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Fresh Start Financial Statement Reporting - Additional Information (Detail) (USD $)
 1 Months Ended
Apr. 30, 2013
Dec. 31, 2014
Dec. 31, 2013
Fresh-Start Adjustment [Line Items]      
Enterprise value $ 185,000,000ambc_PlanOfReorganizationEnterpriseValue    
Allocated amount of Net Operating Loss (NOL) 3,650,000,000ambc_AllocatedNetOperatingLossSubsidiary    
Allocated amount of Net Operating Loss (NOL) 479,000,000ambc_AllocatedNetOperatingLossesFirstTranche    
Percentage of notional federal tax liability 15.00%ambc_NetOperatingLossesTollingPaymentFirstTranche    
Allocated amount of Net Operating Loss (NOL) 1,057,000,000ambc_AllocatedNetOperatingLossesSecondTranche    
Percentage of notional federal tax liability 40.00%ambc_NetOperatingLossesTollingPaymentSecondTranche    
Allocated amount of Net Operating Loss (NOL) 1,057,000,000ambc_AllocatedNetOperatingLossesThirdTranche    
Percentage of notional federal tax liability 10.00%ambc_NetOperatingLossesTollingPaymentThirdTranche    
Allocated amount of Net Operating Loss (NOL) 1,057,000,000ambc_AllocatedNetOperatingLossesFourthTranche    
Percentage of notional federal tax liability 15.00%ambc_NetOperatingLossesTollingPaymentFourthTranche    
Tax credits carried forward 60,000,000ambc_MaximumAlternativeMinimumTaxTollingPaymentCredit 10,359,000ambc_MaximumAlternativeMinimumTaxTollingPaymentCredit 4,269,000ambc_MaximumAlternativeMinimumTaxTollingPaymentCredit
Upfront cash 30,000,000ambc_UpfrontCashReceivedFromSubsidiary    
Other operating payments 15,000,000ambc_TollingPaymentCredit    
Junior Surplus Notes To Be Issued 350,000,000ambc_Ambc_JuniorSurplusNotesToBeIssued    
Interest on junior surplus notes 5.10%ambc_InterestRateOnSurplusNotes    
Minimum [Member]      
Fresh-Start Adjustment [Line Items]      
Discount rate 12.00%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Capital investment 135,000,000ambc_PotentialCapitalRaise
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Rate of return on investment 6.00%ambc_RateOfReturnOnInvestment
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Discount rate of investment 25.00%ambc_DiscountRateOnReturnOnInvestment
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Maximum [Member]      
Fresh-Start Adjustment [Line Items]      
Discount rate 17.00%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Capital investment 190,000,000ambc_PotentialCapitalRaise
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Rate of return on investment 8.00%ambc_RateOfReturnOnInvestment
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Discount rate of investment 35.00%ambc_DiscountRateOnReturnOnInvestment
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Ambac Assurance [Member]      
Fresh-Start Adjustment [Line Items]      
Maximum Reimbursement Of Operating Expenses 5,000,000ambc_MaximumReimbursementOfOperatingExpenses
/ dei_LegalEntityAxis
= ambc_AmbacAssuranceMember		    
Surplus Notes [Member]      
Fresh-Start Adjustment [Line Items]      
Discount rate 10.60%us-gaap_FairValueInputsDiscountRate
/ invest_InvestmentAxis
= ambc_SurplusNotesMember		    
Two Thousand And Seventeen [Member] | Ambac Assurance [Member]      
Fresh-Start Adjustment [Line Items]      
Maximum Reimbursement Of Operating Expenses after 2017 $ 4,000,000ambc_MaximumReimbursementOfOperatingExpensesafter2017
/ dei_LegalEntityAxis
= ambc_AmbacAssuranceMember
/ us-gaap_RestructuringCostAndReserveAxis
= ambc_TwoThousandAndSeventeenMember