Reportable Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Non-interest revenues	$ 8,425	$ 5,791	$ 15,659	$ 13,771
Revenue from contracts with customers	6,762	4,357	12,416	10,653
Interest income	2,140	2,426	4,332	5,472
Interest expense	322	542	684	1,258
Total revenues net of interest expense	10,243	7,675	19,307	17,985
Pretax segment income (loss)	2,940	622	5,933	1,074
Total assets	186,973	189,000	186,973	189,000	$ 191,367
Corporate and Other
Segment Reporting Information [Line Items]
Non-interest revenues	(58)	(74)	(136)	(121)
Revenue from contracts with customers	(7)	(6)	(13)	(16)
Interest income	42	49	86	179
Interest expense	57	122	132	346
Total revenues net of interest expense	(73)	(147)	(182)	(288)
Pretax segment income (loss)	(308)	(387)	(520)	(738)
Total assets	37,000	59,000	37,000	59,000
GCSG | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	4,464	3,024	8,283	7,030
Revenue from contracts with customers	3,223	1,927	5,837	4,729
Interest income	1,749	1,971	3,557	4,382
Interest expense	174	272	362	600
Total revenues net of interest expense	6,039	4,723	11,478	10,812
Pretax segment income (loss)	1,882	843	4,037	1,102
Total assets	90,000	81,000	90,000	81,000
GCS | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	2,815	2,014	5,247	4,802
Revenue from contracts with customers	2,411	1,652	4,463	4,024
Interest income	345	402	681	901
Interest expense	111	154	227	354
Total revenues net of interest expense	3,049	2,262	5,701	5,349
Pretax segment income (loss)	839	(22)	1,504	(3)
Total assets	46,000	38,000	46,000	38,000
GMNS | Operating Segments
Segment Reporting Information [Line Items]
Non-interest revenues	1,204	827	2,265	2,060
Revenue from contracts with customers	1,135	784	2,129	1,916
Interest income	4	4	8	10
Interest expense	(20)	(6)	(37)	(42)
Total revenues net of interest expense	1,228	837	2,310	2,112
Pretax segment income (loss)	527	188	912	713
Total assets	$ 14,000	$ 11,000	$ 14,000	$ 11,000