Noninterest Revenue and Noninterest Expense - Components of Noninterest Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Noninterest Income (Expense) [Abstract]
Legal expense	$ 20	$ (107)	$ 90	$ 172
FDIC-related expense	$ 349	$ 353	$ 1,100	$ 1,110