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]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting changes, net of tax					$ 5		$ (5)
Adjusted balance, beginning of period					9,647		658
Beginning balance at Dec. 31, 2017				$ 4,379	9,642	$ (1,194)	663
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(92)
Stock-based compensation plans expense				105
Issuance of shares for warrant exercise				(7)
Net income	$ 1,611				1,611
Dividends declared on preferred stock	0				0
Dividends declared on common stock					(285)
Treasury stock acquired						0
Issuance of shares under incentive and stock compensation plans						109
Net shares acquired related to employee incentive and stock compensation plans						(36)
Issuance of shares for warrant exercise						7
Total other comprehensive income (loss)							(2,177)
Ending balance at Sep. 30, 2018	$ 12,729	$ 0	$ 4	4,385	10,973	(1,114)	(1,519)
Preferred Shares Outstanding, beginning of period at Dec. 31, 2017		0
Preferred Shares Outstanding
Stock Issued During Period, Shares, New Issues		0
Preferred Shares Outstanding, end of period at Sep. 30, 2018		0
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2017			356,835
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			0
Issuance of shares under incentive and stock compensation plans			2,373
Return of shares under incentive and stock compensation plans to treasury stock			(694)
Issuance of shares for warrant exercise			162
Common Shares Outstanding, at end of period at Sep. 30, 2018			358,676
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.80
Cash dividends declared per preferred share	$ 0
Cumulative effect of accounting changes, net of tax					0		0
Adjusted balance, beginning of period					10,649		(1,353)
Beginning balance at Jun. 30, 2018				4,374	10,649	(1,128)	(1,353)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(9)
Stock-based compensation plans expense				22
Issuance of shares for warrant exercise				(2)
Net income	$ 432				432
Dividends declared on preferred stock	0				0
Dividends declared on common stock					(108)
Treasury stock acquired						0
Issuance of shares under incentive and stock compensation plans						14
Net shares acquired related to employee incentive and stock compensation plans						(2)
Issuance of shares for warrant exercise						2
Total other comprehensive income (loss)							(166)
Ending balance at Sep. 30, 2018	$ 12,729	$ 0	$ 4	4,385	10,973	(1,114)	(1,519)
Preferred Shares Outstanding, beginning of period at Jun. 30, 2018		0
Preferred Shares Outstanding
Stock Issued During Period, Shares, New Issues		0
Preferred Shares Outstanding, end of period at Sep. 30, 2018		0
Common Shares Outstanding, beginning of period (in thousands) at Jun. 30, 2018			358,359
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Treasury stock acquired			0
Issuance of shares under incentive and stock compensation plans			331
Return of shares under incentive and stock compensation plans to treasury stock			(57)
Issuance of shares for warrant exercise			43
Common Shares Outstanding, at end of period at Sep. 30, 2018			358,676
Shares Granted or Issued, Share-based Payment Arrangement [Abstract]
Cash dividends declared per common share	$ 0.30
Cash dividends declared per preferred share	$ 0
Cumulative effect of accounting changes, net of tax					0		0
Adjusted balance, beginning of period					11,055		(1,579)
Beginning balance at Dec. 31, 2018	$ 13,101			4,378	11,055	(1,091)	(1,579)
Ending balance at Jun. 30, 2019				4,300	11,836	(984)	(198)
Preferred Shares Outstanding, beginning of period at Dec. 31, 2018		13,800
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	(1,600)
Common Shares Outstanding, at end of period at Jun. 30, 2019			361,605
Beginning balance at Dec. 31, 2018	$ 13,101			4,378	11,055	(1,091)	(1,579)
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 under incentive and stock compensation plans						112
Net shares acquired related to employee incentive and stock compensation plans						(38)
Issuance of shares for warrant exercise						80
Total other comprehensive income (loss)							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
Stock Issued During Period, Shares, New Issues		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	$ 1,125,000,000.00
Cumulative effect of accounting changes, net of tax					0		0
Adjusted balance, beginning of period					11,836		(198)
Beginning balance at Jun. 30, 2019				4,300	11,836	(984)	(198)
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 under incentive and stock compensation plans						27
Net shares acquired related to employee incentive and stock compensation plans						(7)
Issuance of shares for warrant exercise						0
Total other comprehensive income (loss)							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
Stock Issued During Period, Shares, New Issues		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	(1,100)		(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