CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total		Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive (Loss) Income
Balance (in shares) at Dec. 31, 2017			84			28
Balance at Dec. 31, 2017			$ 1	$ 2,356	$ 3,005	$ (2,105)	$ (151)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 1,096				1,096
Foreign currency translation adjustments	(84)	[1]					(84)
Fixed price diesel swaps	(2)						(2)
Stock compensation expense, net (in shares)			1
Stock compensation expense, net				102
Exercise of common stock options				2
Shares repurchased and retired				(52)
Repurchase of common stock (in shares)			5			5
Repurchase of common stock						$ (765)
Balance (in shares) at Dec. 31, 2018			80			33
Balance at Dec. 31, 2018			$ 1	2,408	4,101	$ (2,870)	(237)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,174				1,174
Foreign currency translation adjustments	49	[1]					49
Fixed price diesel swaps	2						2
Stock compensation expense, net				61
Exercise of common stock options				11
Shares repurchased and retired				(40)
Repurchase of common stock (in shares)			6			6
Repurchase of common stock						$ (830)
Balance (in shares) at Dec. 31, 2019			74			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	890				890
Foreign currency translation adjustments	40	[1]					40	[2]
Fixed price diesel swaps	0
Stock compensation expense, net (in shares)			1
Stock compensation expense, net				70
Exercise of common stock options				1
Shares repurchased and retired				(29)
Repurchase of common stock (in shares)			3			3
Repurchase of common stock						$ (257)
Balance (in shares) at Dec. 31, 2020			72			42
Balance at Dec. 31, 2020	$ 4,545		$ 1	$ 2,482	$ 6,165	$ (3,957)	$ (146)	[2]

[1] There were no material reclassifications from accumulated other comprehensive loss reflected in other comprehensive income (loss) during the years ended December 31, 2020, 2019 or 2018. There was no material tax impact related to the foreign currency translation adjustments during the years ended December 31, 2020, 2019 or 2018. See note 14 to the consolidated financial statements for a discussion addressing our determination pertaining to the permanent reinvestment of unremitted foreign earnings. There were no material taxes associated with other comprehensive income (loss) during the years ended December 31, 2020, 2019 or 2018.

[2] As of December 31, 2020, 2019 and 2018, the Accumulated Other Comprehensive Loss balance primarily reflects foreign currency translation adjustments.