Issuance of Warrants in Connection with Sale of Subsidiary Issuance of Warrants in Connection with Sale of Subsidiary Issuance of Warrants in Connection with Sale of Subsidiary Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Restatement [Axis] Revision of Prior Period [Axis] Debt and Equity Securities, FV-NI [Line Items] Debt and Equity Securities, FV-NI [Line Items] Parsed Investment Type [Axis] Parsed Investment Type [Axis] Parsed Investment Type Debt Securities, Available-for-Sale Debt Securities, Available-for-Sale [Table Text Block] Estimated Future Premium Payments Maximum Discounted Rate Estimated Future Premium Payments Maximum Discounted Rate Estimated Future Premium Payments Maximum Discounted Rate Realized Investment Gains (Losses) Realized Investment Gains (Losses) Cash Provided by (Used in) Discontinued Operation Cash Provided by (Used in) Discontinued Operation Award Timing Predetermined Award Timing Predetermined [Flag] Entity File Number Entity File Number Business Combination, Number of Days to Calculate VWAP Business Combination, Number of Days to Calculate VWAP Business Combination, Number of Days to Calculate VWAP Additional Paid-in Capital [Member] Additional Paid-in Capital [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] Disposal Group, Including Discontinued Operation, Derivative, Gain (Loss) On Derivative, Net Disposal Group, Including Discontinued Operation, Derivative, Gain (Loss) On Derivative, Net Disposal Group, Including Discontinued Operation, Derivative, Gain (Loss) On Derivative, Net Shor term debt extension fee Shor term debt extension fee Shor term debt extension fee Tabular List, Table Tabular List [Table Text Block] Other investments Other Investments Income Other Investments Income Other Investments Income New Accounting Pronouncements, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Past Due Premiums Receivable Past Due Premiums Receivable Past Due Premiums Receivable Proceeds from Divestiture of Businesses, Net of Cash Divested Proceeds from Divestiture of Businesses, Net of Cash Divested Secured Overnight Financing Rate (SOFR) Secured Overnight Financing Rate (SOFR) [Member] Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities Fair Value, by Balance Sheet Grouping [Table Text Block] Redeemable Noncontrolling Interest, Equity, Redemption Value Redeemable Noncontrolling Interest, Equity, Redemption Value Position [Axis] Position [Axis] Liabilities for net financial guarantees written Guarantees, Fair Value Disclosure Measurement Basis [Axis] Measurement Basis [Axis] Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Debt Security Category [Domain] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Revenue from Contract with Customer Revenue from Contract with Customer [Text Block] Foreign Exchange Temporary Equity, Foreign Currency Translation Adjustments Continuing Operations Continuing Operations [Member] Current Income Tax Expense (Benefit) Current Income Tax Expense (Benefit) Determination Date [Axis] Determination Date [Axis] Determination Date [Axis] Fair Value Inputs Maturity Fair Value Inputs Maturity Fair value inputs maturity. Disposal Group, Including Discontinued Operation, Assets Disposal Group, Including Discontinued Operation, Assets Adjustment to Compensation, Amount Adjustment to Compensation Amount Business Combination, Percentage Ownership Retained by Rollover Shareholders Business Combination, Percentage Ownership Retained by Rollover Shareholders Business Combination, Percentage Ownership Retained by Rollover Shareholders Consolidation, Policy Consolidation, Policy [Policy Text Block] Multi-peril Multi-peril [Member] Multi-peril Share-based compensation Share-Based Payment Arrangement, Noncash Expense Amortized Cost And Fair Value Debt Securities [Abstract] Amortized Cost And Fair Value Debt Securities [Abstract] Amortized Cost and Fair Value Debt Securities [Abstract] Derivative and other assets Derivative and other assets Derivative and other assets Share-based Payment Arrangement, Option [Member] Share-Based Payment Arrangement, Option [Member] Income Taxes Paid Income Taxes Paid Income Taxes Paid Business Combination, Value of Shares Issued for Beat Acquisition Business Combination, Value of Shares Issued for Beat Acquisition Business Combination, Value of Shares Issued for Beat Acquisition Antidilutive Securities [Axis] Antidilutive Securities [Axis] Total Ambac Financial Group, Inc. stockholders’ equity Equity, Attributable to Parent Measurement Frequency [Axis] Measurement Frequency [Axis] Schedule of Available-for-sale Securities [Table] Debt Securities, Available-for-Sale [Table] Other Comprehensive Income (Loss), Net of Tax [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Common stock, shares authorized Common Stock, Shares Authorized 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] Mortgage Backed And Home Equity [Member] Mortgage Backed And Home Equity [Member] Mortgage Backed and Home Equity [Member] Financial assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Fair Value, Recurring [Member] Fair Value, Recurring [Member] Goodwill and Finte-Lived Intangible Assets, Foreign Currency Translation Gain (Loss) Goodwill and Finte-Lived Intangible Assets, Foreign Currency Translation Gain (Loss) Goodwill and Finte-Lived Intangible Assets, Foreign Currency Translation Gain (Loss) Fair Value Inputs Yield Rate Fair Value Inputs Yield Rate Fair Value Inputs Yield Rate Premiums Receivable, Net Premiums Receivable, Net Cash Cash and Cash Equivalents, Fair Value Disclosure Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Disposal Groups, Including Discontinued Operations, Disclosure Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Maximum [Member] Maximum [Member] Net Income (Loss) Attributable to Noncontrolling Interest Net Income (Loss) Attributable to Noncontrolling Interest Finite-Lived Intangible Assets, Net Finite-Lived Intangible Assets, Net Debt Securities, Available-for-sale, Unrealized Loss Position Debt Securities, Available-for-Sale, Unrealized Loss Position Amortized Cost, Due after ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Reclassifications Reclassifications [Text Block] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Investment Owned, at Fair Value Fair value of securities that include benefit of guarantees provided by financial guarantors Investment Owned, Fair Value Direct Premiums Earned Direct Premiums Earned External Credit Rating, Standard & Poor's [Domain] External Credit Rating, Standard & Poor's [Domain] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Other Assets [Member] Other Assets [Member] Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax 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. Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] 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. Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company All Trans All Trans [Member] All Trans Discontinued Operations, Held-for-Sale or Disposed of by Sale Discontinued Operations, Held-for-Sale or Disposed of by Sale [Member] Business Combination Type of Consideration Paid [Axis] Business Combination Type of Consideration Paid [Axis] Business Combination Type of Consideration Paid Total gains or losses included in earnings for the period Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings Losses and loss expenses, net Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Insurance Type and Tier Identifier [Axis] Insurance Type and Tier Identifier [Axis] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Weighted average discounted rate of estimated future premium payments to be paid by the VIEs 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. Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Impact on Shareholders Equity Related to Sale of Discontinued Operation Impact on Shareholders Equity Related to Sale of Discontinued Operation Impact on Shareholders Equity Related to Sale of Discontinued Operation Ambac Assurance [Member] Ambac Assurance [Member] Ambac assurance. Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Interest Expense, Operating Interest Expense, Operating Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Adjustment of NCI to fair value Adjustment of NCI to fair value Adjustment of NCI to fair value Business Combination Type of Consideration Paid [Domain] Business Combination Type of Consideration Paid [Domain] Business Combination Type of Consideration Paid [Domain] Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Payments to Noncontrolling Interests Payments to Noncontrolling Interests Income (Loss) from Continuing Operations before Income Taxes, Domestic Income (Loss) from Continuing Operations before Income Taxes, Domestic Standard & Poor's, B- Rating [Member] Standard & Poor's, B- Rating [Member] 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] Document Fiscal Period Focus Document Fiscal Period Focus Short Term Debt Duration Fee Short Term Debt Duration Fee Short Term Debt Duration Fee Disposal Group, Including Discontinued Operation, Net Assets Held-For Sale Disposal Group, Including Discontinued Operation, Net Assets Held-For Sale Disposal Group, Including Discontinued Operation, Net Assets Held-For Sale Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Award Timing Method Award Timing Method [Text Block] Income (Loss) from Continuing Operations, Per Basic Share Income (Loss) from Continuing Operations, Per Basic Share Award Type [Axis] Award Type [Axis] Indefinite-Lived License Agreements Indefinite-Lived License Agreements 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. Accumulated Translation Adjustment [Member] Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Parent Company Parent Company [Member] Business Combination, Pro Forma Information Business Combination, Pro Forma Information [Table Text Block] Investor Owned And Public Utilities [Member] Investor Owned And Public Utilities [Member] Investor Owned and Public Utilities [Member] Trading Symbol Trading Symbol Components of VIE Gain (Loss) [Table Text Block] Components of VIE Gain (Loss) [Table Text Block] [Table Text Block] for Components of VIE Gain (Loss) [Table] Collateralized Securities Collateralized Securities [Member] Number of Admitted Carriers Owned Number of Admitted Carriers Owned Number of Admitted Carriers Owned Number of new common stock issued Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Entity Address, City or Town Entity Address, City or Town Short-Term Debt, Type [Domain] Short-Term Debt, Type [Domain] Disposal Group, Including Discontinued Operation, Gain (Loss) On Extinguishment Of Debt Disposal Group, Including Discontinued Operation, Gain (Loss) On Extinguishment Of Debt Disposal Group, Including Discontinued Operation, Gain (Loss) On Extinguishment Of Debt Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Effect of foreign exchange on cash and cash equivalents - discontinued operations Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Statement of Income Location, Balance [Domain] Statement of Income Location, Balance [Domain] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] 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. Business Combination, Consideration Transferred Business Combination, Consideration Transferred Entity Emerging Growth Company Entity Emerging Growth Company Total Comprehensive Income Net Of Tax Less NCI Total Comprehensive Income Net Of Tax Less NCI Total Comprehensive Income Net Of Tax Less NCI Derivative, Collateral, Right to Reclaim Cash Value of right to reclaim cash collateral and posted margin, recorded in Other assets Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Not Offset Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Derivative, Gain (Loss) on Derivative, Net Gains in change in fair value of the call options Derivative, Gain (Loss) on Derivative, Net 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. III [Member] Surveillance Category Three [Member] Surveillance category three. Bet Capital Partners Bet Capital Partners [Member] Bet Capital Partners Common stock, shares outstanding Common Stock, Shares, Outstanding Insurance [Abstract] Insurance [Abstract] Insurance Claims Insurance Claims [Member] 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] Global Public Finance [Member] Global Public Finance [Member] Global public finance. Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Disposal Group, Including Discontinued Operation, Policyholder Benefits And Claims Incurred, Net Disposal Group, Including Discontinued Operation, Policyholder Benefits And Claims Incurred, Net Disposal Group, Including Discontinued Operation, Policyholder Benefits And Claims Incurred, Net Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Schedule of Finite-Lived Intangible Assets, Future Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] 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. Afg [Member] Afg [Member] Afg [Member] Pledged Status [Domain] Pledged Status [Domain] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Provision (benefit) for income taxes from continuing operations Income Tax Expense (Benefit) Income tax expense (benefit) Income Tax Expense (Benefit) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Other Assets Other Assets Credit Rating, Standard & Poor's [Axis] Credit Rating Source [Axis] Credit Rating, Standard & Poor's [Axis] Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable Issuance of Equity Interest in Subsidiary Issuance of Equity Interest in Subsidiary Issuance of Equity Interest in Subsidiary Preferred Stock, Shares Issued Preferred Stock, Shares Issued Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Parsed Investment Type [Domain] Parsed Investment Type [Domain] Parsed Investment Type [Domain] Managing General Agency Underwriter Managing General Agency Underwriter [Member] Managing General Agency Underwriter Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Marine and Energy Marine and Energy Marine and Energy Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, Tax Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, Tax Housing Revenue [Member] Housing Revenue [Member] Housing Revenue [Member] Allowance for Credit Loss, Receivable, Other, Current Allowance for Credit Loss, Receivable, Other, Current Other income Items Other income Items Recognized Under ASC 606 Other income Items Recognized Under ASC 606 Business Combination, AAC Cash Consideration for Beat Acquisition Business Combination, AAC Cash Consideration for Beat Acquisition Business Combination, AAC Cash Consideration for Beat Acquisition Mortgage And Other Asset Backed Securities [Member] Mortgage And Other Asset Backed Securities [Member] Mortgage And Other Asset Backed Securities [Member] Insurance Intangible Asset [Member] Insurance Intangible Asset [Member] Insurance Intangible Asset [Member] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Goodwill, Acquired During Period Goodwill, Acquired During Period Schedule of Error Corrections and Prior Period Adjustments Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] Mergers, Acquisitions and Dispositions Disclosures Mergers, Acquisitions and Dispositions Disclosures [Text Block] Payments to Acquire Businesses, Net of Cash Acquired Payments to Acquire Businesses, Net of Cash Acquired All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Background And Basis Of Presentation [Line Items] Background And Basis Of Presentation [Line Items] Background And Basis Of Presentation [Line Items] Past Due Premiums Past Due Premiums Past Due Premiums Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Ceded premiums payable Reinsurance Payable NetIncestment Income And Realized Investment Gains (Losses) NetIncestment Income And Realized Investment Gains (Losses) NetIncestment Income And Realized Investment Gains (Losses) Net Cash Provided by (Used in) Operating Activities, Total Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Change in Nonredeemable NCI Resulting From Purchase of Shares From Minority Interest Owners Change in Nonredeemable NCI Resulting From Purchase of Shares From Minority Interest Owners Change in Nonredeemable NCI Resulting From Purchase of Shares From Minority Interest Owners Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Proceeds from Sale of Debt Securities, Available-for-Sale Proceeds from Sale of Debt Securities, Available-for-Sale Debt Securities, Available-for-Sale, Excluding Accrued Interest Debt Securities, Available-for-Sale, Excluding Accrued Interest Preferred stock, par value Preferred Stock, Par or Stated Value Per Share Subsequent Event Subsequent Event [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Depreciation Depreciation Derivative liabilities Derivative Liability, Subject to Master Netting Arrangement, before Offset Gain (Loss) on Derivative Instruments [Member] Gain (Loss) on Derivative Instruments [Member] Equity Components [Axis] Equity Components [Axis] Noncontrolling Interest, Change in Redemption Value Noncontrolling Interest, Change in Redemption Value Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Number of Reportable Segments Number of Reportable Segments Compensation and Employee Benefit Plans Compensation and Employee Benefit Plans [Text Block] Repayments of Debt, Maturing in More than Three Months Repayments of Debt, Maturing in More than Three Months Policyholder Benefits and Claims Incurred, Net Policyholder Benefits and Claims Incurred, Net Entity Address, State or Province Entity Address, State or Province 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] Disposal Group, Including Discontinued Operation, Litigation Recoveries Disposal Group, Including Discontinued Operation, Litigation Recoveries Disposal Group, Including Discontinued Operation, Litigation Recoveries Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic Surety Product Line Surety Product Line [Member] Antidilutive Security, Excluded EPS Calculation [Table] Antidilutive Security, Excluded EPS Calculation [Table] Euro Member Countries, Euro Euro Member Countries, Euro Loans Loans, Estimated fair value Loans Receivable, Fair Value Disclosure Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Discontinued Operation Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Discontinued Operation Individual: Individual [Axis] Income Tax Jurisdiction [Domain] Income Tax Jurisdiction [Domain] Debt Securities, Available for sale, Unrealized Loss Position, Including Pledged Securities Debt Securities, Available for sale, Unrealized Loss Position, Accumulated Loss, Less than 12 Months, Including Pledged Securities Debt Securities, Available for sale, Unrealized Loss Position, Accumulated Loss, Less than 12 Months, Including Pledged Securities Entities [Table] Entities [Table] Reinsurer, Other Reinsurer, Other [Member] Maximum Exposure To Loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Debt Securities , Available for sale, Continuous Unrealized Loss Position, Debt Securities , Available for sale, Continuous Unrealized Loss Position, Debt Securities , Available for sale, Continuous Unrealized Loss Position, Less than 12 Months, Including Pledged Securities Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Redeemable Noncontrolling Interest Redeemable Noncontrolling Interest [Member] Redeemable Noncontrolling Interest Repayments of Long-Term Debt Repayments of Long-Term Debt Subsidiary, Ownership Percentage, Noncontrolling Owner Subsidiary, Ownership Percentage, Noncontrolling Owner Business Combination, Acquisition of Less than 100 Percent, Nonredeemable Noncontrolling Interest, Fair Value Business Combination, Acquisition of Less than 100 Percent, Nonredeemable Noncontrolling Interest, Fair Value Business Combination, Acquisition of Less than 100 Percent, Nonredeemable Noncontrolling Interest, Fair Value Entity Interactive Data Current Entity Interactive Data Current Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] Standard Poors A Plus Plus Rating Standard Poors A Plus Plus Rating Standard Poors A Plus Plus Rating Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Interest Income, Debt Securities, Available-for-Sale, Operating Interest Income, Debt Securities, Available-for-Sale, Operating Beginning premium receivable Ending premium receivable Financial Guarantee Insurance Contracts, Premium Receivable Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Accident & Health Accident & Health Accident & Health Ownership [Domain] Ownership [Domain] Proceeds from (Payments to) Noncontrolling Interests Proceeds from (Payments to) Noncontrolling Interests Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest Entity Central Index Key Entity Central Index Key PEO Name PEO Name Premium Receivable, Allowance for Credit Loss [Table Text Block] Premium Receivable, Allowance for Credit Loss [Table Text Block] Total revenues Revenues Revenues Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Elements [Abstract] Currency Swaps [Member] Currency Swap [Member] Payments to Acquire Interest in Subsidiaries and Affiliates Payments to Acquire Interest in Subsidiaries and Affiliates Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Changes to noncontrolling interest Changes to noncontrolling interest Changes to noncontrolling interest Disposal Group, Including Discontinued Operation, Investment Disposal Group, Including Discontinued Operation, Investment Premiums Written, Net Premiums written, net of reinsurance Premiums Written, Net Premium Receivable, Allowance for Credit Loss Premium Receivable, Allowance for Credit Loss Mortgage-Backed Securities, Other Mortgage-Backed Securities, Other [Member] Class of Warrant or Right, Exercise Price of Warrants or Rights Class of Warrant or Right, Exercise Price of Warrants or Rights Exercise Price Award Exercise Price Other International [Member] Other International [Member] Other international. Entity Filer Category Entity Filer Category Disposal Group, Including Discontinued Operation, Variable Interest Entity Assets Disposal Group, Including Discontinued Operation, Variable Interest Entity Assets Disposal Group, Including Discontinued Operation, Variable Interest Entity Assets Class of Stock [Domain] Class of Stock [Domain] Loss Reserves [Member] Loss Reserves Claim Liability [Member] Loss Reserves Claim Liability [Member] Catastrophic Event [Axis] Subsequent Event Type [Axis] Face Amount (Buy) Long [Member] Uncollateralized Credit Exposure Supoorted by Unlimited Uncapped Indemnity Uncollateralized Credit Exposure Supoorted by Unlimited Uncapped Indemnity Uncollateralized Credit Exposure Supoorted by Unlimited Uncapped Indemnity Disposal Group, Including Discontinued Operation, Consideration Disposal Group, Including Discontinued Operation, Consideration Statement of Financial Position Location, Balance [Axis] Statement of Financial Position Location, Balance [Axis] 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 Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents Public Finance [Member] Public Finance [Member] Public Finance [Member] Finite-Lived Intangible Assets, Gross Finite-Lived Intangible Assets, Gross Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Total expenses Benefits, Losses and Expenses Benefits, Losses and Expenses Entity Address, Address Line One Entity Address, Address Line One AOCI Attributable to Parent [Member] Retained Earnings [Member] AOCI Attributable to Parent [Member] Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Disposal Group, Including Discontinued Operation, Operating Income (Loss) Disposal Group, Including Discontinued Operation, Operating Income (Loss) Investments [Domain] Investments [Domain] Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Redeemable Noncontrolling Interest, Equity, Carrying Amount Redeemable Noncontrolling Interest, Equity, Carrying Amount Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] Discontinued Operation, Tax Effect of Income (Loss) from Discontinued Operation During Phase-out Period Discontinued Operation, Tax Effect of Income (Loss) from Discontinued Operation During Phase-out Period Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] Ownership [Axis] Ownership [Axis] Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Proceeds from sales of other invested assets Proceeds from Sale and Maturity of Other Investments Net Investment Income [Abstract] Net Investment Income [Abstract] Fair Value as of Grant Date Award Grant Date Fair Value Nature of Expense [Axis] Nature of Expense [Axis] NOL allocated amount Operating Loss Carryforwards Labor and Related Expense Labor and Related Expense Type and Tier Identifier [Domain] Type and Tier Identifier [Domain] Document Quarterly Report Document Quarterly Report Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Long-term debt Long-term debt, Estimated fair value Long-Term Debt, Fair Value Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Riverton Riverton [Member] Riverton Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Professional Liability Professional Liability [Member] Professional Liability Other Income or (Loss) [Member] Other Income [Member] Other