Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value
Less than 12 months	$ 4,593	$ 7,990
12 months or more	30,556	40,782
Total	35,149	48,772
Unrealized Losses
Less than 12 months	(486)	(580)
12 months or more	(4,128)	(4,799)
Total	(4,614)	(5,379)
U.S. Treasury and federal agencies securities
Fair Value
Less than 12 months	479	1,989
12 months or more	0	2,157
Total	479	4,146
Unrealized Losses
Less than 12 months	0	(3)
12 months or more	0	(139)
Total	0	(142)
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	70	81
12 months or more	4,780	10,200
Total	4,850	10,281
Unrealized Losses
Less than 12 months	(3)	(2)
12 months or more	(776)	(1,280)
Total	(779)	(1,282)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	3,796	5,439
12 months or more	17,382	19,957
Total	21,178	25,396
Unrealized Losses
Less than 12 months	(468)	(556)
12 months or more	(2,695)	(2,674)
Total	(3,163)	(3,230)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	35	141
12 months or more	4,398	4,284
Total	4,433	4,425
Unrealized Losses
Less than 12 months	0	(2)
12 months or more	(403)	(425)
Total	(403)	(427)
Asset-backed securities and other debt securities
Fair Value
Less than 12 months	213	340
12 months or more	3,996	4,184
Total	4,209	4,524
Unrealized Losses
Less than 12 months	(15)	(17)
12 months or more	(254)	(281)
Total	$ (269)	$ (298)