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Background and Business Description - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2021	Feb. 11, 2021	Jan. 19, 2021
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	Apr. 29, 1991
Net realized gains (losses) on extinguishment of debt	$ 33,000,000
Realized Investment Gains (Losses)	2,000,000	$ 8,000,000
Business Acquisition, Percentage of Voting Interests Acquired			80.00%
Parent
Background And Basis Of Presentation [Line Items]
Realized Investment Gains (Losses)	$ 4,000,000
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020
Background And Basis Of Presentation [Line Items]
Note Holders	1
One Dollar Outstanding				$ 1.00	$ 1.00
Payment Amount in Exchange				0.8581
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 | Corolla Notes
Background And Basis Of Presentation [Line Items]
Payment Amount in Exchange					0.9125
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 | Corolla Certificate
Background And Basis Of Presentation [Line Items]
Payment Amount in Exchange					0.6400
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020
Background And Basis Of Presentation [Line Items]
Long-term Debt, Gross				853,000,000
Long-term Debt, Gross and Accrued and Unpaid Interest				1,414,000,000
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 | Corolla Notes
Background And Basis Of Presentation [Line Items]
Long-term Debt Issued in Exchange Transaction					267,000,000
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 | Lease Reducing Notes
Background And Basis Of Presentation [Line Items]
Long-term Debt Issued in Exchange Transaction					$ 13,000,000
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 | Parent Company [Member]
Background And Basis Of Presentation [Line Items]
Long-term Debt, Gross				83,000,000
Ambac Assurance Corporation [Member] | 5.1 % Surplus Notes Due 2020
Background And Basis Of Presentation [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.10%
Ambac Assurance Corporation [Member] | Lease Reducing Notes | 5.1% Junior Surplus Notes, General Account Due 2020
Background And Basis Of Presentation [Line Items]
Long-term Debt Reduced in Exchange				$ 15,000,000
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes Due 2020
Background And Basis Of Presentation [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.10%

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