Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 519	$ 634
Preferred stock dividends	(30)	(53)
Dividends and undistributed earnings allocated to participating securities	0	(1)
Net income available to common shareholders	$ 489	$ 580
Basic average common shares	350,743	353,746
Effect of dilutive securities: common stock options and common stock awards (in shares)	4,947	4,247
Diluted average common shares	355,690	357,993
Anti-dilutive securities (in shares)	255	918
Earnings per common share:
Basic (in USD per share)	$ 1.39	$ 1.64
Diluted (in USD per share)	$ 1.37	$ 1.62