Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Costs and expenses:
Amortization of intangible assets	$ 34	$ 32	$ 32
Depreciation	82	79	69
Amortization adjustment	67	62	53
Stock-based compensation:
Stock-based compensation	118	96	85
Cost of Revenue
Stock-based compensation:
Stock-based compensation	1
Selling and Marketing
Stock-based compensation:
Stock-based compensation	21	21	20
Technology and Content
Stock-based compensation:
Stock-based compensation	51	40	40
General and Administrative
Stock-based compensation:
Stock-based compensation	45	35	25
Acquired Technology
Costs and expenses:
Amortization of intangible assets	8	8	7
Website Development Costs
Costs and expenses:
Depreciation	$ 59	$ 54	$ 46