Income [Member] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Interest Rate Date Change [Axis] Interest Rate Date Change [Axis] Interest Rate Date Change Investment Type [Axis] Investment Type [Axis] Total investments (net of allowance for credit losses of $0 and $0) Investments Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Business Disposal, AAC Accumulated Other Comprehensive Loss Business Disposal, AAC Accumulated Other Comprehensive Loss Business Disposal, AAC Accumulated Other Comprehensive Loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Actuarial gains (losses) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Accumulated Gain (Loss), Financial Liability, Fair Value Option, Including Portion Attributable to Noncontrolling Interest [Member] Accumulated Gain (Loss), Financial Liability, Fair Value Option, Including Portion Attributable to Noncontrolling Interest [Member] Non-PEO NEO Non-PEO NEO [Member] Letters of Credit Outstanding, Amount Letters of Credit Outstanding, Amount General Liability General Liability [Member] Credit Risk Derivatives, at Fair Value, Net [Abstract] Credit Risk Derivatives, at Fair Value, Net [Abstract] Debt Securities, Available-for-sale, Allowance for Credit Loss Debt Securities, Available-for-Sale, Allowance for Credit Loss Position [Domain] Position [Domain] Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Fee Income Fee Income Change in short-term investments Payments for (Proceeds from) Short-Term Investments Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Standard & Poor's, A+ Rating Standard & Poor's, A+ Rating [Member] IA [Member] Surveillance Category Onea [Member] Surveillance Category OneA [Member] Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Capacity Marine Capacity Marine [Member] Capacity Marine Award Type [Domain] Award Type [Domain] Payment for Debt Extinguishment or Debt Prepayment Cost Payment for Debt Extinguishment or Debt Prepayment Cost Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] 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. Discontinued Operations, Disposed of by Sale Discontinued Operations, Disposed of by Sale [Member] Compensation Amount Outstanding Recovery Compensation Amount Debt Securities Available for Sale Unrealized Loss Measured as a Percent of Amortized Cost Debt Securities Available for Sale Unrealized Loss Measured as a Percent of Amortized Cost Debt Securities Available for Sale Unrealized Loss Measured as a Percent of Amortized Cost Derivative Financial Instruments, Liabilities [Member] Derivative Financial Instruments, Liabilities [Member] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Unsecured Reinsurance Recoverables Unsecured Reinsurance Recoverables Represents reinsurance recoverables on paid and unpaid losses and deferred ceded premiums, net of ceded premiums payables due to reinsurers, letters of credit, and collateral posted for the benefit of the cedant. 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] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Contract with Customer, Liability, Revenue Recognized Contract with Customer, Liability, Revenue Recognized Total Fair Value [Member] Estimate of Fair Value Measurement [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Reporting Unit [Domain] Reporting Unit [Domain] Hedge Funds, Multi-strategy [Member] Hedge Funds, Multi-strategy [Member] Schedule of Investments [Line Items] Investment [Line Items] Schedule of Investments [Line Items] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Derivative Asset, Fair Value, Amount Not Offset Against Collateral Derivative Asset, Subject to Master Netting Arrangement, before Offset of Collateral Amortized Cost, Due after one year through five years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Insurance Linked [Member] Insurance Linked [Member] Insurance Linked [Member] [Member] Schedule Of Earnings Per Share [Line Items] Schedule Of Earnings Per Share [Line Items] Schedule Of Earnings Per Share [Line Items] Revenues: Revenues [Abstract] Number of Reinsurers Covering Majority Number of Reinsurers Covering Majority Number of Reinsurers Covering Majority Amortized Cost, Due after five years through ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 EBITDA EBITDA EBITDA Loan Origination Commitments [Member] Loans [Member] Loan Origination Commitments [Member] Accumulated other comprehensive income Beginning Balance Ending Balance Accumulated Other Comprehensive Income (Loss), Net of Tax Financial Instruments [Domain] Financial Instruments [Domain] Disposal Group, Including Discontinued Operation, Restricted Cash Disposal Group, Including Discontinued Operation, Restricted Cash Disposal Group, Including Discontinued Operation, Restricted Cash Determination Date [Domain] Determination Date [Domain] [Domain] for Determination Date [Axis] Provision for Income Taxes [Table] Provision for Income Taxes [Table] Provision for Income Taxes [Table] Performance Shares [Member] Performance Shares [Member] Disposal Group, Including Discontinued Operation, Reclassification From AOCI At Closing Disposal Group, Including Discontinued Operation, Reclassification From AOCI At Closing Disposal Group, Including Discontinued Operation, Reclassification From AOCI At Closing Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Investment [Line Items] Net Investment Income [Line Items] Postemployment Benefits [Abstract] Property Property [Member] Property Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Minimum [Member] Minimum [Member] Business Disposal, Life of Warrants Issued in Connection with AAC Disposal Business Disposal, Life of Warrants Issued in Connection with AAC Disposal Business Disposal, Life of Warrants Issued in Connection with AAC Disposal Disposal Group, Including Discontinued Operation, Other Assets Disposal Group, Including Discontinued Operation, Other Assets Company Selected Measure Name Company Selected Measure Name US Government Debt Securities [Member] US Government Debt Securities [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Niche Specialty Risk Niche Specialty Risk Niche Specialty Risk Other Structured Finance [Member] Other Structured Finance [Member] Other Structured Finance [Member] Debt Disclosure Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Collateral [Domain] Collateral Held [Domain] Noncontrolling Interest Policy Noncontrolling Interest Policy [Policy Text Block] Noncontrolling Interest Policy Current Foreign Tax Expense (Benefit) Current Foreign Tax Expense (Benefit) Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Disposal Group, Including Discontinued Operation, Revenue Disposal Group, Including Discontinued Operation, Revenue Weighted Average Number of Shares Outstanding, Diluted Weighted average number of common shares and potential dilutive shares used for diluted earnings per share Weighted Average Number of Shares Outstanding, Diluted Segment Reporting, Policy Segment Reporting, Policy [Policy Text Block] Specialty Property And Casualty Insurance Specialty Property And Casualty Insurance [Member] Specialty Property And Casualty Insurance Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Derivative [Table] Derivative [Table] Investments, Equity Interest Percent Investments, Equity Interest Percent Investments, Equity Interest Percent Disposal Group, Including Discontinued Operation, Prepaid Reinsurance Premiums Disposal Group, Including Discontinued Operation, Prepaid Reinsurance Premiums Disposal Group, Including Discontinued Operation, Prepaid Reinsurance Premiums Entity Small Business Entity Small Business Business Combination, Voting Equity Interest Acquired, Percentage Business Combination, Voting Equity Interest Acquired, Percentage Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Other Cost and Expense, Operating Other Cost and Expense, Operating Business Combination, Acquisition of Less than 100 Percent, Nonredeemable Business Combination, Acquisition of Less than 100 Percent, Nonredeemable Business Combination, Acquisition of Less than 100 Percent, Nonredeemable Noncontrolling Interest, Fair Value Schedule of Income Before Income Tax, Domestic and Foreign [Line Items] Schedule of Income Before Income Tax, Domestic and Foreign [Line Items] [Line Items] for Schedule of Income Before Income Tax, Domestic and Foreign [Table] Weighted-Average Remaining Term (years) Derivative, Average Remaining Maturity Preferred Stock, Shares Outstanding Preferred Stock, Shares Outstanding Securities acquired (transferred) in connection with financial guarantee commutations Securities acquired (transferred) in connection with financial guarantee commutations Securities acquired (transferred) in connection with financial guarantee commutations Current State and Local Tax Expense (Benefit) Current State and Local Tax Expense (Benefit) Long-Term Debt Long-Term Debt [Text Block] Entity Ex Transition Period Document Transition Report Derivative Liabilities Net Amount Derivative Liabilities Net Amount Derivative Liabilities Net Amount Estimated Fair Value, Due after one year through five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Long-term Debt [Member] Long-term Debt [Member] Long-Term Debt [Member] Underlying Securities Award Underlying Securities Amount Debt Securities, Available-for-sale, Realized Gain Debt Securities, Available-for-Sale, Realized Gain Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document and Entity Information [Abstract] Income Taxes Income Tax Disclosure [Text Block] Marine Marine [Member] Marine Business Disposal, Termination Fee Business Disposal, Termination Fee Business Disposal, Termination Fee United Kingdom [Member] UNITED KINGDOM Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Net liability fair value of all derivative instruments linked to Ambac's own credit risk Derivative, Net Liability Position, Aggregate Fair Value Schedule of Investments [Table] Schedule of Investments [Table] Derivative Asset, Fair Value, Amount Offset Against Collateral Derivative Asset, Including Not Subject to Master Netting Arrangement, after Offset and Deduction Total stockholders’ equity Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Equity, Including Portion Attributable to Noncontrolling Interest Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member] Interest Rate Swap One [Member] Interest rate swap one. Shares Acquired, Average Cost Per Share Shares Acquired, Average Cost Per Share Document Type Document Type Other assets Equity Method Investments, Fair Value Disclosure Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Net Income Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Additional paid-in capital Additional Paid in Capital Product and Service [Axis] Product and Service [Axis] Ceded Credit Risk, Reinsurer [Domain] Reinsurer, Name [Domain] Revenue from Contract with Customer, Excluding Assessed Tax Revenue from Contract with Customer, Excluding Assessed Tax 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. Assumed Reinsurance Premiums Earned Assumed Premiums Earned Investment Income [Table] Investment Income [Table] Gross insured contractual payments outstanding: Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Professional Liability Insurance Professional Liability Insurance [Member] Xchange Xchange [Member] Xchange Share Repurchase Program, Authorized, Amount Share Repurchase Program, Authorized, Amount Gain (Loss) on Investments [Member] Gain (Loss) on Investments [Member] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Disposal Group Name [Axis] Disposal Group Name [Axis] Tax payments related to shares withheld for share-based compensation plans Payment, Tax Withholding, Share-Based Payment Arrangement Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Net Income (Loss) Available to Common Stockholders, Basic Net of tax and noncontrolling interest Net Income (Loss) Available to Common Stockholders, Basic Interest Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding, Interest Entity Information [Line Items] Entity Information [Line Items] Disposal Group, Including Discontinued Operation, Operating Income (Loss) Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Disposal Group, Including Discontinued Operation, Reinsurance Payable Disposal Group, Including Discontinued Operation, Reinsurance Payable Disposal Group, Including Discontinued Operation, Reinsurance Payable Premium receipts Financial Guarantee Insurance Contracts, Premium Receivable, Proceeds from Premiums Received Other Investment Not Readily Marketable, Fair Value Other Investment Not Readily Marketable, Fair Value Earnings Per Share, Diluted Earnings Per Share, Diluted Non-standard Personal Auto Non-standard Personal Auto [Member] Non-standard Personal Auto Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Estimated Fair Value, Due after five years through ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 IV [Member] Surveillance Category Four [Member] Surveillance category four. Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Treasury Stock, Common, Shares Treasury Stock, Common, Shares Background and Business Description Business Description and Basis of Presentation [Text Block] Consolidation Items [Domain] Consolidation Items [Domain] Postemployment Benefits, Period Expense Postemployment Benefits, Period Expense Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Debt Security Category [Axis] Debt Security Category [Axis] Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Ceded Credit Risk, Reinsurer [Axis] Reinsurer, Name [Axis] Disposal Group, Including Discontinued Operation, Estimated Closing Costs Disposal Group, Including Discontinued Operation, Estimated Closing Costs Disposal Group, Including Discontinued Operation, Estimated Closing Costs Disposal Group, Including Discontinued Operation, Amortization Disposal Group, Including Discontinued Operation, Amortization Disposal Group, Including Discontinued Operation, Amortization Debt Securities, Available-for-Sale, Current Debt Securities, Available-for-Sale, Current Reinsurance Recoverables, Including Reinsurance Premium Paid Reinsurance Recoverables, Including Reinsurance Premium Paid Domestic Tax Jurisdiction [Member] Domestic Tax Jurisdiction [Member] Disposal Group, Including Discontinued Operation, Intangible Assets Disposal Group, Including Discontinued Operation, Intangible Assets Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] PWIC PWIC [Member] PWIC NONREDEMABLE NONCONTROLLING INTEREST NONREDEMABLE NONCONTROLLING INTEREST [Member] NONREDEMABLE NONCONTROLLING INTEREST Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Number Of Consolidated Variable Interest Entities Number Of Consolidated Variable Interest Entities Number of consolidated variable interest entities. Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Trade Names Trade Names [Member] Reportable Geographical Components [Member] Reportable Geographical Components [Member] Coupon rate Fair Value Inputs Coupon Rate Fair Value Inputs Coupon Rate Fair value inputs coupon rate. Expiration Date Trading Arrangement Expiration Date Other Commitments [Domain] Other Commitments [Domain] Schedule of Foreign Exchange Contracts, Statement of Financial Position Schedule of Foreign Exchange Contracts, Statement of Financial Position [Table Text Block] 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. 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] Stockholders’ equity: Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Foreign Obligations [Member] Debt Security, Government, Non-US [Member] Debt Security, Government, Non-US [Member] Fixed Income Securities [Member] Fixed Income Securities [Member] Business Combination, Volume Weighted Average Price Business Combination, Volume Weighted Average Price Business Combination, Volume Weighted Average Price Global Structured Finance [Member] Global Structured Finance [Member] Global structured finance. Equity Method Investments [Table Text Block] Equity Method Investments [Table Text Block] Other Investments [Member] Other Investments [Member] Investments [Member] Investments [Member] Disposal Group, Including Discontinued Operation, Realized Investment Gains (Losses) Disposal Group, Including Discontinued Operation, Realized Investment Gains (Losses) Disposal Group, Including Discontinued Operation, Realized Investment Gains (Losses) Ceded Reinsurance Premiums Written Ceded Premiums Written Ceded Premiums Written Schedule of Income Before Income Tax, Domestic and Foreign [Table] Schedule of Income Before Income Tax, Domestic and Foreign [Table] Schedule of Income Before Income Tax, Domestic and Foreign [Table] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Loss 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. Business Combination, Consideration Paid in Cash Business Combination, Consideration Paid in Cash Business Combination, Consideration Paid in Cash Entity Current Reporting Status Entity Current Reporting Status Fair Value of Securities Deposited in Connection wtih Letter of Credit Fair Value of Securities Deposited in Connection wtih Letter of Credit Fair Value of Securities Deposited in Connection wtih Letter of Credit Derivative [Line Items] Derivative [Line Items] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Tier 2 Notes Tier 2 Notes [Member] Tier 2 Notes Collateral [Axis] Collateral Held [Axis] Business Disposal, Warrant Strike Price in Connection with Disposal Business Disposal, Warrant Strike Price in Connection with Disposal Business Disposal, Warrant Strike Price in Connection with Disposal Consolidated Entities [Domain] Variable Interest Entity, Classification [Domain] Consolidated Entities [Domain] Amortized Cost, Due in one year or less Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One Specialty Automobile Specialty Automobile Specialty Automobile Interest Rate Date Change [Domain] Interest Rate Date Change [Domain] Interest Rate Date Change [Domain] Transaction [Domain] Transaction [Domain] Corporate Segment Corporate Segment [Member] Insurance [Line Items] Insurance [Line Items] Insurance [Line Items] Financial Instrument [Axis] Financial Instrument [Axis] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Executive Category: Executive Category [Axis] Foreign Exchange Forward Foreign Exchange Forward [Member] Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Business Disposal, Percent of Common Shares Issued in Connection with Disposal Business Disposal, Percent of Common Shares Issued in Connection with Disposal Business Disposal, Percent of Common Shares Issued in Connection with Disposal Octave Ventures Octave Ventures [Member] Octave Ventures Other Operating Income (Expense), Net Other Operating Income (Expense), Net Fixed Income Securities, Trading Fixed Income Securities, Trading [Member] Fixed Income Securities, Trading Interest Expense, Operating and Nonoperating Interest Expense, Operating and Nonoperating Current Fiscal Year End Date Current Fiscal Year End Date Loss And Loss Adjustment Expense Reserves [Line Items] Loss And Loss Adjustment Expense Reserves [Line Items] Loss And Loss Adjustment Expense Reserves [Line Items] Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Workers' Compensation Insurance Workers' Compensation Insurance [Member] Ceded premiums payable Increase (Decrease) in Reinsurance Payables Claim and loss expense (payments) recoveries, net of subrogation and reinsurance Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Derivative Liability Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities Derivative Liability Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax Prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest Interest Rate Contract [Member] Interest Rate Contract [Member] Other Insurance Contracts Other Insurance Contracts [Member] Other Insurance Contracts Noncontrolling Interest Disclosure Noncontrolling Interest Disclosure [Text Block] Disposal Group, Including Discontinued Operation, Operating Expense Disposal Group, Including Discontinued Operation, Operating Expense Unallocated Loss Adjustment Expense Reserve Unallocated Loss Adjustment Expense Reserve [Member] Unallocated Loss Adjustment Expense Reserve 6351 Surety Insurance 6351 Surety Insurance [Member] Receivables, Net, Current Receivables, Net, Current Stock Issued During Period, Value, Acquisitions Stock Issued During Period, Value, Acquisitions OCTAVE EBITDA OCTAVE EBITDA OCTAVE EBITDA Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 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] Reclassification from nonredeemable noncontrolling interest including remeasurement at fair value Reclassification from nonredeemable noncontrolling interest including remeasurement at fair value Reclassification from nonredeemable noncontrolling interest including remeasurement at fair value Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value Collateral Pledged [Member] Collateral Pledged [Member] Other Property Other Property [Member] Financial Guarantee Financial Guarantee [Member] Debt Securities, Available-for-sale, Allowance for Credit Loss, Not to Sell before Recovery, Credit Loss, Previously Recorded, Expense (Reversal) Debt Securities, Available-for-Sale, Allowance for Credit Loss, Not to Sell before Recovery, Credit Loss, Previously Recorded, Expense (Reversal) External Credit Rating, Investment Grade External Credit Rating, Investment Grade [Member] Measure: Measure [Axis] Other Professional Other Professional [Member] Other Professional Credit Rating, Moody's [Axis] Credit Rating, Moody's [Axis] Share Repurchase Program, Remaining Authorized, Amount Share Repurchase Program, Remaining Authorized, Amount Securities Financing Transaction [Axis] Securities Financing Transaction [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Net Investment Income [Member] Investment Income [Member] Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Present Value of Expected Net Cash Flows-Recoveries [Member] Present Value of Expected Net Cash Flows-Recoveries [Member] Recoveries [Member] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Numerator of basic and diluted EPS Numerator of basic and diluted EPS Numerator of basic and diluted EPS Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Investment expense Investment Income, Investment Expense Entity Tax Identification Number Entity Tax Identification Number United Kingdom, Pounds United Kingdom, Pounds Face Amount (Sell) Short [Member] Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share Schedule of Weighted Average Number of Shares [Table Text Block] Common stock, shares issued Common Stock, Shares, Issued Number of Variable Interest Entities Consolidated During the Period Number of Variable Interest Entities Consolidated During the Period Number of Variable Interest Entities Consolidated During the Period Commercial Mortgage Backed Securities [Member] Commercial Mortgage-Backed Securities [Member] Summary of Location and Amount of Gains and Losses of Derivative Contracts Derivatives Not Designated as Hedging Instruments [Table Text Block] Financial Guarantee Insurance Contracts, Premium Received over Contract Period Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Table Text Block] Goodwill and Intangible Assets Disclosure Goodwill and Intangible Assets Disclosure [Text Block] Percentage of Ceded Reinsurance Recoverable Represented by Top Three Percentage of Ceded Reinsurance Recoverable Represented by Top Three Percentage of Ceded Reinsurance Recoverable Represented by Top Three 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. Schedule of Goodwill Schedule of Goodwill [Table Text Block] Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Unearned Premium Reserve [Member] Unearned Premium Reserve [Member] Unearned Premium Reserve [Member] 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] Segment Reporting, Reconciling Item, Corporate Nonsegment Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Security Exchange Name Security Exchange Name Interim Period, Costs Not Allocable [Domain] Interim Period, Costs Not Allocable [Domain] Reinsurance Recoverable, Allowance for Credit Loss Reinsurance Recoverable, Allowance for Credit Loss Ambac UK [Member] Ambac Uk [Member] Ambac UK [Member] Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Discontinued Operation Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Discontinued Operation Collateralized Mortgage Backed Securities [Member] Collateralized Mortgage-Backed Securities [Member] I/SL [Member] Surveillance Category One [Member] Surveillance Category One [Member] Business Combination, Consideration Transferred, Equity Interest, Type [Domain] Business Combination, Consideration Transferred, Equity Interest, Type [Domain] Ceded Reinsurance Premiums Earned Ceded Premiums Earned Financial Guarantee Insurance Contracts, Claim Liability [Line Items] Financial Guarantee Insurance Contracts, Claim Liability [Line Items] Expenses: Operating Expenses [Abstract] Reduction in VIE Long-term DEbt Due to Deconsolidation Reduction in VIE Long-term DEbt Due to Deconsolidation Reduction in VIE Long-term DEbt Due to