REVENUE - Loyalty and Other Incentive Programs (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Mar. 31, 2018	Jun. 30, 2021	Dec. 31, 2020
Loyalty Programs | OpenTable
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Loyalty and other incentive programs, expiration period for reward points	3 years
Expiration period for no qualifying activity		12 months
Accrued expenses and other current liabilities | Loyalty Programs
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Liabilities for loyalty and other incentive program incentives		$ 16	$ 21
Accrued expenses and other current liabilities | Other Incentive Programs
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Liabilities for loyalty and other incentive program incentives		$ 40	$ 60