Business Segments and Revenue from Contracts with Customers Business Segments and Revenue from Contracts with Customers - Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total contract revenue	$ 894	$ 804
Revenue from other sources	398	387
Total non-interest income	1,292	1,191
Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	714	596
Revenue from other sources	236	261
Total non-interest income	950	857
Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	145	169
Revenue from other sources	15	5
Total non-interest income	160	174
Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	36	39
Revenue from other sources	151	148
Total non-interest income	187	187
Other
Disaggregation of Revenue [Line Items]
Total contract revenue	(1)	0
Revenue from other sources	(4)	(27)
Total non-interest income	(5)	(27)
Interchange Fees, Contracts
Disaggregation of Revenue [Line Items]
Total contract revenue	758	643
Interchange Fees, Contracts | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	702	594
Interchange Fees, Contracts | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	46	42
Interchange Fees, Contracts | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	11	7
Interchange Fees, Contracts | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	(1)	0
Service Charges And Other Customer Fees, Contracts
Disaggregation of Revenue [Line Items]
Total contract revenue	100	130
Service Charges And Other Customer Fees, Contracts | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0
Service Charges And Other Customer Fees, Contracts | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	75	98
Service Charges And Other Customer Fees, Contracts | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	25	32
Service Charges And Other Customer Fees, Contracts | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0
Other Contract Revenue
Disaggregation of Revenue [Line Items]
Total contract revenue	36	31
Other Contract Revenue | Operating segments | Credit Card
Disaggregation of Revenue [Line Items]
Total contract revenue	12	2
Other Contract Revenue | Operating segments | Consumer Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	24	29
Other Contract Revenue | Operating segments | Commercial Banking
Disaggregation of Revenue [Line Items]
Total contract revenue	0	0
Other Contract Revenue | Other
Disaggregation of Revenue [Line Items]
Total contract revenue	$ 0	$ 0