REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 2,160	$ 630	$ 3,301	$ 2,918
Online accommodation reservation services \| Revenue Benchmark \| Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk percentage	83.00%	86.00%	84.00%	85.00%
Other sources of online travel reservation services and advertising and other revenues \| Revenue Benchmark \| Product Concentration Risk \| Maximum
Disaggregation of Revenue [Line Items]
Concentration risk percentage	10.00%	10.00%	10.00%	10.00%
United States
Disaggregation of Revenue [Line Items]
Revenues	$ 393	$ 105	$ 590	$ 390
The Netherlands
Disaggregation of Revenue [Line Items]
Revenues	1,601	444	2,412	2,121
Other
Disaggregation of Revenue [Line Items]
Revenues	$ 166	$ 81	$ 299	$ 407

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration