Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments [Member] Operating Segments [Member] Inter-segment Eliminations [Member] Intersegment Eliminations [Member] Corporate, Non-Segment [Member] Corporate, Non-Segment [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Predecessor [Member] Predecessor [Member] Successor [Member] Successor [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Financial Guarantee [Member] Financial Guarantee [Member] Financial Services [Member] Financial Services [Member] Financial Services. Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Unaffiliated Customers [Member] Unaffiliated Customers [Member] Unaffiliated Customers [Member] Equity Method Investee [Member] Equity Method Investee [Member] Sales Information [Line Items] Sales Information [Line Items] Sales Information [Line Items] Revenues: Revenues [Abstract] Total revenues before expenses and reorganization items Revenues Pre-tax income (loss) from continuing operations: Income (Loss) from Continuing Operations Attributable to Parent [Abstract] Pre-tax (loss) income from continuing operations Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Total assets Assets Net investment income Net Investment Income Amortization of insurance intangible assets Amortization of Intangible Assets Interest expense Interest Expense, Debt Goodwill, Impairment Loss Goodwill, Impairment Loss Insurance [Abstract] Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Table] Summary Of Ceded Par And Net Unsecured Reinsurance Recoverable [Table] Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Table] Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Domain] Ceded Credit Risk, Reinsurer [Domain] Class of Financing Receivable [Axis] Class of Financing Receivable, Type [Axis] Class of Financing Receivable [Domain] Class of Financing Receivable, Type [Domain] Credit Rating, Moody's [Axis] Credit Rating, Moody's [Axis] External Credit Rating, Moody's [Domain] External Credit Rating, Moody's [Domain] Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items] Summary Of Ceded Par And Net Unsecured Reinsurance Recoverable [Line Items] Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items] Derivative Instruments and Hedging Activities Disclosure [Abstract] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Swaps [Member] Interest Rate Swap [Member] Futures Contracts [Member] Futures Contracts [Member] Futures contracts. Credit Derivatives [Member] Credit Derivatives [Member] Credit derivatives. Other Contracts [Member] Other Contract [Member] Currency Swaps [Member] Currency Swap [Member] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entities [Member] Variable Interest Entity [Member] Variable Interest Entity [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Gross Amounts of Recognized Assets, Derivative Assets Financial And Derivative Assets Gross Recognized Amount Financial and Derivative Assets Gross Recognized Amount Gross Amounts of Recognized Liabilities, Derivative Liabilities Financial And Derivative Liability Gross Recognized Amount Financial and Derivative Liability Gross Recognized Amount Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities Amount Of Gross Derivative Asset Or Liabilities At Fair Value Presented As Offset Under Master Netting Agreement Amount Of Gross Derivative Asset Or Liabilities At Fair Value Presented As Offset Under Master Netting Agreement Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets Derivative Asset Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities Derivative Liability Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Assets Derivative Assets Gross Amount Of Collateral Cash And Securities Pledged Not Offset Derivative Assets Gross Amount Of Collateral Cash And Securities Pledged Not Offset Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset Net Amount, Derivative Assets Derivative Assets Net Amount Derivative Assets Net Amount Net Amount, Derivative Liabilities Derivative Liabilities Net Amount Derivative Liabilities Net Amount Summary Of Rollforward Of Subrogation By Estimation Approach [Table] Summary Of Rollforward Of Subrogation By Estimation Approach [Table] Summary of rollforward of RMBS subrogation, by estimation approach. Mortgage Loans on Real Estate, Write-down or Reserve by Loan [Axis] Mortgage Loans on Real Estate, Write-down or Reserve by Loan [Axis] Mortgage Loans on Real Estate, Write-down or Reserve, Loan [Domain] Mortgage Loans on Real Estate, Write-down or Reserve, Loan [Domain] Random Samples [Member] Random Samples [Member] Random samples. Adverse Samples [Member] Adverse Samples [Member] Adverse samples. Summary Of Rollforward Of Subrogation By Estimation Approach [Line Items] Summary Of Rollforward Of Subrogation By Estimation Approach [Line Items] Summary of rollforward of RMBS subrogation, by estimation approach. Subrogation By Estimation Approach [Roll Forward] Subrogation By Estimation Approach [Roll Forward] Subrogation By Estimation Approach [Roll Forward] Discounted RMBS subrogation (gross of reinsurance), beginning balance Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration. Changes recognized Changes Recognized In Residential Mortgage Backed Security [Abstract] Changes Recognized in Residential Mortgage Backed Security [Abstract] Additional Transactions Reviewed Changes in RMBS Subrogation Additional Transactions Reviewed Changes in RMBS Subrogation This element represents the change in subrogation due to additional transactions reviewed. Changes in Estimation Approach In Rmbs Subrogation Changes in Estimation Approach In Rmbs Subrogation This element represents the change in subrogation due to changes in estimation approach. Impact of sponsor actions Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation The change in RMBS subrogation due to the impact of sponsor actions which includes loan repurchases, direct payments, and other contributions from sponsors. Other Changes Rmbs Subrogation Other Changes Rmbs Subrogation This element represents the changes in RMBS subrogation for reasons other than additional transactions being reviewed, adverse loans being reviewed or due to adverse loans being repurchased by the sponsor. Discounted RMBS subrogation (gross of reinsurance), ending balance Fair Value Inputs, Liabilities, Quantitative Information [Table] Fair Value Inputs, Liabilities, Quantitative Information [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Investment Type [Member] Investment Type [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Collateralized Debt Obligations [Member] Collateralized Debt Obligations [Member] Fair Value Inputs, Liabilities, Quantitative Information [Line Items] Fair Value Inputs, Liabilities, Quantitative Information [Line Items] Notional outstanding Derivative, Notional Amount Weighted average life (WAL) in years Fair Value Input Weighted Average Life Fair value input weighted average life. Weighted average quotes Fair Value Input Weighted Average Credit Derivative Quote As Percentage Of Notional Fair value input weighted average credit derivative quote as percentage of notional. CVA percentage Percentage Of Credit Value Adjustment Credit valuation adjustment (CVA) as a percentage of the credit derivative liability calculated excluding the CVA. Weighted average credit rating Fair Value Input Weighted Average Credit Rating Fair value input weighted average credit rating. Fair value of derivative liabilities Derivative Liability, Fair Value, Amount Not Offset Against Collateral Segment Information Segment Reporting Disclosure [Text Block] Income Tax Disclosure [Abstract] Net Income Loss Reconciliation [Table] Net Income Loss Reconciliation [Table] Net Income Loss Reconciliation [Table] Determination Date [Axis] Determination Date [Axis] Determination Date [Axis] Determination Date [Domain] Determination Date [Domain] [Domain] for Determination Date [Axis] PrePostDetermination [Domain] Post Determination [Member] Post Determination [Member] Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Tier A [Member] Tier A [Member] Tier A [Member] Tier B [Member] Tier B [Member] Tier B [Member] Tier C [Member] Tier C [Member] Tier C [Member] Tier D [Member] Tier D [Member] Tier D [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Ambac Assurance [Member] Ambac Assurance [Member] Ambac assurance. AFG [Member] Afg [Member] Afg [Member] Net Income Loss Reconciliation [Line Items] Net Income Loss Reconciliation [Line Items] Net Income Loss Reconciliation [Line Items] Income Tax Examination, Penalties and Interest Accrued Income Tax Examination, Penalties and Interest Accrued Percentage Of Notional Federal Tax Liability Percentage Of Notional Federal Tax Liability Percentage Of Notional Federal Tax Liability Amount Of Loss Carry Forward Relinquish By Which Loss Carry Forward Exceed Amount Of Loss Carry Forward Relinquish By Which Loss Carry Forward Exceed Amount of loss carry forward relinquish by which loss carry forward exceed AACNetTaxableIncome AACNetTaxableIncome AACNetTaxableIncome Tolling Payment Payable to AFG Tolling Payment Payable to AFG Tolling Payment Payable to AFG AdditionalTollingPaymentPayabletoAFG AdditionalTollingPaymentPayabletoAFG AdditionalTollingPaymentPayabletoAFG TierABCCredit TierABCCredit TierABCCredit TierACreditUsage TierACreditUsage TierACreditUsage NOL allocated amount Operating Loss Carryforwards NOL applicable percentage Net Operating Loss Percentage Net Operating Loss Percentage AACNetTaxableIncomeFromTierA AACNetTaxableIncomeFromTierA AACNetTaxableIncomeFromTierA AACNetTaxableIncomeFromTierB AACNetTaxableIncomeFromTierB AACNetTaxableIncomeFromTierB AdditionalAACNetTaxableIncomeFromTierB AdditionalAACNetTaxableIncomeFromTierB AdditionalAACNetTaxableIncomeFromTierB Accounting Policies [Abstract] Background And Basis Of Presentation [Table] Background And Basis Of Presentation [Table] Background And Basis Of Presentation [Table] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] Background And Basis Of Presentation [Line Items] Background And Basis Of Presentation [Line Items] Background And Basis Of Presentation [Line Items] Entity Incorporation, Date of Incorporation Entity Incorporation, Date of Incorporation Number of reportable segments Number of Reportable Segments Proceeds from the sale of Junior Surplus Notes of the Segregated Account Proceeds From The Sale Of Junior Surplus Notes Proceeds from the sale of Segregated Account Junior Surplus Notes from Ambac Financial Group to a newly formed Trust Net par exposure for policies allocated to the Segregated Account Net Par Exposure For Policies Allocated To Segregated Account Net par outstanding for policies allocated to the Segregated Account of Ambac Assurance. Investment Warrants Expiration Date Investment Warrants Expiration Date Minimum surplus amount Minimum Surplus Amount Minimum surplus amount that will cap the benefits of the Reinsurance Agreement between Ambac Assurance and the Segregated Account of Ambac Assurance. Payment of permitted policy claim (percent) Payment As Percentage Of Permitted Policy Claim Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that were paid in cash from September 2012 through June 2014. Common stock, shares authorized Common Stock, Shares Authorized Common Stock, Par or Stated Value Per Share Common Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred Stock, Par or Stated Value Per Share Preferred Stock, Par or Stated Value Per Share Common stock, shares issued Common Stock, Shares, Issued Warrants Distributed In Bankruptcy Class of Warrant or Right, Number of Securities Called by Warrants or Rights Warrants issued exercise price Class of Warrant or Right, Exercise Price of Warrants or Rights Statutory Accounting Practices, Statutory Capital and Surplus, Balance Statutory Accounting Practices, Statutory Capital and Surplus, Balance Derivative [Table] Derivative [Table] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member] Interest Rate Swap One [Member] Interest rate swap one. Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items] Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items] Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items] Derivative products, Notional Amount Fair Value Inputs, Assets, Quantitative Information [Table] Fair Value Inputs, Assets, Quantitative Information [Table] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Asset-backed Securities [Member] Asset-backed Securities [Member] US Commercial ABS Transaction [Member] United States Transactions [Member] United States Transactions [Member] European Transactions [Member] European Transactions [Member] European ABS transactions. Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Real Estate [Member] Real Estate [Member] Hedge Funds, Multi-strategy [Member] Hedge Funds, Multi-strategy [Member] Interest Rate Contract [Member] Interest Rate Contract [Member] Illiquid Investments [Member] Illiquid Investments [Member] Illiquid Investments [Member] Underlying Asset Class [Axis] Underlying Asset Class [Axis] Underlying Asset Class [Domain] Underlying Asset Class [Domain] U.S. Agency Obligations [Member] US Government Agencies Debt Securities [Member] Derivative [Member] Derivative [Member] Corporate Debt Securities [Member] Corporate Debt Securities [Member] Credit Derivative [Member] Credit Derivative [Member] Credit derivative. CLO [Member] Collateralized Loan Obligations [Member] Other [Member] Underlying, Other [Member] Fair Value Inputs, Assets, Quantitative Information [Line Items] Fair Value Inputs, Assets, Quantitative Information [Line Items] Fair Value Inputs Coupon Rate Fair Value Inputs Coupon Rate Fair value inputs coupon rate. Other investments Other Investments Weighted average reference obligation price Fair Value Input Weighted Average Obligation Price Fair value input weighted average obligation price. Weighted average relative change ratio Fair Value Input Weighted Average Relative Change Ratio Fair value input weighted average relative change ratio. Fair Value Inputs Maturity Fair Value Inputs Maturity Fair value inputs maturity. Fair Value Inputs Yield Fair Value Inputs Yield Fair value inputs yield. Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Other Contracts [Member] Other Contracts [Member] Other contracts. Futures Contracts [Member] Future [Member] Municipal Bonds [Member] Municipal Bonds [Member] Corporate Obligations [Member] Foreign Obligations [Member] Foreign Government Debt Securities [Member] US Government Debt Securities [Member] US Government Debt Securities [Member] Residential Mortgage-Backed Securities [Member] Residential Mortgage Backed Securities [Member] Short-Term [Member] Short-term Investments [Member] Other Assets [Member] Other Assets [Member] Other [Member] Other Debt Obligations [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Interest Rate Swaps - Liability Position [Member] Other Liabilities [Member] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Total Fair Value [Member] Estimate of Fair Value Measurement [Member] Carrying Amount [Member] Reported Value Measurement [Member] Total Pooled Investment [Member] Total Pooled Investment [Member] Total Pooled Investment [Member] Investments Measured at NAV as a Practical Expedient [Member] Investments Measured at NAV as a Practical Expedient [Member] Investments Measured at NAV as a Practical Expedient [Member] Variable Interest Entity [Member] Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] Financial assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Fixed income securities Available-for-sale Securities Fixed income securities, pledged as collateral Security Owned and Pledged as Collateral, Fair Value Short term investments Other Short-term Investments Cash Cash and Cash Equivalents, Fair Value Disclosure Restricted cash Restricted Cash And Cash Equivalents Fair Value Disclosure Fair value of restricted cash and cash equivalents. Loans Loans Receivable, Fair Value Disclosure Derivative assets Derivative Asset, Fair Value, Gross Asset Derivative assets - interest rate swaps - liability position Derivative Asset, Fair Value, Gross Liability Other assets Equity Method Investments, Fair Value Disclosure Total financial assets Assets, Fair Value Disclosure Financial liabilities: Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Obligations under investment and repurchase agreements Guaranteed Investment Agreements Fair Value Disclosure Guaranteed investment agreements at fair value. Derivative liabilities - interest rate swaps - asset position Derivative Liability, Fair Value, Gross Asset Derivative liabilities Derivative Liability, Fair Value, Gross Liability Liabilities for net financial guarantees written Guarantees, Fair Value Disclosure Long-term debt Long-term Debt, Fair Value Total financial liabilities Financial and Nonfinancial Liabilities, Fair Value Disclosure Schedule of Goodwill [Table] Schedule of Goodwill [Table] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Goodwill [Line Items] Goodwill [Line Items] Summary of Activity in Goodwill for Financial Guarantee Reporting Unit Schedule of Goodwill [Table Text Block] Investments, Debt and Equity Securities [Abstract] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Fixed Income Securities [Member] Fixed Income Securities [Member] Fixed Income Investments And Other Investments [Member] Fixed Income Investments And Other Investments [Member] Fixed income investments and other investments Member. U.S. Government Obligations [Member] Securities Pledged as Collateral [Member] Securities Pledged as Collateral [Member] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Available For Sale Securities Gross Unrealized Loss Accumulated In Investments Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Estimated Fair Value Non - credit other - than - temporary Impairments Non Credit Other Than Temporary Impairments On Investments Non credit other than temporary impairments on investments. Insurance [Table] Insurance [Table] Insurance [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Loss Reserves [Member] Loss Reserves Claim Liability [Member] Loss Reserves Claim Liability [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum [Member] Maximum [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Insurance Intangible Asset [Member] Insurance Asset [Member] Insurance Asset [Member] Insurance [Line Items] Insurance [Line Items] Insurance [Line Items] Estimated Future Premium Payments Weighted Average Discounted Rate Estimated Future Premium Payments Weighted Average Discounted Rate Weighted average discounted rate of estimated future premium payments to be paid by the VIEs. Amount Of Insured Par Outstanding Ceded To Reinsurer Amount Of Insured Par Outstanding Ceded To Reinsurer Amount of insured par outstanding ceded to reinsurer. Ceded Principal Outstanding Major Reinsurer Percentage Ceded Principal Outstanding Major Reinsurer Percentage Ceded Principal Outstanding Major Reinsurer Percentage. Financial Guarantee Gross Outstanding Principal Assumed From Third Parties Financial Guarantee Gross Outstanding Principal Assumed From Third Parties Financial Guarantee Gross Outstanding Principal Assumed from third parties. Deferred Ceded Premiums And Reinsurance Recoverables Deferred Ceded Premiums And Reinsurance Recoverables Includes the unexpired portion of financial guarantee premiums ceded on policies as of the balance sheet date and reinsurance recoverables on claims or claim adjustment expense paid by the ceding insurer. Reinsurance Payable Reinsurance Payable Accrued rate of interest on outstanding policy obligations (percent) Deferred Amounts and Junior Deferred Amounts Accrued Interest Rate Reflects the effective interest rate on Deferred Amounts and Junior Deferred Amounts of the Segregated Account of Ambac as directed by the Rehabilitator of the Segregated Account. Weighted average risk-free interest rate Financial Guarantee Insurance Contracts, Premium Received over Contract Period, Premium Receivable, Weighted Average Risk Free Discount Rate Weighted average period of future premiums Financial Guarantee Insurance Contracts, Premium Received over Contract Period, Premium Receivable, Weighted Average Collection Period Transactions with non-investment grade internal ratings Percentage Premiums Receivable Related To Transactions With Non Investment Grade Internal Ratings Percentage of financial guarantee premiums receivable related to insured transactions with non-investment grade internal ratings. Non-investment grade RMBS on total premiums receivable Percentage Of Premiums Receivable Related To Non Investment Grade Rmbs Transactions Percentage of financial guarantee premiums receivable related to RMBS insured transactions with non-investment grade internal ratings. Percentage Of Premiums Receivable Related To Non Investment Grade Structured Ins Transactions Percentage Of Premiums Receivable Related To Non Investment Grade Structured Ins Transactions Percentage Of Premiums Receivable Related To Non Investment Grade Structured Ins Transactions Percentage of student loan transactions on total premium receivables Percentage Of Premiums Receivable Related To Student Loan Transactions Percentage of financial guarantee premiums receivable related to Student Loan insured transactions with non-investment grade internal ratings. Percentage related to asset-backed transaction Percentage Premiums Receivable Related To Asset Backed Transactions Percentage Premiums Receivable Related To Certain Asset Backed Transactions With Non Investment Grade Internal Rating Uncollectable premium receivables Premiums Receivable, Allowance for Doubtful Accounts Past due premiums on policies insuring non-investment grade obligations amount Premiums Past Due On Non Investment Grade Obligation Past due premiums on policies insuring internally rated non-investment grade obligations. Accelerated premium revenue for retired obligations Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount Reinsurance recoveries of losses included in losses and loss expenses Policyholder Benefits and Claims Incurred, Ceded Weighted average risk-free rate used to discount loss reserves Financial Guarantee Insurance Contracts, Claim Liability, Weighted Average Risk Free Discount Rate Losses and loss expense reserves ceded to reinsurers Loss Reserves Ceded To Reinsurers The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims expected to be paid or incurred by the ceding insurer. Subrogation recoveries Balance Of Gross Rmbs Subrogation Recoveries This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration. Subrogation recoveries, net of reinsurance Balance Of Rmbs Subrogation Recoveries Net Of Reinsurance This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration, net of reinsurance. Intangible amortization expense Insurance intangible asset Intangible Assets, Net (Excluding Goodwill) Accumulated amortization on insurance intangible asset Accumulated Amortization On Intangible Asset Accumulated Amortization on Intangible Asset Letters of Credit Outstanding, Amount Letters of Credit Outstanding, Amount Percentage of Premiums Receivable Related To Non Investment Grade Lease Securitizations Percentage of Premiums Receivable Related To Non Investment Grade Lease Securitizations Percentage of Premiums Receivable Related to Non Investment Grade Lease Securitizations Percentage Of Premiums Receivable Related To Non Investment Grade Student Loan Transactions Percentage Of Premiums Receivable Related To Non Investment Grade Student Loan Transactions Percentage of financial guarantee premiums receivable related to Student Loan insured transactions with non-investment grade internal ratings. Summary of Financial Information by Reportable Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Gross Premiums Written, Net Premiums Earned and Net Change in Fair Value of Credit Derivatives Disclosure Of Gross Premiums Written Net Premiums Earned Credit Derivatives Table [Text Block] Schedule of Gross Premiums Written, Net Premiums Earned and Net Change in Fair Value of Credit Derivatives by Location of Risk. Statement [Table] Statement [Table] Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] Statement [Line Items] Statement [Line Items] Summary of Gross Fair Values of Individual Derivative Instruments Fair Values Derivatives Balance Sheet Location By Derivative Contract Type [Table Text Block] Schedule that discloses the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position. Summary of Location and Amount of Gains and Losses of Derivative Contracts Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Summary of Gross Principal Notional Outstanding for CDS Contracts Disclosure of Credit Derivatives [Table Text Block] Summarize Information by Major Category of CDS Contracts Schedule Of Information By Major Category Of Credit Derivatives Contracts Table [Text Block] Schedule of information by major category of credit derivatives contracts. Summary of Notional Amounts of AFS's Trading Derivative Products Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Amortized Cost And Fair Value Debt Securities [Abstract] Amortized Cost and Fair Value Debt Securities [Abstract] Investment [Table] Investment [Table] Debt Security [Axis] Debt Security [Axis] Major Types of Debt Securities [Domain] Major Types of Debt Securities [Domain] Ambac UK [Member] Ambac Uk [Member] Ambac UK [Member] National Century Financial Enterprises, Inc. [Member] National Century Financial Enterprises Inc [Member] National Century Financial Enterprises Inc [Member] Below Investment Grade Securities and Non-Rated Securities [Member] Below Investment Grade Securities And Non Rated Securities [Member] Below investment grade securities and non-rated securities. Ambac Wrapped Securities [Member] Ambac Wrapped Securities [Member] Ambac Wrapped Securities [Member] Gains (losses) on securities held as of reporting date [Member] Gains (losses) on securities held as of reporting date [Member] Gains (losses) on securities held as of reporting date [Member] Investment [Line Items] Investment [Line