Noninterest Revenue and Noninterest Expense - Card Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total card income	$ 1,020	$ 1,167	$ 2,295	$ 2,081
Interchange and merchant processing income
Disaggregation of Revenue [Line Items]
Total card income	4,723	4,309	9,082	8,215
Rewards costs and partner payments
Disaggregation of Revenue [Line Items]
Total card income	(3,527)	(2,689)	(6,411)	(5,214)
Adjustment to credit card rewards liability			330
Other card income
Disaggregation of Revenue [Line Items]
Total card income	$ (176)	$ (453)	$ (376)	$ (920)
Deferred revenues, recognition period			12 months