REVENUE RECOGNITION - Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 5,040	$ 4,849	$ 11,727	$ 11,314
United States
Disaggregation of Revenue [Line Items]
Revenues	421	441	1,204	1,243
The Netherlands
Disaggregation of Revenue [Line Items]
Revenues	4,057	3,889	9,016	8,718
Other
Disaggregation of Revenue [Line Items]
Revenues	$ 562	$ 519	$ 1,507	$ 1,353
Online accommodation reservation services [Member] | Product Concentration Risk | Revenue Benchmark [Member]
Disaggregation of Revenue [Line Items]
Concentration risk percentage	88.00%	88.00%	87.00%	87.00%
Maximum | Other sources of online travel reservation services or advertising and other revenues [Member] | Product Concentration Risk | Revenue Benchmark [Member]
Disaggregation of Revenue [Line Items]
Concentration risk percentage	10.00%	10.00%	10.00%	10.00%