Contracts Accounted for as Insurance - Net Earned Premiums (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Guarantor Obligations [Line Items]
Scheduled net earned premiums	$ 70	$ 70	$ 139	$ 149
Accelerations from refundings and terminations	8	5	12	133
Accretion of discount on net premiums receivable	6	6	13	12
Financial guaranty insurance net earned premiums	84	81	164	294
Specialty net earned premiums	1	1	2	2
Net earned premiums	$ 85	$ 82	$ 166	296
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Accelerations from refundings and terminations				$ 104