Booking (BKNG) 10-Q 9 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 02, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	Booking Holdings Inc.
Entity Central Index Key	0001075531
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		43,291,345

UNAUDITED CONSOLIDATED BALANCE

UNAUDITED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 2,334	$ 2,624
Short-term investments in marketable securities	1,981	3,660
Accounts receivable, net of allowance for doubtful accounts of $61 at each date	1,491	1,523
Prepaid expenses and other current assets	1,271	600
Total current assets	7,077	8,407
Property and equipment, net	695	656
Operating lease assets	635	0
Intangible assets, net	2,078	2,125
Goodwill	2,907	2,910
Long-term investments	8,445	8,408
Other assets	529	181
Total assets	22,366	22,687
Current liabilities:
Accounts payable	934	1,134
Accrued expenses and other current liabilities	1,877	1,399
Deferred merchant bookings	1,797	1,022
Convertible debt	968	0
Total current liabilities	5,576	3,555
Deferred income taxes	513	370
Operating lease liabilities	488	0
Long-term U.S. transition tax liability	1,166	1,166
Other long-term liabilities	89	162
Long-term debt	7,619	8,649
Total liabilities	15,451	13,902
Commitments and Contingencies
Stockholders' equity:
Common stock, $0.008 par value; authorized 1,000,000,000 shares, 63,121,930 and 62,948,762 shares issued, respectively	0	0
Treasury stock, 18,935,914 and 17,317,126 shares, respectively	(17,567)	(14,711)
Additional paid-in capital	5,519	5,445
Retained earnings	19,132	18,367
Accumulated other comprehensive loss	(169)	(316)
Total stockholders' equity	6,915	8,785
Total liabilities and stockholders' equity	$ 22,366	$ 22,687

UNAUDITED CONSOLIDATED BALANC_2

UNAUDITED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 61	$ 61
Common stock, par value (in dollars per share)	$ 0.008	$ 0.008
Common stock, authorized shares (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	63,121,930	62,948,762
Treasury stock, shares (in shares)	18,935,914	17,317,126

UNAUDITED CONSOLIDATED STATEMEN

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Agency revenues		$ 1,949	$ 2,113
Merchant revenues		603	526
Advertising and other revenues		285	289
Total revenues		2,837	2,928
Operating expenses:
Performance marketing		1,030	1,106
Brand marketing		163	101
Sales and other expenses		215	166
Personnel, including stock-based compensation of $74 and $71, respectively		501	499
General and administrative		191	163
Information technology		65	60
Depreciation and amortization		116	103
Total operating expenses		2,281	2,198
Operating income		556	730
Other income (expense):
Interest income		35	47
Interest expense		(66)	(70)
Net unrealized gains on marketable equity securities		451	55
Foreign currency transactions and other		(8)	(9)
Total other income		412	23
Earnings before income taxes		968	753
Income tax expense		203	146
Net income	[1]	$ 765	$ 607
Net income applicable to common stockholders per basic common share (in dollars per share)		$ 17.01	$ 12.56
Weighted-average number of basic common shares outstanding (in shares)		45,007	48,349
Net income applicable to common stockholders per diluted common share (in dollars per share)		$ 16.85	$ 12.34
Weighted-average number of diluted common shares outstanding (in shares)		45,436	49,205
[1]	The Company realized net gains of $1 million for the three months ended March 31, 2019 from sales of investments in debt securities.

UNAUDITED CONSOLIDATED STATEM_2

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Stock-based compensation expense	$ 74	$ 71

UNAUDITED CONSOLIDATED STATEM_3

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Other comprehensive income, net of tax
Net income (1)	[1]	$ 765	$ 607
Foreign currency translation adjustments, net of tax charge of $8 and tax benefit of $16, respectively (2)	[2]	(12)	61
Net unrealized gains on debt securities, net of tax charge of $51 and tax benefit of $2, respectively (1)	[1]	159	0
Comprehensive income		$ 912	$ 668
[1]	The Company realized net gains of $1 million for the three months ended March 31, 2019 from sales of investments in debt securities.
[2]	Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar denominated net assets, net of the impact of net investment hedges. During the three months ended March 31, 2019 and 2018, the Company recorded a tax benefit of $11 million and a tax charge of $10 million, respectively, related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the introduction of the U.S. Tax Cuts and Jobs Act (the "Tax Act"). Foreign currency translation adjustments also include a tax charge of $19 million and a tax benefit of $26 million for the three months ended March 31, 2019 and 2018, respectively, associated with the Company's Euro-denominated debt, which was designated as a net investment hedge against the impact of currency fluctuations on the Company's Euro-denominated net assets (see Note 9).

UNAUDITED CONSOLIDATED STATEM_4

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Realized Investment Gains (Losses)	$ 1	$ 1
Tax (benefit) associated with gain (loss) on components of foreign currency translation	8	(16)
Tax (benefit) associated with gain (loss) on components of unrealized gain (loss) on debt securities	51	(2)
Currency translation adjustment on deemed repatriation tax liability
Tax (benefit) associated with gain (loss) on components of foreign currency translation	(11)	10
Net Investment Hedging
Tax (benefit) associated with gain (loss) on components of foreign currency translation	$ 19	$ (26)

UNAUDITED CONSOLIDATED STATEM_5

UNAUDITED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions		Total		Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of accounting standards updates		$ 189					$ 430	$ (241)
Balance (in shares) at Dec. 31, 2017				62,689,000	(14,217,000)
Balance at Dec. 31, 2017		11,261		$ 0	$ (8,699)	$ 5,783	13,939	238
Increase (Decrease) in Stockholders' Equity
Net income		607	[1]				607
Foreign currency translation adjustments, net of taxes		61	[2]					61
Net unrealized gains (losses) on marketable securities, net of taxes	[1]	0
Reclassification adjustment for convertible debt in mezzanine		(48)				(48)
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)				149,000
Exercise of stock options and vesting of restricted stock units and/or performance share units		$ 0		$ 0		0
Repurchase of common stock (in shares)		(373,119)			(373,000)
Repurchase of common stock		$ (732)			$ (732)
Stock-based compensation and other stock-based payments		71				71
Conversion of debt		(773)				(773)
Balance (in shares) at Mar. 31, 2018				62,838,000	(14,590,000)
Balance at Mar. 31, 2018		10,636		$ 0	$ (9,431)	5,033	14,976	58
Balance (in shares) at Dec. 31, 2018				62,949,000	(17,317,000)
Balance at Dec. 31, 2018		8,785		$ 0	$ (14,711)	5,445	18,367	(316)
Increase (Decrease) in Stockholders' Equity
Net income		765	[1]				765
Foreign currency translation adjustments, net of taxes		(12)	[2]					(12)
Net unrealized gains (losses) on marketable securities, net of taxes		159	[1]					159
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)				173,000
Exercise of stock options and vesting of restricted stock units and/or performance share units		$ 0		$ 0		0
Repurchase of common stock (in shares)		(1,618,788)			(1,619,000)
Repurchase of common stock		$ (2,856)			$ (2,856)
Stock-based compensation and other stock-based payments		74				74
Balance (in shares) at Mar. 31, 2019				63,122,000	(18,936,000)
Balance at Mar. 31, 2019		$ 6,915		$ 0	$ (17,567)	$ 5,519	$ 19,132	$ (169)
[1]	The Company realized net gains of $1 million for the three months ended March 31, 2019 from sales of investments in debt securities.
[2]	Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar denominated net assets, net of the impact of net investment hedges. During the three months ended March 31, 2019 and 2018, the Company recorded a tax benefit of $11 million and a tax charge of $10 million, respectively, related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the introduction of the U.S. Tax Cuts and Jobs Act (the "Tax Act"). Foreign currency translation adjustments also include a tax charge of $19 million and a tax benefit of $26 million for the three months ended March 31, 2019 and 2018, respectively, associated with the Company's Euro-denominated debt, which was designated as a net investment hedge against the impact of currency fluctuations on the Company's Euro-denominated net assets (see Note 9).

UNAUDITED CONSOLIDATED STATEM_6

UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Statement of Cash Flows [Abstract]
Net income	[1]	$ 765	$ 607
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		116	103
Provision for uncollectible accounts		40	29
Deferred income tax expense		89	9
Net unrealized gains on marketable equity securities		(451)	(55)
Stock-based compensation expense and other stock-based payments		78	71
Operating lease amortization		42	0
Amortization of debt discount and debt issuance costs		14	17
Contingent consideration fair value adjustment		7	0
Changes in assets and liabilities:
Accounts receivable		(24)	(96)
Prepaid expenses and other current assets		(669)	(709)
Accounts payable, accrued expenses and other current liabilities		561	632
Other long-term assets and liabilities		(418)	32
Net cash provided by operating activities		150	640
INVESTING ACTIVITIES:
Purchase of investments		(445)	(714)
Proceeds from sale and maturity of investments		2,665	2,481
Additions to property and equipment		(111)	(131)
Net cash provided by investing activities		2,109	1,636
FINANCING ACTIVITIES:
Proceeds from revolving credit facility		250	0
Repayments of short-term borrowings		(25)	0
Payments for conversion of senior notes		0	(1,487)
Payments for repurchase of common stock		(2,773)	(718)
Net cash used in financing activities		(2,548)	(2,205)
Effect of exchange rate changes on cash and cash equivalents and restricted cash and cash equivalents		(2)	11
Net (decrease) increase in cash and cash equivalents and restricted cash and cash equivalents		(291)	82
Total cash and cash equivalents and restricted cash and cash equivalents, beginning of period		2,645	2,563
Total cash and cash equivalents and restricted cash and cash equivalents, end of period		2,354	2,645
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the period for income taxes		816	784
Cash paid during the period for interest		$ 68	$ 74
[1]	The Company realized net gains of $1 million for the three months ended March 31, 2019 from sales of investments in debt securities.

BASIS OF PRESENTATION

BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION	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 ("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 for interim reporting. As permitted under those rules, the Company condensed or omitted certain footnotes or other financial information that are normally required by 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, 2018 . The Unaudited Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries, including its primary brands of Booking.com, KAYAK, priceline, agoda, Rentalcars.com and OpenTable. All inter-company accounts 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 Unaudited Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Foreign currency transactions and other" 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. Unaudited Consolidated Statements of Comprehensive Income Subsequent to the issuance of the Company’s unaudited interim consolidated financial statements for the three and nine months ended September 30, 2018, the Company identified an error in the previously issued Unaudited Consolidated Statements of Comprehensive Income associated with the Company’s adoption of a new accounting update during the first quarter of 2018. This new accounting update amended the guidance on the recognition and measurement of financial instruments. The effect of adopting this new accounting update resulted in an increase of $241 million to the Company’s retained earnings for the net unrealized gain, net of tax, related to marketable equity securities, with an offsetting adjustment to accumulated other comprehensive income as of January 1, 2018. However, in the Unaudited Consolidated Statements of Comprehensive Income for the three months ended March 31, 2018, six months ended June 30, 2018 and nine months ended September 30, 2018, the Company incorrectly presented the $241 million as a component of other comprehensive income (referred to as “Reclassification of net unrealized gains on marketable equity securities to retained earnings, net of tax charge”). Accordingly, the Company corrected the foregoing presentation error in the accompanying Unaudited Consolidated Statement of Comprehensive Income for the three months ended March 31, 2018. As a result of this correction, total comprehensive income in the Company’s previously reported Unaudited Consolidated Statements of Comprehensive Income increased from $427 million to $668 million for the three months ended March 31, 2018. The correction of this error had no effect on the Company’s previously reported Unaudited Consolidated Balance Sheets, Unaudited Consolidated Statements of Operations, Unaudited Consolidated Statements of Changes in Stockholders’ Equity and Unaudited Consolidated Statements of Cash Flows. The effect of adopting this new accounting update has been presented correctly in the audited Consolidated Statement of Comprehensive Income included in the Consolidated Financial Statements in the Form 10-K for the year ended December 31, 2018. The Company will present the correction in the Unaudited Consolidated Statements of Comprehensive Income for the six months ended June 30, 2018 and the nine months ended September 30, 2018 to be included in the Form 10-Qs for the second and third quarters of 2019. Reclassifications — Certain amounts from prior periods have been reclassified to conform to the current year presentation. Restricted Cash and Cash Equivalents: Restricted cash and cash equivalents at March 31, 2019 and December 31, 2018 principally relates to the minimum cash requirement for Rentalcars.com's insurance business established in 2017. The following table reconciles cash and cash equivalents and restricted cash and cash equivalents reported in the Unaudited Consolidated Balance Sheets to the total amount shown in the Unaudited Consolidated Statements of Cash Flows (in millions): March 31, December 31, As included in the Unaudited Consolidated Balance Sheets: Cash and cash equivalents $ 2,334 $ 2,624 Restricted cash and cash equivalents included in prepaid expenses and other current assets 20 21 Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Unaudited Consolidated Statements of Cash Flows $ 2,354 $ 2,645 Recent Accounting Pronouncements Adopted Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In August 2018, the Financial Accounting Standards Board ("FASB") issued a new accounting update to address a customer's accounting for implementation costs incurred in a cloud computing arrangement that is a service contract and also added certain disclosure requirements related to implementation costs incurred for internal-use software and cloud computing arrangements. The amendment aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The Company utilizes various third-party computer systems and third-party service providers, including global distribution systems serving the accommodation, rental car and airline industries. The Company uses both internally-developed systems and third-party systems to operate its services, including transaction processing, order management and financial systems. The Company adopted this update on January 1, 2019 and applied it on a prospective basis. The adoption of this update did not have a material impact to the Unaudited Consolidated Financial Statements. Leases In February 2016, the FASB issued a new accounting standard which requires lessees to recognize an asset and a liability on the balance sheet for the rights and obligations created by entering into lease transactions. The new standard retains the dual-model concept by requiring entities to determine if a lease is an operating or financing lease. The new standard also expands qualitative and quantitative disclosures for lessees. The Company adopted this new standard on January 1, 2019 on a modified retrospective basis and has elected not to restate comparative periods. The Company elected other options, which allow the Company to use its previous evaluations regarding if an arrangement contains a lease, if a lease is an operating or financing lease and what costs are capitalized as initial direct costs prior to adoption. The Company also elected to combine lease and non-lease components. Upon the adoption of the new lease standard, on January 1, 2019, the Company recognized operating lease assets of $646 million and total operating lease liabilities of $646 million (including a current liability of $152 million ) in the consolidated balance sheet and reclassified certain balances related to existing leases. There was no impact to retained earnings at adoption. See Note 7 for more information on leases. Other Recent Accounting Pronouncements Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued a new accounting update to simplify the test for goodwill impairment by eliminating Step 2, which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill, which requires a hypothetical purchase price allocation, with the carrying amount of that reporting unit's goodwill. Under this update, an entity would perform its quantitative annual or interim goodwill impairment test using the current Step 1 test and recognize an impairment charge for the excess of the carrying value of a reporting unit over its fair value. For public business entities, this update is effective for their annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests occurring after January 1, 2017. The update will be applied prospectively. The Company plans to adopt this update in the first quarter of 2020. Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued a new accounting update on the measurement of credit losses for financial assets measured at amortized cost, which includes accounts receivable and available-for-sale debt securities. For financial assets measured at amortized cost, this update requires an entity to (1) estimate its lifetime expected credit losses upon recognition of the financial assets and establish an allowance to present the net amount expected to be collected, (2) recognize this allowance and changes in the allowance during subsequent periods through net income and (3) consider relevant information about past events, current conditions and reasonable and supportable forecasts in assessing the lifetime expected credit losses. For available-for-sale debt securities, this update made several targeted amendments to the existing other-than-temporary impairment model, including (1) requiring disclosure of the allowance for credit losses, (2) allowing reversals of the previously recognized credit losses until the entity has the intent to sell, is more-likely-than-not required to sell the securities or the maturity of the securities, (3) limiting impairment to the difference between the amortized cost basis and fair value and (4) not allowing entities to consider the length of time that fair value has been less than amortized cost as a factor in evaluating whether a credit loss exists. This update is effective for public business entities for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Entities are required to apply this update on a modified retrospective basis with a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact to its Consolidated Financial Statements of adopting this update and does not expect it to have a material impact.

