Employee Benefit Plans Stock-Based Compensation Expense Recognized in Noninterest Expense (Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Performance Stock Units, Cash Distributions	$ 1	$ 2	$ 76	$ 79