Goodwill and Intangible Assets, Net - Components of Intangible Assets with Definite Lives (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Life (in years)	4 years 3 months 18 days
Gross Carrying Amount	$ 228	$ 224
Accumulated Amortization	(140)	(112)
Intangible assets with definite lives, net	$ 88	112
Trade Names and Trademarks
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Life (in years)	5 years 9 months 18 days
Gross Carrying Amount	$ 57	58
Accumulated Amortization	(28)	(20)
Intangible assets with definite lives, net	$ 29	38
Customer Lists and Supplier Relationships
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Life (in years)	3 years 7 months 6 days
Gross Carrying Amount	$ 88	87
Accumulated Amortization	(53)	(43)
Intangible assets with definite lives, net	$ 35	44
Subscriber Relationships
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Life (in years)	3 years 8 months 12 days
Gross Carrying Amount	$ 34	35
Accumulated Amortization	(25)	(22)
Intangible assets with definite lives, net	$ 9	13
Technology and Other
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Life (in years)	3 years 3 months 18 days
Gross Carrying Amount	$ 49	44
Accumulated Amortization	(34)	(27)
Intangible assets with definite lives, net	$ 15	$ 17