Investments - Schedule of Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value for Fixed Income Securities (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	$ 53,447	$ 49,649
Gross unrealized gains	1,143	650
Gross unrealized losses	(629)	(1,434)
Fair value	53,961	48,865
U.S. government and agencies
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	9,125	8,624
Gross unrealized gains	162	114
Gross unrealized losses	(41)	(119)
Fair value	9,246	8,619
Municipal
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	8,223	6,049
Gross unrealized gains	131	109
Gross unrealized losses	(96)	(152)
Fair value	8,258	6,006
Corporate
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	33,480	31,951
Gross unrealized gains	799	397
Gross unrealized losses	(483)	(1,143)
Fair value	33,796	31,205
Foreign government
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,446	1,286
Gross unrealized gains	37	17
Gross unrealized losses	(6)	(13)
Fair value	1,477	1,290
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,173	1,739
Gross unrealized gains	14	13
Gross unrealized losses	(3)	(7)
Fair value	$ 1,184	$ 1,745