Investments in Debt and Equity Securities - Summary of investments in an unrealized loss position that are not other-than-temporarily impaired (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	$ 1,656	$ 2,203
Less than 12 months - Unrealized losses	34	70
12 months or more - Fair Value	1,371	585
12 months or more - Unrealized losses	106	78
Fair Value	3,027	2,788
Unrealized Losses	140	148
Other U.S. and non-U.S. government bonds
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	13	19
Less than 12 months - Unrealized losses	0	1
12 months or more - Fair Value	26	20
12 months or more - Unrealized losses	4	4
Fair Value	39	39
Unrealized Losses	4	5
Corporate bonds and other debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	1,414	1,815
Less than 12 months - Unrealized losses	26	46
12 months or more - Fair Value	947	357
12 months or more - Unrealized losses	62	50
Fair Value	2,361	2,172
Unrealized Losses	88	96
Asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	57	75
Less than 12 months - Unrealized losses	1	2
12 months or more - Fair Value	92	55
12 months or more - Unrealized losses	4	3
Fair Value	149	130
Unrealized Losses	5	5
U.S. governmental agency
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	131	229
Less than 12 months - Unrealized losses	5	16
12 months or more - Fair Value	218	98
12 months or more - Unrealized losses	26	15
Fair Value	349	327
Unrealized Losses	31	31
Residential
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	0	2
Less than 12 months - Unrealized losses	0	0
12 months or more - Fair Value	2	1
12 months or more - Unrealized losses	1	1
Fair Value	2	3
Unrealized Losses	1	1
Commercial
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	41	63
Less than 12 months - Unrealized losses	2	5
12 months or more - Fair Value	86	54
12 months or more - Unrealized losses	9	5
Fair Value	127	117
Unrealized Losses	$ 11	$ 10