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Subsequent Events (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	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