REVENUE RECOGNITION

REVENUE RECOGNITION	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION Disaggregation of revenue Geographic Information The Company's international information consists of the results of Booking.com, agoda and Rentalcars.com and the results of the international businesses of KAYAK and OpenTable. This classification is independent of where the consumer resides, where the consumer is physically located while using the Company's services or the location of the travel service provider or restaurant. For example, a reservation made through Booking.com (which is domiciled in the Netherlands) at a hotel in New York by a consumer in the United States is part of the Company's international results. The Company's geographic information is as follows (in millions): International Total revenues for the three months ended March 31, United States The Netherlands Other Total 2019 $ 380 $ 2,005 $ 452 $ 2,837 2018 379 2,123 426 2,928 Revenue by Type of Service Approximately 84% and 85% of the Company's revenue for the three months ended March 31, 2019 and 2018 , respectively, relates to online accommodation reservation services. Revenue from all other sources of online travel reservation services or advertising and other revenues each represent less than 10% of the Company's total revenues. Deferred Revenue Cash payments received from travelers in advance of the Company completing its service obligations are included in "Deferred merchant bookings" in the Company's Unaudited Consolidated Balance Sheets and are comprised principally of amounts owed to the travel service providers as well as the Company's deferred revenue for its commission or margin and fees. At March 31, 2019 and December 31, 2018 , deferred merchant bookings includes deferred revenue of $246 million and $149 million , respectively. The Company expects to complete its service obligation within one year of booking. In the three months ended March 31, 2019 , the Company recognized revenue of $97 million and cancellations of $10 million related to the deferred revenue balance at December 31, 2018 . The offsetting increase of $204 million in the deferred revenue balance for the three months ended March 31, 2019 is principally driven by payments received from travelers, net of amounts payable to travel service providers, in the period for those online travel reservations that the Company receives cash payments in advance of completing its service obligations. Loyalty Programs The Company provides loyalty programs, where participating consumers are awarded loyalty points on current transactions that can be redeemed in the future. At March 31, 2019 and December 31, 2018 , liabilities of $80 million and $73 million , respectively, for loyalty program incentives were included in "Accrued expenses and other current liabilities" in the Unaudited Consolidated Balance Sheets. The Company’s largest loyalty program is at OpenTable, where points can be redeemed for qualifying reservations at participating restaurants, third-party gift cards and accommodation reservations booked through some of the Company’s other platform s. The estimated fair value of the incentives that are expected to be redeemed is recognized as a reduction of revenues at the time the incentives are granted. In the first quarter of 2018, OpenTable introduced a three-year time-based expiration for points earned by diners, which reduced its loyalty program liability by $27 million .

STOCK-BASED EMPLOYEE COMPENSATI

STOCK-BASED EMPLOYEE COMPENSATION	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED EMPLOYEE COMPENSATION	STOCK-BASED EMPLOYEE COMPENSATION Stock-based compensation expense included in personnel expenses in the Unaudited Consolidated Statements of Operations was $74 million and $71 million for the three months ended March 31, 2019 and 2018 , respectively. Stock-based compensation expense is recognized in the consolidated financial statements based upon fair value. Fair value is recognized as an expense on a straight-line basis over the employee's requisite service period 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. Stock-based compensation expense related to performance share units reflects the estimated probable outcome at the end of the performance period. The fair value of employee stock options assumed in acquisitions was determined using the Black-Scholes model and the market value of the Company's common stock at the respective acquisition dates. Restricted Stock Units and Performance Share Units The following table summarizes the activity of restricted stock units and performance share units ("share-based awards") during the three months ended March 31, 2019 : Share-Based Awards Shares Weighted-average Grant Date Fair Value Unvested at December 31, 2018 511,562 $ 1,713 Granted 192,775 $ 1,714 Vested (172,432 ) $ 1,443 Performance shares adjustment 127 $ 1,580 Forfeited/Canceled (8,093 ) $ 1,823 Unvested at March 31, 2019 523,939 $ 1,802 At March 31, 2019 , there was $663 million of total future compensation cost related to unvested share-based awards to be recognized over a weighted-average period of 2.3 years. During the three months ended March 31, 2019 , the Company made broad-based grants of 131,683 restricted stock units that generally vest over a three -year period, subject to certain exceptions for terminations other than for "cause," for "good reason" or on account of death or disability. These share-based awards had a total grant date fair value of $226 million based on a weighted-average grant-date fair value per share of $1,714 . Performance share units are payable in shares of the Company's common stock upon vesting. Subject to certain exceptions for terminations other than for "cause," for "good reason" or on account of death or disability, recipients of these performance share units generally must continue their service through the requisite service period in order to receive any shares. Stock-based compensation related to performance share units reflects the estimated probable outcome at the end of the performance period. 2019 Performance Share Units During the three months ended March 31, 2019 , the Company granted 61,092 performance share units to executives and certain other employees. The performance share units had a total grant-date fair value of $105 million based on a weighted-average grant-date fair value per share of $1,714 . The actual number of shares to be issued on the vesting date will be determined upon completion of the performance period which generally ends December 31, 2021 , assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. At March 31, 2019 , the estimated number of probable shares to be issued is a total of 61,092 shares, net of performance share units that were forfeited or vested since the grant date, including 47,674 shares that are not subject to the achievement of minimum performance thresholds. If the maximum performance thresholds are met at the end of the performance period, a maximum number of 122,184 total shares could be issued. 2018 Performance Share Units During the year ended December 31, 2018 , the Company granted 49,721 performance share units with a grant-date fair value of $101 million , based on a weighted-average grant-date fair value per share of $2,034 . The actual number of shares to be issued will be determined upon completion of the performance period which generally ends December 31, 2020 , assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. At March 31, 2019 , there were 44,900 unvested 2018 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. At March 31, 2019 , the number of shares estimated to be issued pursuant to these performance share units at the end of the performance period is a total of 86,157 shares, including 33,590 shares that are not subject to the achievement of minimum performance thresholds. If the maximum performance thresholds are met at the end of the performance period, a maximum of 89,800 shares could be issued pursuant to these performance share units. 2017 Performance Share Units During the year ended December 31, 2017 , the Company granted 73,893 performance share units with a grant-date fair value of $128 million , based on a weighted-average grant date fair value per share of $1,735 . The actual number of shares to be issued will be determined upon completion of the performance period which generally ends December 31, 2019 , assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. At March 31, 2019 , there were 56,506 unvested 2017 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. At March 31, 2019 , the number of shares estimated to be issued pursuant to these performance share units at the end of the performance period is a total of 88,098 shares, including 45,843 shares that are not subject to the achievement of minimum performance thresholds. If the maximum thresholds are met at the end of the performance period, a maximum of 113,012 shares could be issued pursuant to these performance share units. Stock Options All outstanding employee stock options were assumed in acquisitions. The following table summarizes the activity for stock options during the three months ended March 31, 2019 : Employee Stock Options Number of Shares Weighted-average Aggregate Intrinsic Value (in millions) Weighted-average Remaining Contractual Term Balance, December 31, 2018 27,263 $ 387 $ 36 2.8 Exercised (1,164 ) $ 317 Balance, March 31, 2019 26,099 $ 404 $ 35 2.5 Vested and exercisable at March 31, 2019 26,099 $ 404 $ 35 2.5 The aggregate intrinsic value of employee stock options exercised during the three months ended March 31, 2019 and 2018 was $2 million and $4 million , respectively. During the three months ended March 31, 2019 and 2018 , stock options vested for 73 and 83 shares, respectively.

NET INCOME PER SHARE

NET INCOME PER SHARE	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
NET INCOME PER SHARE	NET INCOME PER SHARE The Company computes basic net income per share by dividing net income applicable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net 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. The convertible notes are included in the calculation of diluted net income per share if their inclusion is dilutive under the treasury stock method. A reconciliation of the weighted-average number of shares outstanding used in calculating diluted earnings per share is as follows (in thousands): Three Months Ended 2019 2018 Weighted-average number of basic common shares outstanding 45,007 48,349 Weighted-average dilutive stock options, restricted stock units and performance share units 229 282 Assumed conversion of Convertible Senior Notes 200 574 Weighted-average number of diluted common and common equivalent shares outstanding 45,436 49,205 Anti-dilutive potential common shares 1,282 1,432 Anti-dilutive potential common shares for the three months ended March 31, 2019 include approximately 1 million shares that could be issued under the Company's outstanding convertible notes. Under the treasury stock method, the convertible notes will generally have an anti-dilutive impact on net income per share if the conversion prices for the convertible notes exceed the Company's average stock price.

