Condensed Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Costs and expenses:
Amortization of intangible assets	$ 8	$ 8
Depreciation	20	19
Amortization adjustment	17	14
Stock-based compensation:
Stock-based compensation	29	19
Selling and Marketing
Stock-based compensation:
Stock-based compensation	6	5
Technology and Content
Stock-based compensation:
Stock-based compensation	12	7
General and Administrative
Stock-based compensation:
Stock-based compensation	11	7
Acquired Technology
Costs and expenses:
Amortization of intangible assets	2	2
Website Development Costs
Costs and expenses:
Depreciation	$ 15	$ 12