Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 763	$ 519	$ 694	$ 634	$ 1,282	$ 1,328
Preferred stock dividends	(34)		(32)		(64)	(85)
Dividends and undistributed earnings allocated to participating securities	(1)		0		(1)	(1)
Net income available to common shareholders	728		662		1,217	1,242
Net income available to common shareholders	$ 728		$ 662		$ 1,217	$ 1,242
Basic average common shares	345,889		352,157		348,303	352,952
Effect of dilutive securities: common stock options and common stock awards (in shares)	5,693		4,256		5,131	4,076
Diluted average common shares	351,582		356,413		353,434	357,028
Anti-dilutive securities (in shares)	176		2,989		192	1,580
Earnings per common share:
Basic (in USD per share)	$ 2.11		$ 1.88		$ 3.49	$ 3.52
Diluted (in USD per share)	$ 2.07		$ 1.86		$ 3.44	$ 3.48