Goodwill (Schedule of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill, Impairment Loss	$ (229)	$ 0	$ 0
Goodwill, Reclassification to Assets Held for Sale	4
Goodwill [Roll Forward]
Balance at December 31, 2018	713
Foreign currency translation adjustments	16
Balance at March 31, 2019	504
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
Foreign currency translation adjustments	12
Balance at March 31, 2019	281
Eastern Hemisphere
Goodwill [Line Items]
Goodwill, Impairment Loss	0
Goodwill, Reclassification to Assets Held for Sale	0
Goodwill [Roll Forward]
Balance at December 31, 2018	219
Foreign currency translation adjustments	4
Balance at March 31, 2019	$ 223