Background and Basis of Presentation - Surplus Note Exchange (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Insurance [Line Items]
Net realized gains on extinguishment of debt	$ 0	$ 81	$ 33
Realized Investment Gains (Losses)	(22)	31	7
Parent Company [Member]
Insurance [Line Items]
Realized Investment Gains (Losses)	$ 0	(14)	$ (5)
5.1% Surplus Notes, General Account, Due 2020 [Member]
Insurance [Line Items]
Net realized gains on extinguishment of debt		$ 134
Ambac Assurance Corporation [Member] | 5.1 % Surplus Notes Due 2020 [Member]
Insurance [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.10%	5.10%