Deconsolidation Asset Class [Domain] Asset Class [Domain] 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 Foreign Currency [Abstract] Foreign Currency [Abstract] Disposal Group, Including Discontinued Operation, Other Expense Disposal Group, Including Discontinued Operation, Other Expense Statement [Line Items] Statement [Line Items] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Securities Financing Transaction [Domain] Securities Financing Transaction [Domain] Cash and Cash Equivalent Cash and Cash Equivalent Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Reclassification to nonredeemable noncontrolling interest Reclassification to nonredeemable noncontrolling interest Reclassification to nonredeemable noncontrolling interest Increase (Decrease) in Deferred Income Taxes Increase (Decrease) in Deferred Income Taxes Common Stock [Member] Common Stock [Member] Sovereign And Sub Sovereign [Member] Sovereign And Sub Sovereign [Member] Sovereign And Sub Sovereign [Member] Principal Amount Outstanding of Loans Held-in-portfolio Loan, Held-in-Portfolio, Principal Outstanding Effect of potential dilutive shares Weighted Average Number Diluted Shares Outstanding Adjustment Weighted Average Number of Shares Outstanding, Diluted, Adjustment Disposal Group, Including Discontinued Operation, Valuation Allowance On Assets Held-For-Sale Disposal Group, Including Discontinued Operation, Valuation Allowance On Assets Held-For-Sale Disposal Group, Including Discontinued Operation, Valuation Allowance On Assets Held-For-Sale Statistical Measurement [Domain] Statistical Measurement [Domain] Underlying Asset Class [Axis] Underlying Asset Class [Axis] Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Number of policies Schedule of Insured Financial Obligations with Credit Deterioration, Number of Contracts Issued and Outstanding Ambac Assurance Corporation [Member] Ambac Assurance Corporation [Member] Ambac assurance corporation. Prior Year Claims and Claims Adjustment Expense Prior Year Claims and Claims Adjustment Expense Reinsurance Recoverable, Gross, All Other Reinsurance Recoverable, Gross, All Other Reinsurance Recoverable, Gross, All Other Assured Guaranty Re Ltd Assured Guaranty Re Ltd [Member] Assured Guaranty Re Ltd [Member] Intangible Assets, Gross (Excluding Goodwill) Intangible Assets, Gross (Excluding Goodwill) Asset Class [Axis] Asset Class [Axis] Interest Rate Swap [Member] Interest Rate Swap [Member] Balance at beginning Balance at end Other-than-Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Contract with Customer, Performance Obligation Satisfied in Previous Period Contract with Customer, Performance Obligation Satisfied in Previous Period Unearned premiums Unearned Premiums AFS [Member] Afs [Member] AFS. Niche Specialty Risks Niche Specialty Risks Niche Specialty Risks Surety Surety [Member] Surety Claim liability reported on Balance Sheet, before reinsurance Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Claim Liability Pledged Status [Axis] Pledged Status [Axis] Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net, After Allowance For Closing Costs Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net, After Allowance For Closing Costs Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net, After Allowance For Closing Costs Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Class of Warrant or Right, Outstanding Class of Warrant or Right, Outstanding Earnings Per Share, Basic Earnings Per Share, Basic Earnings Per Share, Basic Net cash provided by (used in) financing activities from continuing operations Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Cash Provided by (Used in) Financing Activity, Continuing Operation Provision for Income Taxes [Line Items] Provision for Income Taxes [Line Items] [Line Items] for Provision for Income Taxes [Table] Business Disposal, Carrying Value of AAC Business Disposal, Carrying Value of AAC Business Disposal, Carrying Value of AAC Total other comprehensive income (loss), net of income tax Other Comprehensive Income (Loss), Net of Tax Average Percentage of Unrealized Loss Versus Amortized Cost for Investment Grade Securities Average Percentage of Unrealized Loss Versus Amortized Cost for Investment Grade Securities Average Percentage of Unrealized Loss Versus Amortized Cost for Investment Grade Securities Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Short-Term Debt Short-Term Debt II [Member] Surveillance Category Two [Member] Surveillance category two. Investment Contracts [Member] Investment Contracts [Member] Investment Contracts [Member] Insurance Commissions and Fees Insurance Commissions and Fees Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Cash and Cash Equivalents Cash and Cash Equivalents [Member] Disposal Group, Including Discontinued Operation, Subrogation Recoverable Disposal Group, Including Discontinued Operation, Subrogation Recoverable Disposal Group, Including Discontinued Operation, Subrogation Recoverable Employer Stop Loss Employer Stop Loss [Member] Employer Stop Loss FX Forwards-Buy GBP/Sell USD FX Forward Buy GBP Sell USD [Member] FX Forward Buy GBP Sell USD Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Average Percentage of Unrealized Loss Versus Amortized Cost for Below Investment Grade Securities Average Percentage of Unrealized Loss Versus Amortized Cost for Below Investment Grade Securities Average Percentage of Unrealized Loss Versus Amortized Cost for Below Investment Grade Securities Stock-based compensation Share-Based Payment Arrangement, Expense Hedging Designation [Domain] Hedging Designation [Domain] Total Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding Goodwill and Intangible Assets Disclosure [Abstract] Stock and Warrants Issued During Period, Value, Preferred Stock and Warrants Stock and Warrants Issued During Period, Value, Preferred Stock and Warrants Total liabilities and stockholders’ equity Liabilities and Equity Standard & Poor's, AA Rating Standard & Poor's, AA Rating [Member] Long term debt Quarterly Amortization Percent for Five Years Long term debt Quarterly Amortization Percent for Five Years Long term debt Quarterly Amortization Percent for Five Years Foreign Currency Transactions and Translations Policy [Policy Text Block] Foreign Currency Transactions and Translations Policy [Policy Text Block] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Deferred Policy Acquisition Cost Deferred Policy Acquisition Cost International Finance [Member] International Finance [Member] International Finance [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Equity Method Investment [Table] Equity Method Investment [Table] Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, before Tax, after Reclassification Adjustment Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, before Tax High Yield Fund High Yield Fund [Member] High Yield Fund Gross claim liability before all subrogation and before reinsurance Schedule of Insured Financial Obligations with Credit Deterioration, Gross Claim Liability Accounting Policies [Abstract] Accounting Policies [Abstract] Loss and Loss Reserves [Axis] Loss and Loss Reserves [Axis] Loss and Loss Reserves [Axis] Business Combination, Total Consideration Business Combination, Total Consideration Business Combination, Total Consideration Revenue Recognition and Deferred Revenue [Abstract] 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. Repayments of Secured Debt Repayments of Secured Debt Repayments of Secured Debt Securities acquired (transferred) in transactions related to Puerto Rico restructurings Securities acquired (transferred) in transactions related to Puerto Rico restructurings Securities acquired (transferred) in transactions related to Puerto Rico restructurings Purchases of other investments Payments to Acquire Other Investments Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease) Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease) Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Total before tax Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Treasury Stock, Common Treasury Stock, Common [Member] General Reinsurance Company General Reinsurance Company [Member] General Reinsurance Company Number of Businesses Owned Number of Businesses Owned Number of Businesses Owned Pay vs Performance Disclosure [Line Items] Collateralized Debt Obligations [Member] Collateralized Debt Obligations [Member] Unearned premiums, net Increase (Decrease) in Unearned Premiums Effects of Reinsurance [Table] Effects of Reinsurance [Table] Liabilities: Liabilities [Abstract] Investment Holdings [Table] Investment Holdings [Table] Business Combination Business Combination [Text Block] SOFR + Credit Agreement SOFR + Credit Agreement [Member] SOFR + Credit Agreement Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) Gain (loss) on foreign currency translation, taxes OCI, Foreign Currency Transaction and Translation Gain (Loss), Arising During Period, Tax 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] Goodwill, Impairment Loss Goodwill, Impairment Loss Other than Temporary Impairment Losses, Investments Other than Temporary Impairment Losses, Investments Variable Interest Entity [Table] Variable Interest Entity [Table] Payments for Repurchase of Redeemable Noncontrolling Interest Payments for Repurchase of Redeemable Noncontrolling Interest Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Total comprehensive income (loss) attributable to shareholders Total net income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Disposal Group Name [Domain] Disposal Group Name [Domain] Name Measure Name Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Estimated Fair Value, Due in one year or less Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Proceeds from matured bonds Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale Operating Loss Carryforwards, Expiration Date Operating Loss Carryforwards, Expiration Date Deferred Income Tax Liabilities, Net Deferred Income Tax Liabilities, Net Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Assumed Reinsurance Premiums Written Assumed Premiums Written Property and Casualty, Commercial Insurance Property and Casualty, Commercial Insurance [Member] Discontinued Operation, Additional Consideration Discontinued Operation, Additional Consideration Discontinued Operation, Additional Consideration Revision of Prior Period, Adjustment Revision of Prior Period, Adjustment [Member] Long-term debt Long-term Debt Long-Term Debt Legal Entity [Axis] Legal Entity [Axis] Total assets Assets Business Combination, FX Forward Rate Lock Business Combination, FX Forward Rate Lock Business Combination, FX Forward Rate Lock Geographical [Domain] Geographical [Domain] Credit Derivatives Contract Type [Axis] Credit Derivatives Contract Type [Axis] QBE Insurance Corporation QBE Insurance Corporation [Member] QBE Insurance Corporation Debt Instrument, Convertible, Type of Equity Security Debt Instrument, Convertible, Type of Equity Security External Credit Rating by Grouping [Domain] External Credit Rating by Grouping [Domain] Cash flows from operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Directors and Officers Liability Insurance Directors and Officers Liability Insurance [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] Private Equity Funds [Member] Private Equity Funds [Member] Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect Variable Interest Entity [Line Items] Variable Interest Entities [Line Items] Variable Interest Entity [Line Items] Warrants [Member] Warrant [Member] Other investments Other Investments Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Debt Securities, Available for sale, Unrealized Loss Position, Accumulated Loss, Including Pledged Securities Debt Securities, Available for sale, Unrealized Loss Position, Accumulated Loss, Including Pledged Securities Debt Securities, Available for sale, Unrealized Loss Position, Accumulated Loss, Including Pledged Securities Capitalized Contract Cost, Net Capitalized Contract Cost, Net Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Environmental Environmental [Member] Environmental Deferred ceded premium Prepaid Reinsurance Premiums Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Allowance for Doubtful Accounts, Premiums and Other Receivables Allowance for Doubtful Accounts, Premiums and Other Receivables Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Specialty Property & Casualty Program Specialty Property & Casualty Program [Member] Specialty Property & Casualty Program Asset Pledged