Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 2,420	$ 2,242	$ 2,593
Preferred stock dividends	(162)	(232)	(188)
Dividends and undistributed earnings allocated to participating securities	(1)	(1)	(1)
Net income available to common shareholders	$ 2,257	$ 2,009	$ 2,404
Basic average common shares	352,865	369,911	371,983
Effect of dilutive securities: common stock options and common stock awards (in shares)	4,241	3,755	4,493
Diluted average common shares	357,106	373,666	376,476
Anti-dilutive securities (in shares)	1,066	2,052	1,011
Earnings per common share:
Basic (in USD per share)	$ 6.40	$ 5.43	$ 6.46
Diluted (in USD per share)	$ 6.32	$ 5.38	$ 6.39