BASIS OF PRESENTATION (Policies)	6 Months Ended
Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Management of Booking Holdings Inc. (the "Company") is responsible for the Unaudited Consolidated Financial Statements included in this document. The Unaudited Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") and include all normal and recurring adjustments that management of the Company considers necessary for a fair presentation of its financial position and operating results. The Company prepared the Unaudited Consolidated Financial Statements following the requirements of the Securities and Exchange Commission ("SEC") for interim reporting. As permitted under those rules, the Company condensed or omitted certain footnotes or other financial information that are normally required by U.S. GAAP for annual financial statements. These statements should be read in combination with the Consolidated Financial Statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2020. The Unaudited Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The functional currency of the Company's subsidiaries is generally the respective local currency. For international operations, assets and liabilities are translated into U.S. Dollars at the rate of exchange existing at the balance sheet date. Income statement amounts are translated at monthly average exchange rates applicable for the period. Translation gains and losses are included as a component of "Accumulated other comprehensive loss" in the accompanying Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Other income (expense), net" in the Unaudited Consolidated Statements of Operations. Revenues, expenses, assets and liabilities can vary during each quarter of the year. Therefore, the results and trends in these interim financial statements may not be the same as those for any subsequent quarter or the full year, especially during the periods that are impacted by the COVID-19 pandemic.
Reclassification	Reclassification Certain amounts from prior periods have been reclassified to conform to the current period presentation.
Recent Accounting Pronouncements Adopted and Other Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted Simplifying the Accounting for Income Taxes The Financial Accounting Standards Board ("FASB") issued a new accounting update relating to income taxes. This update provides an exception to the general methodology for calculating income taxes in an interim period when a year-to-date loss exceeds the anticipated loss for the year. This update also (1) requires an entity to recognize a franchise tax (or similar tax) that is partially based on income as an income-based tax and account for any incremental amount incurred as a non-income-based tax, (2) requires an entity to evaluate when a step-up in the tax basis of goodwill should be considered part of the business combination in which goodwill was originally recognized for accounting purposes and when it should be considered a separate transaction, and (3) requires that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The Company adopted this update on January 1, 2021 and applied the applicable amendments on a prospective basis. The adoption did not have a material impact on the Company's Unaudited Consolidated Financial Statements. Other Recent Accounting Pronouncements Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued a new accounting update relating to convertible instruments and contracts in an entity’s own equity. For convertible instruments, the accounting update reduces the number of accounting models for convertible debt instruments and convertible preferred stock. Limiting the accounting models results in fewer embedded conversion features being separately recognized from the host contract as compared with current U.S. GAAP. The accounting update amends the guidance for the derivatives scope exception for contracts in an entity’s own equity to reduce form-over-substance-based accounting conclusions. The accounting update also simplifies the diluted earnings per share calculation in certain areas. The update is effective for the Company from January 1, 2022. The update can be adopted on either a full or modified retrospective basis. The Company is currently evaluating the impact to its Consolidated Financial Statements of adopting this update.
Share-based Payment Arrangement	Stock-based compensation expense related to performance share units, restricted stock units and stock options is recognized based on fair value on a straight-line basis over the respective requisite service periods and forfeitures are accounted for when they occur. The fair value on the grant date of performance share units and restricted stock units is determined based on the number of units granted and the quoted price of the Company's common stock. For performance share units with market conditions, the effect of the market condition is also considered in the determination of fair value on the grant date using Monte Carlo simulations. The fair value of employee stock options is determined using the Black-Scholes model. Performance share units and restricted stock units are payable in shares of the Company's common stock upon vesting. The Company issues shares of its common stock upon the exercise of stock options. The Company records stock-based compensation expense for performance-based awards using its estimate of the probable outcome at the end of the performance period (i.e., the estimated performance against the performance targets or performance goals, as applicable). The Company periodically adjusts the cumulative stock-based compensation expense recorded when the probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable.
Earnings Per Share	The Company computes basic net (loss) income per share by dividing net (loss) income applicable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net (loss) income per share is based upon the weighted-average number of common and common equivalent shares outstanding during the period. Common equivalent shares related to stock options, restricted stock units and performance share units are calculated using the treasury stock method. Performance share units are included in the weighted-average common equivalent shares based on the number of shares that would be issued if the end of the reporting period were the end of the performance period, if the result would be dilutive. The Company's convertible notes have net share settlement features requiring the Company upon conversion to settle the principal amount of the debt for cash and the conversion premium for cash or shares of the Company's common stock, at the Company's option. Under the treasury stock method, if the conversion prices for the convertible notes exceed the Company's average stock price for the period, the convertible notes generally have no impact on diluted net income per share. The convertible notes are included in the calculation of diluted net income per share if their inclusion is dilutive under the treasury stock method.
