Asset Quality (Nonperforming Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Total nonperforming loans	$ 1,865	$ 2,144
OREO and Foreclosed Assets	170	230
Total nonperforming assets	$ 2,035	$ 2,374
Nonperforming loans to total loans	0.85%	1.02%
Nonperforming assets to total loans, OREO and foreclosed assets	0.92%	1.12%
Nonperforming assets to total assets	0.53%	0.65%
Interest on nonperforming loans - Computed on original terms	$ 114	$ 111
Interest on nonperforming loans - Recognized prior to nonperforming status	19	21
Total commercial lending
Total nonperforming loans	554	655
Total consumer lending
Total nonperforming loans	$ 1,311	$ 1,489