Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 685	$ 563	$ 1,807	$ 1,550
Preferred stock dividends	(55)	(55)	(146)	(137)
Dividends and undistributed earnings allocated to participating securities	(1)	(1)	(2)	(2)
Net income available to common shareholders	$ 629	$ 507	$ 1,659	$ 1,411
Basic average common shares	372,765	388,358	376,430	393,959
Effect of dilutive securities: common stock options and common stock awards (in shares)	5,753	4,854	5,349	4,454
Diluted average common shares	378,518	393,212	381,779	398,413
Anti-dilutive securities (in shares)	0	2,166	250	3,027
Earnings per Common Share:
Basic (in USD per share)	$ 1.69	$ 1.31	$ 4.41	$ 3.58
Diluted (in USD per share)	$ 1.66	$ 1.29	$ 4.35	$ 3.54