Investments - Schedule of Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value for Fixed Income Securities (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	$ 59,338	$ 58,730
Gross unrealized gains	400	777
Gross unrealized losses	(678)	(392)
Fair value	59,060	59,115
U.S. government and agencies
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	12,140	18,165
Gross unrealized gains	10	43
Gross unrealized losses	(108)	(75)
Fair value	12,042	18,133
Municipal
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	6,030	5,617
Gross unrealized gains	43	87
Gross unrealized losses	(83)	(61)
Fair value	5,990	5,643
Corporate
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	35,967	30,050
Gross unrealized gains	315	585
Gross unrealized losses	(449)	(234)
Fair value	35,833	30,401
Foreign government
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,513	1,464
Gross unrealized gains	9	13
Gross unrealized losses	(21)	(17)
Fair value	1,501	1,460
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	2,542	1,348
Gross unrealized gains	5	8
Gross unrealized losses	(14)	(4)
Fair value	2,533	1,352
MBS
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,146	2,086
Gross unrealized gains	18	41
Gross unrealized losses	(3)	(1)
Fair value	$ 1,161	$ 2,126