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	Warrant [Member]	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, 2018				$ 4,378	$ 11,055	$ (1,091)		$ (1,579)	$ 0	$ 11,055
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(91)
Stock-based compensation plans expense				95
Issuance of shares for warrant exercise				(80)
Net income	$ 1,537				1,537
Dividends declared on preferred stock	(16)				(16)
Dividends declared on common stock					(325)
Treasury stock acquired						(90)
Issuance of shares for warrant exercise							$ 80				$ 112
Net shares acquired related to employee incentive and stock compensation plans						(38)
Total other comprehensive income								1,793
Ending balance at Sep. 30, 2019	$ 16,078	$ 334	$ 4	4,302	12,251	(1,027)		214
Preferred Shares Outstanding, beginning of period at Dec. 31, 2018		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Sep. 30, 2019		13,800
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2018			359,151
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			(1,581)
Issuance of shares under incentive and stock compensation plans			2,447
Return of shares under incentive and stock compensation plans to treasury stock			(755)
Issuance of shares for warrant exercise			1,721
Common Shares Outstanding, at end of period at Sep. 30, 2019			360,983
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.90
Cash dividends declared per preferred share	$ 1,125.00
Beginning balance at Jun. 30, 2019				4,300	11,836	(984)		(198)	0	11,836
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(17)
Stock-based compensation plans expense				19
Issuance of shares for warrant exercise				0
Net income	$ 535				535
Dividends declared on preferred stock	(11)				(11)
Dividends declared on common stock					(109)
Treasury stock acquired						(63)
Issuance of shares for warrant exercise							0				27
Net shares acquired related to employee incentive and stock compensation plans						(7)
Total other comprehensive income								412
Ending balance at Sep. 30, 2019	$ 16,078	$ 334	$ 4	4,302	12,251	(1,027)		214
Preferred Shares Outstanding, beginning of period at Jun. 30, 2019		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Sep. 30, 2019		13,800
Common Shares Outstanding, beginning of period (in thousands) at Jun. 30, 2019			361,605
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			(1,076)
Issuance of shares under incentive and stock compensation plans			588
Return of shares under incentive and stock compensation plans to treasury stock			(134)
Issuance of shares for warrant exercise			0
Common Shares Outstanding, at end of period at Sep. 30, 2019			360,983
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.30
Cash dividends declared per preferred share	$ 750.00
Beginning balance at Dec. 31, 2019	$ 16,270			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				(89)
Stock-based compensation plans expense				87
Issuance of shares for warrant exercise				0
Net income	1,200				1,200
Dividends declared on preferred stock	(16)				(16)
Dividends declared on common stock					(348)
Treasury stock acquired	(150)					(150)
Issuance of shares for warrant exercise							0				98
Net shares acquired related to employee incentive and stock compensation plans						(36)
Total other comprehensive income								804
Ending balance at Sep. 30, 2020	$ 17,802	$ 334	$ 4	4,310	13,503	(1,205)		856
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 Sep. 30, 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			2,011
Return of shares under incentive and stock compensation plans to treasury stock			(686)
Issuance of shares for warrant exercise			0
Common Shares Outstanding, at end of period at Sep. 30, 2020			358,234
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.975
Cash dividends declared per preferred share	$ 1,125.00
Beginning balance at Jun. 30, 2020				4,299	13,167	(1,211)		479	$ 0	$ 13,167
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(5)
Stock-based compensation plans expense				16
Issuance of shares for warrant exercise				0
Net income	$ 459				459
Dividends declared on preferred stock	(6)				(6)
Dividends declared on common stock					(117)
Treasury stock acquired						0
Issuance of shares for warrant exercise							$ 0				$ 7
Net shares acquired related to employee incentive and stock compensation plans						(1)
Total other comprehensive income								377
Ending balance at Sep. 30, 2020	$ 17,802	$ 334	$ 4	$ 4,310	$ 13,503	$ (1,205)		$ 856
Preferred Shares Outstanding, beginning of period at Jun. 30, 2020		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Sep. 30, 2020		13,800
Common Shares Outstanding, beginning of period (in thousands) at Jun. 30, 2020			358,099
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			0
Issuance of shares under incentive and stock compensation plans			151
Return of shares under incentive and stock compensation plans to treasury stock			(16)
Issuance of shares for warrant exercise			0
Common Shares Outstanding, at end of period at Sep. 30, 2020			358,234
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