Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 694	$ 634	$ 587	$ 508	$ 1,328	$ 1,095
Preferred stock dividends	(32)		(50)		(85)	(105)
Dividends and undistributed earnings allocated to participating securities	0		0		(1)	(1)
Net income available to common shareholders	$ 662		$ 537		$ 1,242	$ 989
Basic average common shares	352,157		373,773		352,952	375,832
Effect of dilutive securities: common stock options and common stock awards (in shares)	4,256		3,804		4,076	3,633
Diluted average common shares	356,413		377,577		357,028	379,465
Anti-dilutive securities (in shares)	2,989		3,345		1,580	2,665
Earnings per common share:
Basic (in USD per share)	$ 1.88		$ 1.44		$ 3.52	$ 2.63
Diluted (in USD per share)	$ 1.86		$ 1.42		$ 3.48	$ 2.61