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Investments - Summary of Roll-Forward of Ambac's Cumulative Credit Impairments that were Recognized in Earnings on Securities Held (Parenthetical) (Detail) (Successor Ambac [Member], USD $) In Thousands, unless otherwise specified | 1 Months Ended
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Apr. 30, 2013
Successor Ambac [Member] |
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] |
Cumulative credit impairments for Successor | $ 0

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- Definition Credit Related Impairment On Investment + References No definition available. + Details
Name: | ambc_CreditRelatedImpairmentOnInvestment
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration