Investments - Schedule of Available-for-Sale Securities Whose Value is Below Amortized Cost (Details) $ in Millions	Mar. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Fair Value
Nine months or greater, but less than twelve months	$ 18,261	$ 16,851
Twelve months or greater	41,476	43,082
Total	59,737	59,933
Gross Unrealized Losses
Nine months or greater, but less than twelve months	2,180	1,999
Twelve months or greater	5,455	4,967
Total	$ 7,635	$ 6,966
Number of Securities
Total | security	7,093	7,167
Fair Value Decline, Greater Than 20%
Fair Value
Less than six months	$ 3,677	$ 2,480
Six months or greater, but less than nine months	423	321
Nine months or greater, but less than twelve months	254	321
Twelve months or greater	3,563	3,485
Total	7,917	6,607
Gross Unrealized Losses
Less than six months	1,296	916
Six months or greater, but less than nine months	158	90
Nine months or greater, but less than twelve months	80	106
Twelve months or greater	1,454	1,336
Total	$ 2,988	$ 2,448
Number of Securities
Less than six months | security	687	529
Six months or greater, but less than nine months | security	131	79
Nine months or greater, but less than twelve months | security	68	87
Twelve months or greater | security	731	704
Total | security	1,617	1,399