Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 587	$ 508	$ 733	$ 659	$ 1,095	$ 1,392
Preferred stock dividends	(50)		(36)		(105)	(91)
Dividends and undistributed earnings allocated to participating securities	0		0		(1)	(1)
Net income available to common shareholders	$ 537		$ 697		$ 989	$ 1,300
Basic average common shares	373,773		365,619		375,832	366,524
Effect of dilutive securities: common stock options and common stock awards (in shares)	3,804		4,791		3,633	4,891
Diluted average common shares	377,577		370,410		379,465	371,415
Anti-dilutive securities (in shares)	3,345		1,206		2,665	2
Earnings per common share:
Basic (in USD per share)	$ 1.44		$ 1.91		$ 2.63	$ 3.55
Diluted (in USD per share)	$ 1.42		$ 1.88		$ 2.61	$ 3.50