Items] Asset Backed Securities Fair Value Disclosure Asset Backed Securities Fair Value Disclosure Asset-backed securities guaranteed by Ambac UK. Fair value of below investment grade securities and non-rated securities Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Fair Value Fair value of below investment grade securities and non rated securities in a continuous unrealized loss position. Gross unrealized loss Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Aggregate Losses Aggregate losses of below investment grade securities and non rated securities in a continuous unrealized loss position. Future payment of permitted policy claim (percent) Current Payment as a Percentage of Permitted Policy Claim Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that are to be paid in cash from July 2014 forward as approved by the Rehabilitation Court. Unrealized losses on securities Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Cash recoveries Litigation Settlement, Amount Securities fair value Fair Value Of Securities Deposited With Governmental Authorities Fair value of securities deposited with governmental authorities. Other investments Other Investments Income Other Investments Income Fair Value of Securities Placed in Trust Fair Value of Securities Placed in Trust Fair Value of Securities Placed in Trust Loan Origination Commitments [Member] Loan Origination Commitments [Member] Long-term Debt [Member] Long-term Debt [Member] Derivative Financial Instruments, Liabilities [Member] Derivative Financial Instruments, Liabilities [Member] Investment Contracts [Member] Investment Contracts [Member] Loans Receivable [Member] Loans Receivable [Member] Fair Value, Inputs, Level 3 [Member] Investments [Member] Investments [Member] European ABS Transactions [Member] Available-for-sale Securities [Member] Available-for-sale Securities [Member] Fair Value Of Consolidated Variable Interest Entity Debt Obligations Valued Using Unobservable Inputs By Asset Class Fair Value Of Consolidated Variable Interest Entity Debt Obligations Valued Using Unobservable Inputs By Asset Class Fair Value of consolidated VIE debt obligations valued using unobservable inputs by asset class Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Fair value measurement with unobservable inputs reconciliation recurring basis asset or liability. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Additions Of Consolidated Vies Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Additions Of Consolidated Vies Fair value of financial instruments measured on a recurring basis using unobservable inputs added as a result of new consolidated variable interest entities. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings Amount of gain or loss included in earnings arising from financial instruments measured on a recurring basis using unobservable inputs. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss Amount of gain or loss included in other comprehensive income arising from financial instruments measured on a recurring basis using unobservable inputs. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases Amount of purchases of financial instruments measured on a recurring basis using unobservable inputs. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues Amount of issuances related to financial instruments measured on a recurring basis using unobservable inputs. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales Amount of sales of financial instruments measured on a recurring basis using unobservable inputs. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements Amount of settlements related to financial instruments measured on a recurring basis using unobservable inputs. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three Amount of change in fair value of financial instruments measured on a recurring basis using unobservable inputs arising from transfers into level 3 of the fair value hierarchy. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three Amount of change in fair value of financial instruments measured on a recurring basis using unobservable inputs arising from transfers out of level 3 of the fair value hierarchy. Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies Fair value of financial instruments measured on a recurring basis using unobservable inputs removed as a result of the deconsolidation of variable interest entities. Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held The amount of gains or losses included in earnings attributable to unrealized gains or losses on financial instruments measured on a recurring basis using unobservable inputs that are still held at the reporting date. Value of right to reclaim cash collateral and posted margin, recorded in "Other assets" Derivative, Collateral, Right to Reclaim Cash Value of obligation to return cash collateral, recorded in "Other liabilities" Derivative, Collateral, Obligation to Return Cash Number of outstanding credit derivative transactions include ratings based collateral-posting triggers Derivative, Credit Risk Related Contingent Features, Triggering Circumstances Number of credit derivative contracts Number Of Credit Derivative Contracts On Adversely Classified Credit Listing Number of Credit Derivative Contracts on adversely classified credit listing. Net liability fair value of credit derivative contracts Derivative Liability Fair Value For Credit Derivative Contracts On Adversely Classified Credit Listing Derivative Liability Fair Value For Credit Derivative Contracts On Adversely Classified Credit Listing Notional value of credit derivative contracts Notional Principal Outstanding Of Credit Derivative Contracts On Adversely Classified Credit Listing Notional principal outstanding of Credit Derivative Contracts on adversely classified credit listing. Gains in change in fair value of the call options Derivative, Gain (Loss) on Derivative, Net Net liability fair value of all derivative instruments linked to Ambac's own credit risk Derivative, Net Liability Position, Aggregate Fair Value Fair value of posted assets as collateral Collateral Already Posted, Aggregate Fair Value Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Net Investment Income [Member] Investment Income [Member] Realized Gains Or (Losses) and Other Settlements On Credit Derivative Contracts [Member] Realized Gains Or Losses And Other Settlements On Credit Derivative Contracts [Member] Realized gains or losses and other settlements on credit derivative contracts. Unrealized Gains Or (Losses) On Credit Derivative Contracts [Member] Unrealized Gains Or Losses On Credit Derivative Contracts [Member] Unrealized gains or losses on credit derivative contracts. Income Loss On Variable Interest Entities [Member] Income Loss On Variable Interest Entities [Member] Income (loss) on variable interest entities. Other Income or (Loss) [Member] Other Income [Member] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Total gains or losses included in earnings for the period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Total gains or losses included in earnings for the period Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings Schedule Of Balance Of Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Table] Schedule Of Balance Of Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Table] Schedule of balance of subrogation recoveries and related claim liabilities by estimation approach. Valuation Technique [Axis] Valuation Technique [Axis] Valuation Technique [Domain] Valuation Technique [Domain] Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items] Gross loss reserve before subrogation recoveries Schedule Of Insured Financial Obligations With Credit Deterioration Rmbs Gross Claim Liabilities Before Subrogation Recoveries This element represents the related gross claim liability for RMBS financial guarantee insurance contracts with credit deterioration that have estimated subrogation recoveries. Subrogation recoveries Gross loss reserve after subrogation recoveries Schedule Of Insured Financial Obligations With Credit Deterioration Rmbs Gross Claim Liabilities After Subrogation Recoveries This element represents the related gross claim liability net of subrogation recoveries for RMBS financial guarantee insurance contracts with credit deterioration that have estimated subrogation recoveries. Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation Adverse Loans Repurchased By Sponsor Change in Rmbs Subrogation Adverse Loans Repurchased By Sponsor Change in Rmbs Subrogation This element represents the change in Rmbs subrogation due to adverse loans repurchased by the sponsor. Loss Reserves Ceded To Reinsurers Ceded Loss And Loss Expenses Paid Not Yet Recovered Ceded Loss And Loss Expenses Paid Not Yet Recovered Ceded Loss And Loss Expenses Paid Not Yet Recovered Credit Derivatives Contract Type [Axis] Credit Derivatives Contract Type [Axis] Credit Derivatives Contract Type [Domain] Credit Derivatives Contract Type [Domain] Other Derivatives [Member] Other Credit Derivatives [Member] Credit Rating Source [Axis] Credit Rating Source [Axis] Credit Rating Source [Domain] Credit Rating Source [Domain] AAA Rating [Member] Aaa Rating [Member] AAA Rating. AA Rating [Member] Aa Rating [Member] AA Rating. A Rating [Member] [Member] A Rating [Member] [Member] A Rating [Member] [Member] A Rating [Member] Rating [Member] Rating. BBB Rating [Member] Bbb Rating [Member] BBB Rating. Below Investment Grade Rating [Member] Below Investment Grade Rating [Member] Below investment grade rating. Ambac Rating Notional Disclosures [Abstract] Foreign Currency [Abstract] Information by Financial Statement Line Item [Axis] Information by Financial Statement Line Item [Axis] Loss and Loss Reserves [Domain] Financial Statement Line Items with Differences in Reported Amount and Reporting Currency Denominated Amounts [Domain] Loss and Loss Reserves [Member] Lossandlossreserves [Member] Lossandlossreserves [Member] Cash Equivalents [Member] Cash Equivalents [Member] Gain (Loss) on Investments [Member] Gain (Loss) on Investments [Member] Premiums Receivable [Member] Premiums Receivable [Member] Foreign Currency Transaction Gain (Loss), before Tax Foreign Currency Transaction Gain (Loss), before Tax Fair Value Measurements Fair Value Disclosures [Text Block] Cash and Securities Pledged Directly from Investment Portfolio [Member] Investment Portfolio [Member] Investment portfolio. Cash and Securities Pledged from Its Derivative Counterparties [Member] Derivative Counterparties [Member] Derivative counterparties. Fair Value of Cash and Underlying Securities Fair Value Of Cash And Underlying Securities Total fair value of cash and underlying securities pledged. Fair Value of Cash and Securities Pledged to Investment and Repurchase Agreement Counterparties Fair Value Of Cash And Securities Pledged To Investment And Repurchase Agreement Counterparties Fair value of cash and securities pledged to investment and repurchase agreement counterparties. Fair Value of Cash and Securities Pledged to Derivative Counterparties Fair Value Of Cash And Securities Pledged To Derivative Counterparties Fair value of cash and securities pledged to derivative counterparties. United States Transactions [Member] Available-for-sale Securities Coupon rate Yield Basis of Presentation and Significant Accounting Policies [Text Block] Basis of Presentation and Significant Accounting Policies [Text Block] Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Foreign Currency Transactions and Translations Policy [Policy Text Block] Foreign Currency Transactions and Translations Policy [Policy Text Block] Reclassifications Reclassification, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Balance at beginning Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Additions for credit impairments recognized on: Other Than Temporary Impairments Additions For Credit Impairments Recognized [Abstract] Other than temporary impairments additions for credit impairments recognized. Securities not previously impaired Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment Securities previously impaired Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses Reductions for credit impairments previously recognized on: Other Than Temporary Impairments Reductions For Credit Impairments Previously Recognized [Abstract] Other than temporary impairments reductions for credit impairments previously recognized. Securities that matured or were sold during the period Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold Balance at end Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Change in Status Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Change in Status Schedule Of Finite Lived Intangible Assets Amortization Expense [Table] Schedule Of Finite Lived Intangible Assets Amortization Expense [Table] Schedule Of Finite Lived Intangible Assets Amortization Expense [Table] Insurance Intangible Asset [Member] Insurance Intangible Asset [Member] Insurance Intangible Asset [Member] Amortization Of Intangible Assets [Line Items] Amortization Of Intangible Assets [Line Items] Amortization Of Intangible Assets [Line Items] Intangible Assets, Gross (Excluding Goodwill) Intangible Assets, Gross (Excluding Goodwill) 2016 Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year 2017 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2018 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Five Thereafter Finite-Lived Intangible Assets, Amortization Expense, after Year Five AFS [Member] Afs [Member] AFS. Interest Rate Swaps-Basis Swaps [Member] Basis Swap [Member] Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Other Consumer Asset-Backed [Member] Other Consumer Asset Backed [Member] Other consumer asset-backed. Other Commercial Asset-Backed [Member] Other Commercial Asset Backed [Member] Other commercial asset. Global Structured Finance [Member] Global Structured Finance [Member] Global structured finance. Global Public Finance [Member] Global Public Finance [Member] Global public finance. Variable Interest Entities [Line Items] Variable Interest Entity [Line Items] Maximum Exposure To Loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Insurance Assets Variable Interest Entity Nonconsolidated Carrying Amount Insurance Assets The carrying amount of insurance assets in the reporting entity's statement of financial position that relate to the entity's variable interests in Variable Interest Entities (VIEs) where the VIEs are not consolidated. Insurance Liabilities Variable Interest Entity Nonconsolidated Carrying Amount Insurance Liabilities The carrying amount of insurance liabilities in the reporting entity's statement of financial position that relate to the entity's variable interests in Variable Interest Entities (VIEs) where the VIEs are not consolidated. Derivative Liabilities Variable Interest Entity Nonconsolidated Carrying Amount Derivative Net Assets Or Liabilities The net carrying amount of derivative assets or liabilities in the reporting entity's statement of financial position that relate to the entity's variable interests in Variable Interest Entities (VIEs) where the VIEs are not consolidated. Statement of Cash Flows [Abstract] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Surplus Notes [Member] Surplus Notes [Member] Surplus Notes [Member] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income (loss) attributable to common stockholders Net Income (Loss) Attributable to Parent Net (loss) gain Net Income (Loss) Attributable to Noncontrolling Interest Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Amortization and Accretion, Net Amortization of bond premium and discount Accretion (Amortization) of Discounts and Premiums, Investments Share-based compensation Share-based Compensation Deferred income taxes Increase (Decrease) in Deferred Income Taxes Current income taxes Increase (Decrease) in Income Taxes Payable Unearned premiums, net Increase (Decrease) in Unearned Premiums Losses and loss expenses, net Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Ceded premiums payable Increase (Decrease) in Reinsurance Payables Investment income due and accrued Increase (Decrease) in Accrued Investment Income Receivable Premium receivables Increase (Decrease) in Premiums Receivable Accrued interest payable Increase (Decrease) in Interest Payable, Net Net mark-to-market (gains) losses Unrealized Gain (Loss) on Derivatives Net realized investment gains Realized Investment Gains (Losses) Other-than-temporary impairment charges Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net Net realized (gains) losses on extinguishment of debt Gains (Losses) on Extinguishment of Debt Variable interest entity activities Variable Interest Entity, Measure of Activity, Operating Income or Loss Other, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Proceeds from sales of bonds Proceeds from Sale of Available-for-sale Securities Proceeds from matured bonds Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Purchases of bonds Payments to Acquire Available-for-sale Securities Proceeds from sales of other invested assets Proceeds from Sale and Maturity of Other Investments Purchases of other invested assets Payments to Acquire Other Investments Change in short-term investments Payments for (Proceeds from) Short-term Investments Loans Payments for (Proceeds from) Loans Receivable Change in swap collateral receivable Increase (Decrease) Cash Collateral from Counterparties Other, net Payments for (Proceeds from) Other Investing Activities Net cash (used in) investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from Variable Interest Entity Secured Borrowing Proceeds Received from a Secured Borrowing Proceeds from Variable Interest Entity Secured Borrowing Paydowns of a secured borrowing Paydown Of Variable Interest Entity Secured Borrowing Paydown of variable interest entity secured borrowing. Proceeds from warrant exercises Proceeds from Warrant Exercises Warrants Purchased During Period Dollars Warrants Purchased During Period Dollars Warrants Purchased During Period Dollars Payments for investment agreement draws Payments From Drawdowns Of Borrowings Under Guaranteed Investment Agreements Payments from drawdowns of investment and payment agreements. Such agreements provide the contract holders an agreed upon rate of return pursuant to the terms of the underlying contract. These contracts represent lending by the contract holders to the entity in return for a guaranteed interest rate until maturity, unless called earlier if the contracts provide that option to the contract holders. Payments for extinguishment of long-term debt Repayments of Long-term Debt Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Effect of Exchange Rate on Cash and Cash Equivalents Effect of Exchange Rate on Cash and Cash Equivalents Net cash flow Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents end of period Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Income taxes Income Taxes Paid Interest on secured borrowing Interest Paid On Variable Interest Entity Secured Borrowing Interest paid on variable interest entity secured borrowing. Interest on investment agreements Interest Paid On Investment Agreements Interest Paid On Investment Agreements Interest Expense Interest Expense Cash payments related to reorganization items: Cash Receipts And Payments Related To Reorganization Items [Abstract] Cash receipts and payments related to reorganization items [Abstract] Background and Business Description Business Description and Basis of Presentation [Text Block] Earnings Per Share [Abstract] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Warrants [Member] Warrant [Member] Employee Stock Option [Member] Employee Stock Option [Member] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Performance Shares [Member] Performance Shares [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Weighted average number of common shares used for basic earnings per share Weighted Average Number of Shares Outstanding, Basic Effect of potential dilutive shares: Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Effect of potential dilutive shares Weighted Average Number Diluted Shares Outstanding Adjustment Weighted average number of common shares and potential dilutive shares used for diluted earnings per share Weighted Average Number of Shares Outstanding, Diluted Income Statement [Abstract] Unrealized (loss) gain on securities, taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Gain (loss) on foreign currency translation, taxes Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax Amortization of postretirement benefit, taxes Other Comprehensive Income Loss Amortization Pension And Other Postretirement Benefit Plans Net Prior Service Cost Recognized In Net Periodic Pension Cost Net Of Taxes Other Comprehensive Income Loss Amortization Pension And Other Postretirement Benefit Plans Net Prior Service Cost Recognized In Net Periodic Pension Cost Net Of Taxes Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Report Date [Axis] Report Date [Axis] Financial Statement Filing Date [Domain] Financial Statement Filing Date [Domain] Retained Earnings [Member] Retained Earnings [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Domain] Adjustments for Change in Accounting Principle [Domain] Adjustments for Error Corrections [Axis] Adjustments for Error Corrections [Axis] Adjustments for Error Correction [Domain] Adjustments for Error Correction [Domain] New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification Net Realized and Unrealized Gain (Loss) on Trading Securities Net Realized and Unrealized Gain (Loss) on Trading Securities Trading Securities, Realized Gain (Loss) Trading Securities, Realized Gain (Loss) Fixed income securities Investment Income Interest On Debt Securities Investment Income Interest On Debt Securities Short-term investments Investment Income Insurance Entity Short Term Investments Investment Income Insurance Entity Short Term Investments Loans Investment Income Interest On Loans Receivable Investment Income Interest On Loans Receivable Investment expense Investment Income, Investment Expense Securities available-for-sale and short-term Interest and Dividend Income, Securities, Operating, Available-for-sale Total net investment income Equity [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Other Postretirement Benefit Plan, Defined Benefit [Member] Other Postretirement Benefit Plan [Member] Accumulated Translation Adjustment [Member] Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Changes In Accumulated Other Comprehensive Income [Roll Forward] Changes In Accumulated Other Comprehensive Income [Roll Forward] Changes In Accumulated Other Comprehensive Income [Roll Forward] Beginning Balance Accumulated Other Comprehensive Income (Loss), Net of Tax Other comprehensive income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amounts reclassified from accumulated other comprehensive income Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Net current period other comprehensive income Other Comprehensive Income Loss Excluding Noncontrolling Interest Net Of Tax Net of tax amount of other comprehensive income (loss) excluding noncontrolling interest. Ending Balance Schedule of Deferred Income Tax Assets and Liabilities [Table] Schedule of Deferred Income Tax Assets and Liabilities [Table] Schedule of Deferred Income Tax Assets and Liabilities [Table] Schedule of Deferred Income Tax Assets and Liabilities [Line Items] Schedule of Deferred Income Tax Assets and Liabilities [Line Items] [Line Items] for Schedule of Deferred Income Tax Assets and Liabilities [Table] Deferred tax liabilities: Deferred Tax Liabilities, Net [Abstract] Insurance intangible Deferred Tax Liabilities, Intangible Assets Variable interest entities Current Liabilities Variable Interest Entity Current Liabilities Variable Interest Entity Investments Deferred Tax Liabilities, Investments Unearned premiums and credit fees Deferred Tax Liabilities Unearned Premium Revenue Deferred Tax Liabilities Unearned Premium Revenue Undistributed Earnings of Foreign Subsidiaries Undistributed Earnings of Foreign Subsidiaries Other Deferred Tax Liabilities, Other Deferred Tax Liabilities, Gross, Noncurrent Deferred Tax Liabilities, Gross, Noncurrent Deferred tax assets: Deferred Tax Assets, Net [Abstract] Net operating loss and capital carryforward Deferred Tax Assets, Operating Loss Carryforwards Current Assets Variable Interest Entity Current Assets Variable Interest Entity Current Assets Variable Interest Entities Loss reserves Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves Compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation AMT Credits Maximum Alternative Minimum Tax Tolling Payment Credit Maximum Alternative Minimum Tax Tolling Payment Credit Other Deferred Tax Assets, Other Sub total deferred tax assets Deferred Tax Assets, Gross Valuation allowance Deferred Tax Assets, Valuation Allowance Total deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Deferred Tax Liabilities, Net Deferred Tax Liabilities, Net Income Tax Contingency [Table] Income Tax Contingency [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] United States [Member] UNITED STATES New York State [Member] NEW YORK New York City [Member] New York City [Member] New York city. United Kingdom [Member] UNITED KINGDOM Italy [Member] ITALY Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Tax Year Income Tax Examination, Year under Examination Schedule of Insured Financial Obligations with Credit Deterioration [Table] Schedule of Insured Financial Obligations with Credit Deterioration [Table] Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] Schedule of Insured Financial Obligations with Credit Deterioration [Line Items] Loss and loss expense reserves Liability for Claims and Claims Adjustment Expense, Financial Guarantee Insurance Contracts Subrogation recoverable Salvage and Subrogation Recoveries, Value Liability for Claims Liability for Claims and Claims Adjustment