REVENUE - Disaggregation of revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 630	$ 3,850	$ 2,918	$ 6,687
Online accommodation reservation services [Member] | Revenue Benchmark [Member] | Product Concentration Risk [Member]
Disaggregation of Revenue [Line Items]
Concentration risk percentage	86.00%	87.00%	85.00%	86.00%
Other sources of online travel reservation services or advertising and other revenues [Member] | Revenue Benchmark [Member] | Product Concentration Risk [Member] | 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	$ 105	$ 400	$ 390	$ 766
The Netherlands
Disaggregation of Revenue [Line Items]
Revenues	444	2,997	2,121	5,069
Other
Disaggregation of Revenue [Line Items]
Revenues	$ 81	$ 453	$ 407	$ 852