Investment Securities - Fair Value and Gross Unrealized Losses by Aging Category (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Available-for-sale securities
Less than 12 months, Fair value	$ 17,896	$ 10,737
Less than 12 months, Gross unrealized losses	195	49
12 months or more, Fair Value	11,545	16,033
12 months or more, Gross unrealized losses	808	866
Total fair value	29,441	26,770
Total gross unrealized losses	1,003	915
Total mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	201	309
Less than 12 months, Gross unrealized losses	4	3
12 months or more, Fair Value	2,687	3,657
12 months or more, Gross unrealized losses	149	205
Total fair value	2,888	3,966
Total gross unrealized losses	153	208
U.S. GSEs and government agencies mortgage-backed securities
Available-for-sale securities
Total fair value	5,000	4,600
Residential: U.S. Mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	143	81
Less than 12 months, Gross unrealized losses	1	0
12 months or more, Fair Value	1,089	1,160
12 months or more, Gross unrealized losses	67	68
Total fair value	1,232	1,241
Total gross unrealized losses	68	68
Residential: Non-U.S. mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	0	0
Less than 12 months, Gross unrealized losses	0	0
12 months or more, Fair Value	212	722
12 months or more, Gross unrealized losses	0	1
Total fair value	212	722
Total gross unrealized losses	0	1
Commercial mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	58	228
Less than 12 months, Gross unrealized losses	3	3
12 months or more, Fair Value	1,386	1,775
12 months or more, Gross unrealized losses	82	136
Total fair value	1,444	2,003
Total gross unrealized losses	85	139
Obligations of U.S. states and municipalities
Available-for-sale securities
Less than 12 months, Fair value	9,704	2,134
Less than 12 months, Gross unrealized losses	158	20
12 months or more, Fair Value	2,181	2,278
12 months or more, Gross unrealized losses	268	246
Total fair value	11,885	4,412
Total gross unrealized losses	426	266
Non-U.S. government debt securities
Available-for-sale securities
Less than 12 months, Fair value	7,355	7,145
Less than 12 months, Gross unrealized losses	32	23
12 months or more, Fair Value	4,493	4,987
12 months or more, Gross unrealized losses	329	336
Total fair value	11,848	12,132
Total gross unrealized losses	361	359
Corporate debt securities
Available-for-sale securities
Less than 12 months, Fair value	9	9
Less than 12 months, Gross unrealized losses	0	0
12 months or more, Fair Value	47	79
12 months or more, Gross unrealized losses	29	28
Total fair value	56	88
Total gross unrealized losses	29	28
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Less than 12 months, Fair value	458	932
Less than 12 months, Gross unrealized losses	0	2
12 months or more, Fair Value	1,122	3,744
12 months or more, Gross unrealized losses	14	26
Total fair value	1,580	4,676
Total gross unrealized losses	14	28
Asset-backed securities: Other
Available-for-sale securities
Less than 12 months, Fair value	169	208
Less than 12 months, Gross unrealized losses	1	1
12 months or more, Fair Value	1,015	1,288
12 months or more, Gross unrealized losses	19	25
Total fair value	1,184	1,496
Total gross unrealized losses	$ 20	$ 26