Expense Special Purpose Entities, Including Variable Interest Entities Schedule of Variable Interest Entities [Table Text Block] Statement of Financial Position [Abstract] Assets: Assets [Abstract] Fixed income securities, available for sale, at fair value (amortized cost: $5,806,949 and $4,992,756) Available-for-sale Securities, Debt Securities Restricted cash Restricted Cash and Cash Equivalents Fixed income securities pledged as collateral, available for sale, at fair value (amortized cost: $64,777 and $64,612) Available-for-sale Securities Pledged as Collateral Short-term investments, available for sale, at fair value (amortized cost: $130,732 and $225,789) Other investments (includes $391,075 and $285,261 at fair value) Other Investments and Securities, at Cost Total investments Investments Cash and cash equivalents Receivable for securities Other Receivables Investment income due and accrued Accrued Investment Income Receivable Loans Loans Receivable, Net Premium receivables Premiums Receivable, Net Reinsurance recoverable on paid and unpaid losses Reinsurance Recoverables Deferred ceded premium Prepaid Reinsurance Premiums Subrogation recoverable Loans Financing Receivable, Net Derivative assets Income Taxes Receivable Income Taxes Receivable, Current Goodwill Goodwill Other assets Other Assets Total assets Variable interest entity assets: Variable Interest Entity Classification Of Carrying Amount Assets [Abstract] Variable Interest Entity Classification Of Carrying Amount Assets [Abstract] Liabilities: Liabilities [Abstract] Unearned premiums Unearned Premiums Ceded premiums payable Obligations under investment agreements Borrowings under Guaranteed Investment Agreements Deferred taxes Current taxes Accrued Income Taxes, Current Long-term debt Long-term Debt Accrued interest payable Interest Payable Derivative liabilities Other liabilities Other Liabilities Payable for securities purchased Investment-related Liabilities Total liabilities Liabilities Variable interest entity liabilities: Variable Interest Entity Consolidated Carrying Amount Liabilities [Abstract] Variable Interest Entity Consolidated Carrying Amount Liabilities [Abstract] Stockholders’ equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none Preferred Stock, Value, Issued Common stock, par value $0.01 per share; 130,000,000 shares authorized; issued and outstanding shares: 45,121,788 and 45,044,222 Common Stock, Value, Outstanding Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive income Retained earnings Retained Earnings (Accumulated Deficit) Treasury stock, shares at cost: 0 and 8,202 Treasury Stock, Value Total Ambac Financial Group, Inc. stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Total stockholders’ equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and stockholders’ equity Liabilities and Equity Deferred Income Tax Liabilities, Net Deferred Income Tax Liabilities, Net Reorganization [Abstract] Reorganization [Abstract] Fresh-Start Adjustments [Table] Fresh-Start Adjustments [Table] Fresh-Start Adjustment [Line Items] Fresh-Start Adjustment [Line Items] Deferred Amounts and Junior Deferred Amounts Accrued Interest Rate Business Acquisition, Percentage of Voting Interests Acquired Business Acquisition, Percentage of Voting Interests Acquired Deferred Policy Acquisition Cost, Amortization Expense Deferred Policy Acquisition Cost, Amortization Expense Goodwill [Roll Forward] Goodwill [Roll Forward] Beginning balance Goodwill recorded in connection with emergence from Chapter 11 Goodwill, Written off Related to Bankruptcy Claim Bankruptcy Claim Goodwill, Written off Related to Bankruptcy Claim Bankruptcy Claim Accumulated impairment loss Ending balance Intangible assets Finite-Lived Intangible Assets, Net U.S. Trustee Fees Debtor Reorganization Items, Debtor-in-Possession Facility Financing Costs Professional fees Debtor Reorganization Items, Legal and Advisory Professional Fees Gain From Cancellation and Satisfaction of Predecessor Ambac Debt Debtor Reorganization Items, Gain (Loss) on Settlement of Other Claims, Net Fresh Start Adjustments Debtor Reorganization Items Fresh Start Adjustments Impact of the fresh start adjustments on Predecessor's Consolidated Statements of Total Comprehensive Income Reorganization items Reorganization Items Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments Available-for-sale Securities [Table Text Block] Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments Held by Successor Ambac, by Contractual Maturity Investments Classified by Contractual Maturity Date [Table Text Block] Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments Schedule of Unrealized Loss on Investments [Table Text Block] Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments Gain (Loss) on Investments [Table Text Block] Summary of Roll-Forward of Ambac's Cumulative Credit Losses on Debt Securities for Which Portion of Other-than-Temporary Impairment was Recognized in Other Comprehensive Income Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table Text Block] Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged Summary Of Sources Of Collateral Received Held And Way Of Pledging Collateral Table [Text Block] Summary of the sources of collateral either received from various counterparties where the company can sell or re-pledge or held directly in the investment portfolio and how that collateral was pledged to various investment agreement, derivative and repurchase agreement counterparties. Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities Fair Value And Weighted Average Underlying Rating Of Securities Covered By Guarantees Table [Text Block] Fair Value And Weighted Average Underlying Rating Of Securities Covered by Guarantees [Table Text Block] Summary of Net Investment Income Investment Income [Table Text Block] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Provision for Income Taxes [Table] Provision for Income Taxes [Table] Provision for Income Taxes [Table] Provision for Income Taxes [Line Items] Provision for Income Taxes [Line Items] [Line Items] for Provision for Income Taxes [Table] Current Income Tax Expense (Benefit) Current Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Income tax expense (benefit) Income Tax Expense (Benefit) Document And Entity Information [Abstract] Document and Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Current Reporting Status Entity Current Reporting Status Entity Voluntary Filers Entity Voluntary Filers Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Public Float Entity Public Float Net Income Per Share Earnings Per Share [Text Block] Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] Ambac [Member] Ambac [Member] Ambac. Loss Contingencies [Line Items] Loss Contingencies [Line Items] Loss Contingency, Damages Sought, Value Gain Contingency, Unrecorded Amount Litigation settlement amount Gain (Loss) Related to Litigation Settlement Gain (Loss) Related to Litigation Settlement Internal Credit Rating [Member] Internal Credit Assessment [Domain] Minimum [Member] Minimum [Member] Other Investments Fair Value Input Weighted Average Credit Derivative Quote As Percentage Of Notional Fair Value Input Weighted Average Credit Rating Percentage of investment portfolio valued using dealer quotes Percentage Of Investment Portfolio Valued Using Dealer Quotes Investment portfolio valued using dealer quotes. Percentage of investment portfolio valued using external pricing services Percentage Of Investment Portfolio Valued Using External Pricing Services Percentage of investment portfolio valued using external pricing services. Percentage of investment portfolio valued using internal valuation models Percentage Of Investment Portfolio Valued Using Internal Valuation Models Percentage of investment portfolio valued using internal valuation models. PercentageofInvestedPortfiliowhereProjectedCashFlowsConsistSolelyofDeferredAmountsandInterest PercentageofInvestedPortfiliowhereProjectedCashFlowsConsistSolelyofDeferredAmountsandInterest PercentageofInvestedPortfiliowhereProjectedCashFlowsConsistSolelyofDeferredAmountsandInterest Credit valuation adjustment included in fair value of credit derivative liabilities Derivative Credit Risk Valuation Adjustment, Derivative Liabilities Credit valuation adjustment included in fair value of derivative liabilities other than credit derivatives Derivatives Credit Risk Valuation Adjustment Derivative Liabilities Other Than Credit Derivatives Amount of credit risk valuation adjustment to derivative liabilities other than credit derivatives, to properly reflect the credit quality of the entity. Percentage of CDS gross par outstanding used in the determination of CDS fair values Percentage Of Credit Derivatives Gross Par Outstanding Using Third Party Reference Obligation Quotes In Determination Of Fair Value Percentage of credit derivatives gross par outstanding using third party reference obligation quotes in determination of fair value. Percentage of CDS derivative liability used in the determination of CDS fair values Percentage Of Credit Derivatives Liability Using Third Party Reference Obligation Quotes In Determination Of Fair Value Percentage of credit derivatives liability using third party reference obligation quotes ion determination of fair value. Percentage of CDS gross par outstanding using internally estimated reference obligation prices in determination of fair value Percentage Of Credit Derivative Gross Par Outstanding Using Internally Estimated Reference Obligation Prices In Determination Of Fair Value Percentage of credit derivative gross par outstanding using internally estimated reference obligation prices in determination of fair value. Percentage of CDS liability using internally estimated reference obligation prices in determination of fair value Percentage Of Credit Derivative Liability Using Internally Estimated Reference Obligation Prices In Determination Of Fair Value Percentage of credit derivative liability using internally estimated reference obligation prices in determination of fair value. Basis point fee received for issuing a CDS on reference obligation base fee Fair Value Measurement Process Description For Credit Derivatives Base Fee Hypothetical base fee received on a credit derivative contract used in the description of the valuation processes in place for fair value measurement of credit derivatives. Credit spread of reference obligation of a base transaction Fair Value Measurement Process Description For Credit Derivatives Base Reference Obligation Spread Hypothetical base reference obligation spread used in the description of the valuation processes in place for fair value measurement of credit derivatives. Relative change ratio of CDS fee to cash market spread Fair Value Measurement Process Description For Credit Derivatives Base Relative Change Ratio Hypothetical base relative change ratio for a credit derivative contract used in the description of the valuation processes in place for fair value measurement of credit derivatives. Full relative change ratio of CDS fee to cash market spread Fair Value Measurement Process Description For Credit Derivatives Full Relative Change Ratio Full relative change ratio comparable to certain default used in the description of the valuation processes in place for fair value measurement of credit derivative. Basis point fee received for issuing a CDS on reference obligation hypothetical fee Fair Value Measurement Process Description For Credit Derivatives Revised Hypothetical Fee Hypothetical revised fee required on credit derivative contract used in the description of the valuation processes in place for fair value measurement of credit derivatives. Relative change ratio of CDS fee to cash market spread Fair Value Measurement Process Description For Credit Derivatives Revised Hypothetical Fee With Credit Down Grade Hypothetical revised fee required on credit derivative given a certain credit downgrade used in the description of the valuation processes in place for fair value measurement of credit derivatives. Credit spread of reference obligation of revised transaction Fair Value Measurement Process Description For Credit Derivatives Revised Hypothetical Reference Obligation Spread Two Hypothetical revised reference obligation spread (second example) used in the description of the valuation processes in place for fair value measurement of credit derivatives. Additional basis point fee need to receive for issuing a CDS on obligation Fair Value Measurement Process Description For Credit Derivatives Hypothetical Incremental Fee Hypothetical incremental credit derivative fee used in the description of the valuation processes in place for fair value measurement of credit derivatives. Additional basis points fee increase on change of reference obligation spread Fair Value Measurement Process Description For Credit Derivatives Hypothetical Incremental Fee With Credit Deterioration Hypothetical incremental credit derivative fee given a certain credit downgrade used in the description of the valuation processes in place for fair value measurement of credit derivative. Revised relative change ratio of CDS fee to cash market spread Fair Value Measurement Process Description For Credit Derivatives Revised Relative Change Ratio Hypothetical revised relative change ratio used in the description of the valuation processes in place for fair value measurement of credit derivatives. Estimated remaining life Fair Value Measurement Process Description For Credit Derivatives Remaining Life Hypothetical remaining contract life used in the description of the valuation processes in place for fair value measurement of credit derivatives. Fair value of consolidated VIE debt obligations valued using unobservable inputs by asset class Weighted average discounted rate of estimated future premium payments to be paid by the VIEs Fair Value Input Weighted Average Life Effects of Reinsurance [Table] Effects of Reinsurance [Table] Currency [Axis] Currency [Axis] All Currencies [Domain] All Currencies [Domain] Euro Member Countries, Euro Euro Member Countries, Euro Loss And Loss Adjustment Expense Reserves [Line Items] Loss And Loss Adjustment Expense Reserves [Line Items] Loss And Loss Adjustment Expense Reserves [Line Items] Policyholder Benefits and Claims Incurred, Ceded Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Beginning gross loss and loss expense reserves Less reinsurance on loss and loss expense reserves Beginning balance of net loss and loss expense reserves Liability for Unpaid Claims and Claims Adjustment Expense, Net Current year: Liability For Unpaid Claims And Claims Adjustment Expense Changes In Current Year [Abstract] Changes in liability for unpaid claims and claims adjustment expense related to reserves and recoveries established in the current year, net of reinsurance. ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear Claim and loss expense payments, net of subrogation and reinsurance Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Total current year Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Current Year Liability for unpaid claims and claims adjustment expense change in loss reserves current year. Prior years: Liability For Unpaid Claims And Claims Adjustment Expense Changes In Prior Years [Abstract] Liability for Unpaid Claims and Claims Adjustment Expense Changes in Prior Years [Abstract] Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance Liability For Unpaid Claims And Claims Adjustment Expense Change In Previously Established Loss Reserves Prior Years Liability for Unpaid Claims and Claims Adjustment Expense Change in Previously Established Loss Reserves Prior Years Claim and loss expense (payments) recoveries, net of subrogation and reinsurance Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Change in previously established RMBS subrogation recoveries, net of reinsurance Liability For Unpaid Claims And Claims Adjustment Expense Change In Established Subrogation Recoveries Prior Years Liability for Unpaid Claims and Claims Adjustment Expense Change in Established Subrogation Recoveries Prior Years Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year Net change in loss and loss expense reserves Change In Loss And Loss Expense Reserves Net The increase (decrease) during the reporting period in the loss and loss expense reserve accounts, net of subrogation and reinsurance. Liability for Unpaid Claims and Claims Adjustment Expense, Net Add reinsurance on loss and loss expense reserves Ending gross loss and loss expense reserves Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Table] Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Table] Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Table] Loss and Loss Reserves [Axis] Loss and Loss Reserves [Axis] Loss and Loss Reserves [Axis] Loss and Loss Reserves [Domain] Loss and Loss Reserves [Domain] [Domain] for Loss and Loss Reserves [Axis] Unpaid Claims-Claims [Member] Unpaid Claims-Claims [Member] Claims [Member] Unpaid Claims-Accrued Interest [Member] Unpaid Claims-Accrued Interest [Member] Accrued Interest [Member] Present Value of Expected Net Cash Flows- Claims and Loss Expenses [Member] Present Value of Expected Net Cash Flows- Claims and Loss Expenses [Member] Claims and Loss Expenses [Member] Present Value of Expected Net Cash Flows-Recoveries [Member] Present Value of Expected Net Cash Flows-Recoveries [Member] Recoveries [Member] Unearned Premium Reserve [Member] Unearned Premium Reserve [Member] Unearned Premium Reserve [Member] Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items] Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items] [Line Items] for Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Table] Policyholder Benefits and Claims Incurred, Ceded Subrogation recoverable Claim liability reported on Balance Sheet, before reinsurance Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Claim Liability Income Taxes Income Tax Disclosure [Text Block] Schedule Of Earnings Per Share [Table] Schedule Of Earnings Per Share [Table] Schedule Of Earnings Per Share [Table] Schedule Of Earnings Per Share [Line Items] Schedule Of Earnings Per Share [Line Items] Schedule Of Earnings Per Share [Line Items] Number of new common stock issued WarrantBuyBackAuthorizedDollars FirstWarrantBuyBackAuthorizedDollars FirstWarrantBuyBackAuthorizedDollars Warrants Purchased During Period Shares Warrants Purchased During Period Shares Warrants Purchased During Period Shares Warrants Purchased During Period Dollars Warrants Repurchased Average Cost per Warrant Warrants Repurchased Average Cost per Warrant Warrants Repurchased Average Cost per Warrant Par value of common stock issued Class of Warrant or Right, Number of Securities Called by Warrants or Rights Exercise price of common stock Common stock shares issued Stock Issued During Period, Shares, New Issues Warrant exercised Warrant Exercised During Period Shares Warrant Exercised During Period Shares Warrants outstanding Warrants Outstanding Warrants Outstanding SecondWarrantBuyBackAuthorizedDollars SecondWarrantBuyBackAuthorizedDollars SecondWarrantBuyBackAuthorizedDollars Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount RemainingWarrantBuyBackAuthorizedDollars RemainingWarrantBuyBackAuthorizedDollars RemainingWarrantBuyBackAuthorizedDollars Reinsurance Premiums for Insurance Companies, by Product Segment [Table] Reinsurance Premiums for Insurance Companies, by Product Segment [Table] Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items] Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items] Direct Premiums Written Direct Premiums Written Assumed Reinsurance Premiums Written Assumed Premiums Written Ceded Reinsurance Premiums Written Ceded Premiums Written Premiums written, net of reinsurance Premiums Written, Net Direct Premiums Earned Direct Premiums Earned Assumed Reinsurance Premiums Earned Assumed Premiums Earned Ceded Reinsurance Premiums Earned Ceded Premiums Earned Reinsurance on premiums earned, Net Premiums Earned, Net, Financial Guarantee Insurance Contracts Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Variable Interest Entities [Member] Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member] Investments: Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Net realized investment gains Gain (Loss) on Investments, Excluding Other than Temporary Impairments Income tax expense (benefit) Net of tax and noncontrolling interest Net Income (Loss) Available to Common Stockholders, Basic Prior service cost Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax Actuarial gains (losses) Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax Total before tax Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Schedule of Loss And Loss Expense Reserves And Subrogation Recoverable Table [Table Text Block] Schedule of Loss And Loss Expense Reserves And Subrogation Recoverable Table [Table Text Block] Tabular disclosure that provides regarding the balance sheet line items for the liability "Loss and Loss Expense Reserves" and the asset "Subrogation Recoverable". Includes the various components of Unpaid Claims, Accrued Interest on Unpaid Claims, Present Value of Future Expected Claims and Loss Expenses, Present Vlaue of Future Expected Recoveries and the related Unearned Premium Revenue liability. Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) Financial Guarantee Insurance Contracts Premium Receivable Activity Table [Text Block] Financial guarantee insurance contracts premium receivable activity. Effect of Reinsurance on Premiums Written and Earned Schedule Of Reinsurance On Premiums Written And Earned Table [Text Block] Schedule Of Reinsurance On Premiums Written And Earned Table [Text Block] Summarized Future Gross Undiscounted Premiums Expected to be Collected and Future Expected Premiums Earned, Net of Reinsurance Financial Guarantee Insurance Contracts Premium Receivable Premium Expected To Be Collected And Future Expected Premiums Earned Table [Text Block] Financial guarantee insurance contracts premium receivable premium expected to be collected and future expected premiums to be earned, net of reinsurance. Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable Schedule of Insured Financial Obligations with Credit Deterioration [Table Text Block] Summary of Balance of Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach Summary Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach Table [Text Block] Tabular presentation of balance of RMBS subrogation recoveries and the related claim liabilities, by estimation approach. Summary of Rollforward of RMBS Subrogation, by Estimation Approach Summary Of Balance Of Rmbs Subrogation Recoveries By Estimation Approach Table [Text Block] Tabular presentation of rollforward of RMBS subrogation, by estimation approach. Schedule Of Reinsurance Recoverable And Provision By Category Of Reinsurer [Table Text Block] Schedule Of Reinsurance Recoverable And Provision By Category Of Reinsurer [Table Text Block] Provides the percentage ceded to reinsurers unsecured reinsurance recoverable and rating levels. Tax Credit Carryforward [Table] Tax Credit Carryforward [Table] Capital Loss Carryforward [Member] Capital Loss Carryforward [Member] U. S. Federal Net Operating Tax [Member] Domestic Tax Authority [Member] Segregated Account [Member] Segregated Account [Member] Segregated Account [Member] Tax Credit Carryforward [Line Items] Tax Credit Carryforward [Line Items] Unrecognized Tax Benefits, Interest on Income Taxes Accrued Unrecognized Tax Benefits, Interest on Income Taxes Accrued Operating tax carryforward expiration year start Operating Tax Carryforward Expiration Year Start Operating tax carryforward expiration year start. Operating tax carryforward expiration year end Operating Tax Carryforward Expiration Year End Operating tax carryforward expiration year end. Bankruptcy Claims, Amount Paid to Settle Claims Bankruptcy Claims, Amount Paid to Settle Claims Amount Of Loss Carryforward Relinquishment Amount Of Loss Carryforward Relinquishment Amount Of Loss Carryforward Relinquishment Net Operating Loss Carry Forwards Reduced For Cancellation Of Indebtedness Income And Interest Expense Net Operating Loss Carry Forwards Reduced For Cancellation Of Indebtedness Income And Interest Expense Net Operating Loss Carry Forwards Reduced For Cancellation Of Indebtedness Income And Interest Expense Reportable Geographical Components [Member] Reportable Geographical Components [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Other International [Member] Other International [Member] Other international. