Noninterest Revenue and Noninterest Expense - Card Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total card income	$ 1,005	$ 1,169	$ 4,002	$ 3,138
Interchange and merchant processing income
Disaggregation of Revenue [Line Items]
Total card income	6,117	4,757	16,959	13,479
Rewards costs and partner payments
Disaggregation of Revenue [Line Items]
Total card income	(4,860)	(3,497)	(12,676)	(9,895)
Other card income
Disaggregation of Revenue [Line Items]
Total card income	$ (252)	$ (91)	$ (281)	$ (446)