Investment	The Company assesses the classification of its investments in the Consolidated Balance Sheets as short-term or long-term at the individual security level. Classification as short-term or long-term is based upon the maturities of the securities, as applicable, and the Company's expectations regarding the timing of sales and redemptions. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage or in connection with a commercial relationship are included in "Long-term investments" in the Consolidated Balance Sheets, except in situations where the Company expects the investment to be realized in cash, redeemed or sold within one year. The Company has classified its investments in debt securities as available-for-sale securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is also considered a debt security for accounting purposes. Available-for-sale debt securities are reported at estimated fair value (see Note 6) with the aggregate unrealized gains and losses, net of tax, reflected in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. If the amortized cost basis of an available-for-sale security exceeds its fair value and if the Company has the intention to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis, an impairment is recognized in the Unaudited Consolidated Statements of Operations. If the Company does not have the intention to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis and the Company determines that the decline in fair value below the amortized cost basis of an available-for-sale security is entirely or partially due to credit-related factors, the credit loss is measured and recognized as an allowance for expected credit losses along with the related expense in the Unaudited Consolidated Statements of Operations. The allowance is measured as the amount by which the debt security’s amortized cost basis exceeds the Company’s best estimate of the present value of cash flows expected to be collected. The fair values of these investments are based on the specific quoted market price of the securities or comparable securities at the balance sheet dates. Unobservable inputs are also used when little or no market data is available. See Note 6 for information related to fair value measurements. Investments in equity securities include equity securities with readily determinable fair values and equity securities without readily determinable fair values. Equity securities with readily determinable fair values are reported at estimated fair value with changes in fair value recognized in "Other income (expense), net" in the Unaudited Consolidated Statements of Operations. The Company also holds investments in equity securities of private companies, over which the Company does not have the ability to exercise significant influence or control. The Company elected to measure these investments at cost less impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer.
Fair Value Measurement	Investments See Note 5 for additional information related to the Company's investments. The valuation of investments in Trip.com Group convertible debt securities are considered "Level 2" valuations because the Company has access to quoted prices, but does not have visibility into the volume and frequency of trading for these investments. A market approach is used for recurring fair value measurements and the valuation techniques use inputs that are observable, or can be corroborated by observable data, in an active marketplace. Investments in private companies measured using Level 3 inputs The Company’s investments measured using Level 3 inputs primarily consist of preferred stock investments in privately-held companies that are classified as either debt securities or equity securities without readily determinable fair values. Fair values of privately held securities are estimated using a variety of valuation methodologies, including both market and income approaches. The Company has used valuation techniques appropriate for the type of investment and the information available about the investee as of the valuation date to determine fair value. Recent financing transactions in the investee, such as new investments in preferred stock, are generally considered the best indication of the enterprise value and therefore used as a basis to estimate fair value. As applicable, the Company also considers publicly disclosed information for certain merger transactions (not yet consummated), including those involving special purpose acquisition companies. However, based on a number of factors, such as the proximity in timing to the valuation date or the volume or other terms of these financing transactions, the Company may also use other valuation techniques to supplement this data, including the income approach. In addition, an option-pricing model (“OPM”) is utilized to allocate value to the various classes of securities of the investee, including the class owned by the Company. In certain situations, the current value method ("CVM") is utilized to allocate value to the various classes of equity based on their as-converted values. The OPM and CVM include assumptions around the investees' expected time to liquidity and volatility.
Accounts Receivable and Allowance for Credit Losses	The Company has identified the relevant risk characteristics, of its customers and the related receivables and prepayments, which include the following: size, type (alternative accommodations vs. hotels) or geographic location of the customer, or a combination of these characteristics. Receivables with similar risk characteristics have been grouped into pools. For each pool, the Company considers the historical credit loss experience, current economic conditions, supportable forecasts of future economic conditions, and any recoveries in assessing the lifetime expected credit losses. Other key factors that influence the expected credit loss analysis include customer demographics, payment terms offered in the normal course of business to customers, the nature of competition, and industry-specific factors that could impact the Company's receivables. Additionally, external data and macroeconomic factors are considered. This is assessed at each quarter based on the Company’s specific facts and circumstances.
Goodwill	The Company tests goodwill for impairment on an annual basis and between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The Company tests goodwill at a reporting unit level. The Company’s annual goodwill impairment tests are performed as of September 30.
Long-Lived Assets, Including Intangible Assets and Operating Lease Assets	The Company reviews long-lived assets, including intangible assets and operating lease assets, whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the ability to recover the carrying value of the assets from the estimated undiscounted future net cash flows, before interest and taxes, of the related asset group.
Income Tax	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.