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Gross Premiums Written Premiums Written, Gross Net premiums earned Net Change In Fair Value Of Credit Derivatives Gain (Loss) on Derivative Instruments, Net, Pretax Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Summary of information by major category of CDS contracts Summary Of Information By Major Category Of Credit Derivatives Contracts [Abstract] Summary of information by major category of CDS contracts. Number of CDS transactions Derivative, Number of Instruments Held Derivative, Average Remaining Maturity Derivative, Average Remaining Maturity Gross principal notional outstanding Net derivative liabilities at fair value Fixed income securities, amortized cost Available-for-sale Debt Securities, Amortized Cost Basis Fixed income securities pledged as collateral, amortized cost Available For Sale Securities Pledged As Collateral Amortized Cost Basis Amortized cost basis of available for sale securities that serve as collateral for borrowings. Short-term investments, amortized cost Other Short Term Investments Amortized Cost This item represents the amortized cost of other short term investments not otherwise specified in the taxonomy that will be realized in a short period of time, usually less than one year, net of adjustments made for accretion, amortization, other-than-temporary impairments. Preferred stock, par value Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Common stock, par value Common stock, shares outstanding Common Stock, Shares, Outstanding Treasury stock, shares Treasury Stock, Shares Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) [Member] London Interbank Offered Rate (LIBOR) [Member] Consolidated Entities [Member] Consolidated Entities [Member] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Sponsored Variable Interest Entities [Member] Sponsored Variable Interest Entities [Member] Sponsored variable interest entities. Asset-Backed Securities and Utility Obligations [Member] Asset Backed Securities And Utility Obligations [Member] Asset-backed securities and utility obligations. Equity Method Investments Equity Method Investments Number of RMBS Sold Number of RMBS Sold Number of RMBS Sold Cash Received From Delaware Trust Cash Received From Delaware Trust Cash Received From Delaware Trust Number of DeConsolidated Variable Interest Entities Number of DeConsolidated Variable Interest Entities Number of DeConsolidated Variable Interest Entities Number of VIEs AAC Transferred Assets To Number of VIEs AAC Transferred Assets To Number of VIEs AAC Transferred Assets To Number of VIEs Liquidated Number of VIEs Liquidated Number of VIEs Liquidated Secured Debt Secured Debt Par Value of Securities Placed in Trust Par Value of Securities Placed in Trust Par Value of Securities Placed in Trust Securities Issued by Delaware Trust Securities Issued by Delaware Trust Securities Issued by Delaware Trust Interest Rate on Securities Issued by Delaware Trust Interest Rate on Securities Issued by Delaware Trust Interest Rate on Securities Issued by Delaware Trust Fair value of special purpose entities Number of individual transactions with special purpose entities Number Of Transactions With Sponsored Special Purpose Entities Inception To Date The number of asset transfer transactions executed with Ambac's sponsored medium term note special purpose entities since the inception of those entities. Number of transactions outstanding with special purpose entities Number Of Transactions Outstanding With Sponsored Special Purpose Entities The number of asset transfer transactions executed with Ambac's sponsored medium term note special purpose entities that are still outstanding at the reporting date. Total principal amount of debt outstanding Face Amount Of Debt Outstanding Issued By Sponsored Special Purpose Entities The total principal amount of outstanding debt issued by Ambac's sponsored medium term note special purpose entities. Weighted average life Weighted Average Life Of Assets Held By Sponsored Special Purpose Entities The weighted average remaining life of assets held by Ambac's sponsored medium term note special purpose entities at the reporting date. Average rating of assets held by sponsored special purpose entities Weighted Average Rating Of Assets Held By Sponsored Special Purpose Entities The weighted average credit rating of assets held by Ambac's sponsored medium term note special purpose entities at the reporting date. Number of consolidated Variable Interest Entities Number Of Consolidated Variable Interest Entities Number of consolidated variable interest entities. Consolidated VIE assets Variable Interest Entity, Consolidated, Carrying Amount, Assets Consolidated VIE liabilities Variable Interest Entity, Consolidated, Carrying Amount, Liabilities variable interest entities deconsolidation gain loss variable interest entities deconsolidation gain loss variable interest entities deconsolidation gain loss Credit Deterioration Surveillance Category [Axis] Credit Deterioration Surveillance Category [Axis] Surveillance Category [Domain] Surveillance Category [Domain] I/SL [Member] Surveillance Category One Survey List [Member] Surveillance Category One Survey List [Member] IA [Member] Surveillance Category Onea [Member] Surveillance Category OneA [Member] II [Member] Surveillance Category Two [Member] Surveillance category two. III [Member] Surveillance Category Three [Member] Surveillance category three. IV [Member] Surveillance Category Four [Member] Surveillance category four. V [Member] Surveillance Category Five [Member] Surveillance category five. Number of policies Schedule of Insured Financial Obligations with Credit Deterioration, Number of Contracts Issued and Outstanding Remaining weighted-average contract period (in years) Insured Financial Obligations with Credit Deterioration, Remaining Weighted Average Contract Period Gross insured contractual payments outstanding: Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding [Abstract] Principal Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding, Principal Interest Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding, Interest Total Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding Gross undiscounted claim liability Schedule Of Insured Financial Obligations With Credit Deterioration Gross Undiscounted Claim Liability This element represents the gross undiscounted claim liability for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued. Discount, gross claim liability Schedule Of Insured Financial Obligations With Credit Deterioration Discount On Gross Claim Liability This element represents the discounting on the gross claim liability for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued. Gross claim liability before all subrogation and before reinsurance Schedule of Insured Financial Obligations with Credit Deterioration, Gross Claim Liability Less: Less Discounted Rmbs Subrogation Before Reinsurance [Abstract] Less Discounted Rmbs Subrogation Before Reinsurance [Abstract] Gross RMBS subrogation Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Undiscounted Claim Liability Gross Undiscounted Rmbs Subrogation This element represents the reduction to gross undiscounted claim liability for gross undiscounted subrogation on insured RMBS financial obligations with credit deterioration. Discount, RMBS subrogation Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Discount On Rmbs Subrogation This element represents the discounting on the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration. Discounted RMBS subrogation, before reinsurance Less: Discounted Other Subrogation Before Reinsurance [Abstract] Discounted other subrogation, before reinsurance. Gross other subrogation Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Undiscounted Claim Liability Gross Undiscounted Other Subrogation This element represents the reduction to gross undiscounted claim liability for gross undiscounted subrogation on insured financial obligations with credit deterioration, excluding subrogation on insured RMBS financial obligations with credit deterioration. Discount, other subrogation Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Discount On Other Subrogation This element represents the discount on the gross subrogation on insured financial obligations with credit deterioration, excluding the discount on the gross subrogation on insured RMBS financial obligations with credit deterioration. Discounted other subrogation, before reinsurance Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Other Subrogation This element represents the reduction to gross claim liability for subrogation on insured financial obligations with credit deterioration, excluding the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration. Gross claim liability, net of all subrogation and discounts, before reinsurance Schedule of Insured Financial Obligations with Credit Deterioration, Net Claim Liability Less: Unearned premium reserves Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Unearned Premium Revenue Plus: Loss adjustment expenses reserves Schedule Of Insured Financial Obligations With Credit Deterioration Loss Adjustment Expenses Reserve This element represents the amount of loss adjustment expense reserves represent the costs estimated to be incurred in the settlement of unpaid claims related to financial guarantee insurance contracts and presented in the schedule of insured financial obligations with credit deterioration in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued. Reinsurance recoverable reported on Balance Sheet Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Reinsurance Recoverable Fair Value Of Investments Measured At NAV As Practical Expedient [Table Text Block] Fair Value Of Investments Measured At NAV As Practical Expedient [Table Text Block] [Table Text Block] for Fair Value Of Investments Measured At NAV As Practical Expedient [Table] Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities Fair Value, by Balance Sheet Grouping [Table Text Block] Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 Fair Value Inputs, Liabilities, Quantitative Information [Table Text Block] Summary of Changes in Level 3 Fair Value Category Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Table Text Block] Tabular presentation of Fair value assets and liabilities measured on recurring basis unobservable input reconciliation. Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Table Text Block] Credit Derivatives [Member] Call Options on Long-Term Debt [Member] Call Options on Long-Term Debt [Member] Call Options on Long-Term Debt [Member] US Government Agencies Debt Securities [Member] Non-Agency RMBS [Member] Non-Agency RMBS [Member] Non-Agency RMBS [Member] Investments Contract [Member] Loans [Member] Long-Term Debt [Member] Investment by Class [Member] Derivatives by Class [Member] Balance, beginning of period Additions of VIEs consolidated Included in earnings Deconsolidation of VIEs Balance, end of period The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date Other Asset-Backed Securities [Member] Foreign Government Debt Securities [Member] Less than 12 Months, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Less than 12 Months, Gross Unrealized Loss Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Retained Earnings/Accumulated Deficit [Member] Accumulated Other Comprehensive Income (Loss) [Member] AOCI Attributable to Parent [Member] Preferred Stock [Member] Preferred Stock [Member] Common Stock [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Common Stock Held in Treasury, at Cost [Member] Treasury Stock [Member] Noncontrolling Interest [Member] Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Total comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Stock-based compensation Allocated Share-based Compensation Expense Stock Issued During Period, Value, Share-based Compensation, Gross Stock Issued During Period, Value, Share-based Compensation, Gross Stock Issued During Period, Value, New Issues Stock Issued During Period, Value, New Issues Cost of shares (acquired) issued under equity plan Treasury Stock, Value, Acquired, Cost Method Ending balance Mortgage and Asset-Backed Securities [Member] Mortgage And Other Asset Backed Securities [Member] Mortgage And Other Asset Backed Securities [Member] Standard & Poor's, CC Rating [Member] Standard & Poor's, CC Rating [Member] Standard & Poor's, A- Rating [Member] Standard & Poor's, A- Rating [Member] Standard & Poor's, AA Rating [Member] Standard & Poor's, AA Rating [Member] Standard & Poor's, AA- Rating [Member] Standard & Poor's, AA- Rating [Member] Standard & Poor's, A+ Rating [Member] Standard & Poor's, A+ Rating [Member] Standard & Poor's, CCC Rating [Member] Standard & Poor's, CCC- Rating [Member] Investment [Axis] Investment [Axis] Investment [Domain] Investment [Domain] Ambac Assurance Corporation [Member] Ambac Assurance Corporation [Member] Ambac assurance corporation. National Public Finance Guarantee Corporation [Member] National Public Finance Guarantee Corporation [Member] National Public Finance Guarantee Corporation [Member] Assured Guaranty Municipal Corporation [Member] Assured Guaranty Municipal Corporation [Member] Assured Guaranty Municipal Corporation [Member] MBIA Insurance Corporation [Member] Mbia Insurance Corporation [Member] Mbia Insurance Corporation [Member] Fair value of securities that include benefit of guarantees provided by financial guarantors Investment Owned, at Fair Value United Kingdom, Pounds United Kingdom, Pounds Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount Percentage Premiums Receivable Related To Transactions With Non Investment Grade Internal Ratings Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward] Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward] Beginning premium receivable Financial Guarantee Insurance Contracts, Premium Receivable Premium receipts Financial Guarantee Insurance Contracts, Premium Receivable, Premium Payments Received Adjustments for changes in expected and contractual cash flows Financial Guarantee Insurance Contracts, Premiums Receivable, Adjustment, Change in Period of Contract Accretion of premium receivable discount Financial Guarantee Insurance Contracts, Premiums Receivable, Adjustment, Accretion of Discount on Premium Receivable Financial Guarantee Insurance Contracts Premium Receivable Deconsolidation Of Certain Variable Interest Entity Financial