Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 2,177	$ 2,143	$ 1,980
Preferred stock dividends	(182)	(173)	(130)
Dividends and undistributed earnings allocated to participating securities	(2)	(2)	(2)
Net income available to common shareholders	$ 1,993	$ 1,968	$ 1,848
Basic average common shares	374,793	391,485	407,856
Effect of dilutive securities: common stock options and common stock awards (in shares)	5,420	4,605	5,782
Diluted average common shares	380,213	396,090	413,638
Anti-dilutive securities (in shares)	188	2,143	661
Earnings per Common Share:
Basic (in USD per share)	$ 5.32	$ 5.03	$ 4.53
Diluted (in USD per share)	$ 5.24	$ 4.97	$ 4.47