Business Segments and Revenue from Contracts with Customers - Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total contract revenue	$ 1,001	$ 937
Revenue from other sources	290	287
Non-interest income (loss)	1,291	1,224
Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	813	758
Revenue from other sources	216	153
Non-interest income (loss)	1,029	911
Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	120	133
Revenue from other sources	21	(7)
Non-interest income (loss)	141	126
Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	68	47
Revenue from other sources	172	191
Non-interest income (loss)	240	238
Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	(1)
Revenue from other sources	(119)	(50)
Non-interest income (loss)	(119)	(51)
Interchange fees, net
Disaggregation of Revenue [Line Items]
Total contract revenue	817	752
Interchange fees, net | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	743	688
Interchange fees, net | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	57	50
Interchange fees, net | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	17	15
Interchange fees, net | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	(1)
Service charges and other customer-related fees
Disaggregation of Revenue [Line Items]
Total contract revenue	94	95
Service charges and other customer-related fees | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0
Service charges and other customer-related fees | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	44	64
Service charges and other customer-related fees | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	50	31
Service charges and other customer-related fees | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0
Other
Disaggregation of Revenue [Line Items]
Total contract revenue	90	90
Other | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	70	70
Other | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	19	19
Other | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	1	1
Other | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	$ 0	$ 0