COMMITMENTS AND CONTINGENCIES (Building Construction) (Details) - Booking.com - Headquarters € in Millions, $ in Millions	3 Months Ended
	Sep. 30, 2016 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 EUR (€)
Other Commitments [Line Items]
Contractual obligation	€ 270	$ 123	€ 109
Acquisition of land use rights	€ 43
Ground Lease
Other Commitments [Line Items]
Contractual obligation		$ 80	€ 71