Noninterest Revenue and Noninterest Expense - Card Income (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Non interest Revenue [Line Items]
Credit cost amortization period			12 months
Direct loan origination costs amortization period			12 months
Total card income	[1]		$ 4,435	$ 5,076	$ 4,743
Interchange and merchant processing income
Schedule of Non interest Revenue [Line Items]
Total card income			18,563	20,370	18,808
Reward costs and partner payments(a)
Schedule of Non interest Revenue [Line Items]
Total card income			(13,637)	(14,540)	(13,320)
Adjustment to credit card rewards liability		$ 330
Other card income
Schedule of Non interest Revenue [Line Items]
Total card income			$ (491)	$ (754)	$ (745)
Deferred revenues, recognition period			12 months
Minimum
Schedule of Non interest Revenue [Line Items]
Credit card revenue sharing agreement terms			5 years
Maximum
Schedule of Non interest Revenue [Line Items]
Credit card revenue sharing agreement terms			10 years

[1] In the second quarter of 2020, the Firm reclassified certain spend-based credit card reward costs from marketing expense to be a reduction of card income, with no effect on net income. Prior-period amounts have been revised to conform with the current presentation.