Basis of Presentation - Reclassifications (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)	[1]	$ 629	$ 490
Selling and marketing	[1]	1,210	1,521
Technology and content	[1]	308	297
General and administrative	[1]	187	184
Operating loss		$ (1,294)	(131)
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)	[1]		513
Selling and marketing	[1]		1,535
Technology and content	[1]		429
General and administrative	[1]		191
Depreciation and amortization			52
As reclassified
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)			490
Selling and marketing			1,521
Technology and content			297
General and administrative			184
Depreciation and amortization			$ 228

[1] (1) Includes stock-based compensation as follows:       Cost of revenue $ 3
  $ 3
Selling and marketing 12
  11
Technology and content 20
  19
General and administrative 20
  23