Investments - Schedule of Available-for-Sale Securities Whose Value is Below Amortized Cost (Details) $ in Millions	Jun. 30, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Fair Value
Nine months or greater, but less than twelve months	$ 20,949	$ 30,166
Twelve months or greater	41,155	36,345
Total	62,104	66,511
Gross Unrealized Losses
Nine months or greater, but less than twelve months	3,627	4,537
Twelve months or greater	6,352	6,468
Total	$ 9,979	$ 11,005
Number of Securities
Total | security	6,381	6,985
Fair Value Decline, Greater Than 20%
Fair Value
Less than six months	$ 1,846	$ 5,405
Six months or greater, but less than nine months	1,215	371
Nine months or greater, but less than twelve months	1,516	71
Twelve months or greater	4,651	4,440
Total	9,228	10,287
Gross Unrealized Losses
Less than six months	571	1,621
Six months or greater, but less than nine months	372	198
Nine months or greater, but less than twelve months	498	28
Twelve months or greater	2,294	2,218
Total	$ 3,735	$ 4,065
Number of Securities
Less than six months | security	359	799
Six months or greater, but less than nine months | security	256	216
Nine months or greater, but less than twelve months | security	304	37
Twelve months or greater | security	796	741
Total | security	1,715	1,793