Investments - Schedule of Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value for Fixed Income Securities (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	$ 52,340	$ 53,616
Gross unrealized gains	536	361
Gross unrealized losses	(883)	(1,230)
Fair value	51,993	52,747
U.S. government and agencies
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	10,700	11,423
Gross unrealized gains	123	15
Gross unrealized losses	(118)	(330)
Fair value	10,705	11,108
Municipal
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	7,679	8,985
Gross unrealized gains	18	33
Gross unrealized losses	(223)	(176)
Fair value	7,474	8,842
Corporate
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	30,939	30,630
Gross unrealized gains	354	272
Gross unrealized losses	(526)	(710)
Fair value	30,767	30,192
Foreign government
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,311	1,352
Gross unrealized gains	31	22
Gross unrealized losses	(8)	(10)
Fair value	1,334	1,364
Asset-backed securities (“ABS”)
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,711	1,226
Gross unrealized gains	10	19
Gross unrealized losses	(8)	(4)
Fair value	$ 1,713	$ 1,241