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Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) (Successor Ambac [Member]) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2014 | Dec. 31, 2013
Corporate Obligations [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Coupon rate | 0.35% | 0.35%
Maturity | 19 years 4 months 21 days | 20 years 1 month 19 days
Yield | 5.23% | 6.30%
U.S. Agency Obligations [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Coupon rate |  | 6.98%
Maturity |  | 1 year 4 months 13 days
Yield |  | 0.39%
Asset-backed Securities [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Coupon rate | 0.63% | 0.64%
Maturity | 6 years 8 months 9 days | 7 years 1 month 25 days
Yield | 4.72% | 5.17%

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- Definition Fair value inputs coupon rate. + References No definition available. + Details
Name: | ambc_FairValueInputsCouponRate
Namespace Prefix: | ambc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Fair value inputs maturity. + References No definition available. + Details
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Namespace Prefix: | ambc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Fair value inputs yield. + References No definition available. + Details
Name: | ambc_FairValueInputsYield
Namespace Prefix: | ambc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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