Investments in debt and equity securities - Schedule of available-for-sale securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Debt and Equity Securities
Cost Basis	$ 3,871	$ 3,311
Unrealized Pretax Net Gains (Losses)	(74)	(147)
Fair Value	3,797	3,164
U.S. treasury bonds
Schedule of Debt and Equity Securities
Cost Basis	10	9
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	10	9
Other U.S. and non-U.S. government bonds
Schedule of Debt and Equity Securities
Cost Basis	62	60
Unrealized Pretax Net Gains (Losses)	(2)	(5)
Fair Value	60	55
Corporate bonds and other debt securities
Schedule of Debt and Equity Securities
Cost Basis	3,031	2,561
Unrealized Pretax Net Gains (Losses)	(36)	(95)
Fair Value	2,995	2,466
Asset-backed securities
Schedule of Debt and Equity Securities
Cost Basis	195	187
Unrealized Pretax Net Gains (Losses)	(3)	(5)
Fair Value	192	182
U.S. governmental agency
Schedule of Debt and Equity Securities
Cost Basis	433	364
Unrealized Pretax Net Gains (Losses)	(23)	(31)
Fair Value	410	333
Residential
Schedule of Debt and Equity Securities
Cost Basis	3	3
Unrealized Pretax Net Gains (Losses)	(1)	(1)
Fair Value	2	2
Commercial
Schedule of Debt and Equity Securities
Cost Basis	137	127
Unrealized Pretax Net Gains (Losses)	(9)	(10)
Fair Value	$ 128	$ 117