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 (in shares) at Dec. 31, 2018				80	[1]			33
Balance at Dec. 31, 2018				$ 1		$ 2,408	$ 4,101	$ (2,870)	$ (237)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 175					175
Foreign currency translation adjustments		20	[3],[4]						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 (in shares) at Mar. 31, 2019				79	[1]			35
Balance at Mar. 31, 2019				$ 1		2,394	4,276	$ (3,080)	(216)	[2]
Balance (in shares) at Dec. 31, 2019				74	[1]			39
Balance at Dec. 31, 2019		3,830		$ 1		2,440	5,275	$ (3,700)	(186)	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		173					173
Foreign currency translation adjustments		(103)	[3],[4]						(103)	[2],[5]
Fixed price diesel swaps	[2]								(3)
Stock compensation expense, net (in shares)	[1]			1
Stock compensation expense, net						13
Exercise of common stock options						1
Shares repurchased and retired						(19)
Repurchase of common stock (in shares)				(3)	[1]			(3)
Repurchase of common stock								$ (257)
Balance (in shares) at Mar. 31, 2020				72	[1]			42
Balance at Mar. 31, 2020		$ 3,635		$ 1		$ 2,435	$ 5,448	$ (3,957)	$ (292)	[2]

[1] Common stock outstanding decreased by approximately 6 million net shares during the year ended December 31, 2019.

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

[3] The 2020 activity primarily reflects a significant change in Canadian currency exchange rates.

[4] There were no material reclassifications from accumulated other comprehensive loss reflected in other comprehensive income (loss) during 2020 or 2019. There is no tax impact related to the foreign currency translation adjustments, as the earnings are considered permanently reinvested. We have historically considered the undistributed earnings of our foreign subsidiaries to be indefinitely reinvested. We have not repatriated funds to the U.S. to satisfy domestic liquidity needs, nor do we anticipate the need to do so. If we determine that all or a portion of our foreign earnings are no longer indefinitely reinvested, we may be subject to additional foreign withholding taxes and U.S. state income taxes. There were no material taxes associated with other comprehensive income (loss) during 2020 or 2019.

[5] Primarily reflects a significant change in Canadian currency exchange rates.