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				(74)
Stock-based compensation plans expense				76
Issuance of shares for warrant exercise				(80)
Net income	$ 1,002				1,002
Dividends declared on preferred stock	(5)				(5)
Dividends declared on common stock					(216)
Treasury stock acquired						(27)
Issuance of shares for warrant exercise							$ 80				$ 85
Net shares acquired related to employee incentive and stock compensation plans						(31)
Total other comprehensive income								1,381
Ending balance at Jun. 30, 2019	$ 15,292	$ 334	$ 4	4,300	11,836	(984)		(198)
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 Jun. 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			(505)
Issuance of shares under incentive and stock compensation plans			1,859
Return of shares under incentive and stock compensation plans to treasury stock			(621)
Issuance of shares for warrant exercise			1,721
Common Shares Outstanding, at end of period at Jun. 30, 2019			361,605
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.60
Cash dividends declared per preferred share	$ 375.00
Beginning balance at Mar. 31, 2019				4,329	11,572	(1,014)		(885)	0	11,572
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(6)
Stock-based compensation plans expense				21
Issuance of shares for warrant exercise				(44)
Net income	$ 372				372
Dividends declared on preferred stock	0				0
Dividends declared on common stock					(108)
Treasury stock acquired						(27)
Issuance of shares for warrant exercise							44				14
Net shares acquired related to employee incentive and stock compensation plans						(1)
Total other comprehensive income								687
Ending balance at Jun. 30, 2019	$ 15,292	$ 334	$ 4	4,300	11,836	(984)		(198)
Preferred Shares Outstanding, beginning of period at Mar. 31, 2019		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Jun. 30, 2019		13,800
Common Shares Outstanding, beginning of period (in thousands) at Mar. 31, 2019			360,865
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			(505)
Issuance of shares under incentive and stock compensation plans			325
Return of shares under incentive and stock compensation plans to treasury stock			(20)
Issuance of shares for warrant exercise			940
Common Shares Outstanding, at end of period at Jun. 30, 2019			361,605
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.30
Cash dividends declared per preferred share	$ 0
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				(84)
Stock-based compensation plans expense				71
Issuance of shares for warrant exercise				0
Net income	741				741
Dividends declared on preferred stock	(10)				(10)
Dividends declared on common stock					(231)
Treasury stock acquired	(150)					(150)
Issuance of shares for warrant exercise							0				91
Net shares acquired related to employee incentive and stock compensation plans						(35)
Total other comprehensive income								427
Ending balance at Jun. 30, 2020	$ 17,072	$ 334	$ 4	4,299	13,167	(1,211)		479
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 Jun. 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			1,860
Return of shares under incentive and stock compensation plans to treasury stock			(670)
Issuance of shares for warrant exercise			0
Common Shares Outstanding, at end of period at Jun. 30, 2020			358,099
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.65
Cash dividends declared per preferred share	$ 750.00
Beginning balance at Mar. 31, 2020				4,286	12,819	(1,220)		(957)	$ 0	$ 12,819
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(5)
Stock-based compensation plans expense				18
Issuance of shares for warrant exercise				0
Net income	$ 468				468
Dividends declared on preferred stock	(5)				(5)
Dividends declared on common stock					(115)
Treasury stock acquired						0
Issuance of shares for warrant exercise							$ 0				$ 9
Net shares acquired related to employee incentive and stock compensation plans						0
Total other comprehensive income								1,436
Ending balance at Jun. 30, 2020	$ 17,072	$ 334	$ 4	$ 4,299	$ 13,167	$ (1,211)		$ 479
Preferred Shares Outstanding, beginning of period at Mar. 31, 2020		13,800
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Jun. 30, 2020		13,800
Common Shares Outstanding, beginning of period (in thousands) at Mar. 31, 2020			357,934
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			0
Issuance of shares under incentive and stock compensation plans			175
Return of shares under incentive and stock compensation plans to treasury stock			(10)
Issuance of shares for warrant exercise			0
Common Shares Outstanding, at end of period at Jun. 30, 2020			358,099
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