as Collateral [Member] Asset Pledged as Collateral [Member] Schedule of Components of Income Tax Expense (Benefit) Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] PEO PEO [Member] 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] Pretax income (loss) from continuing operations Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest United States [Member] UNITED STATES Reinsurance Recoverables, Gross Reinsurance Recoverables, Gross Corporate Segment and Other Operating Segment Corporate Segment and Other Operating Segment [Member] Other Comprehensive Income (losss) Net of Tax Portion Attributable to Noncontrolling Interest EBITDA Adjusted Other Comprehensive Income (losss) Net of Tax Portion Attributable to Noncontrolling Interest EBITDA Adjusted Other Comprehensive Income (Loss) Net of Tax Portion Attributable to Noncontrolling Interest EBITDA Adjusted Retained Earnings [Member] Retained Earnings [Member] Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Income Tax Jurisdiction [Axis] Income Tax Jurisdiction [Axis] Income Statement [Abstract] Income Statement [Abstract] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Derivative Asset Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets Derivative Asset Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Disposal Group, Including Discontinued Operation, Premiums Earned, Net Disposal Group, Including Discontinued Operation, Premiums Earned, Net Disposal Group, Including Discontinued Operation, Premiums Earned, Net Interest Expense Interest Expense [Member] Disposal Group, Including Discontinued Operation, Other Revenue Disposal Group, Including Discontinued Operation, Other Revenue Disposal Group, Including Discontinued Operation, Other Revenue Accrued interest payable Increase (Decrease) in Interest Payable, Net Intangible assets, less accumulated amortization Intangible Assets, Net (Excluding Goodwill) DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss, including pledged securities DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss, including pledged securities DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss, including pledged securities ComprehensiveIncomeNetOfTaxLess NCI ComprehensiveIncomeNetOfTaxLess NCI ComprehensiveIncomeNetOfTaxLess NCI Product and Service [Domain] Product and Service [Domain] Student Loans [Member] Student Loans [Member] Student Loans [Member] Standard & Poor's, B Rating [Member] Standard & Poor's, B Rating [Member] V [Member] Surveillance Category Five [Member] Surveillance category five. Income (Loss) from Continuing Operations, Per Diluted Share Income (Loss) from Continuing Operations, Per Diluted Share Investment income Net Investment Income Net Investment Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Total financial liabilities Liabilities, Fair Value Disclosure Notional outstanding Derivative products, Notional Amount Derivative, Notional Amount Business Combination, Consideration Transferred, Equity Interest, Type [Axis] Business Combination, Consideration Transferred, Equity Interest, Type [Axis] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Business Disposal, Cash Expected to be Received Business Disposal, Cash Expected to be Received Business Disposal, Cash Expected to be Received Business Combination, Recognized Asset Acquired and Liability Assumed Business Combination, Recognized Asset Acquired and Liability Assumed [Table Text Block] Disposal Group, Including Discontinued Operation, Premiums Receivable, Net Disposal Group, Including Discontinued Operation, Premiums Receivable, Net Disposal Group, Including Discontinued Operation, Premiums Receivable, Net City Area Code City Area Code Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward] Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Net Income Loss Reconciliation [Line Items] Net Income Loss Reconciliation [Line Items] Net Income Loss Reconciliation [Line Items] Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member] Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member] Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax Premiums Receivable by Risk Classification Code [Table Text Block] Premiums Receivable by Risk Classification Code [Table Text Block] Premiums Receivable by Risk Classification Code [Table Text Block] Debt Securities, Trading, and Equity Securities, FV-NI [Table] Debt Securities, Trading, and Equity Securities, FV-NI [Table] Cash Provided by (Used in) Investing Activity, Discontinued Operation Cash Provided by (Used in) Investing Activity, Discontinued Operation Foreign Exchange Future Foreign Exchange Future [Member] Contract with Customer, Contract Asset, Contract Liability, and Receivable Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] General and Administrative Expense General and Administrative Expense Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Other Consumer Asset-Backed [Member] Other Consumer Asset Backed [Member] Other consumer asset-backed. Standard & Poor's, A Rating Standard & Poor's, A Rating [Member] Interest Receivable Interest Receivable Changes In Accumulated Other Comprehensive Income [Roll Forward] Changes In Accumulated Other Comprehensive Income [Roll Forward] Changes In Accumulated Other Comprehensive Income [Roll Forward] 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. Other liabilities Other Liabilities Other Liabilities Goodwill Goodwill Claim and loss expense payments, net of subrogation and reinsurance Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Equity Securities Excluded From Fair Value Equity Securities Excluded From Fair Value [Member] Equity Securities Excluded From Fair Value Deferred Federal Income Tax Expense (Benefit) Deferred Federal Income Tax Expense (Benefit) Equity investments in pooled funds [Member] Equity investments in pooled funds [Member] Equity investments in pooled funds [Member] Consolidated Entities [Member] Consolidated Entities [Member] Cash Provided by (Used in) Financing Activity, Discontinued Operation Cash Provided by (Used in) Financing Activity, Discontinued Operation Estimated Fair Value due, Total Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value Schedule of Cash Flow Supplemental Information [Axis] Schedule of Cash Flow Supplemental Information [Axis] Schedule of Cash Flow Supplemental Information [Axis] Other Public Finance Sectors [Member] Other Public Finance Sectors [Member] Other Public Finance Sectors [Member] 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. Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Warrants and Rights Outstanding, Term Warrants and Rights Outstanding, Term Debt Securities, Available-for-sale, Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost Other Performance Measure, Amount Other Performance Measure, Amount US Treasury and Government US Treasury and Government [Member] Debt, Current Debt, Current Standard & Poors, No Rating Standard & Poors, No Rating [Member] Standard & Poors, No Rating Real Estate [Member] Real Estate [Member] Class Of Warrant Or Right, Number Of Securities Called By Warrants Or Rights, Percentage Of Fully Diluted Shares Of Common Stock Class Of Warrant Or Right, Number Of Securities Called By Warrants Or Rights, Percentage Of Fully Diluted Shares Of Common Stock Class Of Warrant Or Right, Number Of Securities Called By Warrants Or Rights, Percentage Of Fully Diluted Shares Of Common Stock 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. Derivative Instrument [Axis] Derivative, by Nature [Axis] Derivative Instrument [Axis] Restricted Cash Restricted Cash Financial liabilities: Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Payable for Redeemable Noncontrolling Interest Payable for Redeemable Noncontrolling Interest Payable for Redeemable Noncontrolling Interest Entity [Domain] Entity [Domain] Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Document Fiscal Year Focus Document Fiscal Year Focus Effects of Reinsurance Effects of Reinsurance [Table Text Block] Credit Risk Changes of Fair Value, Net Loss on Discontinued Operation Credit Risk Changes of Fair Value, Net Loss on Discontinued Operation Credit Risk Changes of Fair Value, Net Loss on Discontinued Operation Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount Accrued Liabilities for Commissions, Expense and Taxes Accrued Liabilities for Commissions, Expense and Taxes Reported Value Measurement [Member] Priced Through Pricing Vendors [Member] Reported Value Measurement [Member] Equity [Abstract] Equity [Abstract] Cash Provided by (Used in) Continuing Operation Cash Provided by (Used in) Continuing Operation Segment Reporting Disclosure Segment Reporting Disclosure [Text Block] Trademarks Trademarks [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Securities fair value Fair Value Of Securities Deposited With Governmental Authorities Fair Value Of Securities Deposited With Governmental Authorities Fair value of securities deposited with governmental authorities. Schedule of Cash Flow Supplemental Information [Domain] Schedule of Cash Flow Supplemental Information [Domain] [Domain] for Schedule of Cash Flow Supplemental Information [Axis] Other Debt Obligations [Member] Other [Member] Other Debt Obligations [Member] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Intangible amortization Amortization of Intangible Assets Amortization of Intangible Assets Loans Receivable [Member] Loans Receivable [Member] Restricted Cash and Cash Equivalent, Current Restricted Cash and Cash Equivalent, Current Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Depreciation, Depletion and Amortization Depreciation, Depletion and Amortization Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic Fixed Income Investments [Member] Fixed Income Investments [Member] Cash collateral payable Cash collateral payable Cash collateral payable Nonredeemable Noncontrolling Interest Nonredeemable Noncontrolling Interest [Member] Nonredeemable Noncontrolling Interest Residential Mortgage-Backed Securities [Member] Residential Mortgage-Backed Securities [Member] Revolving Credit Facility Revolving Credit Facility [Member] Adjustments for Change in Accounting Principle [Axis] Change in Accounting Principle, Type [Axis] Direct Premiums Written Direct Premiums Written Arrangement Duration Trading Arrangement Duration Other Credit Derivatives [Member] Other Derivatives [Member] Other Credit Derivatives [Member] Equity Method Investments Excluded From Fair Value Equity Method Investments Excluded From Fair Value Equity Method Investments Excluded From Fair Value Adjustments for Change in Accounting Principle [Domain] Change in Accounting Principle, Type [Domain] Segments [Axis] Segments [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Business Disposal, Potential Out Of Pocket Expense Reimbursement Business Disposal, Potential Out Of Pocket Expense Reimbursement Business Disposal, Potential Out Of Pocket Expense Reimbursement Other, net Payment for (Proceeds from) Other Investing Activity Credit Derivatives Contract Type [Domain] Credit Derivatives Contract Type [Domain] Equity Securities Excluded From Fair Value Table Equity Securities Excluded From Fair Value Equity Securities Excluded From Fair Value Assets: Assets [Abstract] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Other Commitments [Axis] Other Commitments [Axis] Debt Instrument [Axis] Debt Instrument [Axis] Swiss Reinsurance America Corporation Swiss Reinsurance America Corporation [Member] Swiss Reinsurance America Corporation Fair Value Measurements Fair Value Disclosures [Text Block] 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] First Rate Increase First Rate Increase [Member] First Rate Increase VIE long-term debt issued related to Puerto Rico restructurings Reduction in VIE Loans Due to Deconsolidation Reduction in VIE Loans Due to Deconsolidation Proceeds from Short-Term Debt Proceeds from Short-Term Debt Treasury Stock, Value, Acquired, Cost Method Treasury Stock, Value, Acquired, Cost Method Insurance Commissions Insurance Commissions Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Unsecured Reinsurance Recoverable, All Other Unsecured Reinsurance Recoverable, All Other Unsecured Reinsurance Recoverable, All Other Reinsurance Recoverable Credit Exposure Reinsurance Recoverable Credit Exposure Reinsurance Recoverable Credit Exposure Contract with Customer, Receivable, after Allowance for Credit Loss Contract with Customer, Receivable, after Allowance for Credit Loss Ambac Insured Securities Ambac Insured Securities [Member] Ambac Insured Securities Disposal