Fair Value Measurement - Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Carrying amount and estimated fair value financial instruments
Other assets (including other invested assets)	$ 689	$ 746
Long-term debt	(1,700)	(1,699)
Other liabilities	(453)	(498)
Carrying Amount
Carrying amount and estimated fair value financial instruments
Other assets (including other invested assets)	103	115
Financial guaranty insurance contracts	(1,999)	(2,029)
Long-term debt	(1,700)	(1,699)
Other liabilities	(15)	(16)
Estimated Fair Value
Carrying amount and estimated fair value financial instruments
Other assets (including other invested assets)	104	116
Financial guaranty insurance contracts	(1,147)	(1,136)
Long-term debt	(1,596)	(1,579)
Other liabilities	$ (15)	$ (16)