Property and Equipment, Net - Components of Property and Equipment, Net (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 509	$ 493
Less: accumulated depreciation		(252)	(240)
Total		257	253
Capitalized Software and Website Development
Property Plant And Equipment [Line Items]
Property and equipment, gross		276	259
Building
Property Plant And Equipment [Line Items]
Property and equipment, gross	[1]		123
Finance Lease Right-of-Use Asset
Property Plant And Equipment [Line Items]
Property and equipment, gross	[1]	114
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross		44	41
Computer Equipment and Purchased Software
Property Plant And Equipment [Line Items]
Property and equipment, gross		56	52
Furniture, Office Equipment and Other
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 19	$ 18

[1] Refer to “Note 2: Significant Accounting Policies” regarding the transition accounting related to our adoption of ASC 842 and the subsequent accounting for our Headquarters Lease.