Variable Interest Entities - Credit Card Securitizations (Details) - Firm-sponsored credit card trusts - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Minimum undivided interest in credit card trusts	37.00%	26.00%
Undivided interests in Firm-sponsored credit card securitization trusts	$ 15,100,000,000	$ 15,800,000,000
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	$ 3,000,000,000.0	$ 4,500,000,000
Minimum
Variable Interest Entity [Line Items]
Minimum undivided interest in credit card trusts	5.00%