CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions		Total	Common Stock		Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Balance (shares) at Dec. 31, 2017			84	[1]			(28)
Balance at Dec. 31, 2017			$ 1		$ 2,356	$ 3,005	$ (2,105)	$ (151)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 183				183
Foreign currency translation adjustments (1)		(25)						(25)	[2]
Stock compensation expense, net (in shares)	[1]		1
Stock compensation expense, net					19
Exercise of common stock options					1
Shares repurchased and retired					(49)
Repurchase of common stock (in shares)			(1)	[1]			1
Repurchase of common stock							$ (177)
Balance (shares) at Mar. 31, 2018			84	[1]			(29)
Balance at Mar. 31, 2018			$ 1		2,327	3,188	$ (2,282)	(176)	[2]
Balance (shares) at Dec. 31, 2018			80	[1]			(33)
Balance at Dec. 31, 2018		3,403	$ 1		2,408	4,101	$ (2,870)	(237)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		175				175
Foreign currency translation adjustments (1)		20						20	[2]
Fixed price diesel swaps	[2]							1
Stock compensation expense, net (in shares)	[1]		1
Stock compensation expense, net					15
Exercise of common stock options					4
Shares repurchased and retired					(33)
Repurchase of common stock (in shares)			(2)	[1]			2
Repurchase of common stock							$ (210)
Balance (shares) at Mar. 31, 2019			79	[1]			(35)
Balance at Mar. 31, 2019		$ 3,375	$ 1		$ 2,394	$ 4,276	$ (3,080)	$ (216)	[2]

[1] Common stock outstanding decreased by less than 5 million net shares during the year ended December 31, 2018.

[2] The Accumulated Other Comprehensive Loss balance primarily reflects foreign currency translation adjustments.