Basis of Presentation - Reclassifications (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)	[1]	$ 375	$ 548	$ 1,393	$ 1,538
Selling and marketing	[1]	529	1,646	2,035	4,810
Technology and content	[1]	224	304	787	905
General and administrative	[1]	134	210	473	599
Depreciation and amortization		$ 220	228	$ 681	684
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)	[1]		569		1,604
Selling and marketing	[1]		1,660		4,852
Technology and content	[1]		440		1,304
General and administrative	[1]		217		622
Depreciation and amortization			50		154
As reclassified
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue (exclusive of depreciation and amortization shown separately below)			548		1,538
Selling and marketing			1,646		4,810
Technology and content			304		905
General and administrative			210		599
Depreciation and amortization			$ 228		$ 684

[1] (1) Includes stock-based compensation as follows:Cost of revenue$3 $3 $9 $9 Selling and marketing12 11 37 34 Technology and content15 18 53 56 General and administrative17 28 57 76