Variable Interest Entities - Credit Card Securitizations (Details) - Firm-sponsored credit card trusts - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Minimum undivided interest in credit card trusts	39.00%	50.00%
Undivided interests in Firm-sponsored credit card securitization trusts	$ 5,400,000,000	$ 5,300,000,000
Senior securities
Variable Interest Entity [Line Items]
Undivided interests in Firm-sponsored credit card securitization trusts	0	0
Subordinated securities
Variable Interest Entity [Line Items]
Undivided interests in Firm-sponsored credit card securitization trusts	$ 1,500,000,000	$ 3,000,000,000.0
Minimum
Variable Interest Entity [Line Items]
Minimum undivided interest in credit card trusts	5.00%