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Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Transactions
Summary Of Rollforward Of Rmbs Subrogation By Estimation Approach [Line Items]
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012	$ 2,720,266
Additional transactions reviewed	18,981
Additional adverse sample loans reviewed
Adverse loans repurchased by the sponsor	35
All other changes	(216,057)
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012	2,523,225
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012	46
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012	49
Random samples [Member]
Summary Of Rollforward Of Rmbs Subrogation By Estimation Approach [Line Items]
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012	1,262,794
Additional transactions reviewed	54,467
Additional adverse sample loans reviewed
Adverse loans repurchased by the sponsor
All other changes	(236,853)
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012	1,080,408
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012	16
Additional transactions reviewed	6
All other changes
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012	22
Adverse samples [Member]
Summary Of Rollforward Of Rmbs Subrogation By Estimation Approach [Line Items]
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012	1,457,472
Additional transactions reviewed	(35,486)
Additional adverse sample loans reviewed
Adverse loans repurchased by the sponsor	35
All other changes	20,796
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012	$ 1,442,817
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012	30
Additional transactions reviewed	(1)
All other changes	(2)
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012	27

X

- Definition

This element represents the change in RMBS subrogation due to additional adverse sample loans reviewed.

+ References

No definition available.

+ Details

Name:	abk_AdditionalAdverseSampleLoansReviewedChangeInRmbsSubrogation
Namespace Prefix:	abk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

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

+ References

No definition available.

+ Details

Name:	abk_AdditionalTransactionsReviewedChangesInRmbsSubrogation
Namespace Prefix:	abk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

This element represents the change in Rmbs subrogation due to adverse loans repurchased by sponsor.

+ References

No definition available.

+ Details

Name:	abk_AdverseLoansRepurchasedBySponsorChangeInRmbsSubrogation
Namespace Prefix:	abk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Number Of Additional Rmbs Transactions Reviewed With Potential Recoveries

+ References

No definition available.

+ Details

Name:	abk_NumberOfAdditionalRmbsTransactionsReviewedWithPotentialRecoveries
Namespace Prefix:	abk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of total remediation transactions.

+ References

No definition available.

+ Details

Name:	abk_NumberOfRemediationTransactions
Namespace Prefix:	abk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

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:	abk_OtherChangesRmbsSubrogation
Namespace Prefix:	abk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Other Changes Rmbs Subrogation Number Of Transactions

+ References

No definition available.

+ Details

Name:	abk_OtherChangesRmbsSubrogationNumberOfTransactions
Namespace Prefix:	abk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Subrogation Rmbs

+ References

No definition available.

+ Details

Name:	abk_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilitySubrogationRmbs
Namespace Prefix:	abk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	abk_SummaryOfRollforwardOfRmbsSubrogationByEstimationApproachLineItems
Namespace Prefix:	abk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration