Reportable Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Non-interest revenues	$ 7,234	$ 7,980
Revenue from contracts with customers	5,654	6,296
Interest income	2,192	3,046
Interest expense	362	716
Total revenues net of interest expense	9,064	10,310
Pretax segment income (loss)	2,993	452
Total assets	193,067	186,000	$ 191,367
Corporate and Other
Segment Reporting Information [Line Items]
Non-interest revenues	(78)	(48)
Revenue from contracts with customers	(7)	(14)
Interest income	45	130
Interest expense	76	224
Total revenues net of interest expense	(109)	(142)
Pretax segment income (loss)	(210)	(349)
Total assets	56,000	42,000
GCSG | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	3,690	3,894
Revenue from contracts with customers	2,490	2,693
Interest income	1,807	2,411
Interest expense	187	328
Total revenues net of interest expense	5,310	5,977
Pretax segment income (loss)	2,124	231
Total assets	81,000	87,000
GCS | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	2,432	2,788
Revenue from contracts with customers	2,053	2,372
Interest income	336	499
Interest expense	116	200
Total revenues net of interest expense	2,652	3,087
Pretax segment income (loss)	665	19
Total assets	42,000	47,000
GMNS | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	1,190	1,346
Revenue from contracts with customers	1,118	1,245
Interest income	4	6
Interest expense	(17)	(36)
Total revenues net of interest expense	1,211	1,388
Pretax segment income (loss)	414	551
Total assets	$ 14,000	$ 10,000