INVESTMENTS

INVESTMENTS	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	INVESTMENTS Short-term and Long-term Investments in Marketable Securities The Company has classified its investments in marketable debt securities as available-for-sale securities. These securities are reported at estimated fair value with the aggregate unrealized gains and losses related to these investments, net of taxes, reflected as a part of " Accumulated other comprehensive loss " in the Unaudited Consolidated Balance Sheets. Classification as a short-term or long-term investment is based upon the maturity of the debt securities. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage are included in "Long-term investments" in the Unaudited Consolidated Balance Sheets. As of March 31, 2019 , the Company does not consider any of its investments to be other-than-temporarily impaired. The Company's investments in marketable equity securities, which are included in "Long-term investments" in the Unaudited Consolidated Balance Sheets, are reported at estimated fair value with changes in fair value of these equity securities recognized in " Net unrealized gains on marketable equity securities " in the Unaudited Consolidated Statements of Operations. The following table summarizes, by major security type, the Company's investments in marketable securities at March 31, 2019 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 218 $ — $ — $ 218 U.S. government securities 242 — (1 ) 241 Corporate debt securities 1,519 1 (6 ) 1,514 U.S. government agency securities 1 — — 1 Commercial paper 4 — — 4 Time deposits and certificates of deposit 3 — — 3 Total $ 1,987 $ 1 $ (7 ) $ 1,981 Long-term investments in marketable securities: Debt securities: International government securities $ 879 $ 5 $ — $ 884 U.S. government securities 250 — (4 ) 246 Corporate debt securities 3,794 12 (23 ) 3,783 Ctrip convertible debt securities 1,275 69 — 1,344 Marketable equity securities 1,105 383 (1 ) 1,487 Total $ 7,303 $ 469 $ (28 ) $ 7,744 The Company's investment policy seeks to preserve capital and maintain sufficient liquidity to meet operational and other needs of the business. At March 31, 2019 , the weighted-average life of the Company’s investments in marketable debt securities, excluding its investment in Ctrip.com International Ltd. ("Ctrip") convertible debt securities, was approximately 1.4 years with an average credit quality of A+/A1/A+. The Company invests in international government securities with high credit quality. At March 31, 2019 , investments in international government securities principally included debt securities issued by the governments of the Netherlands, France, Belgium, Germany, Austria and Finland. The following table summarizes, by major security type, the Company's investments in marketable securities at December 31, 2018 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 314 $ — $ — $ 314 U.S. government securities 658 — (2 ) 656 Corporate debt securities 2,693 — (12 ) 2,681 U.S. government agency securities 1 — — 1 Commercial paper 7 — — 7 Time deposits and certificates of deposit 1 — — 1 Total $ 3,674 $ — $ (14 ) $ 3,660 Long-term investments in marketable securities: Debt securities: International government securities $ 797 $ 3 $ — $ 800 U.S. government securities 299 — (6 ) 293 Corporate debt securities 4,445 4 (48 ) 4,401 Ctrip Convertible debt securities 1,275 — (98 ) 1,177 Marketable equity securities 1,105 3 (72 ) 1,036 Total $ 7,921 $ 10 $ (224 ) $ 7,707 Investments in Ctrip In May 2015 and August 2014, the Company invested $250 million and $500 million , respectively, in five -year senior convertible notes issued at par value by Ctrip. In December 2015, the Company invested $500 million in a Ctrip ten -year senior convertible note issued at par value, which included a put option allowing the Company, at its option, to require a prepayment in cash from Ctrip at the end of the sixth year of the note. In September 2016, the Company invested $25 million in a Ctrip six -year senior convertible note issued at par value, which included a put option allowing the Company, at its option, to require prepayment in cash from Ctrip at the end of the third year of the note. The Company determined that the economic characteristics and risks of the put option are clearly and closely related to the note, and therefore did not meet the requirement for separate accounting as embedded derivatives. The Company evaluated the conversion features for all Ctrip senior convertible notes and only the conversion feature associated with the September 2016 investment met the definition of an embedded derivative (see Note 6 ). The Company monitors the conversion features of these notes to determine whether they meet the definition of an embedded derivative during each reporting period. The Ctrip convertible notes have been marked-to-market in accordance with the accounting guidance for available-for-sale securities. At March 31, 2019 , the Company had also invested $655 million in Ctrip American Depositary Shares ("ADSs"). For the three months ended March 31, 2019 and 2018 , "Net unrealized gains on marketable equity securities" in the Unaudited Consolidated Statements of Operations included a net unrealized gain of $360 million and $55 million , respectively, related to Ctrip ADSs. At March 31, 2019 , the Company did not have significant influence over Ctrip. Investment in Meituan Dianping In October 2017, the Company invested $450 million in preferred shares of Meituan Dianping, the leading e-commerce platform for local services in China. The investment has been classified as a marketable equity security since Meituan Dianping's initial public offering in September 2018. For the three months ended March 31, 2019 , "Net unrealized gains on marketable equity securities" in the Unaudited Consolidated Statement of Operations included an unrealized gain of $91 million related to this investment. At March 31, 2019 , the Company did not have significant influence over Meituan Dianping. Long-term Investments without Readily Determinable Fair Value The Company held investments in equity securities of private companies, which are typically at an early stage of development, of $501 million at both March 31, 2019 and December 31, 2018 , principally related to the Company's investment of $500 million in July 2018 in preferred shares of Didi Chuxing, the leading mobile transportation and ride-hailing platform in China. These investments are measured 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 and are included in "Long-term investments" in the Company's Unaudited Consolidated Balance Sheets. The Company determined that no adjustments were required to the carrying value of these investments at March 31, 2019 . Other Long-term Investments The Company held an investment of $200 million in preferred shares of Grab, a leading on-demand transportation and mobile service platform in Southeast Asia, which is included in "Long-term investments" in the Company's Unaudited Consolidated Balance Sheets at March 31, 2019 and December 31, 2018 . The preferred shares are convertible to ordinary shares at the Company’s option and are mandatorily convertible upon an initial public offering. The preferred shares also contain a redemption feature that can be exercised by the Company after June 2023. These features have been evaluated as embedded derivatives, however, they do not meet the requirements to be accounted for separately. The investment is classified as a debt security for accounting purposes and categorized as available-for-sale. The investment is reported at estimated fair value with the aggregate unrealized gains and losses, net of taxes, reflected as a part of "Accumulated other comprehensive loss" in the Unaudited Consolidated Balance Sheet.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Financial assets and liabilities carried at fair value at March 31, 2019 are classified in the categories described in the table below (in millions): Level 1 Level 2 Level 3 Total ASSETS: Cash and restricted cash equivalents: Money market funds $ 1,727 $ — $ — $ 1,727 Time deposits and certificates of deposit 26 — — 26 Short-term investments in marketable securities: International government securities — 218 — 218 U.S. government securities — 241 — 241 Corporate debt securities — 1,514 — 1,514 U.S. government agency securities — 1 — 1 Commercial paper — 4 — 4 Time deposits and certificates of deposit 3 — — 3 Long-term investments in marketable securities: International government securities — 884 — 884 U.S. government securities — 246 — 246 Corporate debt securities — 3,783 — 3,783 Ctrip convertible debt securities — 1,344 — 1,344 Marketable equity securities 1,487 — — 1,487 Other long-term investment — — 200 200 Derivatives: Currency exchange derivatives — 1 — 1 Total assets at fair value $ 3,243 $ 8,236 $ 200 $ 11,679 LIABILITIES Currency exchange derivatives $ — $ 2 $ — $ 2 The table above does not include contingent consideration related to a business acquisition (see Note 13 ). Financial assets carried at fair value at December 31, 2018 are classified in the categories described in the table below (in millions): Level 1 Level 2 Level 3 Total Cash and restricted cash equivalents: Money market funds $ 2,061 $ — $ — $ 2,061 International government securities — 21 — 21 U.S. government securities — 1 — 1 Commercial paper — 2 — 2 Time deposits and certificates of deposit 25 — — 25 Short-term investments in marketable securities: International government securities — 314 — 314 U.S. government securities — 656 — 656 Corporate debt securities — 2,681 — 2,681 U.S. government agency securities — 1 — 1 Commercial paper — 7 — 7 Time deposits and certificates of deposit 1 — — 1 Long-term investments in marketable securities: International government securities — 800 — 800 U.S. government securities — 293 — 293 Corporate debt securities — 4,401 — 4,401 Ctrip convertible debt securities — 1,177 — 1,177 Marketable equity securities 1,036 — — 1,036 Other long-term investment — — 200 200 Derivatives: Currency exchange derivatives — 4 — 4 Total assets at fair value $ 3,123 $ 10,358 $ 200 $ 13,681 The table above does not include contingent consideration related to a business acquisition (see Note 13 ). There are three levels of inputs to measure fair value. The definition of each input is described below: Level 1 : Quoted prices in active markets that are accessible by the Company at the measurement date for identical assets and liabilities. Level 2 : Inputs that are observable, either directly or indirectly. Such prices may be based upon quoted prices for identical or comparable securities in active markets or inputs not quoted on active markets, but corroborated by market data. Level 3 : Unobservable inputs are used when little or no market data is available. Investments in corporate debt securities, U.S. and international government securities, commercial paper, government agency securities and certain 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 all of these investments. For the Company's 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. See Note 5 for information on the carrying value of the Company's investments in marketable securities. The investment in Grab, reported at a fair value of $200 million at both March 31, 2019 and December 31, 2018, is considered a "Level 3" valuation and measured using management's estimates that incorporate current market participant expectations of future cash flows considered alongside recent financing transactions of the investee and other relevant information. The Company's derivative instruments are valued using pricing models. Pricing models take into account the contract terms as well as multiple inputs where applicable, such as interest rate yield curves, option volatility and currency rates. Derivatives are considered "Level 2 " fair value measurements. The Company's derivative instruments are typically short-term in nature. At March 31, 2019 and December 31, 2018 , the Company's cash consisted of bank deposits. Other financial assets and liabilities, including restricted cash and cash equivalents, accounts receivable, accounts payable, accrued expenses and deferred merchant bookings, are carried at cost which approximates their fair value because of the short-term nature of these items. See Note 9 for the estimated fair value of the Company's outstanding Senior Notes. In the normal course of business, the Company is exposed to the impact of foreign currency fluctuations. The Company mitigates these risks by following established risk management policies and procedures, including the use of derivatives. The Company does not use derivatives for trading or speculative purposes. All derivative instruments are recognized in the Unaudited Consolidated Balance Sheets at fair value. Gains and losses resulting from changes in the fair value of derivative instruments that are not designated as hedging instruments for accounting purposes are recognized in the Unaudited Consolidated Statements of Operations in the period that the changes occur. Changes in the fair value of derivatives designated as net investment hedges were recorded as foreign currency translation adjustments to offset a portion of the foreign currency translation adjustment from Euro-denominated net assets held by certain subsidiaries and were recognized in the Unaudited Consolidated Balance Sheets in " Accumulated other comprehensive loss ." Derivatives Not Designated as Hedging Instruments — The Company is exposed to adverse movements in currency exchange rates as the operating results of its international operations are translated from local currency into U.S. Dollars upon consolidation. The Company enters into average-rate derivative contracts to hedge translation risks from short-term currency exchange rate fluctuations for the Euro, British Pound Sterling and certain other currencies versus the U.S. Dollar. At March 31, 2019 and December 31, 2018 , there were no outstanding derivative contracts related to foreign currency translation risks. The Company also enters into foreign currency forward contracts to hedge its exposure to the impact of movements in currency exchange rates on its transactional balances denominated in currencies other than the functional currency. Derivative assets are included in "Prepaid expenses and other current assets" and derivative liabilities are included in "Accrued expenses and other current liabilities" in the Unaudited Consolidated Balance Sheets. Derivatives associated with these transaction risks resulted in foreign currency losses of $13 million and foreign currency gains of $21 million for the three months ended March 31, 2019 and 2018 , respectively. These mark-to-market adjustments on the derivative contracts, offset by the effect of changes in currency exchange rates on transactions denominated in currencies other than the functional currency, resulted in net losses of $8 million and $5 million for the three months ended March 31, 2019 and 2018 , respectively. The net impacts related to these derivatives are reported in "Foreign currency transactions and other" in the Unaudited Consolidated Statements of Operations. The settlement of derivative contracts not designated as hedging instruments resulted in net cash inflows of $1 million and $18 million for the three months ended March 31, 2019 and 2018 , respectively, and are reported within " Net cash provided by operating activities " in the Unaudited Consolidated Statements of Cash Flows. Embedded Derivative — In September 2016, the Company invested $25 million in a Ctrip convertible note (see Note 5 ). The Company determined that the conversion option for this note met the definition of an embedded derivative that required separate accounting. At March 31, 2019 and December 31, 2018 , the embedded derivative had an estimated fair value of $0.9 million and $0.1 million , respectively, and is reported in the Unaudited Consolidated Balance Sheets with its host contract in "Long-term investments." The embedded derivative is bifurcated for fair value measurement purposes only. The mark-to-market adjustments are included in "Foreign currency transactions and other" in the Company's Unaudited Consolidated Statements of Operations.

LEASES

LEASES	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lessee Operating and Financing Leases	LEASES Adoption of ASC Topic 842, Leases On January 1, 2019, the Company adopted ASC 842, Leases , using a modified retrospective method applied to all contracts as of January 1, 2019. Therefore, for reporting periods beginning after December 31, 2018, the financial statements are prepared in accordance with the current lease standard and the financial statements for all periods prior to January 1, 2019 are presented under the previous lease standard ("ASC 840"). The Company determines if an arrangement is a lease, or contains a lease, when a contract is signed. The Company determines if a lease is an operating or financing lease and records a lease asset and a lease liability upon lease commencement, which is the date when the underlying asset is made available for use by the lessor. The Company has operating leases for office space, data centers and one land lease for Booking.com's headquarters (see Note 13 ). The Company has no finance leases as of March 31, 2019 . For office space, data centers and land, the Company has elected to combine the fixed payments to lease the asset and any fixed non-lease payments (such as maintenance or utility charges) when calculating the lease asset and lease liability. The Company recognizes lease expense on a straight-line basis over the lease term. Certain of our lease agreements include rent payments which are adjusted periodically for inflation. Any change in payments due to changes in inflation rates are recognized as variable lease expense as they are incurred. Variable lease expense also includes costs for property taxes, insurance and services provided by the lessor which are charged based on usage or performance. Most leases have one or more options to renew, with renewal terms that can initially extend the lease term for various periods up to 9 years . The exercise of renewal options for office space and data centers is at the Company’s discretion and are included if they are reasonably certain to be exercised. The land lease for Booking.com's headquarters has an initial term which expires in 2065, at which time the lease payments will be adjusted based on the value of the land on the reassessment date. The Company considered the initial term of the land lease to be its expected period of use. As of March 31, 2019 , the Company’s weighted-average remaining lease term for all leases was approximately 8.2 years. When the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate as its discount rate to determine the present value of its lease payments. The incremental borrowing rates approximate the rate the Company would pay to borrow in the currency of the lease payments on a collateralized basis for the weighted-average life of the lease. As of March 31, 2019 , the Company’s weighted-average discount rate was approximately 2.0% . The Company recognized the following related to leases in its Unaudited Consolidated Balance Sheet at March 31, 2019 (in millions): Leases Classification in Consolidated Balance Sheet March 31, 2019 Operating lease assets Operating lease assets $ 635 Lease Liabilities: Current operating lease liabilities Accrued expenses and other current liabilities $ 153 Non-current operating lease liabilities Operating lease liabilities 488 Total operating lease liabilities $ 641 As of March 31, 2019 , the operating lease liabilities will mature over the following periods (in millions): Remainder of 2019 $ 123 2020 152 2021 119 2022 73 2023 54 2024 36 Thereafter 154 Total remaining lease payments $ 711 Less: Imputed interest (70 ) Total operating lease liabilities $ 641 As of March 31, 2019 , the Company has entered into leases that have not yet commenced with future lease payments of approximately $7 million which are not reflected in the table above. These operating leases will commence in 2019 with lease terms of up to 5 years and will be recognized upon lease commencement. In addition, the Company signed an agreement for a lease in the city of Manchester in the United Kingdom for the headquarters of Rentalcars.com (see Note 13 ). At December 31, 2018 , minimum lease payments for operating leases having an initial term in excess of one year under ASC 840 were as follows (in millions): 2019 $ 164 2020 142 2021 110 2022 66 2023 52 Thereafter 190 Total minimum lease payments $ 724 The Company recognized the following related to operating leases in its Unaudited Consolidated Statement of Operations (in millions): Leases Classification in Unaudited Consolidated Statement of Operations Three Months Ended March 31, 2019 Lease expense General and administrative and Information technology $ 45 Variable lease expense General and administrative and Information technology 13 Less: Sublease income General and administrative (1 ) Total lease expense, net of sublease income $ 57 Supplemental cash flow information related to operating leases are as follows (in millions): Leases Three Months Ended March 31, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 47 Operating lease assets obtained in exchange for operating lease liabilities 42

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at March 31, 2019 and December 31, 2018 consisted of the following (in millions): March 31, 2019 December 31, 2018 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Amortization Supply and distribution agreements $ 1,095 $ (422 ) $ 673 $ 1,099 $ (408 ) $ 691 3 - 20 years Technology 173 (125 ) 48 173 (121 ) 52 1 - 7 years Patents 2 (2 ) — 2 (2 ) — 15 years Internet domain names 40 (30 ) 10 41 (30 ) 11 5 - 20 years Trade names 1,810 (463 ) 1,347 1,810 (439 ) 1,371 4 - 20 years Non-compete agreements — — — 1 (1 ) — Total intangible assets $ 3,120 $ (1,042 ) $ 2,078 $ 3,126 $ (1,001 ) $ 2,125 Intangible assets are amortized on a straight-line basis. Amortization expense was $45 million and $47 million for the three months ended March 31, 2019 and 2018 , respectively. A substantial portion of the Company's intangibles and goodwill relates to the acquisitions of OpenTable in July 2014 and KAYAK in May 2013. There were no events or changes in circumstances to indicate a potential impairment to goodwill or intangible assets at March 31, 2019 . Acquisition In November 2018, the Company paid $134 million , net of cash acquired, to complete the acquisition of HotelsCombined, a hotel meta-search company. The purchase price allocation has not been completed at March 31, 2019 . The Company's Unaudited Consolidated Financial Statements include the accounts of this business starting at the acquisition date. Revenues and earnings of this business since the acquisition date and pro forma results of operations have not been presented separately as such financial information is not material to the Company's results of operations.

