Goodwill (Schedule of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill, Impairment Loss	$ (102)	$ (229)	$ 0	$ (331)	$ 0	$ 0
Goodwill, Reclassification to Assets Held for Sale				4
Goodwill [Roll Forward]
Balance at December 31, 2018		713		713
Foreign currency translation adjustments				17
Balance at June 30, 2019	403			403
Western Hemisphere
Goodwill [Line Items]
Goodwill, Impairment Loss				(229)
Goodwill, Reclassification to Assets Held for Sale				4
Goodwill [Roll Forward]
Balance at December 31, 2018		494		494
Foreign currency translation adjustments				12
Balance at June 30, 2019	281			281
Eastern Hemisphere
Goodwill [Line Items]
Goodwill, Impairment Loss				102
Goodwill, Reclassification to Assets Held for Sale				0
Goodwill [Roll Forward]
Balance at December 31, 2018		$ 219		219
Foreign currency translation adjustments				5
Balance at June 30, 2019	$ 122			$ 122