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v2.4.1.9

Income Taxes - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2011 | Dec. 31, 2014 | Dec. 31, 2013 | Apr. 30, 2013 | Dec. 31, 2012 | Dec. 31, 2010
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
Unrecognized Tax Benefits, Interest on Income Taxes Accrued |  | $ 0 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued | $ 0 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued | $ 0 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued | $ 0 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued |
Income Tax Examination, Penalties and Interest Accrued | 3,650,000 us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued |  |  |  |  |
NOL allocated amount |  | 5,401,573 us-gaap_OperatingLossCarryforwards |  |  |  |
Operating tax carryforward expiration year start |  | 2029 |  |  |  |
Operating tax carryforward expiration year end |  | 2034 |  |  |  |
Net Operating Loss Carry Forwards Reduced For Cancellation Of Indebtedness Income And Interest Expense |  |  | 816,380 ambc_NetOperatingLossCarryForwardsReducedForCancellationOfIndebtednessIncomeAndInterestExpense |  |  |
Percentage Of Notional Federal Tax Liability | 25.00%ambc_PercentageOfNotionalFederalTaxLiability |  |  |  |  |
AFG [Member] |  |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
NOL allocated amount |  | 1,379,082 us-gaap_OperatingLossCarryforwards / dei_LegalEntityAxis = ambc_AfgMember |  |  |  |
Ambac [Member] |  |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
Bankruptcy Claims, Amount Paid to Settle Claims |  |  |  | 1,900 us-gaap_BankruptcyClaimsAmountPaidToSettleClaims / dei_LegalEntityAxis = ambc_AmbacMember |  |
Amount Of Loss Carry Forward Relinquish By Which Loss Carry Forward Exceed |  |  |  |  |  | 3,400,000 ambc_AmountOfLossCarryForwardRelinquishByWhichLossCarryForwardExceed / dei_LegalEntityAxis = ambc_AmbacMember
Amount Of Loss Carryforward Relinquishment |  |  |  |  |  | 1,059,988 ambc_AmountOfLossCarryforwardRelinquishment / dei_LegalEntityAxis = ambc_AmbacMember
Segregated Account [Member] |  |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
Bankruptcy Claims, Amount Paid to Settle Claims |  |  |  | 100,000 us-gaap_BankruptcyClaimsAmountPaidToSettleClaims / dei_LegalEntityAxis = ambc_SegregatedAccountMember |  |
U. S. Federal Net Operating Tax [Member] |  |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
NOL allocated amount |  | 4,986,206 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_DomesticCountryMember |  |  |  |
United States [Member] |  |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
NOL allocated amount |  | 167,004 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = country_US |  |  |  |
United Kingdom [Member] |  |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |  |
NOL allocated amount |  | $ 248,363 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = country_GB |  |  |  |

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