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Subsequent Events (Detail) (USD $) In Millions, unless otherwise specified | 9 Months Ended
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Sep. 30, 2012
Subsequent Event | $ 800

X
- Definition Loss Contingency Damages Sought Amount + References No definition available. + Details
Name: | abk_LossContingencyDamagesSoughtAmount
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration