Consolidated Statement of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock, at cost	Accumulated Other Comprehensive Income (Loss), net of tax
Beginning balance at Dec. 31, 2014			$ 9,123	$ 11,191	$ (2,527)	$ 928
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans			(165)
Stock-based compensation plans expense			78
Tax benefit on employee stock options and share-based awards			27
Issuance of shares for warrant exercise			(90)		90
Treasury stock retired			0		0
Net (loss) income	$ 1,682			1,682
Dividends declared on common stock				(323)
Treasury stock acquired					(1,250)
Issuance of shares under incentive and stock compensation plans					184
Net shares acquired related to employee incentive and stock compensation plans					(54)
Total other comprehensive income (loss)						(1,257)
Ending balance at Dec. 31, 2015	17,642	$ 5	8,973	12,550	(3,557)	(329)
Common Shares Outstanding, beginning of period (in thousands) (in shares) at Dec. 31, 2014		424,416
Common Shares Outstanding
Treasury stock acquired (in shares)		(28,431)
Issuance of shares under incentive and stock compensation plans (in shares)		4,877
Return of shares under incentive and stock compensation plans to treasury stock (in shares)		(1,311)
Issuance of shares for warrant exercise (in shares)		2,270
Common Shares Outstanding, end of period (in shares) at Dec. 31, 2015		401,821
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans			(143)
Stock-based compensation plans expense			74
Tax benefit on employee stock options and share-based awards			5
Issuance of shares for warrant exercise			(16)		16
Treasury stock retired			(3,646)		3,647
Net (loss) income	896			896
Dividends declared on common stock				(332)
Treasury stock acquired					(1,330)
Issuance of shares under incentive and stock compensation plans					153
Net shares acquired related to employee incentive and stock compensation plans					(54)
Total other comprehensive income (loss)						(8)
Ending balance at Dec. 31, 2016	16,903	$ 4	5,247	13,114	(1,125)	(337)
Common Shares Outstanding
Treasury stock acquired (in shares)		(30,782)
Issuance of shares under incentive and stock compensation plans (in shares)		3,766
Return of shares under incentive and stock compensation plans to treasury stock (in shares)		(1,243)
Issuance of shares for warrant exercise (in shares)		387
Common Shares Outstanding, end of period (in shares) at Dec. 31, 2016		373,949
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans			(76)
Stock-based compensation plans expense			104
Tax benefit on employee stock options and share-based awards			0
Issuance of shares for warrant exercise			(67)		67
Treasury stock retired			(829)		829
Net (loss) income	(3,131)			(3,131)
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)
Total other comprehensive income (loss)						1,000
Ending balance at Dec. 31, 2017	$ 13,494	$ 4	$ 4,379	$ 9,642	$ (1,194)	$ 663
Common Shares Outstanding
Treasury stock acquired (in shares)		(20,218)
Issuance of shares under incentive and stock compensation plans (in shares)		2,301
Return of shares under incentive and stock compensation plans to treasury stock (in shares)		(747)
Issuance of shares for warrant exercise (in shares)		1,550
Common Shares Outstanding, end of period (in shares) at Dec. 31, 2017		356,835