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Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2012 Transactions | Dec. 31, 2011 Transactions
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Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |
Count | 49 | 46
Gross loss reserve before subrogation recoveries | $ 3,563,344 | $ 3,777,581
Subrogation recoveries | (2,523,225) | (2,720,266)
Gross loss reserve after subrogation recoveries | 1,040,119 | 1,057,315
Adverse samples [Member] |  |
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |
Count | 27 | 30
Gross loss reserve before subrogation recoveries | 2,331,878 | 2,637,479
Subrogation recoveries | (1,442,817) | (1,457,472)
Gross loss reserve after subrogation recoveries | 889,061 | 1,180,007
Random samples [Member] |  |
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |
Count | 22 | 16
Gross loss reserve before subrogation recoveries | 1,231,466 | 1,140,102
Subrogation recoveries | (1,080,408) | (1,262,794)
Gross loss reserve after subrogation recoveries | $ 151,058 | $ (122,692)

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
- Details
Name: | abk_ScheduleOfBalanceOfRmbsSubrogationRecoveriesAndRelatedClaimLiabilitiesByEstimationApproachLineItems
Namespace Prefix: | abk_
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: | abk_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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: | abk_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesAfterSubrogationRecoveries
Namespace Prefix: | abk_
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: | abk_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRmbsGrossClaimLiabilitiesBeforeSubrogationRecoveries
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant