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Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail) (Successor [Member], USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors $ 2,199,719us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCMinusRatingMember
/ invest_InvestmentAxis
= ambc_AmbacAssuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 119,492us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsARatingMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyMunicipalCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 67,895us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAMinusRatingMember
/ invest_InvestmentAxis
= ambc_NationalPublicFinanceGuaranteeCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Standard & Poor's, A- Rating [Member] | MBIA Insurance Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   55,086us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAMinusRatingMember
/ invest_InvestmentAxis
= ambc_MbiaInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Standard & Poor's, CCC+ Rating [Member] | Ambac Assurance Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   1,811,879us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCPlusRatingMember
/ invest_InvestmentAxis
= ambc_AmbacAssuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   449,555us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAPlusRatingMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyMunicipalCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Standard & Poor's, A+ Rating [Member] | MBIA Insurance Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 32,460us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAPlusRatingMember
/ invest_InvestmentAxis
= ambc_MbiaInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   532,752us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAAMinusRatingMember
/ invest_InvestmentAxis
= ambc_NationalPublicFinanceGuaranteeCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyCorpMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		 2,917us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyCorpMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ invest_InvestmentAxis
= ambc_FinancialGuaranteeInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		 2,869us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ invest_InvestmentAxis
= ambc_FinancialGuaranteeInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Standard & Poor's, CCC Rating [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 2,419,566us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCRatingMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Standard & Poor's, BB- Rating [Member]
    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   2,855,058us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsBBMinusRatingMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 53,164us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ invest_InvestmentAxis
= ambc_AmbacAssuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Municipal Bonds [Member] | Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 119,492us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsARatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyMunicipalCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Municipal Bonds [Member] | Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 67,895us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ invest_InvestmentAxis
= ambc_NationalPublicFinanceGuaranteeCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Municipal Bonds [Member] | Standard & Poor's, CCC+ Rating [Member] | Ambac Assurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   64,596us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCPlusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ invest_InvestmentAxis
= ambc_AmbacAssuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   372,392us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAPlusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyMunicipalCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   532,752us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAAMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ invest_InvestmentAxis
= ambc_NationalPublicFinanceGuaranteeCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, CCC Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 240,551us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Municipal Bonds [Member] | Standard & Poor's, BB- Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   969,740us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsBBMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_MunicipalBondsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsARatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyMunicipalCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Corporate Debt Securities [Member] | Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ invest_InvestmentAxis
= ambc_NationalPublicFinanceGuaranteeCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Corporate Debt Securities [Member] | Standard & Poor's, A- Rating [Member] | MBIA Insurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   55,086us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ invest_InvestmentAxis
= ambc_MbiaInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   77,163us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAPlusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyMunicipalCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, A+ Rating [Member] | MBIA Insurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 32,460us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAPlusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ invest_InvestmentAxis
= ambc_MbiaInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Corporate Debt Securities [Member] | Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsAAMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ invest_InvestmentAxis
= ambc_NationalPublicFinanceGuaranteeCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, CCC Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 32,460us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Corporate Debt Securities [Member] | Standard & Poor's, BB- Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   132,249us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsBBMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_CorporateDebtSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 2,146,555us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ invest_InvestmentAxis
= ambc_AmbacAssuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC+ Rating [Member] | Ambac Assurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   1,747,283us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCPlusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ invest_InvestmentAxis
= ambc_AmbacAssuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Mortgage and Asset-Backed Securities [Member] | Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyCorpMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		 2,917us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ invest_InvestmentAxis
= ambc_AssuredGuarantyCorpMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Mortgage and Asset-Backed Securities [Member] | Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ invest_InvestmentAxis
= ambc_FinancialGuaranteeInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		 2,869us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsDRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ invest_InvestmentAxis
= ambc_FinancialGuaranteeInsuranceCorporationMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 2,146,555us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, BB- Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   1,753,069us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsBBMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= ambc_MortgageAndOtherAssetBackedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Short-Term [Member] | Standard & Poor's, CCC Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsCCCRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_ShortTermInvestmentsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember		  
Short-Term [Member] | Standard & Poor's, BB- Rating [Member]    
Investment [Line Items]    
Fair value of securities that include benefit of guarantees provided by financial guarantors   $ 0us-gaap_InvestmentOwnedAtFairValue
/ invest_CreditRatingSourceAxis
= us-gaap_StandardPoorsBBMinusRatingMember
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_ShortTermInvestmentsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember