COMMITMENTS AND CONTINGENCIES (Details) ₺ in Millions, € in Millions, $ in Millions			1 Months Ended																	6 Months Ended		24 Months Ended
	Feb. 08, 2022 USD ($)	Feb. 08, 2022 EUR (€)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 EUR (€)	Dec. 31, 2021 TRY (₺)	Aug. 31, 2021 USD ($)	Aug. 31, 2021 EUR (€)	Jun. 30, 2021 USD ($)	Jun. 30, 2021 EUR (€)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 EUR (€)	Jan. 31, 2019 USD ($)	Jan. 31, 2019 EUR (€)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 EUR (€)	Jun. 30, 2022 USD ($)	Jun. 30, 2022 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 TRY (₺)	Jun. 30, 2022 EUR (€)	Apr. 30, 2022 USD ($)	Apr. 30, 2022 EUR (€)	Dec. 31, 2021 EUR (€)	Mar. 31, 2021 EUR (€)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 EUR (€)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 EUR (€)
Commitments and Contingencies
Unrecognized tax benefits			$ 120																	$ 113
Standby Letters of Credit
Commitments and Contingencies
Letters of credit issued			511																	812
Booking.com | Headquarters
Commitments and Contingencies
Contractual obligation																				5				€ 5
Booking.com | Headquarters | Headquarters Vendors
Commitments and Contingencies
Contractual obligation																				17				16
Booking.com | Headquarters | Ground Lease
Commitments and Contingencies
Remaining lease payments																				70				67
French Tax Audit
Commitments and Contingencies
Unrecognized tax benefits																													$ 59	€ 50
Estimated reasonably possible loss in excess of amount accrued																				21				20
French Tax Audit | Tax Years 2006 Through 2012
Commitments and Contingencies
Assessed taxes																		$ 372	€ 356
Payment required to appeal a litigation matter or avoid collection enforcement														$ 372	€ 356
French Tax Audit | Tax Years 2011 through 2012
Commitments and Contingencies
Assessed taxes	$ 3	€ 3
Amount of tax deposit refunded																									$ 3	€ 3
French Tax Audit | Tax Year 2013
Commitments and Contingencies
Assessed taxes												$ 73	€ 70
French Tax Audit | Tax Years 2016 Through 2018
Commitments and Contingencies
Assessed taxes			81	€ 78
French Tax Assessment, transfer taxes | Tax Years 2011 Through 2015
Commitments and Contingencies
Assessed taxes												41	39
Italian Tax Audit
Commitments and Contingencies
Unrecognized tax benefits										$ 16																		€ 13
Italian Tax Audit | Other assets, net
Commitments and Contingencies
Unrecognized tax benefits			6																	6				5			€ 5
Italian Tax Audit | Tax Year 2013
Commitments and Contingencies
Assessed taxes																$ 50	€ 48
Payment required to appeal a litigation matter or avoid collection enforcement												10	10
Italian Tax Audit | Tax Year 2014
Commitments and Contingencies
Assessed taxes												$ 61	€ 58
Italian Tax Audit | Tax Year 2015
Commitments and Contingencies
Assessed taxes										$ 33	€ 31
Italian Tax Audit | Tax Years 2013 And 2014
Commitments and Contingencies
Unrecognized tax benefits																															$ 5	€ 4
Italian Tax Audit | Tax Years 2013 through 2019
Commitments and Contingencies
Recommended tax assessment								$ 161	€ 154
Italian Tax Audit | Tax Years 2016 Through 2018
Commitments and Contingencies
Assessed taxes						$ 119	€ 114
Italian Tax Audit | Tax Years 2014 Through 2015
Commitments and Contingencies
Payment required to appeal a litigation matter or avoid collection enforcement																				67	€ 64
Turkish Tax Audit
Commitments and Contingencies
Assessed taxes																						$ 50	₺ 835
Payment required to appeal a litigation matter or avoid collection enforcement			$ 7		₺ 118
Pension-related litigation
Commitments and Contingencies
Estimated reasonably possible loss in excess of amount accrued																				$ 328				€ 313