Basis of Presentation - Reclassifications (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue	[1]	$ 374	$ 381	$ 685	$ 1,010
Selling and marketing	[1]	1,199	291	1,863	1,496
Technology and content	[1]	276	271	523	586
General and administrative	[1]	$ 184	149	$ 340	334
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue			389		1,018
Selling and marketing			296		1,506
Technology and content			255		563
General and administrative			152		339
As reclassified
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue			381		1,010
Selling and marketing			291		1,496
Technology and content			271		586
General and administrative			$ 149		$ 334

[1] (1) Includes stock-based compensation as follows:Cost of revenue$6 $3 $11 $6 Selling and marketing32 13 49 25 Technology and content32 18 59 38 General and administrative50 20 84 40