Background and Business Description - Additional Information (Details)	3 Months Ended
	Mar. 31, 2024 level3FinancialInstruments USD ($)
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	Apr. 29, 1991
Number of Admitted Carriers Owned \| $	5
Number of Reportable Segments \| level3FinancialInstruments	3
Background and Business Description	1. BACKGROUND AND BUSINESS DESCRIPTION The following description provides an update of Note 1. Background and Business Description in the Notes to the Consolidated Financial Statements included in Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, and should be read in conjunction with the complete descriptions provided in the Form 10-K. Capitalized terms used, but not defined herein, and in the other footnotes to the Consolidated Financial Statements included in this Quarterly Report on Form 10-Q shall have the meanings ascribed thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. Ambac Financial Group, Inc. (“AFG”), headquartered in New York City, is a financial services holding company incorporated in the state of Delaware on April 29, 1991. References to “Ambac,” the “Company,” “we,” “our,” and “us” are to AFG and its subsidiaries, as the context requires. Ambac's principal businesses include: •Legacy Financial Guarantee Insurance — Ambac's legacy financial guarantee business includes the activities of Ambac Assurance Corporation ("AAC") and its wholly owned subsidiaries, including Ambac Assurance UK Limited (“Ambac UK”) and Ambac Financial Services LLC ("AFS"). Both AAC and Ambac UK (the "Legacy Financial Guarantee Companies") have financial guarantee insurance portfolios that have been in runoff since 2008. AFS provided interest rate derivatives to financial guarantee customers and used derivatives to hedge interest rate risk in AAC's insurance and investment portfolios. AFS' remaining derivative positions include a limited number of legacy customer swaps and their associated hedges. •Specialty Property & Casualty Insurance — Ambac's Specialty Property & Casualty Insurance program business. Currently includes five admitted carriers and an excess and surplus lines (“E&S” or “nonadmitted”) insurer (collectively, “Everspan”). Everspan carriers have an A.M. Best rating of 'A-' (Excellent) that was affirmed on June 13, 2023. •Insurance Distribution — Ambac's specialty property and casualty ("P&C") insurance distribution business, which could include Managing General Agents and Underwriters (collectively "MGAs"), insurance brokers, and other distribution businesses. Currently, Ambac's insurance distribution platform includes Xchange Benefits, LLC (“Xchange”), a P&C MGA specializing in accident and health products; All Trans Risk Solutions, LLC ("All Trans"), an MGA specializing in specialty commercial automobile insurance for specific "for-hire" auto clauses; Capacity Marine Corporation ("Capacity Marine"), a wholesale and retail brokerage and reinsurance intermediary specializing in marine and international risk and Riverton Insurance Agency, Corp. ("Riverton"), which was acquired on August 1, 2023, an insurance services business specializing in professional liability lines and consisting of an MGA and a retail agency. The Company reports these three business operations as segments; see Note 3. Segment Information for further information.