INCOME TAXES (Notes)	3 Months Ended
INCOME TAXES (Notes)	Mar. 31, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Income tax expense consists of U.S. and international income taxes, determined using an estimate of the Company's annual effective tax rate, which is based upon the applicable tax rates and tax laws of the countries in which the income is generated. A deferred tax liability is recognized for all taxable temporary differences, and a deferred tax asset is recognized for all deductible temporary differences and operating loss and tax credit carryforwards. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. The Company considers many factors when assessing the likelihood of future realization of the deferred tax assets, including its recent cumulative earnings experience by taxing jurisdiction, expectations of future income, tax planning strategies, the carryforward periods available for tax reporting purposes and other relevant factors. The Company's effective tax rate for the three months ended March 31, 2021 was 80.2%, compared to 3.1% for the three months ended March 31, 2020. The Company's 2021 effective tax rate differs from the U.S. federal statutory tax rate of 21%, primarily due to the effect of higher international tax rates and certain non-deductible expenses, partially offset by the benefit of the Netherlands Innovation Box Tax. The Company's 2020 effective tax rate differs from the U.S. federal statutory tax rate of 21%, primarily due to the non-deductible goodwill impairment charge related to OpenTable and KAYAK and the valuation allowances recorded against the deferred tax assets generated from the impairment of a long-term investment. The Company's effective tax rate for the three months ended March 31, 2021 was higher than the three months ended March 31, 2020, primarily due to the effect of higher international tax rates, certain non-deductible expenses, and discrete U.S. tax expenses related to unrealized gains on equity securities. In addition, the lower effective tax rate for the three months ended March 31, 2020 reflected the non-deductible goodwill impairment charge related to OpenTable and KAYAK. During the three months ended March 31, 2021, a majority of the Company's income was reported in the Netherlands, where Booking.com is based. According to Dutch corporate income tax law, income generated from qualifying innovative activities is taxed at a rate of 9% ("Innovation Box Tax") for periods beginning on or after January 1, 2021 rather than the Dutch statutory rate of 25%. Previously, the Innovation Box Tax rate had been 7%. A portion of Booking.com's earnings during the three months ended March 31, 2021 qualified for Innovation Box Tax treatment, which had a beneficial impact on the Company's effective tax rate for that period. During the three months ended March 31, 2020, the Company did not benefit from the Innovation Box Tax. The aggregate amount of unrecognized tax benefits for all matters at March 31, 2021 and December 31, 2020 was $100 million and $84 million, respectively. The unrecognized tax benefits, if recognized, would impact the effective tax rate. As of March 31, 2021 and December 31, 2020, total gross interest and penalties accrued was $32 million and $31 million, respectively. The majority of these unrecognized tax benefits are included in "Other long-term liabilities" and "Other assets, net" in the Consolidated Balance Sheets.

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.