Investments - Schedule of Available-for-Sale Securities Whose Value is Below Amortized Cost (Details) $ in Millions	Sep. 30, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Fair Value
Nine months or greater, but less than twelve months	$ 19,634	$ 30,166
Twelve months or greater	39,228	36,345
Total	58,862	66,511
Gross Unrealized Losses
Nine months or greater, but less than twelve months	3,584	4,537
Twelve months or greater	5,387	6,468
Total	$ 8,971	$ 11,005
Number of Securities
Total | security	5,999	6,985
Fair Value Decline, Greater Than 20%
Fair Value
Less than six months	$ 1,168	$ 5,405
Six months or greater, but less than nine months	465	371
Nine months or greater, but less than twelve months	750	71
Twelve months or greater	5,284	4,440
Total	7,667	10,287
Gross Unrealized Losses
Less than six months	518	1,621
Six months or greater, but less than nine months	161	198
Nine months or greater, but less than twelve months	220	28
Twelve months or greater	2,216	2,218
Total	$ 3,115	$ 4,065
Number of Securities
Less than six months | security	185	799
Six months or greater, but less than nine months | security	133	216
Nine months or greater, but less than twelve months | security	192	37
Twelve months or greater | security	907	741
Total | security	1,417	1,793