DEBT

DEBT	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
DEBT	DEBT Short-term Borrowing On December 31, 2018 , the Company had a bank overdraft of $25 million which was reported in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheet at December 31, 2018 and was repaid in January 2019. Revolving Credit Facility In June 2015, the Company entered into a $2.0 billion five -year unsecured revolving credit facility with a group of lenders. Borrowings under the revolving credit facility will bear interest, at the Company’s option, at a rate per annum equal to either (i) the adjusted London Inter-bank Offered Rate ("LIBOR") for the interest period in effect for such borrowing plus an applicable margin ranging from 0.875% to 1.50% ; or (ii) the greatest of (a) Bank of America, N.A.'s prime lending rate, (b) the federal funds rate plus 0.50% , and (c) an adjusted LIBOR for an interest period of one month plus 1.00% , plus an applicable margin ranging from 0.00% to 0.50% . Undrawn balances available under the revolving credit facility are subject to commitment fees at the applicable rate ranging from 0.085% to 0.20% . The revolving credit facility provides for the issuance of up to $70 million of letters of credit as well as borrowings of up to $50 million on same-day notice, referred to as swingline loans. Borrowings under the revolving credit facility may be made in U.S. Dollars, Euros, British Pounds Sterling and any other foreign currency agreed to by the lenders. The proceeds of loans made under the facility would be used for working capital and general corporate purposes, which could include acquisitions, share repurchases or debt repayments. There were $5 million of letters of credit issued under the facility at both March 31, 2019 and December 31, 2018 . There were no borrowings outstanding under this revolving credit facility at December 31, 2018 . At March 31, 2019 , there were $250 million of borrowings outstanding with a weighted-average interest rate of 3.5% due in the second quarter of 2019, which is included in "Accrued expenses and other current liabilities" in the Unaudited Consolidated Balance Sheet. In addition, in April 2019, the Company borrowed an additional $150 million under this revolving credit facility, which is due in May 2019 with an interest rate of 3.5% . Outstanding Debt Outstanding debt at March 31, 2019 consisted of the following (in millions): March 31, 2019 Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Cost Carrying Value Current liabilities: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (32 ) $ 968 Long-term debt: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (56 ) $ 944 0.8% (€1 Billion) Senior Notes due March 2022 1,123 (4 ) 1,119 2.15% (€750 Million) Senior Notes due November 2022 842 (3 ) 839 2.75% Senior Notes due March 2023 500 (3 ) 497 2.375% (€1 Billion) Senior Notes due September 2024 1,123 (10 ) 1,113 3.65% Senior Notes due March 2025 500 (3 ) 497 3.6% Senior Notes due June 2026 1,000 (6 ) 994 1.8% (€1 Billion) Senior Notes due March 2027 1,123 (4 ) 1,119 3.55% Senior Notes due March 2028 500 (3 ) 497 Total long-term debt $ 7,711 $ (92 ) $ 7,619 Outstanding debt at December 31, 2018 consisted of the following (in millions): December 31, 2018 Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Cost Carrying Value Long-term debt: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (39 ) $ 961 0.9% Convertible Senior Notes due September 2021 1,000 (61 ) 939 0.8% (€1 Billion) Senior Notes due March 2022 1,143 (5 ) 1,138 2.15% (€750 Million) Senior Notes due November 2022 858 (4 ) 854 2.75% Senior Notes due March 2023 500 (3 ) 497 2.375% (€1 Billion) Senior Notes due September 2024 1,143 (10 ) 1,133 3.65% Senior Notes due March 2025 500 (3 ) 497 3.6% Senior Notes due June 2026 1,000 (6 ) 994 1.8% (€1 Billion) Senior Notes due March 2027 1,143 (4 ) 1,139 3.55% Senior Notes due March 2028 500 (3 ) 497 Total long-term debt $ 8,787 $ (138 ) $ 8,649 Based on the closing price of the Company's common stock for the prescribed measurement periods for the three months ended March 31, 2019 and December 31, 2018 , the contingent conversion thresholds on the 2020 Notes (as defined below) and 2021 Notes (as defined below) were not exceeded, therefore, these notes were not convertible at the option of the holder. The 2020 Notes were reported as non-current liabilities in the Unaudited Consolidated Balance Sheet at December 31, 2018 and reclassified as current liabilities at March 31, 2019 since the holders will have the right to convert all or any portion of the 2020 Notes at March 15, 2020 regardless of the Company's stock price. Fair Value of Debt At March 31, 2019 and December 31, 2018 , the estimated fair value of the outstanding Senior Notes was approximately $9.5 billion and $9.3 billion , respectively, and was considered a "Level 2 " fair value measurement (see Note 6 ). Fair value was estimated based upon actual trades at the end of the reporting period or the most recent trade available as well as the Company's stock price at the end of the reporting period. A substantial portion of the market value of the Company's debt in excess of the outstanding principal amount relates to the conversion premium on the Convertible Senior Notes. Convertible Senior Notes If the note holders exercise their option to convert, the Company delivers cash to repay the principal amount of the notes and delivers shares of common stock or cash, at its option, to satisfy the conversion value in excess of the principal amount. If the Company's convertible debt is redeemed or converted prior to maturity, a gain or loss on extinguishment is recognized. The gain or loss is the difference between the fair value of the debt component immediately prior to extinguishment and its carrying value. To estimate the fair value of the debt at the conversion date, the Company estimates its straight debt borrowing rate, considering its credit rating and straight debt of comparable corporate issuers. Description of Convertible Senior Notes In August 2014, the Company issued in a private placement $1.0 billion aggregate principal amount of Convertible Senior Notes due September 15, 2021, with an interest rate of 0.9% (the "2021 Notes"). The Company paid $11 million in debt issuance costs during the year ended December 31, 2014 related to this offering. The 2021 Notes are convertible, subject to certain conditions, into the Company's common stock at a conversion price of $2,055.50 per share. The 2021 Notes are convertible, at the option of the holder, prior to September 15, 2021, upon the occurrence of specific events, including but not limited to a change in control, or if the closing sales price of the Company's common stock for at least 20 trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is more than 150% of the conversion price in effect for the notes on the last trading day of the immediately preceding quarter. In the event that all or substantially all of the Company's common stock is acquired on or prior to the maturity of the 2021 Notes in a transaction in which the consideration paid to holders of the Company's common stock consists of all or substantially all cash, the Company would be required to make additional payments in the form of additional shares of common stock to the holders of the 2021 Notes in an aggregate value ranging from $0 to $375 million depending upon the date of the transaction and the then current stock price of the Company. At June 15, 2021, holders will have the right to convert all or any portion of the 2021 Notes, regardless of the Company's stock price. The 2021 Notes may not be redeemed by the Company prior to maturity. The holders may require the Company to repurchase the 2021 Notes for cash in certain circumstances. Interest on the 2021 Notes is payable on March 15 and September 15 of each year. In May 2013, the Company issued in a private placement $1.0 billion aggregate principal amount of Convertible Senior Notes due June 15, 2020, with an interest rate of 0.35% (the "2020 Notes"). The 2020 Notes were issued with an initial discount of $20 million . The Company paid $1 million in debt issuance costs during the year ended December 31, 2013 related to this offering. The 2020 Notes are convertible, subject to certain conditions, into the Company's common stock at a conversion price of $1,315.10 per share. The 2020 Notes are convertible, at the option of the holder, prior to June 15, 2020, upon the occurrence of specific events, including but not limited to a change in control, or if the closing sales price of the Company's common stock for at least 20 trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is more than 150% of the conversion price in effect for the notes on the last trading day of the immediately preceding quarter. In the event that all or substantially all of the Company's common stock is acquired on or prior to the maturity of the 2020 Notes in a transaction in which the consideration paid to holders of the Company's common stock consists of all or substantially all cash, the Company would be required to make additional payments in the form of additional shares of common stock to the holders of the 2020 Notes in an aggregate value ranging from $0 to $397 million depending upon the date of the transaction and the then current stock price of the Company. At March 15, 2020, holders will have the right to convert all or any portion of the 2020 Notes, regardless of the Company's stock price. The 2020 Notes may not be redeemed by the Company prior to maturity. The holders may require the Company to repurchase the 2020 Notes for cash in certain circumstances. Interest on the 2020 Notes is payable on June 15 and December 15 of each year. In March 2012, the Company issued in a private placement $1.0 billion aggregate principal amount of Convertible Senior Notes due March 15, 2018, with an interest rate of 1.0% (the "2018 Notes"). The 2018 Notes were convertible, subject to certain conditions, into the Company's common stock at a conversion price of $944.61 per share. In March 2018, in connection with the maturity of the remaining outstanding 2018 Notes, the Company paid $714 million to satisfy the aggregate principal amount due and paid an additional $773 million in satisfaction of the conversion value in excess of the principal amount. Cash-settled convertible debt, such as the Company's Convertible Senior Notes, is separated into debt and equity components at issuance and each component is assigned a value. The value assigned to the debt component is the estimated fair value, at the issuance date, of a similar bond without the conversion feature. The difference between the bond cash proceeds and this estimated fair value, representing the value assigned to the equity component, is recorded as a debt discount. Debt discount is amortized using the effective interest rate method over the period from the origination date through the stated maturity date. The Company estimated the straight debt borrowing rates at debt origination to be 3.18% for the 2021 Notes, 3.13% for the 2020 Notes and 3.50% for the 2018 Notes. The yield to maturity was estimated at an at-market coupon priced at par. Debt discount after tax of $83 million ( $143 million before tax) related to the 2021 Notes, $92 million ( $154 million before tax) related to the 2020 Notes and $81 million ( $135 million before tax) related to the 2018 Notes less financing costs associated with the equity component of the respective convertible notes was recorded in additional paid-in capital in the balance sheet at debt origination. For the three months ended March 31, 2019 and 2018 , the Company recognized interest expense of $15 million and $20 million , respectively, related to convertible notes, which was almost entirely comprised of the amortization of debt discount of $12 million and $14 million , respectively, and the contractual coupon interest of $3 million and $5 million , respectively. The remaining interest expense relates to the amortization of debt issuance costs. For the three months ended March 31, 2019 and 2018 , included in the amortization of debt discount mentioned above was $1 million of original issuance discount related to the 2020 Notes for each period. The remaining period for amortization of debt discount and debt issuance costs is the period until the stated maturity date for the respective debt. The weighted-average effective interest rates for the three months ended March 31, 2019 and 2018 are 3.2% and 3.3% , respectively. Other Long-term Debt Other long-term debt had a total carrying value of $6.7 billion at both March 31, 2019 and December 31, 2018 . Debt discount is amortized using the effective interest rate method over the period from the origination date through the stated maturity date. The Company estimated the effective interest rates at debt origination to be 0.84% for the Senior Notes maturing in March 2022 (the "March 2022 Notes"), 2.20% for the Senior Notes maturing in November 2022 (the "November 2022 Notes"), 2.78% for the Senior Notes maturing in March 2023, 2.48% for the Senior Notes maturing in September 2024 (the "September 2024 Notes"), 3.68% for the Senior Notes maturing in March 2025, 3.62% for the Senior Notes maturing in June 2026, 1.80% for the Senior Notes maturing in March 2027 (the "March 2027 Notes") and 3.56% for the Senior Notes maturing in March 2028. For the three months ended March 31, 2019 and 2018 , the Company recognized interest expense of $42 million and $43 million , respectively, related to other long-term debt, which was almost entirely comprised of $40 million and $42 million , respectively, related to the contractual coupon interest. The remaining interest expense relates to the amortization of debt discount and debt issuance costs. The remaining period for amortization of debt discount and debt issuance costs is the period until the stated maturity dates for the respective debt. The aggregate principal value of the Euro-denominated March 2022 Notes, November 2022 Notes, September 2024 Notes and March 2027 Notes and accrued interest thereon was designated as a hedge of the Company's net investment in certain Euro functional currency subsidiaries. The foreign currency transaction gains or losses on these liabilities are measured based upon changes in spot rates and are recorded in "Accumulated other comprehensive loss" in the Unaudited Consolidated Balance Sheets. The Euro-denominated net assets of these subsidiaries are translated into U.S. Dollars at each balance sheet date, with the effects of foreign currency changes also reported in "Accumulated other comprehensive loss" in the Unaudited Consolidated Balance Sheets. Since the notional amount of Euro-denominated debt and related interest have been less than the notional amount of the Company's net investment, the Company has not incurred any ineffectiveness on this hedge. The Company plans to dedesignate a portion of this hedge in the second quarter of 2019. The foreign currency transaction gains or losses on the Euro-denominated debt that is not designated as hedging instruments for accounting purposes will be recognized in net income.

TREASURY STOCK

TREASURY STOCK	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
TREASURY STOCK	TREASURY STOCK At March 31, 2019 and December 31, 2018, the Company had a total remaining authorization of $1.8 billion and $4.5 billion , respectively, to repurchase its common stock related to a program authorized by the Company's Board of Directors in 2018 for $8.0 billion . In the second quarter of 2019, the Company's Board of Directors authorized an additional program to repurchase up to $15.0 billion of the Company's common stock. The Company has continued to make repurchases of its common stock in the second quarter of 2019 and may continue to make repurchases of shares under its stock repurchase program, depending on prevailing market conditions, alternate uses of capital and other factors. Whether and when to initiate and/or complete any repurchase of common stock and the amount of common stock repurchased will be determined at the Company's discretion. Additionally, the Board of Directors has given the Company the general authorization to repurchase shares of its common stock withheld to satisfy employee withholding tax obligations related to stock-based compensation. The following table summarizes the Company's stock repurchase activities during the three months ended March 31, 2019 and 2018 , respectively (in millions, except for shares): Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Shares Amount Shares Amount Authorized stock repurchase programs 1,548,083 $ 2,735 314,076 $ 612 General authorization for shares withheld on stock award vesting 70,705 121 59,043 120 Total 1,618,788 $ 2,856 373,119 $ 732 In the three months ended March 31, 2019 , stock repurchases in March 2019 of 84,229 shares for an aggregate cost of $147 million were settled in April 2019. Stock repurchases in December 2018 of 42,939 shares for an aggregate cost of $74 million were settled in January 2019. For the three months ended March 31, 2019 and 2018 , the Company remitted employee withholding taxes of $111 million and $103 million , respectively, to the tax authorities, which is different from the aggregate cost of the shares withheld for taxes for each period due to the timing in remitting the taxes. The cash remitted to the tax authorities is included in financing activities in the Unaudited Consolidated Statements of Cash Flows. At March 31, 2019 , there were 18,935,914 shares of the Company's common stock held in treasury.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2019
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, 2019 was 21.0% compared to 19.4% for the three months ended March 31, 2018 . The Company's 2018 effective tax rate differs from the U.S. federal statutory tax rate of 21% , primarily due to the benefit of the Netherlands Innovation Box Tax (discussed below) and current year excess tax benefits recognized from the vesting of equity awards, partially offset by the effect of higher international tax rates and U.S. federal and state tax associated with the Company's current year international earnings, resulting from the introduction of the Tax Act. The Company's effective tax rate was higher for the three months ended March 31, 2019 , compared to the three months ended March 31, 2018 , primarily as a result of lower excess tax benefits recognized from the vesting of equity awards and higher discrete tax charges related to unrealized gains on equity securities, partially offset by lower U.S. federal and state tax associated with the Company’s current year international earnings, resulting from the introduction of the Tax Act. During the three months ended March 31, 2019 and 2018 , a substantial majority of the Company's income was generated 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 7% ("Innovation Box Tax") rather than the Dutch statutory rate of 25% . A portion of Booking.com's earnings during the three months ended March 31, 2019 and 2018 qualified for Innovation Box Tax treatment, which had a significant beneficial impact on the Company's effective tax rate for those periods.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME	3 Months Ended
	Mar. 31, 2019
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
ACCUMULATED OTHER COMPREHENSIVE INCOME	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The table below provides the balances for each classification of accumulated other comprehensive loss at March 31, 2019 and December 31, 2018 (in millions): March 31, December 31, Foreign currency translation adjustments, net of tax (1) $ (141 ) $ (129 ) Net unrealized losses on debt securities, net of tax (2) (28 ) (187 ) Accumulated other comprehensive loss $ (169 ) $ (316 ) (1) Foreign currency translation adjustments, net of tax, at March 31, 2019 and December 31, 2018 , include accumulated net losses from fair value adjustments of $35 million after tax ( $53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. Foreign currency translation adjustments, net of tax, include foreign currency transaction gains of $31 million after tax ( $56 million before tax) and foreign currency transaction losses of $26 million after tax ( $20 million before tax) at March 31, 2019 and December 31, 2018 , respectively, associated with the Company's Euro-denominated debt. The Company's Euro-denominated debt is designated as a hedge against the impact of currency fluctuations on its Euro-denominated net assets (see Note 9 ). The remaining balance in foreign currency translation adjustments relates to the cumulative impacts of currency fluctuations on the Company's non-U.S. Dollar denominated net assets. At March 31, 2019 and December 31, 2018 , the Company had deferred tax benefits of $52 million and $41 million , respectively, related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the introduction of the Tax Act. (2) Net unrealized losses on debt securities, net of tax, includes cumulative tax charges of $81 million and $30 million at March 31, 2019 and December 31, 2018 , respectively.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES

BASIS OF PRESENTATION (Policies

BASIS OF PRESENTATION (Policies)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting, Policy	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 ("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 for interim reporting. As permitted under those rules, the Company condensed or omitted certain footnotes or other financial information that are normally required by 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, 2018 . The Unaudited Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries, including its primary brands of Booking.com, KAYAK, priceline, agoda, Rentalcars.com and OpenTable. All inter-company accounts 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 Unaudited Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Foreign currency transactions and other" 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.
Accounting Changes and Error Corrections [Text Block]	Unaudited Consolidated Statements of Comprehensive Income Subsequent to the issuance of the Company’s unaudited interim consolidated financial statements for the three and nine months ended September 30, 2018, the Company identified an error in the previously issued Unaudited Consolidated Statements of Comprehensive Income associated with the Company’s adoption of a new accounting update during the first quarter of 2018. This new accounting update amended the guidance on the recognition and measurement of financial instruments. The effect of adopting this new accounting update resulted in an increase of $241 million to the Company’s retained earnings for the net unrealized gain, net of tax, related to marketable equity securities, with an offsetting adjustment to accumulated other comprehensive income as of January 1, 2018. However, in the Unaudited Consolidated Statements of Comprehensive Income for the three months ended March 31, 2018, six months ended June 30, 2018 and nine months ended September 30, 2018, the Company incorrectly presented the $241 million as a component of other comprehensive income (referred to as “Reclassification of net unrealized gains on marketable equity securities to retained earnings, net of tax charge”). Accordingly, the Company corrected the foregoing presentation error in the accompanying Unaudited Consolidated Statement of Comprehensive Income for the three months ended March 31, 2018. As a result of this correction, total comprehensive income in the Company’s previously reported Unaudited Consolidated Statements of Comprehensive Income increased from $427 million to $668 million for the three months ended March 31, 2018. The correction of this error had no effect on the Company’s previously reported Unaudited Consolidated Balance Sheets, Unaudited Consolidated Statements of Operations, Unaudited Consolidated Statements of Changes in Stockholders’ Equity and Unaudited Consolidated Statements of Cash Flows. The effect of adopting this new accounting update has been presented correctly in the audited Consolidated Statement of Comprehensive Income included in the Consolidated Financial Statements in the Form 10-K for the year ended December 31, 2018. The Company will present the correction in the Unaudited Consolidated Statements of Comprehensive Income for the six months ended June 30, 2018 and the nine months ended September 30, 2018 to be included in the Form 10-Qs for the second and third quarters of 2019.
Reclassification, Policy	Reclassifications — Certain amounts from prior periods have been reclassified to conform to the current year presentation.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy	Restricted Cash and Cash Equivalents: Restricted cash and cash equivalents at March 31, 2019 and December 31, 2018 principally relates to the minimum cash requirement for Rentalcars.com's insurance business established in 2017. The following table reconciles cash and cash equivalents and restricted cash and cash equivalents reported in the Unaudited Consolidated Balance Sheets to the total amount shown in the Unaudited Consolidated Statements of Cash Flows (in millions): March 31, December 31, As included in the Unaudited Consolidated Balance Sheets: Cash and cash equivalents $ 2,334 $ 2,624 Restricted cash and cash equivalents included in prepaid expenses and other current assets 20 21 Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Unaudited Consolidated Statements of Cash Flows $ 2,354 $ 2,645
Recent Accounting Pronouncements Adopted	Recent Accounting Pronouncements Adopted Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In August 2018, the Financial Accounting Standards Board ("FASB") issued a new accounting update to address a customer's accounting for implementation costs incurred in a cloud computing arrangement that is a service contract and also added certain disclosure requirements related to implementation costs incurred for internal-use software and cloud computing arrangements. The amendment aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The Company utilizes various third-party computer systems and third-party service providers, including global distribution systems serving the accommodation, rental car and airline industries. The Company uses both internally-developed systems and third-party systems to operate its services, including transaction processing, order management and financial systems. The Company adopted this update on January 1, 2019 and applied it on a prospective basis. The adoption of this update did not have a material impact to the Unaudited Consolidated Financial Statements. Leases In February 2016, the FASB issued a new accounting standard which requires lessees to recognize an asset and a liability on the balance sheet for the rights and obligations created by entering into lease transactions. The new standard retains the dual-model concept by requiring entities to determine if a lease is an operating or financing lease. The new standard also expands qualitative and quantitative disclosures for lessees. The Company adopted this new standard on January 1, 2019 on a modified retrospective basis and has elected not to restate comparative periods. The Company elected other options, which allow the Company to use its previous evaluations regarding if an arrangement contains a lease, if a lease is an operating or financing lease and what costs are capitalized as initial direct costs prior to adoption. The Company also elected to combine lease and non-lease components. Upon the adoption of the new lease standard, on January 1, 2019, the Company recognized operating lease assets of $646 million and total operating lease liabilities of $646 million (including a current liability of $152 million ) in the consolidated balance sheet and reclassified certain balances related to existing leases. There was no impact to retained earnings at adoption. See Note 7 for more information on leases.
Other Recent Accounting Pronouncements	Other Recent Accounting Pronouncements Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued a new accounting update to simplify the test for goodwill impairment by eliminating Step 2, which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill, which requires a hypothetical purchase price allocation, with the carrying amount of that reporting unit's goodwill. Under this update, an entity would perform its quantitative annual or interim goodwill impairment test using the current Step 1 test and recognize an impairment charge for the excess of the carrying value of a reporting unit over its fair value. For public business entities, this update is effective for their annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests occurring after January 1, 2017. The update will be applied prospectively. The Company plans to adopt this update in the first quarter of 2020. Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued a new accounting update on the measurement of credit losses for financial assets measured at amortized cost, which includes accounts receivable and available-for-sale debt securities. For financial assets measured at amortized cost, this update requires an entity to (1) estimate its lifetime expected credit losses upon recognition of the financial assets and establish an allowance to present the net amount expected to be collected, (2) recognize this allowance and changes in the allowance during subsequent periods through net income and (3) consider relevant information about past events, current conditions and reasonable and supportable forecasts in assessing the lifetime expected credit losses. For available-for-sale debt securities, this update made several targeted amendments to the existing other-than-temporary impairment model, including (1) requiring disclosure of the allowance for credit losses, (2) allowing reversals of the previously recognized credit losses until the entity has the intent to sell, is more-likely-than-not required to sell the securities or the maturity of the securities, (3) limiting impairment to the difference between the amortized cost basis and fair value and (4) not allowing entities to consider the length of time that fair value has been less than amortized cost as a factor in evaluating whether a credit loss exists. This update is effective for public business entities for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Entities are required to apply this update on a modified retrospective basis with a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact to its Consolidated Financial Statements of adopting this update and does not expect it to have a material impact.

LEASES (Policies)

LEASES (Policies)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lessee, Leases	The Company has operating leases for office space, data centers and one land lease for Booking.com's headquarters (see Note 13 ). The Company has no finance leases as of March 31, 2019 . For office space, data centers and land, the Company has elected to combine the fixed payments to lease the asset and any fixed non-lease payments (such as maintenance or utility charges) when calculating the lease asset and lease liability. The Company recognizes lease expense on a straight-line basis over the lease term. Certain of our lease agreements include rent payments which are adjusted periodically for inflation. Any change in payments due to changes in inflation rates are recognized as variable lease expense as they are incurred. Variable lease expense also includes costs for property taxes, insurance and services provided by the lessor which are charged based on usage or performance. Most leases have one or more options to renew, with renewal terms that can initially extend the lease term for various periods up to 9 years . The exercise of renewal options for office space and data centers is at the Company’s discretion and are included if they are reasonably certain to be exercised. The land lease for Booking.com's headquarters has an initial term which expires in 2065, at which time the lease payments will be adjusted based on the value of the land on the reassessment date. The Company considered the initial term of the land lease to be its expected period of use. As of March 31, 2019 , the Company’s weighted-average remaining lease term for all leases was approximately 8.2 years. When the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate as its discount rate to determine the present value of its lease payments. The incremental borrowing rates approximate the rate the Company would pay to borrow in the currency of the lease payments on a collateralized basis for the weighted-average life of the lease. As of March 31, 2019 , the Company’s weighted-average discount rate was approximately 2.0% .

BASIS OF PRESENTATION (Tables)

BASIS OF PRESENTATION (Tables)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Restrictions on Cash and Cash Equivalents	Restricted Cash and Cash Equivalents: Restricted cash and cash equivalents at March 31, 2019 and December 31, 2018 principally relates to the minimum cash requirement for Rentalcars.com's insurance business established in 2017. The following table reconciles cash and cash equivalents and restricted cash and cash equivalents reported in the Unaudited Consolidated Balance Sheets to the total amount shown in the Unaudited Consolidated Statements of Cash Flows (in millions): March 31, December 31, As included in the Unaudited Consolidated Balance Sheets: Cash and cash equivalents $ 2,334 $ 2,624 Restricted cash and cash equivalents included in prepaid expenses and other current assets 20 21 Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Unaudited Consolidated Statements of Cash Flows $ 2,354 $ 2,645

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Geographic Information	The Company's geographic information is as follows (in millions): International Total revenues for the three months ended March 31, United States The Netherlands Other Total 2019 $ 380 $ 2,005 $ 452 $ 2,837 2018 379 2,123 426 2,928

STOCK-BASED EMPLOYEE COMPENSA_2

STOCK-BASED EMPLOYEE COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Activity of unvested restricted stock units and performance share units	Restricted Stock Units and Performance Share Units The following table summarizes the activity of restricted stock units and performance share units ("share-based awards") during the three months ended March 31, 2019 : Share-Based Awards Shares Weighted-average Grant Date Fair Value Unvested at December 31, 2018 511,562 $ 1,713 Granted 192,775 $ 1,714 Vested (172,432 ) $ 1,443 Performance shares adjustment 127 $ 1,580 Forfeited/Canceled (8,093 ) $ 1,823 Unvested at March 31, 2019 523,939 $ 1,802
Schedule of share-based compensation, stock options, activity	Stock Options All outstanding employee stock options were assumed in acquisitions. The following table summarizes the activity for stock options during the three months ended March 31, 2019 : Employee Stock Options Number of Shares Weighted-average Aggregate Intrinsic Value (in millions) Weighted-average Remaining Contractual Term Balance, December 31, 2018 27,263 $ 387 $ 36 2.8 Exercised (1,164 ) $ 317 Balance, March 31, 2019 26,099 $ 404 $ 35 2.5 Vested and exercisable at March 31, 2019 26,099 $ 404 $ 35 2.5

NET INCOME PER SHARE (Tables)

NET INCOME PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Reconciliation of the weighted average number of shares outstanding used in calculating diluted earnings per share	A reconciliation of the weighted-average number of shares outstanding used in calculating diluted earnings per share is as follows (in thousands): Three Months Ended 2019 2018 Weighted-average number of basic common shares outstanding 45,007 48,349 Weighted-average dilutive stock options, restricted stock units and performance share units 229 282 Assumed conversion of Convertible Senior Notes 200 574 Weighted-average number of diluted common and common equivalent shares outstanding 45,436 49,205 Anti-dilutive potential common shares 1,282 1,432

INVESTMENTS (Tables)

INVESTMENTS (Tables)	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	The following table summarizes, by major security type, the Company's investments in marketable securities at March 31, 2019 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 218 $ — $ — $ 218 U.S. government securities 242 — (1 ) 241 Corporate debt securities 1,519 1 (6 ) 1,514 U.S. government agency securities 1 — — 1 Commercial paper 4 — — 4 Time deposits and certificates of deposit 3 — — 3 Total $ 1,987 $ 1 $ (7 ) $ 1,981 Long-term investments in marketable securities: Debt securities: International government securities $ 879 $ 5 $ — $ 884 U.S. government securities 250 — (4 ) 246 Corporate debt securities 3,794 12 (23 ) 3,783 Ctrip convertible debt securities 1,275 69 — 1,344 Marketable equity securities 1,105 383 (1 ) 1,487 Total $ 7,303 $ 469 $ (28 ) $ 7,744 The following table summarizes, by major security type, the Company's investments in marketable securities at December 31, 2018 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 314 $ — $ — $ 314 U.S. government securities 658 — (2 ) 656 Corporate debt securities 2,693 — (12 ) 2,681 U.S. government agency securities 1 — — 1 Commercial paper 7 — — 7 Time deposits and certificates of deposit 1 — — 1 Total $ 3,674 $ — $ (14 ) $ 3,660 Long-term investments in marketable securities: Debt securities: International government securities $ 797 $ 3 $ — $ 800 U.S. government securities 299 — (6 ) 293 Corporate debt securities 4,445 4 (48 ) 4,401 Ctrip Convertible debt securities 1,275 — (98 ) 1,177 Marketable equity securities 1,105 3 (72 ) 1,036 Total $ 7,921 $ 10 $ (224 ) $ 7,707

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Financial instruments carried at fair value	Financial assets and liabilities carried at fair value at March 31, 2019 are classified in the categories described in the table below (in millions): Level 1 Level 2 Level 3 Total ASSETS: Cash and restricted cash equivalents: Money market funds $ 1,727 $ — $ — $ 1,727 Time deposits and certificates of deposit 26 — — 26 Short-term investments in marketable securities: International government securities — 218 — 218 U.S. government securities — 241 — 241 Corporate debt securities — 1,514 — 1,514 U.S. government agency securities — 1 — 1 Commercial paper — 4 — 4 Time deposits and certificates of deposit 3 — — 3 Long-term investments in marketable securities: International government securities — 884 — 884 U.S. government securities — 246 — 246 Corporate debt securities — 3,783 — 3,783 Ctrip convertible debt securities — 1,344 — 1,344 Marketable equity securities 1,487 — — 1,487 Other long-term investment — — 200 200 Derivatives: Currency exchange derivatives — 1 — 1 Total assets at fair value $ 3,243 $ 8,236 $ 200 $ 11,679 LIABILITIES Currency exchange derivatives $ — $ 2 $ — $ 2 The table above does not include contingent consideration related to a business acquisition (see Note 13 ). Financial assets carried at fair value at December 31, 2018 are classified in the categories described in the table below (in millions): Level 1 Level 2 Level 3 Total Cash and restricted cash equivalents: Money market funds $ 2,061 $ — $ — $ 2,061 International government securities — 21 — 21 U.S. government securities — 1 — 1 Commercial paper — 2 — 2 Time deposits and certificates of deposit 25 — — 25 Short-term investments in marketable securities: International government securities — 314 — 314 U.S. government securities — 656 — 656 Corporate debt securities — 2,681 — 2,681 U.S. government agency securities — 1 — 1 Commercial paper — 7 — 7 Time deposits and certificates of deposit 1 — — 1 Long-term investments in marketable securities: International government securities — 800 — 800 U.S. government securities — 293 — 293 Corporate debt securities — 4,401 — 4,401 Ctrip convertible debt securities — 1,177 — 1,177 Marketable equity securities 1,036 — — 1,036 Other long-term investment — — 200 200 Derivatives: Currency exchange derivatives — 4 — 4 Total assets at fair value $ 3,123 $ 10,358 $ 200 $ 13,681

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Operating leases	The Company recognized the following related to leases in its Unaudited Consolidated Balance Sheet at March 31, 2019 (in millions): Leases Classification in Consolidated Balance Sheet March 31, 2019 Operating lease assets Operating lease assets $ 635 Lease Liabilities: Current operating lease liabilities Accrued expenses and other current liabilities $ 153 Non-current operating lease liabilities Operating lease liabilities 488 Total operating lease liabilities $ 641
Operating lease liability maturity	As of March 31, 2019 , the operating lease liabilities will mature over the following periods (in millions): Remainder of 2019 $ 123 2020 152 2021 119 2022 73 2023 54 2024 36 Thereafter 154 Total remaining lease payments $ 711 Less: Imputed interest (70 ) Total operating lease liabilities $ 641
Operating lease minimum lease payments	At December 31, 2018 , minimum lease payments for operating leases having an initial term in excess of one year under ASC 840 were as follows (in millions): 2019 $ 164 2020 142 2021 110 2022 66 2023 52 Thereafter 190 Total minimum lease payments $ 724
Operating lease cost	The Company recognized the following related to operating leases in its Unaudited Consolidated Statement of Operations (in millions): Leases Classification in Unaudited Consolidated Statement of Operations Three Months Ended March 31, 2019 Lease expense General and administrative and Information technology $ 45 Variable lease expense General and administrative and Information technology 13 Less: Sublease income General and administrative (1 ) Total lease expense, net of sublease income $ 57
Operating lease supplemental cash flow	Supplemental cash flow information related to operating leases are as follows (in millions): Leases Three Months Ended March 31, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 47 Operating lease assets obtained in exchange for operating lease liabilities 42

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible assets	The Company's intangible assets at March 31, 2019 and December 31, 2018 consisted of the following (in millions): March 31, 2019 December 31, 2018 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Amortization Supply and distribution agreements $ 1,095 $ (422 ) $ 673 $ 1,099 $ (408 ) $ 691 3 - 20 years Technology 173 (125 ) 48 173 (121 ) 52 1 - 7 years Patents 2 (2 ) — 2 (2 ) — 15 years Internet domain names 40 (30 ) 10 41 (30 ) 11 5 - 20 years Trade names 1,810 (463 ) 1,347 1,810 (439 ) 1,371 4 - 20 years Non-compete agreements — — — 1 (1 ) — Total intangible assets $ 3,120 $ (1,042 ) $ 2,078 $ 3,126 $ (1,001 ) $ 2,125

DEBT (Tables)

DEBT (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Debt	Outstanding Debt Outstanding debt at March 31, 2019 consisted of the following (in millions): March 31, 2019 Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Cost Carrying Value Current liabilities: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (32 ) $ 968 Long-term debt: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (56 ) $ 944 0.8% (€1 Billion) Senior Notes due March 2022 1,123 (4 ) 1,119 2.15% (€750 Million) Senior Notes due November 2022 842 (3 ) 839 2.75% Senior Notes due March 2023 500 (3 ) 497 2.375% (€1 Billion) Senior Notes due September 2024 1,123 (10 ) 1,113 3.65% Senior Notes due March 2025 500 (3 ) 497 3.6% Senior Notes due June 2026 1,000 (6 ) 994 1.8% (€1 Billion) Senior Notes due March 2027 1,123 (4 ) 1,119 3.55% Senior Notes due March 2028 500 (3 ) 497 Total long-term debt $ 7,711 $ (92 ) $ 7,619 Outstanding debt at December 31, 2018 consisted of the following (in millions): December 31, 2018 Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Cost Carrying Value Long-term debt: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (39 ) $ 961 0.9% Convertible Senior Notes due September 2021 1,000 (61 ) 939 0.8% (€1 Billion) Senior Notes due March 2022 1,143 (5 ) 1,138 2.15% (€750 Million) Senior Notes due November 2022 858 (4 ) 854 2.75% Senior Notes due March 2023 500 (3 ) 497 2.375% (€1 Billion) Senior Notes due September 2024 1,143 (10 ) 1,133 3.65% Senior Notes due March 2025 500 (3 ) 497 3.6% Senior Notes due June 2026 1,000 (6 ) 994 1.8% (€1 Billion) Senior Notes due March 2027 1,143 (4 ) 1,139 3.55% Senior Notes due March 2028 500 (3 ) 497 Total long-term debt $ 8,787 $ (138 ) $ 8,649

TREASURY STOCK (Tables)

TREASURY STOCK (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Schedule Of Stock Repurchase Activity [Table Text Block]	The following table summarizes the Company's stock repurchase activities during the three months ended March 31, 2019 and 2018 , respectively (in millions, except for shares): Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Shares Amount Shares Amount Authorized stock repurchase programs 1,548,083 $ 2,735 314,076 $ 612 General authorization for shares withheld on stock award vesting 70,705 121 59,043 120 Total 1,618,788 $ 2,856 373,119 $ 732

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	3 Months Ended
	Mar. 31, 2019
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Balances for each classification of accumulated other comprehensive income (loss)	The table below provides the balances for each classification of accumulated other comprehensive loss at March 31, 2019 and December 31, 2018 (in millions): March 31, December 31, Foreign currency translation adjustments, net of tax (1) $ (141 ) $ (129 ) Net unrealized losses on debt securities, net of tax (2) (28 ) (187 ) Accumulated other comprehensive loss $ (169 ) $ (316 ) (1) Foreign currency translation adjustments, net of tax, at March 31, 2019 and December 31, 2018 , include accumulated net losses from fair value adjustments of $35 million after tax ( $53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. Foreign currency translation adjustments, net of tax, include foreign currency transaction gains of $31 million after tax ( $56 million before tax) and foreign currency transaction losses of $26 million after tax ( $20 million before tax) at March 31, 2019 and December 31, 2018 , respectively, associated with the Company's Euro-denominated debt. The Company's Euro-denominated debt is designated as a hedge against the impact of currency fluctuations on its Euro-denominated net assets (see Note 9 ). The remaining balance in foreign currency translation adjustments relates to the cumulative impacts of currency fluctuations on the Company's non-U.S. Dollar denominated net assets. At March 31, 2019 and December 31, 2018 , the Company had deferred tax benefits of $52 million and $41 million , respectively, related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the introduction of the Tax Act. (2) Net unrealized losses on debt securities, net of tax, includes cumulative tax charges of $81 million and $30 million at March 31, 2019 and December 31, 2018 , respectively.

BASIS OF PRESENTATION Basis of

BASIS OF PRESENTATION Basis of Presentation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Cumulative effect of adoption of accounting standards updates						$ 189
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 912	$ 668
Cash and cash equivalents	2,334			$ 2,624
Restricted cash included in prepaid expenses and other current assets	20			21
Total cash, cash equivalents and restricted cash as shown in the Unaudited Consolidated Statements of Cash Flows	2,354	2,645		2,645		2,563
Operating lease assets	635			0
Total operating lease liabilities	641
Current operating lease liabilities	153
Non-current operating lease liabilities	$ 488			$ 0
Retained Earnings
Cumulative effect of adoption of accounting standards updates						430
Accumulated Other Comprehensive Income (Loss)
Cumulative effect of adoption of accounting standards updates						$ (241)
Previously Reported [Member]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 427
Accounting Standards Update 2016-01 | Retained Earnings
Cumulative effect of adoption of accounting standards updates					$ 241
Accounting Standards Update 2016-02
Operating lease assets			$ 646
Total operating lease liabilities			646
Current operating lease liabilities			$ 152

REVENUE RECOGNITION - Geographi

REVENUE RECOGNITION - Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 2,837	$ 2,928
United States
Disaggregation of Revenue [Line Items]
Revenues	380	379
The Netherlands
Disaggregation of Revenue [Line Items]
Revenues	2,005	2,123
Other
Disaggregation of Revenue [Line Items]
Revenues	$ 452	$ 426
Product Concentration Risk [Member] | Sales Revenue, Net [Member]
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	84.00%	85.00%

REVENUE RECOGNITION - Narrative

REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred Revenue, Revenue Recognized	$ 97
Deferred Revenue, Refund Payments	10
Proceeds from Customers	204
Customer Loyalty Program Liability, Current	80		$ 73
Increase (Decrease) in Customer Loyalty Program Liability		$ (27)
Deferred Merchant Bookings
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue in deferred merchant bookings	$ 246		$ 149

STOCK-BASED EMPLOYEE COMPENSA_3

STOCK-BASED EMPLOYEE COMPENSATION (Stock-based Employee Compensation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense	$ 74	$ 71

STOCK-BASED EMPLOYEE COMPENSA_4

STOCK-BASED EMPLOYEE COMPENSATION (Restricted Stock Units and Performance Share Units) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock Units and Performance Share Units
Share-Based Awards - Shares
Unvested at December 31, 2018	511,562
Granted (in shares)	192,775
Vested (in shares)	(172,432)
Performance share units adjustment (in shares)	127
Forfeited/Canceled (in shares)	(8,093)
Unvested at March 31, 2019	523,939	511,562
Share-Based Awards - Weighted Average Grant Date Fair Value
Unvested (in dollars per share)	$ 1,713
Granted (in dollars per share)	1,714
Vested (in dollars per share)	1,443
Performance share units adjustment (in dollars per share)	1,580
Forfeited/Canceled (in dollars per share)	1,823
Unvested (in dollars per share)	$ 1,802	$ 1,713
Total unrecognized estimated compensation expense, unvested share-based awards	$ 663
Total future compensation cost related to unvested share-based awards, expected period of recognition	2 years 4 months
Restricted Stock Units (RSUs)
Share-Based Awards - Shares
Granted (in shares)	131,683
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 1,714
Vesting period (in years)	3 years
Grant date fair value	$ 226
Performance Share Units 2019 Grants [Member]
Share-Based Awards - Shares
Granted (in shares)	61,092
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 1,714
Grant date fair value	$ 105
Estimated number of probable shares to be issued (in shares)	61,092
Maximum shares that could be issued (in shares)	122,184
Minimum shares that could be issued (in shares)	47,674
Performance Share Units 2018 Grants
Share-Based Awards - Shares
Granted (in shares)		49,721
Unvested at March 31, 2019	44,900
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)		$ 2,034
Grant date fair value		$ 101
Estimated number of probable shares to be issued (in shares)	86,157
Maximum shares that could be issued (in shares)	89,800
Minimum shares that could be issued (in shares)	33,590
Performance Share Units 2017 Grants [Member]
Share-Based Awards - Shares
Granted (in shares)			73,893
Unvested at March 31, 2019	56,506
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)			$ 1,735
Grant date fair value			$ 128
Estimated number of probable shares to be issued (in shares)	88,098
Maximum shares that could be issued (in shares)	113,012
Minimum shares that could be issued (in shares)	45,843

STOCK-BASED EMPLOYEE COMPENSA_5

STOCK-BASED EMPLOYEE COMPENSATION (Stock Options) (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Number of Shares
Beginning balance (in shares)	27,263
Exercised (in shares)	(1,164)
Ending balance (in shares)	26,099		27,263
Weighted-average Exercise Price
Beginning balance (in dollars per share)	$ 387
Exercised (in dollars per share)	317
Ending balance (in dollars per share)	$ 404		$ 387
Aggregate Intrinsic Value	$ 35		$ 36
Weighted Average Remaining Contractual Term	2 years 6 months		2 years 10 months
Vested and exercisable at March 31, 2019
Number of Shares	26,099
Weighted Average Exercise Price (in dollars per share)	$ 404
Aggregate Intrinsic Value	$ 35
Weighted Average Remaining Contractual Term, Exercisable	2 years 6 months
Stock options exercised, total intrinsic value	$ 2	$ 4
Options, vested, number of shares (in shares)	73	83

NET INCOME PER SHARE (Details)

NET INCOME PER SHARE (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Weighted-average number of basic common shares outstanding (in shares)	45,007	48,349
Weighted-average dilutive stock options, restricted stock units and performance share units (in shares)	229	282
Assumed conversion of Convertible Senior Notes (in shares)	200	574
Weighted-average number of diluted common and common equivalent shares outstanding (in shares)	45,436	49,205
Unvested Stock Awards Outstanding and Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive potential common shares (in shares)	1,282	1,432
Convertible Debt [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive potential common shares (in shares)	1,000

