Background and Business Description - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Oct. 29, 2022	Dec. 31, 2021
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation			Apr. 29, 1991
Net realized gains (losses) on extinguishment of debt	$ 0	$ 0	$ 57,000,000	$ 33,000,000
Realized Investment Gains (Losses)	14,000,000	$ 3,000,000	31,000,000	$ 4,000,000
Business Acquisition, Percentage of Voting Interests Acquired						80.00%
Long-term debt	$ 2,201,000,000		$ 2,201,000,000			$ 2,230,000,000
Number of Admitted Carriers Owned	5		5
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, 2021, 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, 2021. 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 business operations include: •Legacy Financial Guarantee Insurance — Ambac's 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 uses derivatives to hedge interest rate risk in AAC's insurance and investment portfolios. •Specialty Property & Casualty Insurance — Ambac's hybrid fronting Specialty Property & Casualty Insurance business. Currently includes five admitted carriers and an excess and surplus lines (“E&S” or “nonadmitted”) insurer, Everspan Indemnity Insurance Company (collectively, “Everspan”). Three of the five admitted carrier were acquired in 2022. Everspan carriers have an AM Best rating of 'A-' (Excellent). •Insurance Distribution — Ambac's specialty property and casualty ("P&C") insurance distribution business, which could include Managing General Agents and Underwriters (collectively "MGAs"), insurance wholesalers, and other distribution businesses, currently includes Xchange Benefits, LLC (“Xchange”) a P&C MGA specializing in accident and health products. Refer to Note 3. Business Combination in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021, for further information relating to this acquisition. As discussed further below, the insurance distribution segment has been expanded to include two acquisitions that occurred in the fourth quarter of 2022. Beginning in the first quarter of 2022, the Company began reporting these three business operations as segments; see Note 3. Segment Information for further information. Strategies to Enhance Shareholder Value The Company's primary goal is to maximize shareholder value through the execution of key strategies for both its (i) Specialty P&C Insurance Platform and (ii) Legacy Financial Guarantee Companies. Specialty P&C Insurance Platform strategic priorities include: •Growing and diversifying the Specialty Property & Casualty insurance business with existing and new program partners. •Building a leading Insurance Distribution business through additional acquisitions and de novo builds, supported by a centralized business services unit including core technology solutions. •Making opportunistic investments that are strategic to the overall Specialty P&C Insurance Platform. Legacy Financial Guarantee Companies’ strategic priorities include: •Actively managing, de-risking and mitigating insured portfolio risk. •Pursuing loss recovery through active litigation and other means, particularly residential mortgage back security representation and warranty litigation. •Improving operating efficiency and optimizing our asset and liability profile. •Exploring, at the appropriate time, strategic options to further maximize value for AFG. The execution of Ambac’s strategy to increase the value of its investment in AAC is subject to the restrictions set forth in the Settlement Agreement, dated as of June 7, 2010 (the "Settlement Agreement"), by and among AAC, Ambac Credit Products LLC ("ACP"), AFG and certain counterparties to credit default swaps with ACP that were guaranteed by AAC; as well as the Stipulation and Order among the Office of the Commissioner of Insurance for the State of Wisconsin (“OCI”), AFG and AAC that became effective on February 12, 2018, as amended (the “Stipulation and Order”); and the indenture for the Tier 2 Notes, each of which requires OCI and, under certain circumstances, holders of the debt instruments benefiting from such restrictions, to approve certain actions taken by or in respect of AAC. In exercising its approval rights, OCI will act for the benefit of policyholders, and will not take into account the interests of AFG. Opportunities for remediating losses on poorly performing insured transactions also depend on market conditions, including the perception of AAC’s creditworthiness, the structure of the underlying risk and associated policy as well as other counterparty specific factors. AAC's ability to commute policies or purchase certain investments may also be limited by available liquidity.
Tier 2 Notes \| Subsequent Event
Background And Basis Of Presentation [Line Items]
Debt Instrument, Face Amount					$ 143,000,000
Ambac Assurance Corporation [Member] \| 5.1% Surplus Notes, General Account, Due 2020 \| Subsequent Event
Background And Basis Of Presentation [Line Items]
Long-term Debt, Gross					$ 721,000,000