Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 583	$ 587	$ 508	$ 764	$ 733	$ 659	$ 1,678	$ 2,156
Preferred stock dividends	(55)			(55)			(160)	(146)
Dividends and undistributed earnings allocated to participating securities	0			(1)			(1)	(2)
Net income available to common shareholders	$ 528			$ 708			$ 1,517	$ 2,008
Basic average common shares	366,732			374,963			372,766	369,368
Effect of dilutive securities: common stock options and common stock awards (in shares)	3,863			4,420			3,595	4,696
Diluted average common shares	370,595			379,383			376,361	374,064
Anti-dilutive securities (in shares)	3,037			1,360			2,559	871
Earnings per common share:
Basic (in USD per share)	$ 1.44			$ 1.89			$ 4.07	$ 5.44
Diluted (in USD per share)	$ 1.42			$ 1.87			$ 4.03	$ 5.37