Investments in debt and equity securities - Schedule of available-for-sale securities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Schedule of Debt and Equity Securities
Cost Basis	$ 4,114	$ 3,871
Unrealized Pretax Net Gains (Losses)	(72)	(74)
Fair Value	4,042	3,797
U.S. treasury bonds
Schedule of Debt and Equity Securities
Cost Basis	10	10
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	10	10
Other U.S. and non-U.S. government bonds
Schedule of Debt and Equity Securities
Cost Basis	71	62
Unrealized Pretax Net Gains (Losses)	(3)	(2)
Fair Value	68	60
Corporate bonds and other debt securities
Schedule of Debt and Equity Securities
Cost Basis	3,199	3,031
Unrealized Pretax Net Gains (Losses)	(29)	(36)
Fair Value	3,170	2,995
Asset-backed securities
Schedule of Debt and Equity Securities
Cost Basis	220	195
Unrealized Pretax Net Gains (Losses)	(1)	(3)
Fair Value	219	192
U.S. governmental agency
Schedule of Debt and Equity Securities
Cost Basis	476	433
Unrealized Pretax Net Gains (Losses)	(33)	(23)
Fair Value	443	410
Residential
Schedule of Debt and Equity Securities
Cost Basis	2	3
Unrealized Pretax Net Gains (Losses)	0	(1)
Fair Value	2	2
Commercial
Schedule of Debt and Equity Securities
Cost Basis	136	137
Unrealized Pretax Net Gains (Losses)	(6)	(9)
Fair Value	$ 130	$ 128