Noninterest Revenue and Noninterest Expense - Card Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total card income	$ 1,647	$ 974	$ 2,997	$ 1,969
Interchange and merchant processing income
Disaggregation of Revenue [Line Items]
Total card income	5,974	3,940	10,842	8,722
Rewards costs and partner payments
Disaggregation of Revenue [Line Items]
Total card income	(4,282)	(2,816)	(7,816)	(6,398)
Other card income
Disaggregation of Revenue [Line Items]
Total card income	$ (45)	$ (150)	$ (29)	$ (355)