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	$ 28,311	$ 17,427
Twelve months or greater	42,533	44,508
Total	70,844	61,935
Gross Unrealized Losses
Nine months or greater, but less than twelve months	4,933	3,526
Twelve months or greater	5,648	6,241
Total	$ 10,581	$ 9,767
Number of Securities
Total | security	7,485	7,605
Fair Value Decline, Greater Than 20%
Fair Value
Less than six months	$ 3,759	$ 2,492
Six months or greater, but less than nine months	423	343
Nine months or greater, but less than twelve months	275	336
Twelve months or greater	3,709	4,094
Total	8,166	7,265
Gross Unrealized Losses
Less than six months	1,318	927
Six months or greater, but less than nine months	158	96
Nine months or greater, but less than twelve months	86	109
Twelve months or greater	1,517	2,922
Total	$ 3,079	$ 4,054
Number of Securities
Less than six months | security	697	533
Six months or greater, but less than nine months | security	131	79
Nine months or greater, but less than twelve months | security	68	90
Twelve months or greater | security	740	997
Total | security	1,636	1,699