BASIS OF PRESENTATION (Policies)

6 Months Ended

Jun. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Management of Booking Holdings Inc. (the "Company") is responsible for the Unaudited Consolidated Financial Statements included in this document. The Unaudited Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") and include all normal and recurring adjustments that management of the Company considers necessary for a fair presentation of its financial position and operating results. The Company prepared the Unaudited Consolidated Financial Statements following the requirements of the Securities and Exchange Commission ("SEC") for interim reporting. As permitted under those rules, the Company condensed or omitted certain footnotes or other financial information that are normally required by U.S. GAAP for annual financial statements. These statements should be read in combination with the Consolidated Financial Statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2020.

The Unaudited Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The functional currency of the Company's subsidiaries is generally the respective local currency. For international operations, assets and liabilities are translated into U.S. Dollars at the rate of exchange existing at the balance sheet date. Income statement amounts are translated at monthly average exchange rates applicable for the period. Translation gains and losses are included as a component of "Accumulated other comprehensive loss" in the accompanying Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Other income (expense), net" in the Unaudited Consolidated Statements of Operations.

Revenues, expenses, assets and liabilities can vary during each quarter of the year. Therefore, the results and trends in these interim financial statements may not be the same as those for any subsequent quarter or the full year, especially during the periods that are impacted by the COVID-19 pandemic.

Reclassification

Certain amounts from prior periods have been reclassified to conform to the current period presentation.

Recent Accounting Pronouncements Adopted and Other Recent Accounting Pronouncements

Recent Accounting Pronouncements Adopted

Simplifying the Accounting for Income Taxes

The Financial Accounting Standards Board ("FASB") issued a new accounting update relating to income taxes. This update provides an exception to the general methodology for calculating income taxes in an interim period when a year-to-date loss exceeds the anticipated loss for the year. This update also (1) requires an entity to recognize a franchise tax (or similar tax) that is partially based on income as an income-based tax and account for any incremental amount incurred as a non-income-based tax, (2) requires an entity to evaluate when a step-up in the tax basis of goodwill should be considered part of the business combination in which goodwill was originally recognized for accounting purposes and when it should be considered a separate transaction, and (3) requires that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date.

The Company adopted this update on January 1, 2021 and applied the applicable amendments on a prospective basis. The adoption did not have a material impact on the Company's Unaudited Consolidated Financial Statements.

Other Recent Accounting Pronouncements

Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity

In August 2020, the FASB issued a new accounting update relating to convertible instruments and contracts in an entity’s own equity. For convertible instruments, the accounting update reduces the number of accounting models for convertible debt instruments and convertible preferred stock. Limiting the accounting models results in fewer embedded conversion features being separately recognized from the host contract as compared with current U.S. GAAP. The accounting update amends the guidance for the derivatives scope exception for contracts in an entity’s own equity to reduce form-over-substance-based accounting conclusions. The accounting update also simplifies the diluted earnings per share calculation in certain areas.

The update is effective for the Company from January 1, 2022. The update can be adopted on either a full or modified retrospective basis. The Company is currently evaluating the impact to its Consolidated Financial Statements of adopting this update.

Share-based Payment Arrangement

Stock-based compensation expense related to performance share units, restricted stock units and stock options is recognized based on fair value on a straight-line basis over the respective requisite service periods and forfeitures are accounted for when they occur. The fair value on the grant date of performance share units and restricted stock units is determined based on the number of units granted and the quoted price of the Company's common stock. For performance share units with market conditions, the effect of the market condition is also considered in the determination of fair value on the grant date using Monte Carlo simulations. The fair value of employee stock options is determined using the Black-Scholes model. Performance share units and restricted stock units are payable in shares of the Company's common stock upon vesting. The Company issues shares of its common stock upon the exercise of stock options. The Company records stock-based compensation expense for performance-based awards using its estimate of the probable outcome at the end of the performance period (i.e., the estimated performance against the performance targets or performance goals, as applicable). The Company periodically adjusts the cumulative stock-based compensation expense recorded when the probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable.

Earnings Per Share

The Company computes basic net (loss) income per share by dividing net (loss) income applicable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net (loss) income per share is based upon the weighted-average number of common and common equivalent shares outstanding during the period.

Common equivalent shares related to stock options, restricted stock units and performance share units are calculated using the treasury stock method. Performance share units are included in the weighted-average common equivalent shares based on the number of shares that would be issued if the end of the reporting period were the end of the performance period, if the result would be dilutive.

The Company's convertible notes have net share settlement features requiring the Company upon conversion to settle the principal amount of the debt for cash and the conversion premium for cash or shares of the Company's common stock, at the Company's option. Under the treasury stock method, if the conversion prices for the convertible notes exceed the Company's average stock price for the period, the convertible notes generally have no impact on diluted net income per share. The convertible notes are included in the calculation of diluted net income per share if their inclusion is dilutive under the treasury stock method.

