Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value
Less than 12 months	$ 8,304	$ 7,990
12 months or more	30,108	40,782
Total	38,412	48,772
Unrealized Losses
Less than 12 months	(319)	(580)
12 months or more	(3,051)	(4,799)
Total	(3,370)	(5,379)
U.S. Treasury and federal agencies securities
Fair Value
Less than 12 months	4,210	1,989
12 months or more	0	2,157
Total	4,210	4,146
Unrealized Losses
Less than 12 months	(4)	(3)
12 months or more	0	(139)
Total	(4)	(142)
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	215	81
12 months or more	4,796	10,200
Total	5,011	10,281
Unrealized Losses
Less than 12 months	(1)	(2)
12 months or more	(605)	(1,280)
Total	(606)	(1,282)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	3,736	5,439
12 months or more	17,651	19,957
Total	21,387	25,396
Unrealized Losses
Less than 12 months	(302)	(556)
12 months or more	(1,992)	(2,674)
Total	(2,294)	(3,230)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	0	141
12 months or more	4,210	4,284
Total	4,210	4,425
Unrealized Losses
Less than 12 months	0	(2)
12 months or more	(280)	(425)
Total	(280)	(427)
Asset-backed securities and other debt securities
Fair Value
Less than 12 months	143	340
12 months or more	3,451	4,184
Total	3,594	4,524
Unrealized Losses
Less than 12 months	(12)	(17)
12 months or more	(174)	(281)
Total	$ (186)	$ (298)