Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value
Less than 12 months	$ 7,990	$ 41,346
12 months or more	40,782	8,190
Total	48,772	49,536
Unrealized Losses
Less than 12 months	(580)	(4,295)
12 months or more	(4,799)	(1,751)
Total	(5,379)	(6,046)
U.S. Treasury and federal agencies securities
Fair Value
Less than 12 months	1,989	2,400
12 months or more	2,157	0
Total	4,146	2,400
Unrealized Losses
Less than 12 months	(3)	(188)
12 months or more	(139)	0
Total	(142)	(188)
Obligations of states and political subdivisions securities
Fair Value
Less than 12 months		0
12 months or more		1
Total		1
Unrealized Losses
Less than 12 months		0
12 months or more		0
Total		0
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	81	10,078
12 months or more	10,200	938
Total	10,281	11,016
Unrealized Losses
Less than 12 months	(2)	(1,170)
12 months or more	(1,280)	(202)
Total	(1,282)	(1,372)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	5,439	22,083
12 months or more	19,957	3,697
Total	25,396	25,780
Unrealized Losses
Less than 12 months	(556)	(2,487)
12 months or more	(2,674)	(1,026)
Total	(3,230)	(3,513)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	141	3,621
12 months or more	4,284	1,059
Total	4,425	4,680
Unrealized Losses
Less than 12 months	(2)	(272)
12 months or more	(425)	(248)
Total	(427)	(520)
Asset-backed securities and other debt securities
Fair Value
Less than 12 months	340	3,164
12 months or more	4,184	2,495
Total	4,524	5,659
Unrealized Losses
Less than 12 months	(17)	(178)
12 months or more	(281)	(275)
Total	$ (298)	$ (453)