Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 714	$ 763	$ 519	$ 555	$ 694	$ 634	$ 1,996	$ 1,883
Preferred stock dividends	(21)			(38)			(85)	(123)
Dividends and undistributed earnings allocated to participating securities	0			0			(1)	(1)
Net income available to common shareholders	693			517			1,910	1,759
Net income available to common shareholders	$ 693			$ 517			$ 1,910	$ 1,759
Basic average common shares (in shares)	347,718			352,586			348,106	352,829
Effect of dilutive securities: common stock options and common stock awards (in shares)	5,776			4,582			5,270	4,142
Diluted average common shares (in shares)	353,494			357,168			353,376	356,971
Anti-dilutive securities (in shares)	97			1,309			119	1,351
Earnings per common share:
Basic (in USD per share)	$ 1.99			$ 1.47			$ 5.49	$ 4.99
Diluted (in USD per share)	$ 1.96			$ 1.45			$ 5.40	$ 4.93