Business and Basis of Presentation Background and Business Description - Additional Information (Details) $ in Thousands	6 Months Ended
Jun. 30, 2025 USD ($) level3FinancialInstruments	Dec. 31, 2024 USD ($)
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	2
Short-Term Debt \| $	$ 150,000	$ 150,000
Short Term Debt Duration Fee	1.00%
Background and Business Description	1. BACKGROUND AND BUSINESS DESCRIPTION Business The following description provides an update of Note 1. Background and Business Description and Note 2. Basis of Presentation and Significant Accounting Policies 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, 2024, 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, 2024. Ambac Financial Group, Inc. (“AFG”), headquartered in New York City, is an insurance 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: •Insurance Distribution — Ambac's specialty property and casualty ("P&C") insurance underwriting and distribution business, includes Managing General Agents and Underwriters (collectively "MGAs" or "MGA/Us"), an insurance broker, and other distribution and underwriting businesses. Insurance Distribution includes Beat Capital Partners Limited, which was acquired on July 31, 2024. At June 30, 2025, Ambac's insurance distribution platform operates in the following lines of business: property, niche specialty risk, accident & health, miscellaneous specialty, reinsurance, marine & energy, specialty auto, other professional and professional Directors & Officers ("D&O") . •Specialty Property & Casualty Insurance — Ambac's Specialty Property & Casualty Insurance program business currently includes five carriers (collectively, “Everspan”). Everspan carriers have an A.M. Best rating of 'A-' (Excellent) which was last affirmed on July 17, 2025. The Company reports these two business operations as segments; see Note 2. Segment Information for further information.

Business and Basis of Presentation Background and Business Description - Additional Information (Details)
$ in Thousands

6 Months Ended

Jun. 30, 2025

USD ($)

level3FinancialInstruments

Dec. 31, 2024

USD ($)

Background And Basis Of Presentation [Line Items]

Entity Incorporation, Date of Incorporation

Apr. 29, 1991

Number of Admitted Carriers Owned

Number of Reportable Segments

Short-Term Debt | $

$ 150,000

Short Term Debt Duration Fee

1.00%

Background and Business Description

1. BACKGROUND AND BUSINESS DESCRIPTION

Business

The following description provides an update of Note 1. Background and Business Description and Note 2. Basis of Presentation and Significant Accounting Policies 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, 2024, 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, 2024.

Ambac Financial Group, Inc. (“AFG”), headquartered in New York City, is an insurance 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:

•Insurance Distribution — Ambac's specialty property and casualty ("P&C") insurance underwriting and distribution business, includes Managing General Agents and Underwriters (collectively "MGAs" or "MGA/Us"), an insurance broker, and other distribution and underwriting businesses. Insurance Distribution includes Beat Capital Partners Limited, which was acquired on July 31, 2024. At June 30, 2025, Ambac's insurance distribution platform operates in the following lines of business: property, niche specialty risk, accident & health, miscellaneous specialty, reinsurance, marine & energy, specialty auto, other professional and professional Directors & Officers ("D&O") .

•Specialty Property & Casualty Insurance — Ambac's Specialty Property & Casualty Insurance program business currently includes five carriers (collectively, “Everspan”). Everspan carriers have an A.M. Best rating of 'A-' (Excellent) which was last affirmed on July 17, 2025.

The Company reports these two business operations as segments; see Note 2. Segment Information for further information.