Contracts Accounted for as Insurance - Gross Premium Receivable Net of Commissions on Assumed Business Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Beginning of year	$ 1,468	$ 1,298	$ 1,372
Financial guaranty insurance premiums receivable	1,550	1,467	1,297	$ 1,371
New business and supplemental premiums, net of commissions	467	353	356
Gross premiums received, net of commissions	(354)	(261)	(345)
Adjustments:
Changes in the expected term and debt service assumptions	(32)	1	2
Accretion of discount, net of commissions on assumed business	26	26	24
Foreign exchange gain (loss) on remeasurement	(24)	51	(111)
Specialty insurance premium receivable	1	1	1	$ 1
End of period	$ 1,551	$ 1,468	$ 1,298