CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income		$ 897	$ 199	$ 141	$ 109	$ 153	$ 187	$ 134	$ 92	$ 1,346	$ 566	$ 585
Other comprehensive income (loss):
Foreign currency translation adjustments										67	28	(174)
Fixed price diesel swaps										0	4	(2)
Other comprehensive income (loss)	[1]									67	32	(176)
Comprehensive income										$ 1,413	$ 598	$ 409

[1] There were no material reclassifications from accumulated other comprehensive loss reflected in other comprehensive income (loss) during the years ended December 31, 2017, 2016 or 2015. There is no tax impact related to the foreign currency translation adjustments, as the earnings are considered permanently reinvested. There were no material taxes associated with other comprehensive income (loss) during the years ended December 31, 2017, 2016 or 2015.