Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 555	$ 694	$ 634	$ 583	$ 587	$ 508	$ 1,883	$ 1,678
Preferred stock dividends	(38)			(55)			(123)	(160)
Dividends and undistributed earnings allocated to participating securities	0			0			(1)	(1)
Net income available to common shareholders	$ 517			$ 528			$ 1,759	$ 1,517
Basic average common shares	352,586			366,732			352,829	372,766
Effect of dilutive securities: equity-based awards (in shares)	4,582			3,863			4,142	3,595
Diluted average common shares	357,168			370,595			356,971	376,361
Anti-dilutive securities (in shares)	1,309			3,037			1,351	2,559
Earnings per common share:
Basic (in USD per share)	$ 1.47			$ 1.44			$ 4.99	$ 4.07
Diluted (in USD per share)	$ 1.45			$ 1.42			$ 4.93	$ 4.03