Noninterest Revenue and Noninterest Expense - Card Income (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total card income	$ 1,328		$ 1,242	$ 3,623	$ 3,323
Interchange and merchant processing income
Disaggregation of Revenue [Line Items]
Total card income	4,781		4,342	13,863	12,557
Rewards costs and partner payments
Disaggregation of Revenue [Line Items]
Total card income	(3,276)		(2,727)	(9,687)	(7,941)
Adjustment to credit card rewards liability		$ 330
Other card income
Disaggregation of Revenue [Line Items]
Total card income	$ (177)		$ (373)	$ (553)	$ (1,293)
Deferred revenues, recognition period	12 months			12 months