Line of Business Information - Components of Other (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting Information [Line Items]
Foreign exchange trading services	$ 431	$ 336	$ 793	$ 667
Client rescoping (revenue impact)			(24)
Repositioning charges			(100)
Client rescoping (expense impact)			(18)
FDIC special assessment		(130)
Income before income tax expense	889	912	1,711	1,510
Client rescoping (revenue impact) before taxes			42
Client rescoping (revenue impact)			24
Client rescoping (expense impact)			18
Repositioning charges			100
FDIC special assessment expense		130
Other
Segment Reporting Information [Line Items]
Foreign exchange trading services	3	0	3	0
Client rescoping (revenue impact)	(24)	0	(24)	0
Repositioning charges	(100)	0	(100)	0
Client rescoping (expense impact)	(18)	0	(18)	0
FDIC special assessment	0	0	0	(130)
Total other income (loss)	1	(1)	1	(1)
Income before income tax expense	(138)	(1)	(138)	(131)
Client rescoping (revenue impact)	24	0	24	0
Client rescoping (expense impact)	18	0	18	0
Repositioning charges	100	0	100	0
FDIC special assessment expense	$ 0	$ 0	$ 0	$ 130