Background and Basis of Presentation - Surplus Note Exchange (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Feb. 11, 2021 USD ($)	Jan. 19, 2021 USD ($)
Insurance [Line Items]
Net realized gains (losses) on extinguishment of debt		$ 33,000,000	$ 0	$ 0
Realized Investment Gains (Losses)		7,000,000	22,000,000	81,000,000
Parent Company [Member]
Insurance [Line Items]
Realized Investment Gains (Losses)		(5,000,000)	(1,000,000)	$ (2,000,000)
Parent [Member]
Insurance [Line Items]
Realized Investment Gains (Losses)		4,000,000
Ambac Assurance Corporation [Member]
Insurance [Line Items]
Long-term Debt, Gross	$ 2,334,000,000	$ 2,334,000,000	$ 2,884,000,000
Ambac Assurance Corporation [Member] | 5.1 % Surplus Notes Due 2020 [Member]
Insurance [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.10%	5.10%	5.10%
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes Due 2020 [Member]
Insurance [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.10%	5.10%	5.10%
Ambac Assurance Corporation [Member] | Corolla Notes
Insurance [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.10%
5.1% Junior Surplus Notes, General Account Due 2020 [Member] | Ambac Assurance Corporation [Member]
Insurance [Line Items]
Long-term Debt, Gross	$ 0	$ 0	$ 365,000,000
5.1% Junior Surplus Notes, General Account Due 2020 [Member] | Ambac Assurance Corporation [Member] | Lease Reducing Notes
Insurance [Line Items]
Long-term Debt Reduced in Exchange					$ 15,000,000
5.1% Junior Surplus Notes, General Account Due 2020 [Member] | Ambac Assurance Corporation [Member] | Corolla Notes
Insurance [Line Items]
Payment Amount in Exchange						$ 0.9125
Note Holders	1
5.1% Junior Surplus Notes, General Account Due 2020 [Member] | Ambac Assurance Corporation [Member] | Corolla Certificate
Insurance [Line Items]
One Dollar Outstanding						1.00
Payment Amount in Exchange						0.64
5.1% Surplus Notes, General Account, Due 2020 [Member] | Ambac Assurance Corporation [Member]
Insurance [Line Items]
Long-term Debt, Gross	$ 785,000,000	$ 785,000,000	$ 531,000,000
5.1% Surplus Notes, General Account, Due 2020 [Member] | Ambac Assurance Corporation [Member] | Corolla Notes
Insurance [Line Items]
Long-term Debt Issued in Exchange Transaction						267,000,000
Corolla Notes | Ambac Assurance Corporation [Member]
Insurance [Line Items]
One Dollar Outstanding						1.00
Lease Reducing Notes | Ambac Assurance Corporation [Member]
Insurance [Line Items]
One Dollar Outstanding					1.00
Payment Amount in Exchange					$ 0.8581
Long-term Debt Issued in Exchange Transaction						$ 13,000,000
Lease Reducing Notes | Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes Due 2020 [Member]
Insurance [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.10%