COMMITMENTS AND CONTINGENCIES (Details) ₺ in Millions, € in Millions, $ in Millions			1 Months Ended																			3 Months Ended		24 Months Ended
	Feb. 08, 2022 USD ($)	Feb. 08, 2022 EUR (€)	Feb. 28, 2022 USD ($)	Feb. 28, 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 (€)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 TRY (₺)	Mar. 31, 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																	$ 119
French Tax Audit
Commitments and Contingencies
Unrecognized tax benefits																													$ 59	€ 50
Estimated reasonably possible loss in excess of amount accrued																						22				€ 20
Italian Tax Audit
Commitments and Contingencies
Unrecognized tax benefits												$ 16																€ 13
Expected required prepayment deposit or bank guarantees																						45	€ 41
Turkish Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties																								$ 56	₺ 824
Payment required to appeal a litigation matter or avoid collection enforcement					8		₺ 118
Pension-related litigation
Commitments and Contingencies
Estimated reasonably possible loss in excess of amount accrued																						335				301
Standby Letters of Credit or Bank Guarantees
Commitments and Contingencies
Letters of credit issued					511																	686
Booking.com | Headquarters
Commitments and Contingencies
Contractual obligation																						9				8
Booking.com | Headquarters | Headquarters Vendors
Commitments and Contingencies
Contractual obligation																						17				15
Booking.com | Headquarters | Ground Lease
Commitments and Contingencies
Remaining lease payments																						75				68
Other assets, net | Italian Tax Audit
Commitments and Contingencies
Unrecognized tax benefits					6																	$ 6				€ 5	€ 5
Tax Year 2013 | French Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties														$ 78	€ 70
Tax Year 2013 | Italian Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties																		$ 53	€ 48
Payment required to appeal a litigation matter or avoid collection enforcement														11	10
Tax Year 2014 | Italian Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties														64	58
Tax Year 2015 | Italian Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties												$ 35	€ 31
Tax Years 2013 And 2014 | Italian Tax Audit
Commitments and Contingencies
Unrecognized tax benefits																															$ 5	€ 4
Tax Years 2013 Through 2019 | Italian Tax Audit
Commitments and Contingencies
Loss Contingency, Tax, Recommended Assessment										$ 171	€ 154
Tax Years 2006 Through 2012 | French Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties																				$ 396	€ 356
Payment required to appeal a litigation matter or avoid collection enforcement																$ 396	€ 356
Tax Years 2011 Through 2015 | French Tax Assessment, transfer taxes
Commitments and Contingencies
Assessed taxes including interest and penalties														$ 44	€ 39
Tax Years 2011 Through 2012 | French Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties	$ (4)	€ (3)
Tax Years 2014 Through 2015 | Italian Tax Audit
Commitments and Contingencies
Payment required to appeal a litigation matter or avoid collection enforcement			$ 26	€ 23
Tax Years 2016 Through 2018 | French Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties					$ 86	€ 78
Tax Years 2016 Through 2018 | Italian Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties								$ 127	€ 114