Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 661	$ 502
Preferred stock dividends	(55)	(55)
Dividends and undistributed earnings allocated to participating securities	(1)	(1)
Net income available to common shareholders	$ 605	$ 446
Basic average common shares	367,439	381,224
Effect of dilutive securities: common stock options and common stock awards (in shares)	5,180	5,193
Diluted average common shares	372,619	386,417
Anti-dilutive securities (in shares)	0	580
Earnings per Common Share:
Basic (in USD per share)	$ 1.65	$ 1.17
Diluted (in USD per share)	$ 1.62	$ 1.15