CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income		$ 310	$ 333	$ 270	$ 183	$ 897	$ 199	$ 141	$ 109	$ 1,096	$ 1,346	$ 566
Other comprehensive income (loss):
Foreign currency translation adjustments										(84)	67	28
Fixed price diesel swaps										(2)	0	4
Other comprehensive (loss) income	[1]									(86)	67	32
Comprehensive income										$ 1,010	$ 1,413	$ 598

[1] There were no material reclassifications from accumulated other comprehensive loss reflected in other comprehensive income (loss) during the years ended December 31, 2018, 2017 or 2016. There is no tax impact related to the foreign currency translation adjustments, as the earnings are considered permanently reinvested (see note 13 to the consolidated financial statements for further discussion addressing this determination). There were no material taxes associated with other comprehensive income (loss) during the years ended December 31, 2018, 2017 or 2016.