Consolidated Statement of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Preferred Stock, end of period	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock, at cost	Accumulated Other Comprehensive Income (Loss), net of tax
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting changes, net of tax					$ 0		$ 0
Adjusted balance beginning of period					13,114		(337)
Beginning balance at Dec. 31, 2016		$ 0		$ 5,247	13,114	$ (1,125)	(337)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans				(76)
Stock-based compensation plans expense				104
Issuance of shares for warrant exercise				(67)
Treasury stock retired				829		829
Net income (loss)	$ (3,131)				(3,131)
Dividends declared on preferred stock	0				0
Dividends declared on common stock					(341)
Treasury stock acquired						(1,028)
Issuance of shares under incentive and stock compensation plans						100
Net shares acquired related to employee incentive and stock compensation plans						(37)
Stock Issued During Period, Value, Treasury Stock Reissued						67
Total other comprehensive income (loss)							1,000
Ending balance at Dec. 31, 2017	$ 13,494	$ 0	$ 4	4,379	9,642	(1,194)	663
Preferred Shares Outstanding, beginning of period at Dec. 31, 2016		0
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Dec. 31, 2017		0
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2016			373,949
Common Shares Outstanding
Treasury stock acquired			(20,218)
Issuance of shares under incentive and stock compensation plans			2,301
Return of shares under incentive and stock compensation plans to treasury stock			(747)
Issuance of shares for warrant exercise			1,550
Common Shares Outstanding, end of period at Dec. 31, 2017			356,835
Common Shares Outstanding
Cash dividends declared per common share	$ 0.94
Preferred Stock, Dividends Per Share, Declared	$ 0
Issuance of preferred stock		$ 0
Cumulative effect of accounting changes, net of tax					5		(5)
Adjusted balance beginning of period					9,647		658
Issuance of shares under incentive and stock compensation plans				(110)
Stock-based compensation plans expense				123
Issuance of shares for warrant exercise				(14)
Treasury stock retired				0		0
Net income (loss)	$ 1,807				1,807
Dividends declared on preferred stock	(6)				(6)
Dividends declared on common stock					(393)
Treasury stock acquired						0
Issuance of shares under incentive and stock compensation plans						132
Net shares acquired related to employee incentive and stock compensation plans						(43)
Stock Issued During Period, Value, Treasury Stock Reissued						14
Total other comprehensive income (loss)							(2,237)
Ending balance at Dec. 31, 2018	$ 13,101	$ 334	$ 4	4,378	11,055	(1,091)	(1,579)
Preferred Shares Outstanding
Issuance of preferred shares		13,800
Preferred Shares Outstanding, end of period at Dec. 31, 2018		13,800
Common Shares Outstanding
Treasury stock acquired			0
Issuance of shares under incentive and stock compensation plans			2,856
Return of shares under incentive and stock compensation plans to treasury stock			849
Issuance of shares for warrant exercise			309
Common Shares Outstanding, end of period at Dec. 31, 2018			359,151
Common Shares Outstanding
Cash dividends declared per common share	$ 1.10
Preferred Stock, Dividends Per Share, Declared	$ 0
Issuance of preferred stock		$ 334
Adjusted balance beginning of period					11,055		(1,579)
Issuance of shares under incentive and stock compensation plans				(100)
Stock-based compensation plans expense				114
Issuance of shares for warrant exercise				(80)
Treasury stock retired				0		0
Net income (loss)	$ 2,085				2,085
Dividends declared on preferred stock	(21)				(21)
Dividends declared on common stock					(434)
Treasury stock acquired						(200)
Issuance of shares under incentive and stock compensation plans						135
Net shares acquired related to employee incentive and stock compensation plans						(41)
Stock Issued During Period, Value, Treasury Stock Reissued						80
Total other comprehensive income (loss)							1,631
Ending balance at Dec. 31, 2019	$ 16,270	$ 334	$ 4	$ 4,312	12,685	$ (1,117)	52
Preferred Shares Outstanding
Issuance of preferred shares		0
Preferred Shares Outstanding, end of period at Dec. 31, 2019		13,800
Common Shares Outstanding
Treasury stock acquired			(3,412)
Issuance of shares under incentive and stock compensation plans			2,906
Return of shares under incentive and stock compensation plans to treasury stock			796
Issuance of shares for warrant exercise			1,721
Common Shares Outstanding, end of period at Dec. 31, 2019			359,570
Common Shares Outstanding
Cash dividends declared per common share	$ 1.20
Preferred Stock, Dividends Per Share, Declared	$ 1,125.00
Issuance of preferred stock		$ 0
Cumulative effect of accounting changes, net of tax					$ 0		$ 0