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	[2]
Balance (in shares) at Dec. 31, 2019				74	[1]			39
Balance at Dec. 31, 2019				$ 1		$ 2,440	$ 5,275	$ (3,700)	$ (186)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 385					385
Foreign currency translation adjustments		(58)	[3],[4]						(58)	[5]
Fixed price diesel swaps		(3)							(3)
Stock compensation expense, net (in shares)	[1]			1
Stock compensation expense, net						28
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 Jun. 30, 2020				72	[1]			42
Balance at Jun. 30, 2020				$ 1		2,450	5,660	$ (3,957)	(247)
Balance (in shares) at Mar. 31, 2020				72	[1]			42
Balance at Mar. 31, 2020				$ 1		2,435	5,448	$ (3,957)	(292)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		212					212
Foreign currency translation adjustments		45	[3],[4]						45	[5]
Fixed price diesel swaps		0
Stock compensation expense, net						15
Balance (in shares) at Jun. 30, 2020				72	[1]			42
Balance at Jun. 30, 2020				$ 1		2,450	5,660	$ (3,957)	(247)
Balance (in shares) at Dec. 31, 2020				72	[1]			42
Balance at Dec. 31, 2020		4,545		$ 1		2,482	6,165	$ (3,957)	(146)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		496					496
Foreign currency translation adjustments		28	[3],[4]						28
Fixed price diesel swaps		1							1
Stock compensation expense, net						56
Shares repurchased and retired						(32)
Balance (in shares) at Jun. 30, 2021				72	[1]			42
Balance at Jun. 30, 2021		5,094		$ 1		2,506	6,661	$ (3,957)	(117)
Balance (in shares) at Mar. 31, 2021				72	[1]			42
Balance at Mar. 31, 2021				$ 1		2,473	6,368	$ (3,957)	(140)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		293					293
Foreign currency translation adjustments		23	[3],[4]						23
Fixed price diesel swaps		0
Stock compensation expense, net						35
Shares repurchased and retired						(2)
Balance (in shares) at Jun. 30, 2021				72	[1]			42
Balance at Jun. 30, 2021		$ 5,094		$ 1		$ 2,506	$ 6,661	$ (3,957)	$ (117)

[1] Common stock outstanding decreased by approximately 2 million net shares during the year ended December 31, 2020.

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

[3] There were no material reclassifications from accumulated other comprehensive loss reflected in other comprehensive income (loss) during 2021 or 2020. There was no material tax impact related to the foreign currency translation adjustments. We have historically considered the undistributed earnings of our foreign subsidiaries to be indefinitely reinvested, and, accordingly, no taxes were provided on such earnings prior to the fourth quarter of 2020. In the fourth quarter of 2020, we identified $135 of cash in our foreign operations in excess of near-term working capital needs, and determined that this amount could no longer be considered indefinitely reinvested. As a result, our prior assertion that all undistributed earnings of our foreign subsidiaries should be considered indefinitely reinvested changed. We continue to expect that the remaining balance of our undistributed foreign earnings will be indefinitely reinvested. If we determine that all or a portion of such 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 2021 or 2020.

[4] The 2020 activity primarily reflects significant changes in Canadian currency exchange rates.

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