Investments - Schedule of Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value for Fixed Income Securities (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	$ 54,383	$ 53,616
Gross unrealized gains	633	361
Gross unrealized losses	(581)	(1,230)
Fair value	54,435	52,747
U.S. government and agencies
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	15,640	11,423
Gross unrealized gains	86	15
Gross unrealized losses	(14)	(330)
Fair value	15,712	11,108
Municipal
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	7,451	8,985
Gross unrealized gains	29	33
Gross unrealized losses	(194)	(176)
Fair value	7,286	8,842
Corporate
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	27,849	30,630
Gross unrealized gains	470	272
Gross unrealized losses	(357)	(710)
Fair value	27,962	30,192
Foreign government
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,385	1,352
Gross unrealized gains	18	22
Gross unrealized losses	(12)	(10)
Fair value	1,391	1,364
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	973	1,130
Gross unrealized gains	14	19
Gross unrealized losses	(4)	(4)
Fair value	983	1,145
MBS
Debt Securities, Available-for-Sale [Line Items]
Amortized cost, net	1,085	96
Gross unrealized gains	16	0
Gross unrealized losses	0	0
Fair value	$ 1,101	$ 96

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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