Investments - Schedule of Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value for Fixed Income Securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	$ 49,979	$ 45,370
Gross unrealized, Gains	29	92
Gross unrealized, Losses	(3,237)	(2,977)
Fixed income securities	46,771	42,485
U.S. government and agencies
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	8,629	8,123
Gross unrealized, Gains	1	6
Gross unrealized, Losses	(385)	(231)
Fixed income securities	8,245	7,898
Municipal
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	7,044	6,500
Gross unrealized, Gains	3	36
Gross unrealized, Losses	(463)	(326)
Fixed income securities	6,584	6,210
Corporate
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	32,007	28,562
Gross unrealized, Gains	16	46
Gross unrealized, Losses	(2,317)	(2,345)
Fixed income securities	29,706	26,263
Foreign government
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,196	997
Gross unrealized, Gains	0	0
Gross unrealized, Losses	(61)	(40)
Fixed income securities	1,135	957
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,103	1,188
Gross unrealized, Gains	9	4
Gross unrealized, Losses	(11)	(35)
Fixed income securities	$ 1,101	$ 1,157