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	Sep. 30, 2023	Dec. 31, 2022
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	$ 1,834	$ 2,203
Less than 12 months - Unrealized losses	34	70
12 months or more - Fair Value	1,476	585
12 months or more - Unrealized losses	124	78
Fair Value	3,310	2,788
Unrealized Losses	158	148
Other U.S. and non-U.S. government bonds
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	19	19
Less than 12 months - Unrealized losses	0	1
12 months or more - Fair Value	25	20
12 months or more - Unrealized losses	4	4
Fair Value	44	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	1,660	1,815
Less than 12 months - Unrealized losses	29	46
12 months or more - Fair Value	972	357
12 months or more - Unrealized losses	64	50
Fair Value	2,632	2,172
Unrealized Losses	93	96
Asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	35	75
Less than 12 months - Unrealized losses	0	2
12 months or more - Fair Value	88	55
12 months or more - Unrealized losses	4	3
Fair Value	123	130
Unrealized Losses	4	5
U.S. governmental agency
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	102	229
Less than 12 months - Unrealized losses	4	16
12 months or more - Fair Value	281	98
12 months or more - Unrealized losses	41	15
Fair Value	383	327
Unrealized Losses	45	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	18	63
Less than 12 months - Unrealized losses	1	5
12 months or more - Fair Value	108	54
12 months or more - Unrealized losses	10	5
Fair Value	126	117
Unrealized Losses	$ 11	$ 10