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Losses and Loss Expense Reserve - Summary of Balance of Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011
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Schedule Of Balance Of Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] |  |
Subrogation recoveries | $ 2,688,867 | $ 2,720,266
Subrogation recoveries included in subrogation recoverable | 785,519 | 829,469
Loss and loss expense reserves included in subrogation recoverable | $ 1,903,348 | $ 1,890,797

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- Details
Name: | abk_ScheduleOfBalanceOfSubrogationRecoveriesAndRelatedClaimLiabilitiesByEstimationApproachLineItems
Namespace Prefix: | abk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- 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_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilitySubrogation
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Subrogation recoverables included within loss and loss expense reserves on the balance sheet. + References No definition available. + Details
Name: | abk_SubrogationRecoverableIncludedInLossAndLossExpenseReserves
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Subrogation recoveries included in subrogation recoverable on the balance sheet. + References No definition available. + Details
Name: | abk_SubrogationRecoveriesIncludedInSubrogationRecoverable
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant