 2,206,598	$ 2,720,266
Changes recognized
Additional Transactions Reviewed Changes in RMBS Subrogation	0	2,451	24,565	18,981
Changes in Estimation Approach In Rmbs Subrogation	0	0	198,875	0
Impact of sponsor actions	(54,195)	98	(146,270)	0
Other Changes Rmbs Subrogation	13,888ambc_OtherChangesRmbsSubrogation	(278,869)ambc_OtherChangesRmbsSubrogation	239,772ambc_OtherChangesRmbsSubrogation	(216,057)ambc_OtherChangesRmbsSubrogation
Discounted RMBS subrogation (gross of reinsurance), ending balance	2,482,918	2,206,598	2,523,540	2,523,225
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	1,080,408	1,004,252	953,825	1,262,794
Changes recognized
Additional Transactions Reviewed Changes in RMBS Subrogation	0	2,451	24,565	54,467
Changes in Estimation Approach In Rmbs Subrogation	0	0	1,417,556	0
Impact of sponsor actions	(54,195)	0	(146,270)	0
Other Changes Rmbs Subrogation	(21,961)	(52,878)	273,864	(236,853)
Discounted RMBS subrogation (gross of reinsurance), ending balance	1,004,252	953,825	2,523,540	1,080,408
Adverse Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	1,442,817	1,478,666	1,252,773	1,457,472
Changes recognized
Additional Transactions Reviewed Changes in RMBS Subrogation	0	0	0	(35,486)
Changes in Estimation Approach In Rmbs Subrogation	0	0	(1,218,681)	0
Impact of sponsor actions	0	98	0	0
Other Changes Rmbs Subrogation	35,849	(225,991)	(34,092)	20,796
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 1,478,666	$ 1,252,773	$ 0	$ 1,442,817

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

No definition available.

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

- 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

- Details

Name:	ambc_ChangesRecognizedInResidentialMortgageBackedSecurityAbstract
Namespace Prefix:	ambc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

- 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

- 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

- Details

Name:	ambc_SubrogationByEstimationApproachRollForward
Namespace Prefix:	ambc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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