Basis of Presentation - Reclassifications (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)	[1]	$ 389	$ 500	$ 1,018	$ 990
Selling and marketing	[1]	296	1,643	1,506	3,164
Technology and content	[1]	255	304	563	601
General and administrative	[1]	152	205	339	389
Depreciation and amortization		232	228	461	456
Operating income (loss)		$ (849)	265	$ (2,143)	134
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)	[1]		522		1,035
Selling and marketing	[1]		1,657		3,192
Technology and content	[1]		435		864
General and administrative	[1]		214		405
Depreciation and amortization			52		104
As reclassified
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)			500		990
Selling and marketing			1,643		3,164
Technology and content			304		601
General and administrative			205		389
Depreciation and amortization			$ 228		$ 456

[1] (1) Includes stock-based compensation as follows:               Cost of revenue $ 3
  $ 3
  $ 6
  $ 6
Selling and marketing 13
  12
  25
  23
Technology and content 18
  19
  38
  38
General and administrative 20
  25
  40
  48