Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income	$ 634	$ 508
Preferred stock dividends	(53)	(55)
Dividends and undistributed earnings allocated to participating securities	(1)	(1)
Net income available to common shareholders	$ 580	$ 452
Basic average common shares	353,746	377,915
Effect of dilutive securities: common stock options and common stock awards (in shares)	4,247	3,788
Diluted average common shares	357,993	381,703
Anti-dilutive securities (in shares)	918	1,951
Earnings per common share:
Basic (in USD per share)	$ 1.64	$ 1.20
Diluted (in USD per share)	$ 1.62	$ 1.18