Guarantee Insurance Contracts Premium Receivable Deconsolidation Of Certain Variable Interest Entity Financial guarantee insurance contracts premium receivable deconsolidation of certain variable interest entity. Uncollectable premiums Allowance for Doubtful Accounts Receivable, Period Increase (Decrease) Other adjustments (including foreign exchange) Financial Guarantee Insurance Contracts, Premiums Receivable, Adjustment, Other Adjustments Ending premium receivable Percentage Of Premiums Receivable Related To Non Investment Grade Rmbs Transactions Percentage Of Premiums Receivable Related To Student Loan Transactions Percentage Premiums Receivable Related To Asset Backed Transactions Premiums Receivable, Allowance for Doubtful Accounts Premiums Past Due On Non Investment Grade Obligation Major Jurisdictions Summary of Income Tax Examinations [Table Text Block] Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule of Components of Income Tax Expense (Benefit) Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule Of Income Taxes Charged Credited Directly To Equity Schedule Of Income Taxes Charged Credited Directly To Equity [Table Text Block] Schedule Of Income Taxes Charged Credited Directly To Equity [Table Text Block] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Unrecognized Tax Benefits Roll Forward Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Schedule of Net Operating Loss And Tax Credit Carryovers Schedule of Net Operating Loss And Tax Credit Carryovers [Table Text Block] Schedule of Net Operating Loss And Tax Credit Carryovers [Table Text Block] Loans, Estimated fair value Long-term debt, Estimated fair value Loans, Unpaid principal balance Loans Unpaid Principal Balance This represents the amount of principal outstanding on loans receivable that are presented on the balance sheet at fair value, whether such presentation is as a separate caption or parenthetical disclosure. Long-term debt, Unpaid principal balance Long Term Debt Unpaid Principal Balance This represents the amount of principal outstanding on long-term debt that is presented on the balance sheet at fair value, whether such presentation is as a separate caption or parenthetical disclosure. Variable Interest Entity, Consolidated, Carrying Amount, Liabilities Net investment income: Net Investment Income [Abstract] Securities available-for-sale and short-term Other investments Other Investment Income Other investment income not specified in the taxonomy. Other-than-temporary impairment losses: Other than Temporary Impairment Losses, Investments [Abstract] Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Portion of other-than-temporary impairment recognized in other comprehensive income Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest Net other-than-temporary impairments Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Change in fair value of credit derivatives: Credit Risk Derivatives, at Fair Value, Net [Abstract] Gain (Loss) on Sale of Derivatives Gain (Loss) on Sale of Derivatives Unrealized gains (losses) Net change in fair value of credit derivatives Derivative products Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net Net realized gains (losses) on extinguishment of debt Other Operating Income (Expense), Net Other Operating Income (Expense), Net Income (loss) on variable interest entities Total revenues Expenses: Operating Expenses [Abstract] Losses and loss expense (benefit) Policyholder Benefits and Claims Incurred, Net, Financial Guarantee Insurance intangible amortization Operating expenses Other Underwriting Expense Total expenses (benefit) Benefits, Losses and Expenses Pre-tax income (loss) Provision for income taxes Less: net (gain) loss attributable to noncontrolling interest Other comprehensive income (loss), after tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized gains (losses) on securities, net of deferred income taxes of $0 Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Gains (losses) on foreign currency translation, net of deferred income taxes of $0 Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Changes to postretirement benefit, net of tax of $0 Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Total other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Total comprehensive income (loss) Less: comprehensive (loss) gain attributable to the noncontrolling interest: Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest [Abstract] Net (gain) loss Currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Total comprehensive income (loss) attributable to Ambac Financial Group, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Earnings Per Share, Basic Earnings Per Share, Basic Earnings Per Share, Diluted Earnings Per Share, Diluted Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share Schedule of Weighted Average Number of Shares [Table Text Block] Trading Securities [Table] Trading Securities [Table] Net Change in Fair Value of Credit Derivatives [Member] Net Change In Fair Value Of Credit Derivatives [Member] Net change in fair value of credit derivatives. Derivative Products [Member] Derivative Products [Member] Derivative products. Other Income [Member] Derivative, by Nature [Axis] Derivative, by Nature [Axis] Derivative, Name [Domain] Derivative, Name [Domain] Financial Services Derivatives Products [Member] Financial Services Derivatives Products [Member] Financial Services derivatives products. Schedule of Trading Securities and Other Trading Assets [Line Items] Schedule of Trading Securities and Other Trading Assets [Line Items] Derivative instruments, gain (loss) recognized in income, net, Total Goodwill, Impairment Loss Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts [Text Block] Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities Summary Of Fair Value Of Fixed Income Securities By Asset Type Held By Consolidated Variable Interest Entities Table [Text Block] Tabular presentation of fair value of fixed income securities by asset type held by consolidated variable interest entities. Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities Supplemental Information About Loans Held As Assets And Long Term Debt Associated With Variable Interest Entities Table [Text Block] Supplemental information about the loans held as assets and long-term debt associated with consolidated variable interest entities, when reported under the fair value option. Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities Variable Interest Entity Not Primary Beneficiary Table [Text Block] Tabular presentation of the carrying amounts of assets and liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interests in non-consolidated variable interest entities (VIEs) resulting from financial guarantee and credit derivative contracts, and the maximum exposure to loss as a result of its involvement with such VIEs. Gross realized gains on securities Available-for-sale Securities, Gross Realized Gains Gross realized losses on securities Available-for-sale Securities, Gross Realized Losses Foreign exchange (losses) gains Net realized (losses) gains Future premiums expected to be collected, March 31, 2016 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Next Quarter Future premiums expected to be collected, June 30. 2016 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Second Quarter Future premiums expected to be collected, September 30, 2016 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Third Quarter Future premiums expected to be collected, December 31, 2016 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Fourth Quarter Future premiums expected to be collected, December 31, 2017 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year Two Future premiums expected to be collected, December 31, 2018 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year Three Future premiums expected to be collected, December 31, 2019 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year Four Future premiums expected to be collected, December 31, 2020 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year Five Future premiums expected to be collected, December 31, 2025 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year Six Through Ten Future premiums expected to be collected, December 31, 2030 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 11 Through 15 Future premiums expected to be collected, December 31, 2035 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 16 Through 20 Future premiums expected to be collected, December 31, 2040 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 21 Through 25 Future premiums expected to be collected, December 31, 2045 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 26 Through 30 Future premiums expected to be collected, December 31, 2050 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 31 Through 35 Future premiums expected to be collected, December 31, 2055 Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 36 Through 40 Future premiums expected to be collected, December 31, 2060 Financial Guarantee Insurance Contracts Premium Expected To Be Collected More Than Forty And Within Forty Five Years From Balance Sheet Date Amount of premium receivables under financial guarantee insurance contracts expected to be collected in the forty-first through the forty-fifth fiscal year following the latest fiscal year. Future premiums expected to be collected, Total Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected Future expected premium to be earned, net of reinsurance, March 31, 2016 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Next Quarter Future expected premiums to be earned, net of reinsurance, June 30, 2016 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Second Quarter Future expected premiums to be earned, net of reinsurance, September 30, 2016 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Third Quarter Future expected premiums to be earned, net of reinsurance, December 31, 2016 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Fourth Quarter Future expected premiums to be earned, net of reinsurance, December 31, 2017 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Two Future expected premiums to be earned, net of reinsurance, December 31, 2018 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Three Future expected premiums to be earned, net of reinsurance, December 31, 2019 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Four Future expected premiums to be earned, net of reinsurance, December 31, 2020 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Five Future expected premiums to be earned, net of reinsurance, December 31, 2025 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Six Through Ten Future expected premiums to be earned, net of reinsurance, December 31, 2030 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year 11 Through 15 Future expected premiums to be earned, net of reinsurance, December 31, 2035 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year 16 Through 20 Future expected premiums to be earned, net of reinsurance, December 31, 2040 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year 21 Through 25 Future expected premiums to be earned, net of reinsurance, December 31, 2045 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year 26 Through 30 Future expected premiums to be earned, net of reinsurance, December 31, 2050 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year 31 Through 35 Future expected premiums to be earned, net of reinsurance, December 31, 2055 Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year 36 Through 40 Future expected premiums to be earned, net of reinsurance, December 31, 2060 Financial Guarantee Insurance Contracts Future Expected Premium Revenue To Be Recognized More Than Forty And Within Forty Five Years From Balance Sheet Date Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the forty-first through forty-fifth fiscal year following the latest fiscal year. Future expected premiums to be earned, net of reinsurance, Total Financial Guarantee Insurance Contracts, Unearned Premium Revenue Amortized Cost, Due in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis Amortized Cost, Due after one year through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis Amortized Cost, Due after five years through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis Amortized Cost, Due after ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis Amortized Cost, Total Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Amortized Cost Estimated Fair Value, Due in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value Estimated Fair Value, Due after one year through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value Estimated Fair Value, Due after five years through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value Estimated Fair Value, Due after ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value Estimated Fair Value due, Total Available-for-sale Securities, Debt Maturities, Single Maturity Date