INVESTMENTS (Details)

INVESTMENTS (Details) - USD ($) $ in Millions	Sep. 12, 2016	Dec. 11, 2015	May 26, 2015	Aug. 07, 2014	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jul. 17, 2018	Oct. 31, 2017
Schedule of Investments [Line Items]
Net unrealized gains on marketable equity securities					$ 451	$ 55
Marketable securities:
Short-term investments in marketable securities					$ 1,981		$ 3,660
Investments [Abstract]
Weighted average life of all fixed income investments, excluding the Company's investment in Ctrip convertible debt securities					1 year 5 months
Investment in equity securities without readily determinable FV					$ 501		501
Ctrip.com International, Ltd.
Schedule of Investments [Line Items]
Net unrealized gains on marketable equity securities					360	$ 55
Meituan-Dianping
Schedule of Investments [Line Items]
Net unrealized gains on marketable equity securities					91
Investments in Equity securities:
Cost Method Investments									$ 450
Didi Chuxing
Investments [Abstract]
Investment in equity securities without readily determinable FV								$ 500
Grab
Investments [Abstract]
Debt Securities, Available-for-sale, Noncurrent					200		200
Short-term Investments
Marketable securities:
Cost					1,987		3,674
Gross Unrealized Gains					1		0
Gross Unrealized Losses					(7)		(14)
Short-term investments in marketable securities					1,981		3,660
Short-term Investments | International government securities
Debt securities:
Cost					218		314
Gross Unrealized Gains					0		0
Gross Unrealized Losses					0		0
Fair Value					218		314
Short-term Investments | U.S. government securities
Debt securities:
Cost					242		658
Gross Unrealized Gains					0		0
Gross Unrealized Losses					(1)		(2)
Fair Value					241		656
Short-term Investments | Corporate debt securities
Debt securities:
Cost					1,519		2,693
Gross Unrealized Gains					1		0
Gross Unrealized Losses					(6)		(12)
Fair Value					1,514		2,681
Short-term Investments | U.S. government agency securities
Debt securities:
Cost					1		1
Gross Unrealized Gains					0		0
Gross Unrealized Losses					0		0
Fair Value					1		1
Short-term Investments | Commercial paper
Debt securities:
Cost					4		7
Gross Unrealized Gains					0		0
Gross Unrealized Losses					0		0
Fair Value					4		7
Short-term Investments | Time deposits and certificates of deposit
Debt securities:
Cost					3		1
Gross Unrealized Gains					0		0
Gross Unrealized Losses					0		0
Fair Value					3		1
Long-term Investments
Investments in Equity securities:
Cost					1,105		1,105
Gross Unrealized Gains					383		3
Gross Unrealized Losses					(1)		(72)
Fair Value					1,487		1,036
Marketable securities:
Cost					7,303		7,921
Gross Unrealized Gains					469		10
Gross Unrealized Losses					(28)		(224)
Long-term investments					7,744		7,707
Long-term Investments | Ctrip.com International, Ltd.
Investments in Equity securities:
Cost					655
Long-term Investments | International government securities
Debt securities:
Cost					879		797
Gross Unrealized Gains					5		3
Gross Unrealized Losses					0		0
Fair Value					884		800
Long-term Investments | U.S. government securities
Debt securities:
Cost					250		299
Gross Unrealized Gains					0		0
Gross Unrealized Losses					(4)		(6)
Fair Value					246		293
Long-term Investments | Corporate debt securities
Debt securities:
Cost					3,794		4,445
Gross Unrealized Gains					12		4
Gross Unrealized Losses					(23)		(48)
Fair Value					3,783		4,401
Long-term Investments | Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost	$ 25	$ 500	$ 250	$ 500	1,275		1,275
Gross Unrealized Gains					69		0
Gross Unrealized Losses					0		(98)
Fair Value					$ 1,344		$ 1,177
Investments [Abstract]
Debt investment term	6 years	10 years	5 years	5 years

FAIR VALUE MEASUREMENTS Fair va

FAIR VALUE MEASUREMENTS Fair value measurements (Details) - Recurring Basis - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
ASSETS:
Total assets at fair value	$ 11,679	$ 13,681
Foreign Currency Contracts
ASSETS:
Total assets at fair value	1	4
LIABILITIES:
Total liabilities at fair value	2
Other Long-term Investments [Member]
ASSETS:
Total assets at fair value	200	200
Money market funds | Cash Equivalents
ASSETS:
Total assets at fair value	1,727	2,061
International government securities | Cash Equivalents
ASSETS:
Total assets at fair value		21
International government securities | Short-term Investments
ASSETS:
Total assets at fair value	218	314
International government securities | Long-term Investments
ASSETS:
Total assets at fair value	884	800
U.S. government securities | Cash Equivalents
ASSETS:
Total assets at fair value		1
U.S. government securities | Short-term Investments
ASSETS:
Total assets at fair value	241	656
U.S. government securities | Long-term Investments
ASSETS:
Total assets at fair value	246	293
Corporate debt securities | Short-term Investments
ASSETS:
Total assets at fair value	1,514	2,681
Corporate debt securities | Long-term Investments
ASSETS:
Total assets at fair value	3,783	4,401
U.S. government agency securities | Short-term Investments
ASSETS:
Total assets at fair value	1	1
Commercial paper | Cash Equivalents
ASSETS:
Total assets at fair value		2
Commercial paper | Short-term Investments
ASSETS:
Total assets at fair value	4	7
Time deposits and certificates of deposit | Cash Equivalents
ASSETS:
Total assets at fair value	26	25
Time deposits and certificates of deposit | Short-term Investments
ASSETS:
Total assets at fair value	3	1
Marketable equity securities | Long-term Investments
ASSETS:
Total assets at fair value	1,487	1,036
Level 1
ASSETS:
Total assets at fair value	3,243	3,123
Level 1 | Foreign Currency Contracts
ASSETS:
Total assets at fair value	0	0
LIABILITIES:
Total liabilities at fair value	0
Level 1 | Other Long-term Investments [Member]
ASSETS:
Total assets at fair value	0	0
Level 1 | Money market funds | Cash Equivalents
ASSETS:
Total assets at fair value	1,727	2,061
Level 1 | International government securities | Cash Equivalents
ASSETS:
Total assets at fair value		0
Level 1 | International government securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | International government securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | U.S. government securities | Cash Equivalents
ASSETS:
Total assets at fair value		0
Level 1 | U.S. government securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | U.S. government securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | Corporate debt securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | Corporate debt securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | U.S. government agency securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | Commercial paper | Cash Equivalents
ASSETS:
Total assets at fair value		0
Level 1 | Commercial paper | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 1 | Time deposits and certificates of deposit | Cash Equivalents
ASSETS:
Total assets at fair value	26	25
Level 1 | Time deposits and certificates of deposit | Short-term Investments
ASSETS:
Total assets at fair value	3	1
Level 1 | Marketable equity securities | Long-term Investments
ASSETS:
Total assets at fair value	1,487	1,036
Level 2
ASSETS:
Total assets at fair value	8,236	10,358
Level 2 | Foreign Currency Contracts
ASSETS:
Total assets at fair value	1	4
LIABILITIES:
Total liabilities at fair value	2
Level 2 | Other Long-term Investments [Member]
ASSETS:
Total assets at fair value	0	0
Level 2 | Money market funds | Cash Equivalents
ASSETS:
Total assets at fair value	0	0
Level 2 | International government securities | Cash Equivalents
ASSETS:
Total assets at fair value		21
Level 2 | International government securities | Short-term Investments
ASSETS:
Total assets at fair value	218	314
Level 2 | International government securities | Long-term Investments
ASSETS:
Total assets at fair value	884	800
Level 2 | U.S. government securities | Cash Equivalents
ASSETS:
Total assets at fair value		1
Level 2 | U.S. government securities | Short-term Investments
ASSETS:
Total assets at fair value	241	656
Level 2 | U.S. government securities | Long-term Investments
ASSETS:
Total assets at fair value	246	293
Level 2 | Corporate debt securities | Short-term Investments
ASSETS:
Total assets at fair value	1,514	2,681
Level 2 | Corporate debt securities | Long-term Investments
ASSETS:
Total assets at fair value	3,783	4,401
Level 2 | U.S. government agency securities | Short-term Investments
ASSETS:
Total assets at fair value	1	1
Level 2 | Commercial paper | Cash Equivalents
ASSETS:
Total assets at fair value		2
Level 2 | Commercial paper | Short-term Investments
ASSETS:
Total assets at fair value	4	7
Level 2 | Time deposits and certificates of deposit | Cash Equivalents
ASSETS:
Total assets at fair value	0	0
Level 2 | Time deposits and certificates of deposit | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 2 | Marketable equity securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3
ASSETS:
Total assets at fair value	200	200
Level 3 | Foreign Currency Contracts
ASSETS:
Total assets at fair value	0	0
LIABILITIES:
Total liabilities at fair value	0
Level 3 | Other Long-term Investments [Member]
ASSETS:
Total assets at fair value	200	200
Level 3 | Money market funds | Cash Equivalents
ASSETS:
Total assets at fair value	0	0
Level 3 | International government securities | Cash Equivalents
ASSETS:
Total assets at fair value		0
Level 3 | International government securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | International government securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | U.S. government securities | Cash Equivalents
ASSETS:
Total assets at fair value		0
Level 3 | U.S. government securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | U.S. government securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | Corporate debt securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | Corporate debt securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | U.S. government agency securities | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | Commercial paper | Cash Equivalents
ASSETS:
Total assets at fair value		0
Level 3 | Commercial paper | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | Time deposits and certificates of deposit | Cash Equivalents
ASSETS:
Total assets at fair value	0	0
Level 3 | Time deposits and certificates of deposit | Short-term Investments
ASSETS:
Total assets at fair value	0	0
Level 3 | Marketable equity securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Ctrip.com International, Ltd. | Ctrip convertible debt securities | Long-term Investments
ASSETS:
Total assets at fair value	1,344	1,177
Ctrip.com International, Ltd. | Level 1 | Ctrip convertible debt securities | Long-term Investments
ASSETS:
Total assets at fair value	0	0
Ctrip.com International, Ltd. | Level 2 | Ctrip convertible debt securities | Long-term Investments
ASSETS:
Total assets at fair value	1,344	1,177
Ctrip.com International, Ltd. | Level 3 | Ctrip convertible debt securities | Long-term Investments
ASSETS:
Total assets at fair value	$ 0	$ 0

FAIR VALUE MEASUREMENTS Equity

FAIR VALUE MEASUREMENTS Equity investments without readily determinable fair values and derivatives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Sep. 12, 2016	Dec. 11, 2015	May 26, 2015	Aug. 07, 2014
Derivatives Not Designated as Hedging Instruments
Foreign currency gains (losses), net of derivative activity	$ 8	$ 5
Foreign Currency Contracts, Translation Risk
Derivatives Not Designated as Hedging Instruments
Foreign currency derivative instruments not designated as hedging instruments at fair value, net	0		$ 0
Foreign Currency Contracts, Transaction Risk
Derivatives Not Designated as Hedging Instruments
Foreign currency gains (losses) recorded in foreign currency transactions and other	(13)	21
Foreign Currency Contracts
Derivatives Not Designated as Hedging Instruments
Net cash inflow from settlement of derivative contracts included in operating activities	1	$ 18
Ctrip.com International, Ltd. | Ctrip convertible debt securities | Long-term Investments
Derivatives Not Designated as Hedging Instruments
Cost of Ctrip convertible notes	1,275		1,275	$ 25	$ 500	$ 250	$ 500
Embedded derivative, fair value of embedded derivative	$ 0.9		$ 0.1

LEASES Operating lease (Details

LEASES Operating lease (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Finance leases	$ 0
Weighted average remaining lease term of operating leases	8 years 2 months
Weighted average discount rate of operating leases	2.00%
Leases, Operating [Abstract]
Operating lease assets	$ 635	$ 0
Current operating lease liabilities	153
Non-current operating lease liabilities	488	0
Total operating lease liabilities	641
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019	123
2020	152
2021	119
2022	73
2023	54
2024	36
Thereafter	154
Total remaining lease payments	711
Less: Imputed interest	(70)
Total operating lease liabilities	641
Lessee, Operating Lease, Not yet Commenced, Description [Abstract]
Minimum lease payments related to operating leases which have not commenced at period end	7
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019		164
2020		142
2021		110
2022		66
2023		52
Thereafter		190
Total minimum lease payments		$ 724
Income and Expenses, Lessee [Abstract]
Lease expense	45
Variable lease expense	13
Sublease income	(1)
Total lease expense, net of sublease income	57
Cash Flow, Operating Activities, Lessee [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	47
Operating lease assets obtained in exchange for operating lease liabilities	$ 42
Maximum
Lessee, Lease, Description [Line Items]
Initial term of renewal options	9 years
Lessee, Operating Lease, Not yet Commenced, Description [Abstract]
Lease term of operating leases which have not commenced at period end	5 years

INTANGIBLE ASSETS AND GOODWIL_2

INTANGIBLE ASSETS AND GOODWILL (Details) - USD ($) $ in Millions	Nov. 30, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Finite-lived intangible assets
Gross Carrying Amount		$ 3,120		$ 3,126
Accumulated Amortization		(1,042)		(1,001)
Net Carrying Amount		2,078		2,125
Amortization expense		45	$ 47
Supply and distribution agreements
Finite-lived intangible assets
Gross Carrying Amount		1,095		1,099
Accumulated Amortization		(422)		(408)
Net Carrying Amount		673		691
Technology
Finite-lived intangible assets
Gross Carrying Amount		173		173
Accumulated Amortization		(125)		(121)
Net Carrying Amount		48		52
Patents
Finite-lived intangible assets
Gross Carrying Amount		2		2
Accumulated Amortization		(2)		(2)
Net Carrying Amount		$ 0		0
Amortization Period		15 years
Internet domain names
Finite-lived intangible assets
Gross Carrying Amount		$ 40		41
Accumulated Amortization		(30)		(30)
Net Carrying Amount		10		11
Trade Names
Finite-lived intangible assets
Gross Carrying Amount		1,810		1,810
Accumulated Amortization		(463)		(439)
Net Carrying Amount		1,347		1,371
Noncompete Agreements
Finite-lived intangible assets
Gross Carrying Amount		0		1
Accumulated Amortization		0		(1)
Net Carrying Amount		$ 0		$ 0
Minimum | Supply and distribution agreements
Finite-lived intangible assets
Amortization Period		3 years
Minimum | Technology
Finite-lived intangible assets
Amortization Period		1 year
Minimum | Internet domain names
Finite-lived intangible assets
Amortization Period		5 years
Minimum | Trade Names
Finite-lived intangible assets
Amortization Period		4 years
Maximum | Supply and distribution agreements
Finite-lived intangible assets
Amortization Period		20 years
Maximum | Technology
Finite-lived intangible assets
Amortization Period		7 years
Maximum | Internet domain names
Finite-lived intangible assets
Amortization Period		20 years
Maximum | Trade Names
Finite-lived intangible assets
Amortization Period		20 years
HotelsCombined [Member]
Finite-lived intangible assets
Cash paid in business acquisition	$ 134