Group, Including Discontinued Operation, Variable Interest Entity Liabilities Disposal Group, Including Discontinued Operation, Variable Interest Entity Liabilities Disposal Group, Including Discontinued Operation, Variable Interest Entity Liabilities Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] 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. Derivative assets Derivative Asset, Fair Value, Gross Asset Derivative Asset, Subject to Master Netting Arrangement, before Offset Loss Carryforward Indefinite Life Loss Carryforward Indefinite Life Loss Carryforward Indefinite Life Entity Bankruptcy Proceedings, Reporting Current Entity Bankruptcy Proceedings, Reporting Current Entity Registrant Name Entity Registrant Name Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Percentage of investment portfolio valued using dealer quotes Percentage Of Investment Portfolio Valued Using Dealer Quotes Investment portfolio valued using dealer quotes. Municipal Bonds [Member] Municipal Bonds [Member] Disposal Group, Including Discontinued Operation, Liabilities Disposal Group, Including Discontinued Operation, Liabilities Short term debt minimum cash balance required Short term debt minimum cash balance required Short term debt minimum cash balance required Insurance [Table] Insurance [Table] Insurance [Table] 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. Total financial assets Assets, Fair Value Disclosure Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Restatement [Domain] Revision of Prior Period [Domain] Premium Receivable, Credit Loss Expense (Reversal) Premium Receivable, Credit Loss Expense (Reversal) Income Loss On Variable Interest Entities [Member] Income Loss On Variable Interest Entities [Member] Income (loss) on variable interest entities. Entity Incorporation, Date of Incorporation Entity Incorporation, Date of Incorporation Amortization of bond premium and discount Accretion (Amortization) of Discounts and Premiums, Investments Tax Credit Carryforward [Line Items] Tax Credit Carryforward [Line Items] Structured Finance [Member] Structured Finance [Member] Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member] Cash Provided by (Used in) Operating Activity, Continuing Operation Cash Provided by (Used in) Operating Activity, Continuing Operation Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Restatement Determination Date: Restatement Determination Date [Axis] Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Deferred Foreign Income Tax Expense (Benefit) Deferred Foreign Income Tax Expense (Benefit) Weighted average period of future premiums Financial Guarantee Insurance Contracts, Premium Received over Contract Period, Premium Receivable, Weighted Average Collection Period Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Reporting Unit [Axis] Reporting Unit [Axis] Net cash provided by (used in) investing activities from continuing operations Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Cash Provided by (Used in) Investing Activity, Continuing Operation Interest Interest Expense, Debt Disposal Group, Including Discontinued Operation, Net Investment Income Disposal Group, Including Discontinued Operation, Net Investment Income Disposal Group, Including Discontinued Operation, Net Investment Income Amounts reclassified from accumulated other comprehensive income Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Segment Reporting, Revenue Reconciling Item [Line Items] Segment Reporting, Revenue Reconciling Item [Line Items] All Currencies [Domain] All Currencies [Domain] Name Trading Arrangement, Individual Name Underlying Asset Class [Domain] Underlying Asset Class [Domain] Previously Reported Previously Reported [Member] 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] Reconciliation of Revenue from Segments to Consolidated [Table] Reconciliation of Revenue from Segments to Consolidated [Table] Business Combination, Number of Shares Issued for Beat Acquisition Business Combination, Number of Shares Issued for Beat Acquisition Business Combination, Number of Shares Issued for Beat Acquisition Illiquid Investments [Member] Illiquid Investments [Member] Illiquid Investments [Member] Ambac Rating Notional Disclosures [Abstract] Preferred Stock [Member] Preferred Stock [Member] Discontinued Operation, Tax Effect of Discontinued Operation Discontinued Operation, Tax Effect of Discontinued Operation Equity Funds Equity Funds [Member] Investment Portfolio [Member] Investment Portfolio [Member] Investment portfolio. Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net Name Awards Close in Time to MNPI Disclosures, Individual Name Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Business Combination, Credit Facility Cash Used for Beat Acquisition Business Combination, Credit Facility Cash Used for Beat Acquisition Business Combination, Credit Facility Cash Used for Beat Acquisition Treasury stock, shares at cost: 0 and 8,202 Treasury Stock, Value Unrealized (loss) gain on securities, taxes OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Business Combination, Potential Late Closing Penalty Per Day Business Combination, Potential Late Closing Penalty Per Day Business Combination, Potential Late Closing Penalty Per Day Customer Relationships And Trademarks Customer Relationships And Trademarks [Member] Customer Relationships And Trademarks Liability Class [Axis] Liability Class [Axis] Segments [Domain] Segments [Domain] Statement of Income Location, Balance [Axis] Statement of Income Location, Balance [Axis] Income (Loss) from Continuing Operations before Income Taxes, Foreign Income (Loss) from Continuing Operations before Income Taxes, Foreign Derivative, Gain (Loss) on Derivatives, Total Net Derivative, Gain (Loss) on Derivatives, Total Net Derivative, Gain (Loss) on Derivatives, Total Net Third Rate Increase Third Rate Increase [Member] Third Rate Increase Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Statement of Financial Position Location, Balance [Domain] Statement of Financial Position Location, Balance [Domain] Fiduciary Funds Held by Insurance Distribution Subsidiaries Fiduciary Funds Held by Insurance Distribution Subsidiaries Fiduciary Funds Held by Insurance Distribution Subsidiaries Class of Warrant or Right, Number of Securities Called by Warrants or Rights Class of Warrant or Right, Number of Securities Called by Warrants or Rights Unrealized Gains (Losses) on Available-for-Sale Securities [Member] AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member] Premium and commissions receivables Increase (Decrease) in Premiums Receivable Miscellaneous Specialty Miscellaneous Specialty Miscellaneous Specialty Purchases of bonds Payments to Acquire Debt Securities, Available-for-Sale Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none Preferred Stock, Value, Issued Accrued interest payable Interest Payable Interest Payable Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] All Executive Categories All Executive Categories [Member] Current Year Claims and Claims Adjustment Expense Current Year Claims and Claims Adjustment Expense Deferred Policy Acquisition Costs, Amortization Expense Deferred Policy Acquisition Costs, Amortization Expense Common Stock, Value, Issued Common Stock, Value, Issued Premiums Earned, Net Premiums Earned, Net Short-term Investments Short-Term Investments Fair Value Inputs Yield Yield Fair Value Inputs Yield Fair value inputs yield. Preferred Stock, Liquidation Preference, Value Preferred Stock, Liquidation Preference, Value Current Rate Current Rate [Member] Current Rate Niche Specialty Risks Niche Specialty Risks [Member] Niche Specialty Risks Fair Value Measured at Net Asset Value Per Share [Member] Fair Value Measured at Net Asset Value Per Share [Member] Total comprehensive income (loss), net of income tax Total net income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Business Combination [Axis] Business Combination [Axis] Long-term Debt, at par less amortized discount Long-term Debt, at par less amortized discount Long-term Debt, at par less amortized discount Noncontrolling Interest [Member] Noncontrolling Interest [Member] Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables Summary of Net Investment Income Investment Income [Table Text Block] Short-term Investments [Member] Short-Term [Member] Short-Term Investments [Member] Insurance Distribution Insurance Distribution [Member] Insurance Distribution Policyholder Benefits and Claims Incurred, Ceded Policyholder Benefits and Claims Incurred, Ceded Policyholder Benefits and Claims Incurred, Ceded 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] PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Estimated Fair Value, Due after ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Long-Term Debt, Term Long-Term Debt, Term Hedging Designation [Axis] Hedging Designation [Axis] Summary of Gross Fair Values of Individual Derivative Instruments Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location [Table Text Block] Commercial Auto Commercial Auto [Member] Commercial Auto 5.1% Surplus Notes Due 2020 5.1% Surplus Notes Due 2020 [Member] 5.1% Surplus Notes Due 2020 Scenario [Axis] Scenario [Axis] Surveillance Category [Domain] Surveillance Category [Domain] Octave Specialty Limited Octave Specialty Limited [Member] Octave Specialty Limited Business Combination, Acquisition of Less Than 100 Percent, Nonredeemable Noncontrolling Business Combination, Acquisition of Less Than 100 Percent, Nonredeemable Noncontrolling Business Combination, Acquisition of Less Than 100 Percent, Nonredeemable Noncontrolling Interest, Fair Value Other Comprehensive Income Loss Net Of Tax Portion Attributable to Noncontrolling Interest, Adjusted EBITDA Other Comprehensive Income Loss Net Of Tax Portion Attributable to Noncontrolling Interest, Adjusted EBITDA Other Comprehensive Income Loss Net of Tax Portion Attributable to Noncontrolling Interest, for Adjusted EBITDA to Ambac Liability for Future Policy Benefits and Unpaid Claims Disclosure Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Commitments [Member] Commitments [Member] Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Derivative Liability, Fair Value, Amount Offset Against Collateral Derivative Liability, Including Not Subject to Master Netting Arrangement, after Offset and Deduction Derivative Contract [Domain] Derivative Contract [Domain] Debt Securities, Available-for-sale, Realized Loss Available-for-sale Securities, Gross Realized Losses Debt Securities, Available-for-Sale, Realized Loss All Individuals All Individuals [Member] Financial Guarantee Insurance Contracts, Claim Liability [Table] Financial Guarantee Insurance Contracts, Claim Liability [Table] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Disposal Group, Including Discontinued Operation, General and Administrative Expense Disposal Group, Including Discontinued Operation, General and Administrative Expense Name Forgone Recovery, Individual Name Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Cash Provided by (Used in) Operating Activity, Discontinued Operation Cash Provided by (Used in) Operating Activity, Discontinued Operation Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification out of Accumulated Other Comprehensive Income [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Foreign Exchange Foreign Exchange [Member] Goodwill, Foreign Currency Translation, Gain (Loss) Goodwill, Foreign Currency Translation, Gain (Loss) Fixed Income Investments And Other Investments [Member] Fixed Income Investments And Other Investments [Member] Fixed income investments and other investments Member. Put / call option exercise Put / call option exercise Put / call option exercise Schedule Of Earnings Per Share [Table] Schedule Of Earnings Per Share [Table] Schedule Of Earnings Per Share [Table] Short term investments Other Short-Term Investments Disposal Group, Including Discontinued Operation, Other Liabilities Disposal Group, Including Discontinued Operation, Other Liabilities Disposal Group, Including Discontinued Operation, Reinsurance Recoverable For Paid And Unpaid Claims And Claims Adjustments Disposal Group, Including Discontinued Operation, Reinsurance Recoverable For Paid And Unpaid Claims And Claims Adjustments Disposal Group, Including Discontinued Operation, Reinsurance Recoverable For Paid And Unpaid Claims And Claims Adjustments Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Intangible Asset, Finite-Lived [Table] Intangible Asset, Finite-Lived [Table] Geographical [Axis] Geographical [Axis] Transaction Type [Axis] Transaction Type [Axis] Accrued Liabilities for Commissions, Expense and Taxes Increase (Decrease) in Reserve for Commissions, Expense and Taxes Other, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Estimated Future Premium Payments Minimum Discounted Rate Estimated Future Premium Payments Minimum Discounted Rate Estimated Future Premium Payments Minimum Discounted Rate Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset or Liability, Transfers into or out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset or Liability, Transfers into or out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset or Liability, Transfers into or out of Level 3 Foreign Currency Transaction Gain (Loss), before Tax Foreign exchange (losses) gains Gain (Loss), Foreign Currency Transaction, before Tax 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. Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] 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. Title of 12(b) Security Title of 12(b) Security Minimum Cash Liquidity Requirement Minimum Cash Liquidity Requirement Minimum Cash Liquidity Requirement Premium Receivable, Allowance for Credit Loss, Writeoff Premium Receivable, Allowance for Credit Loss, Writeoff Earnings Per Share [Abstract] Earnings Per Share [Abstract] Noncompete Agreements Noncompete Agreements [Member] Loss Adjustment Expenses (Legal Expenses) Loss Adjustment Expenses (Legal Expenses) [Member] Loss Adjustment Expenses (Legal Expenses) Subsidiary, Ownership Percentage, Parent Subsidiary, Ownership Percentage, Parent Beat Beat [Member] Beat Net Amount, Derivative Assets Derivative Assets Net Amount Derivative Assets Net Amount Short-Term Debt, Type [Axis] Short-Term Debt, Type [Axis] Disposal Group, Including Discontinued Operation, Liabilities, Long-Term Debt And Accrued Interest Disposal Group, Including Discontinued Operation, Liabilities, Long-Term Debt And Accrued Interest Disposal Group, Including Discontinued Operation, Liabilities, Long-Term Debt And Accrued Interest SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] Effect of potential dilutive shares: Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Treasury Stock, Shares, Acquired Treasury Stock, Shares, Acquired 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 Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] External Credit Rating by Grouping [Axis] External Credit Rating by Grouping [Axis] AOCI Impact of Disposal of Discontinued Operation AOCI Impact of Disposal of Discontinued Operation AOCI Impact of Disposal of Discontinued Operation Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset Award Timing Disclosures [Line Items] Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments Gain (Loss) on Securities [Table Text Block] Measurement Frequency [Domain] Measurement Frequency [Domain] Beginning balance of net loss and loss expense reserves Liability for Unpaid Claims and Claims Adjustment Expense, Net Liability for Unpaid Claims and Claims Adjustment Expense, Net Other comprehensive income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 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. Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, after Reclassification Adjustment, Tax Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, after Reclassification Adjustment, Tax Net income (loss) attributable to shareholders Net income attributable to common shareholders Net Income (Loss) Attributable to Parent Credit Deterioration Surveillance Category [Axis] Credit Deterioration Surveillance Category [Axis] Major Jurisdictions Summary of Income Tax Examinations [Table Text Block] Excess and General Liability Excess and General Liability [Member] Excess and General Liability Disposal Group, Including Discontinued Operation, Interest Expense Disposal Group, Including Discontinued Operation, Interest Expense Preferred stock, shares authorized Preferred Stock, Shares Authorized Adoption Date Trading Arrangement Adoption Date Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Contract with Customer, Asset, after Allowance for Credit Loss Contract with Customer, Asset, after Allowance for Credit Loss Tax Credit Carryforward [Table] Tax Credit Carryforward [Table] Customer Relationships Customer Relationships [Member] Retained earnings Retained Earnings (Accumulated Deficit) Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Principal Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding, Principal Net gains (losses) on derivative contracts [Domain] Net gains (losses) on derivative contracts [Domain] Net gains (losses) on derivative contracts [Domain] Employee Stop Loss Time When Base Commissions Recognized Begin and End In Months Employee Stop Loss Time When Base Commissions Recognized Begin and End In Months Employee Stop Loss Time When Base Commissions Recognized Begin and End In Months Class of Stock [Axis] Class of Stock [Axis] Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses) Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses) Subsequent Event Type [Domain] Subsequent Event Type [Domain] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Statement [Table] Statement [Table] Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Debt Securities, Available-for-sale, Allowance for Credit Loss, Sell before Recovery Debt Securities, Available-for-Sale, Allowance for Credit Loss, Sell before Recovery Adjustments to reconcile net income to net cash provided by (used in) operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] External Credit Rating, Moody's [Domain] External Credit Rating, Moody's [Domain] AMBAC EBITDA AMBAC EBITDA AMBAC EBITDA Contract with Customer, Liability Contract with Customer, Liability Variable Rate [Domain] Variable Rate [Domain] Organization, Consolidation and Presentation of Financial Statements Disclosure Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Temporary Equity, Accretion to Redemption Value, Adjustment Temporary Equity, Accretion to Redemption Value, Adjustment Subrogation recoverable Subrogation recoverable Salvage and Subrogation Recoveries, Value Schedule of Repurchased Shares Schedule of Repurchased Shares [Table Text Block] Schedule of Repurchased Shares All Adjustments to Compensation All Adjustments to Compensation [Member] Premium Receivable, Allowance for Credit Loss, Recovery Premium Receivable, Allowance for Credit Loss, Recovery Fair value of derivative liabilities Derivative Liability, Fair Value, Amount Not Offset Against Collateral Derivative Liability, Subject to Master Netting Arrangement, before Offset of Collateral Amendment Flag Amendment Flag Deferred Compensation Arrangement with Individual, Allocated Share-Based Compensation Expense Deferred Compensation Arrangement with Individual, Allocated Share-Based Compensation Expense Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments Schedule of Unrealized Loss on Investments [Table Text Block] Other Postretirement Benefits Plan [Member] Other Postretirement Benefits Plan [Member] Disposal Group, Including Discontinued Operation, Liability for Claims and Claims Adjustment Expense Disposal Group, Including Discontinued Operation, Liability for Claims and Claims Adjustment Expense Liability for Claims and Claims Adjustment Expense Liability for Claims Liability for Claims and Claims Adjustment Expense Standard & Poor's, AA+ Rating Standard & Poor's, AA+ Rating [Member] Schedule of Variable Interest Entities Assets and Liabilities [Table Text Block] Schedule of Variable Interest Entities Assets and Liabilities [Table Text Block] Schedule of Variable Interest Entities Assets and Liabilities [Table Text Block] Reinsurance Recoverable, Credit Quality Indicator Reinsurance Recoverable, Credit Quality Indicator [Table Text Block] Termination Date Trading Arrangement Termination Date Affinity Products Affinity Products [Member] Affinity Products Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Investments: Net Assets SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] Net Income Loss Reconciliation [Table] Net Income Loss Reconciliation [Table] Net Income Loss Reconciliation [Table] 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. Weighted Average Number of Shares Outstanding, Basic Weighted average number of common shares used for basic earnings per share Weighted Average Number of Shares Outstanding, Basic Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Corporate costs reallocated to continuing operations Corporate costs reallocated to continuing operations Corporate costs reallocated to continuing operations Segment Reporting [Abstract] Parsed Fixed Income Securities Parsed Fixed Income Securities [Member] Parsed Fixed Income Securities Business Combination, Potential Late Closing Penalty Maximum Business Combination, Potential Late Closing Penalty Maximum Business Combination, Potential Late Closing Penalty Maximum Debt Disclosure [Abstract] Loss and Loss Reserves [Domain] Loss and Loss Reserves [Domain] [Domain] for Loss and Loss Reserves [Axis] Scenario [Domain] Scenario [Domain] Payment for Put/Call Option Payment for Put/Call Option Payment for Put/Call Option Second Rate Increase Second Rate Increase [Member] Second Rate Increase Background And Basis Of Presentation [Table] Background And Basis Of Presentation [Table] Background And Basis Of Presentation [Table] Reinsurance Reinsurance [Member] Reinsurance Investment in less than 100 percent owned, Percentage Investment in less than 100 percent owned, Percentage Investment in less than 100 percent owned, Percentage Interest Paid, Including Capitalized Interest, Operating and Investing Activities Interest Paid, Including Capitalized Interest, Operating and Investing Activities Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Consolidated Entities [Axis] Consolidated Entities [Axis] Common Stock, Par or Stated Value Per Share Common stock, par value Par value of common stock issued Common Stock, Par or Stated Value Per Share Equity Securities, FV-NI, Realized Gain (Loss) Equity Securities, FV-NI, Realized Gain (Loss) Disposal Group, Including Discontinued Operation, Unearned Premiums Disposal Group, Including Discontinued Operation, Unearned Premiums Disposal Group, Including Discontinued Operation, Unearned Premiums Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] FX Forwards-Buy USD/Sell GBP FX Forward Buy USD Sell GBP [Member] FX Forward Buy USD Sell GBP Uncollectable premiums Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease) External Credit Rating, Noninvestment Grade [Member] External Credit Rating, Noninvestment Grade [Member] Non Compensation Expense Non Compensation Expense Non Compensation Expense Cash disposed of related to sale of discontinued operations Cash disposed of related to sale of discontinued operations Cash disposed of related to sale of discontinued operations FX Forwards-Buy GBP/Sell CAD FX Forward Buy GBP Sell CAD [Member] FX Forward Buy GBP Sell CAD Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Insider Trading Arrangements [Line Items] Financial Guarantee Legacy Financial Guarantee [Member] Legacy Financial Guarantee Total liabilities Liabilities Liabilities Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Currency [Axis] Currency [Axis] Amortized Cost, Total Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] 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 Stock Issued During Period, Value, New Issues Stock Issued During Period, Value, New Issues Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Asset-backed Securities [Member] Asset-Backed Securities [Member] Business Combination, Intangible Asset, Acquired, Finite-Lived and Indefinite-Lived Business Combination, Intangible Asset, Acquired, Finite-Lived and Indefinite-Lived [Table Text Block] Variable Rate [Axis] Variable Rate [Axis] Consolidation Items [Axis] Consolidation Items [Axis] Gross Investment Income, Operating Gross Investment Income, Operating Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect, Discontinued Operation Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect, Discontinued Operation Debt Securities, Available-for-Sale Debt Securities, Available-for-Sale Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Nonredeemable Noncontrolling Interest Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code 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. Non-NEOs Non-NEOs [Member] Corporate Debt Securities [Member] Corporate Obligations [Member] Corporate Debt Securities [Member] 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.