Property and Equipment, Net - Additional Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Property Plant And Equipment [Line Items]
Property and equipment, net (Note 6)	$ 195		$ 82
Depreciation of property and equipment, including amortization of internal-use software and website development	47	[1]	30	[1]	20	[1]
Capitalized Software and Website Development
Property Plant And Equipment [Line Items]
Property and equipment, net (Note 6)	61		46
Capitalized computer software and website development costs	47		38
Depreciation of property and equipment, including amortization of internal-use software and website development	30		20		13
Property and equipment, dispositions	22
Accumulated depreciation, dispositions	(20)
Loss on property and equipment, dispositions	$ (2)

[1] Includes amortization of internal use software and website development costs.