Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 620	$ 619	$ 1,122	$ 987
Preferred stock dividends	(36)	(33)	(91)	(82)
Dividends and undistributed earnings allocated to participating securities	0	(1)	(1)	(1)
Net income available to common shareholders	$ 584	$ 585	$ 1,030	$ 904
Basic average common shares	375,395	394,160	378,293	396,790
Effect of dilutive securities: common stock options and common stock awards (in shares)	5,520	4,687	5,196	4,323
Diluted average common shares	380,915	398,847	383,489	401,113
Anti-dilutive securities (in shares)	293	3,277	527	3,426
Earnings per Common Share:
Basic (in USD per share)	$ 1.56	$ 1.48	$ 2.72	$ 2.28
Diluted (in USD per share)	$ 1.53	$ 1.47	$ 2.69	$ 2.25