REVENUE - Disaggregation of revenue (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 2,640	$ 5,040	[1]	$ 5,558	$ 11,727	[1]
Online accommodation reservation services | Revenue Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk percentage	91.00%	88.00%		88.00%	87.00%
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	$ 214	$ 404	[1]	$ 604	$ 1,170	[1]
The Netherlands
Disaggregation of Revenue [Line Items]
Revenues	2,231	4,107	[1]	4,352	9,176	[1]
Other
Disaggregation of Revenue [Line Items]
Revenues	$ 195	$ 529	[1]	$ 602	$ 1,381	[1]

[1] (1) Geographic information for the three and nine months ended September 30, 2019 has been recast to conform to the current period presentation