Goodwill - Changes in the Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Balance at beginning of period	$ 1,196	$ 1,189	$ 1,244
Foreign currency translation	1	7	(55)
Balance at end of period	1,197	1,196	1,189
North America [Member]
Goodwill [Roll Forward]
Balance at beginning of period	1,105	1,105	1,106
Foreign currency translation	0	0	(1)
Balance at end of period	1,105	1,105	1,105
International [Member]
Goodwill [Roll Forward]
Balance at beginning of period	91	84	138
Foreign currency translation	1	7	(54)
Balance at end of period	$ 92	$ 91	$ 84