Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Preferred Stock [Member]	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Retained Earnings	Share-based Payment Arrangement [Member] Treasury Stock
Beginning balance at Dec. 31, 2019				$ 4,312	$ 12,685	$ (1,117)	$ 52		$ 12,667
Beginning balance (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019								$ (18)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(79)
Stock-based compensation plans expense				53
Net income	$ 273				273
Dividends declared on preferred stock	(5)				(5)
Dividends declared on common stock					(116)
Treasury stock acquired	(150)					(150)
Issuance of shares for warrant exercise										$ 82
Net shares acquired related to employee incentive and stock compensation plans						(35)
Total other comprehensive loss							(1,009)
Ending balance at Mar. 31, 2020	$ 15,266	$ 334	$ 4	4,286	12,819	(1,220)	(957)
Preferred Shares Outstanding, beginning of period at Dec. 31, 2019		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Mar. 31, 2020		13,800
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2019			359,570
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired	(2,700)		(2,661)
Issuance of shares under incentive and stock compensation plans			1,685
Return of shares under incentive and stock compensation plans to treasury stock			(660)
Common Shares Outstanding, at end of period at Mar. 31, 2020			357,934
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.325
Cash dividends declared per preferred share	$ 375.00
Beginning balance at Dec. 31, 2020	$ 18,556			4,322	13,918	(1,192)	1,170	$ 0	$ 13,918
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(69)
Stock-based compensation plans expense				57
Net income	249				249
Dividends declared on preferred stock	(5)				(5)
Dividends declared on common stock					(126)
Treasury stock acquired	(123)					(123)
Issuance of shares for warrant exercise										$ 94
Net shares acquired related to employee incentive and stock compensation plans						(25)
Total other comprehensive loss							(906)
Ending balance at Mar. 31, 2021	$ 17,702	$ 334	$ 4	$ 4,310	$ 14,036	$ (1,246)	$ 264
Preferred Shares Outstanding, beginning of period at Dec. 31, 2020		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Mar. 31, 2021		13,800
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2020			358,489
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired	(2,400)		(2,386)
Issuance of shares under incentive and stock compensation plans			1,914
Return of shares under incentive and stock compensation plans to treasury stock			(500)
Common Shares Outstanding, at end of period at Mar. 31, 2021			357,517
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.350
Cash dividends declared per preferred share	$ 375.00