Contracts Accounted for as Insurance - Net Earned Premiums (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Guarantor Obligations [Line Items]
Scheduled net earned premiums	$ 73	$ 70	$ 212	$ 219
Accelerations from refundings and terminations	14	12	26	145
Accretion of discount on net premiums receivable	7	6	20	18
Financial guaranty insurance net earned premiums	94	88	258	382
Specialty net earned premiums	1	1	3	3
Net earned premiums	$ 95	$ 89	$ 261	385
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Accelerations from refundings and terminations				$ 104