DEBT (Revolving Credit Facility

DEBT (Revolving Credit Facility) (Details) - USD ($)	Jun. 19, 2015	Apr. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Bank overdraft				$ 25,000,000
Letters of credit issued			$ 5,000,000	5,000,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 2,000,000,000
Line of credit facility, term	5 years
Line of credit, Current				$ 0
Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee rate	0.085%
Revolving Credit Facility | Minimum | Rate 2C
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee rate	0.20%
Revolving Credit Facility | Maximum | Rate 2C
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum | Rate 1
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.875%
Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum | Rate 1
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Revolving Credit Facility | Federal Funds Purchased | Rate 2B
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Revolving Credit Facility | One Month LIBOR | Rate 2C
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Letter of Credit
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 70,000,000
Swingline Loans
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 50,000,000
3.5% Borrowings - January 2019 [Member] | Revolving Credit Facility
Line of Credit Facility [Line Items]
Short term debt			$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage			3.50%
Subsequent Event | 3.5% Borrowings - April 2019 [Member] | Revolving Credit Facility
Line of Credit Facility [Line Items]
Proceeds from Issuance of Debt		$ 150,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.50%

DEBT (Outstanding Debt) (Detail

DEBT (Outstanding Debt) (Details) $ / shares in Units, $ in Millions	Aug. 20, 2014USD ($)Days$ / shares	May 31, 2013USD ($)Days$ / shares	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Mar. 31, 2019EUR (€)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Aug. 15, 2017	Mar. 10, 2017	May 23, 2016	Nov. 25, 2015	Mar. 13, 2015	Mar. 03, 2015	Sep. 23, 2014	Jun. 30, 2013USD ($)	Mar. 31, 2012USD ($)$ / shares
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 7,711					$ 8,787
Unamortized Debt Discount and Debt Issuance Cost			(92)					(138)
Carrying Value, Long-term debt			7,619					8,649
Description of Senior Notes
Payments Related to Conversion of Senior Notes			0	$ 1,487
0.35% Convertible Senior Notes due June 2020
Debt Instrument
Short-term Debt, Gross			1,000
Carrying Value, Short-term debt			968
Outstanding Principal Amount, Long-term debt								1,000
Unamortized Debt Discount and Debt Issuance Cost			$ (32)					(39)
Carrying Value, Long-term debt								$ 961
Description of Senior Notes
Aggregate principal amount		$ 1,000
Interest rate on Long-term Debt		0.35%	0.35%				0.35%	0.35%	0.35%
Debt financing costs paid						$ 1
Convertible debt conversion price (in dollars per share) | $ / shares		$ 1,315.10
Ratio of closing share price to conversion price as a condition for conversion of the convertible notes, minimum		150.00%
Unamortized debt discount		$ 20
Effective interest rate at debt origination or modification		3.125%
Debt discount related to convertible notes, net of tax																	$ 92
Debt discount related to convertible notes, before tax																	$ 154
Amortization of debt discount included in interest expense			$ 1	1
0.9% Convertible Senior Notes due September 2021
Debt Instrument
Outstanding Principal Amount, Long-term debt			1,000					$ 1,000
Unamortized Debt Discount and Debt Issuance Cost			(56)					(61)
Carrying Value, Long-term debt			$ 944					$ 939
Description of Senior Notes
Aggregate principal amount	$ 1,000
Interest rate on Long-term Debt	0.90%		0.90%				0.90%	0.90%	0.90%
Debt financing costs paid					$ 11
Convertible debt conversion price (in dollars per share) | $ / shares	$ 2,055.50
Ratio of closing share price to conversion price as a condition for conversion of the convertible notes, minimum	150.00%
Effective interest rate at debt origination or modification	3.18%
Debt discount related to convertible notes, net of tax					83
Debt discount related to convertible notes, before tax					$ 143
0.8% (€1 Billion) Senior Notes due March 2022
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 1,123					$ 1,143
Unamortized Debt Discount and Debt Issuance Cost			(4)					(5)
Carrying Value, Long-term debt			$ 1,119					$ 1,138
Description of Senior Notes
Aggregate principal amount | €							€ 1,000,000,000		€ 1,000,000,000
Interest rate on Long-term Debt			0.80%				0.80%	0.80%	0.80%
Effective interest rate at debt origination or modification											0.842%
2.15% (€750 Million) Senior Notes due November 2022
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 842					$ 858
Unamortized Debt Discount and Debt Issuance Cost			(3)					(4)
Carrying Value, Long-term debt			$ 839					$ 854
Description of Senior Notes
Aggregate principal amount | €							€ 750,000,000		€ 750,000,000
Interest rate on Long-term Debt			2.15%				2.15%	2.15%	2.15%
Effective interest rate at debt origination or modification													2.20%
2.75% Senior Notes due March 2023
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 500					$ 500
Unamortized Debt Discount and Debt Issuance Cost			(3)					(3)
Carrying Value, Long-term debt			$ 497					$ 497
Description of Senior Notes
Interest rate on Long-term Debt			2.75%				2.75%	2.75%	2.75%
Effective interest rate at debt origination or modification										2.78%
2.375% (€1 Billion) Senior Notes due September 2024
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 1,123					$ 1,143
Unamortized Debt Discount and Debt Issuance Cost			(10)					(10)
Carrying Value, Long-term debt			$ 1,113					$ 1,133
Description of Senior Notes
Aggregate principal amount | €							€ 1,000,000,000		€ 1,000,000,000
Interest rate on Long-term Debt			2.375%				2.375%	2.375%	2.375%
Effective interest rate at debt origination or modification																2.48%
3.65% Senior Notes due March 2025
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 500					$ 500
Unamortized Debt Discount and Debt Issuance Cost			(3)					(3)
Carrying Value, Long-term debt			$ 497					$ 497
Description of Senior Notes
Interest rate on Long-term Debt			3.65%				3.65%	3.65%	3.65%
Effective interest rate at debt origination or modification														3.68%
3.6% Senior Notes due June 2026
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 1,000					$ 1,000
Unamortized Debt Discount and Debt Issuance Cost			(6)					(6)
Carrying Value, Long-term debt			$ 994					$ 994
Description of Senior Notes
Interest rate on Long-term Debt			3.60%				3.60%	3.60%	3.60%
Effective interest rate at debt origination or modification												3.62%
1.8% (€1 Billion) Senior Notes due March 2027
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 1,123					$ 1,143
Unamortized Debt Discount and Debt Issuance Cost			(4)					(4)
Carrying Value, Long-term debt			$ 1,119					$ 1,139
Description of Senior Notes
Aggregate principal amount | €							€ 1,000,000,000		€ 1,000,000,000
Interest rate on Long-term Debt			1.80%				1.80%	1.80%	1.80%
Effective interest rate at debt origination or modification															1.803%
3.55% Senior Notes due March 2028
Debt Instrument
Outstanding Principal Amount, Long-term debt			$ 500					$ 500
Unamortized Debt Discount and Debt Issuance Cost			(3)					(3)
Carrying Value, Long-term debt			$ 497					$ 497
Description of Senior Notes
Interest rate on Long-term Debt			3.55%				3.55%	3.55%	3.55%
Effective interest rate at debt origination or modification										3.56%
1.0% Convertible Senior Notes due March 2018
Description of Senior Notes
Aggregate principal amount																		$ 1,000
Interest rate on Long-term Debt																		1.00%
Convertible debt conversion price (in dollars per share) | $ / shares																		$ 944.61
Payments Related to Conversion of Senior Notes			$ 714
Debt Conversion, Converted Instrument, Cash			773
Effective interest rate at debt origination or modification																		3.50%
Debt discount related to convertible notes, net of tax																		$ 81
Debt discount related to convertible notes, before tax																		$ 135
Convertible Debt
Description of Senior Notes
Interest expense related to debt			15	20
Coupon Interest expense			3	5
Amortization of debt discount included in interest expense			$ 12	$ 14
Debt, weighted average interest rate			3.20%	3.30%
Other Long-term Debt
Debt Instrument
Carrying Value, Long-term debt			$ 6,700					$ 6,700
Description of Senior Notes
Interest expense related to debt			42	$ 43
Coupon Interest expense			40	$ 42
Minimum | 0.35% Convertible Senior Notes due June 2020
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) | Days		20
Additional payment to debt holder, settled In shares, aggregate value		$ 0
Minimum | 0.9% Convertible Senior Notes due September 2021
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) | Days	20
Additional payment to debt holder, settled In shares, aggregate value	$ 0
Maximum | 0.35% Convertible Senior Notes due June 2020
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) | Days		30
Additional payment to debt holder, settled In shares, aggregate value		$ 397
Maximum | 0.9% Convertible Senior Notes due September 2021
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) | Days	30
Additional payment to debt holder, settled In shares, aggregate value	$ 375
Level 2
Description of Senior Notes
Estimated market value of outstanding debt			$ 9,500					$ 9,300

TREASURY STOCK (Details)

TREASURY STOCK (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Apr. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Remaining authorization to repurchase common stock	$ 1,800	$ 4,500
Authorized stock repurchase programs (in shares)	1,618,788		373,119
Authorized stock repurchase programs	$ 2,856		$ 732
General authorization for shares withheld on stock award vesting (in shares)	70,705		59,043
General authorization for shares withheld on stock award vesting	$ 121		$ 120
Payments Related to Tax Withholding for Share-based Compensation	$ 111		103
Treasury stock, shares (in shares)	18,935,914	17,317,126
Repurchase Program (Q12018)
Equity, Class of Treasury Stock [Line Items]
Amount of common stock repurchases authorized			$ 8,000
Authorized stock repurchase programs (in shares)	1,548,083
Authorized stock repurchase programs	$ 2,735
Treasury Stock Repurchased but unsettled by period end	84,229	42,939
Treasury Stock Repurchased but unsettled by period end, amount	$ 147	$ 74
Repurchase Program (Q12016) and (Q12017)
Equity, Class of Treasury Stock [Line Items]
Authorized stock repurchase programs (in shares)			314,076
Authorized stock repurchase programs			$ 612
Subsequent Event | Repurchase Program (Q22019)
Equity, Class of Treasury Stock [Line Items]
Amount of common stock repurchases authorized				$ 15,000

INCOME TAXES (Details)

INCOME TAXES (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Contingency [Line Items]
Effective income tax rate reconciliation, percent	21.00%	19.40%
Tax and Customs Administration, Netherlands
Income Tax Contingency [Line Items]
Statutory federal rate	25.00%
Effective income tax rate at innovation box tax rate	7.00%

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		$ 6,915	$ 8,785	$ 10,636	$ 11,261
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	[1]	(141)	(129)
Foreign currency translation adjustments | Net Investment Hedging | Euro Senior Notes
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		31	(26)
Stockholders' equity, before tax		56	(20)
Foreign currency translation adjustments | Net Investment Hedging | Foreign Currency Forward
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		(35)	(35)
Stockholders' equity, before tax		(53)	(53)
Net unrealized gains (losses) on marketable securities | Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	[2]	(28)	(187)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		(169)	(316)	$ 58	$ 238
Accumulated Net Investment Gain (Loss) Attributable to Parent | Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent		81	30
Currency translation adjustment on deemed repatriation tax liability [Member] | Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent		$ (52)	$ (41)
[1]	Foreign currency translation adjustments, net of tax, at March 31, 2019 and December 31, 2018, include accumulated net losses from fair value adjustments of $35 million after tax ($53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. Foreign currency translation adjustments, net of tax, include foreign currency transaction gains of $31 million after tax ($56 million before tax) and foreign currency transaction losses of $26 million after tax ($20 million before tax) at March 31, 2019 and December 31, 2018, respectively, associated with the Company's Euro-denominated debt. The Company's Euro-denominated debt is designated as a hedge against the impact of currency fluctuations on its Euro-denominated net assets (see Note 9). The remaining balance in foreign currency translation adjustments relates to the cumulative impacts of currency fluctuations on the Company's non-U.S. Dollar denominated net assets. At March 31, 2019 and December 31, 2018, the Company had deferred tax benefits of $52 million and $41 million, respectively, related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the introduction of the Tax Act.
[2]	Net unrealized losses on debt securities, net of tax, includes cumulative tax charges of $81 million and $30 million at March 31, 2019 and December 31, 2018, respectively.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) ₺ in Millions, € in Millions, £ in Millions, $ in Millions	3 Months Ended					6 Months Ended	12 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2019TRY (₺)	Mar. 31, 2019EUR (€)	Mar. 31, 2018USD ($)	Sep. 30, 2016EUR (€)	Dec. 31, 2018USD ($)ft²	Dec. 31, 2018EUR (€)	Mar. 31, 2019EUR (€)	Mar. 31, 2019GBP (£)
Commitments and Contingencies
Increase in the estimated fair value of contingent consideration liabilities	$ 7			$ 0
Booking.com | Headquarters
Commitments and Contingencies
Contractual obligation	175				€ 270			€ 156
Acquisition of land use rights | €					€ 43
Booking.com | Headquarters | Ground Lease
Commitments and Contingencies
Contractual obligation	82							€ 73
Series of individually immaterial business acquisitions
Commitments and Contingencies
Contingent consideration liability	35
Increase in the estimated fair value of contingent consideration liabilities	7
Series of individually immaterial business acquisitions | Level 3
Commitments and Contingencies
Contingent consideration liability						$ 28
French Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties | €			€ 356
Payment required to appeal a litigation matter	403		€ 356
Taxes Owed For Prior Periods
Commitments and Contingencies
Charge for estimated probable tax owed for prior periods, including applicable interest and penalties						$ 46
Estimated reasonably possible loss in excess of amount accrued	$ 20
Italian Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties | €							€ 48
Turkish Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties | ₺		₺ 433
Manchester, England | Rentalcars.com | Headquarters
Commitments and Contingencies
Area of Real Estate Property | ft²						222,000
Term of lease for office space in Manchester UK for Rentalcars.com	13 years							13 years	13 years
Manchester, England | Rentalcars.com | Headquarters | Operating Lease Obligations
Commitments and Contingencies
Contractual obligation | £									£ 65