Investment

The Company assesses the classification of its investments in the Consolidated Balance Sheets as short-term or long-term at the individual security level. Classification as short-term or long-term is based upon the maturities of the securities, as applicable, and the Company's expectations regarding the timing of sales and redemptions. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage or in connection with a commercial relationship are included in "Long-term investments" in the Consolidated Balance Sheets, except in situations where the Company expects the investment to be realized in cash, redeemed or sold within one year.

The Company has classified its investments in debt securities as available-for-sale securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is also considered a debt security for accounting purposes. Available-for-sale debt securities are reported at estimated fair value (see Note 6) with the aggregate unrealized gains and losses, net of tax, reflected in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. If the amortized cost basis of an available-for-sale security exceeds its fair value and if the Company has the intention to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis, an impairment is recognized in the Unaudited Consolidated Statements of Operations. If the Company does not have the intention to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis and the Company determines that the decline in fair value below the amortized cost basis of an available-for-sale security is entirely or partially due to credit-related factors, the credit loss is measured and recognized as an allowance for expected credit losses along with the related expense in the Unaudited Consolidated Statements of Operations. The allowance is measured as the amount by which the debt security’s amortized cost basis exceeds the Company’s best estimate of the present value of cash flows expected to be collected. The fair values of these investments are based on the specific quoted market price of the securities or comparable securities at the balance sheet dates. Unobservable inputs are also used when little or no market data is available. See Note 6 for information related to fair value measurements.

Investments in equity securities include equity securities with readily determinable fair values and equity securities without readily determinable fair values. Equity securities with readily determinable fair values are reported at estimated fair value with changes in fair value recognized in "Other income (expense), net" in the Unaudited Consolidated Statements of Operations. The Company also holds investments in equity securities of private companies, over which the Company does not have the ability to exercise significant influence or control. The Company elected to measure these investments at cost less impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer.

Fair Value Measurement

Investments

See Note 5 for additional information related to the Company's investments.

The valuation of investments in Trip.com Group convertible debt securities are considered "Level 2" valuations because the Company has access to quoted prices, but does not have visibility into the volume and frequency of trading for these investments. A market approach is used for recurring fair value measurements and the valuation techniques use inputs that are observable, or can be corroborated by observable data, in an active marketplace.

Investments in private companies measured using Level 3 inputs

The Company’s investments measured using Level 3 inputs primarily consist of preferred stock investments in privately-held companies that are classified as either debt securities or equity securities without readily determinable fair values. Fair values of privately held securities are estimated using a variety of valuation methodologies, including both market and income approaches. The Company has used valuation techniques appropriate for the type of investment and the information available about the investee as of the valuation date to determine fair value. Recent financing transactions in the investee, such as new investments in preferred stock, are generally considered the best indication of the enterprise value and therefore used as a basis to estimate fair value. As applicable, the Company also considers publicly disclosed information for certain merger transactions (not yet consummated), including those involving special purpose acquisition companies. However, based on a number of factors, such as the proximity in timing to the valuation date or the volume or other terms of these financing transactions, the Company may also use other valuation techniques to supplement this data, including the income approach. In addition, an option-pricing model (“OPM”) is utilized to allocate value to the various classes of securities of the investee, including the class owned by the Company. In certain situations, the current value method ("CVM") is utilized to allocate value to the various classes of equity based on their as-converted values. The OPM and CVM include assumptions around the investees' expected time to liquidity and volatility.

Accounts Receivable and Allowance for Credit Losses

The Company has identified the relevant risk characteristics, of its customers and the related receivables and prepayments, which include the following: size, type (alternative accommodations vs. hotels) or geographic location of the customer, or a combination of these characteristics. Receivables with similar risk characteristics have been grouped into pools. For each pool, the Company considers the historical credit loss experience, current economic conditions, supportable forecasts of future economic conditions, and any recoveries in assessing the lifetime expected credit losses. Other key factors that influence the expected credit loss analysis include customer demographics, payment terms offered in the normal course of business to customers, the nature of competition, and industry-specific factors that could impact the Company's receivables. Additionally, external data and macroeconomic factors are considered. This is assessed at each quarter based on the Company’s specific facts and circumstances.

Goodwill

The Company tests goodwill for impairment on an annual basis and between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The Company tests goodwill at a reporting unit level. The Company’s annual goodwill impairment tests are performed as of September 30.

Long-Lived Assets, Including Intangible Assets and Operating Lease Assets

The Company reviews long-lived assets, including intangible assets and operating lease assets, whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the ability to recover the carrying value of the assets from the estimated undiscounted future net cash flows, before interest and taxes, of the related asset group.

Income Tax

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.