Booking (BKNG) 10-Q 7 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 31, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Fiscal Period Focus	Q2
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Amendment Flag	false
Document Fiscal Year Focus	2019
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001075531
Entity File Number	1-36691
Entity Registrant Name	Booking Holdings Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	06-1528493
Entity Address, Address Line One	800 Connecticut Avenue
Entity Address, City or Town	Norwalk
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06854
City Area Code	203
Local Phone Number	299-8000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		42,511,903
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common Stock par value $0.008 per share
Trading Symbol	BKNG
Security Exchange Name	NASDAQ
0.800% Senior Notes Due 2022
Entity Information [Line Items]
Title of 12(b) Security	0.800% Senior Notes Due 2022
Trading Symbol	BKNG 22A
Security Exchange Name	NYSE
2.150% Senior Notes Due 2022
Entity Information [Line Items]
Title of 12(b) Security	2.150% Senior Notes Due 2022
Trading Symbol	BKNG 22
Security Exchange Name	NYSE
2.375% Senior Notes Due 2024
Entity Information [Line Items]
Title of 12(b) Security	2.375% Senior Notes Due 2024
Trading Symbol	BKNG 24
Security Exchange Name	NYSE
1.800% Senior Notes Due 2027
Entity Information [Line Items]
Title of 12(b) Security	1.800% Senior Notes Due 2027
Trading Symbol	BKNG 27
Security Exchange Name	NYSE

UNAUDITED CONSOLIDATED BALANCE

UNAUDITED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 5,256	$ 2,624
Short-term investments in marketable securities	1,553	3,660
Accounts receivable, net of allowance for doubtful accounts of $56 and $61, respectively	1,973	1,523
Prepaid expenses and other current assets	1,238	600
Total current assets	10,020	8,407
Property and equipment, net	716	656
Operating lease assets	639	0
Intangible assets, net	2,041	2,125
Goodwill	2,915	2,910
Long-term investments	4,618	8,408
Other assets	545	181
Total assets	21,494	22,687
Current liabilities:
Accounts payable	1,291	1,134
Accrued expenses and other current liabilities	1,740	1,399
Deferred merchant bookings	2,343	1,022
Convertible debt	975	0
Total current liabilities	6,349	3,555
Deferred income taxes	504	370
Operating lease liabilities	495	0
Long-term U.S. transition tax liability	1,063	1,166
Other long-term liabilities	90	162
Long-term debt	7,686	8,649
Total liabilities	16,187	13,902
Commitments and Contingencies
Stockholders' equity:
Common stock, $0.008 par value; authorized 1,000,000,000 shares, 63,143,816 and 62,948,762 shares issued, respectively	0	0
Treasury stock, 20,378,354 and 17,317,126 shares, respectively	(20,173)	(14,711)
Additional paid-in capital	5,599	5,445
Retained earnings	20,111	18,367
Accumulated other comprehensive loss	(230)	(316)
Total stockholders' equity	5,307	8,785
Total liabilities and stockholders' equity	$ 21,494	$ 22,687

UNAUDITED CONSOLIDATED BALANC_2

UNAUDITED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 56	$ 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)	63,143,816	62,948,762
Treasury stock, shares (in shares)	20,378,354	17,317,126

UNAUDITED CONSOLIDATED STATEMEN

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Agency revenues		$ 2,607	$ 2,567	$ 4,556	$ 4,680
Merchant revenues		959	710	1,562	1,236
Advertising and other revenues		284	260	569	549
Total revenues		3,850	3,537	6,687	6,465
Operating expenses:
Performance marketing		1,192	1,142	2,222	2,248
Brand marketing		175	124	338	225
Sales and other expenses		248	203	463	369
Personnel, including stock-based compensation of $79, $75, $153 and $146, respectively		619	522	1,120	1,021
General and administrative		180	159	371	322
Information technology		70	59	135	119
Depreciation and amortization		119	107	235	210
Total operating expenses		2,603	2,316	4,884	4,514
Operating income		1,247	1,221	1,803	1,951
Other income (expense):
Interest income		34	46	69	93
Interest expense		(68)	(65)	(134)	(135)
Net unrealized gains on marketable equity securities		17	21	468	76
Foreign currency transactions and other		(23)	(13)	(31)	(22)
Total other (expense) income		(40)	(11)	372	12
Earnings before income taxes		1,207	1,210	2,175	1,963
Income tax expense		228	232	431	378
Net income	[1]	$ 979	$ 978	$ 1,744	$ 1,585
Net income applicable to common stockholders per basic common share (in dollars per share)		$ 22.62	$ 20.34	$ 39.52	$ 32.87
Weighted-average number of basic common shares outstanding (in shares)		43,251	48,055	44,124	48,202
Net income applicable to common stockholders per diluted common share (in dollars per share)		$ 22.44	$ 20.13	$ 39.17	$ 32.42
Weighted-average number of diluted common shares outstanding (in shares)		43,601	48,550	44,514	48,877
[1]	The Company reclassified from accumulated other comprehensive income net gains of $10 million ( $9 million , net of tax) and $11 million ( $10 million , net of tax) for the three and six months ended June 30, 2019 , respectively, and a net loss of $1 million ( $1 million , net of tax) for the six months ended June 30, 2018 from sales of investments in debt securities. The reclassified net gains (losses) are included in " Foreign currency transactions and other " in the Unaudited Consolidated Statements of Operations.

UNAUDITED CONSOLIDATED STATEM_2

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Stock-based compensation expense	$ 79	$ 75	$ 153	$ 146

UNAUDITED CONSOLIDATED STATEM_3

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax		$ 10		$ 11	$ (1)
Other comprehensive (loss) income, net of tax
Net income	[1]	979	$ 978	1,744	1,585
Foreign currency translation adjustments, net of tax benefits (charges) of $15, ($36), $7 and ($20), respectively (2)	[2]	(16)	(129)	(28)	(68)
Net unrealized (losses) gains on debt securities, net of tax benefits (charges) of $15, ($1), ($36) and $1, respectively (1)		(45)	(5)	114	(5)
Comprehensive income		$ 918	$ 844	$ 1,830	$ 1,512
[1]	The Company reclassified from accumulated other comprehensive income net gains of $10 million ( $9 million , net of tax) and $11 million ( $10 million , net of tax) for the three and six months ended June 30, 2019 , respectively, and a net loss of $1 million ( $1 million , net of tax) for the six months ended June 30, 2018 from sales of investments in debt securities. The reclassified net gains (losses) are included in " Foreign currency transactions and other " in the Unaudited Consolidated Statements of Operations.
[2]	Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar functional currency subsidiaries' net assets, net of the impact of net investment hedges. The Company recorded tax benefits of $4 million and $15 million for the three and six months ended June 30, 2019 , respectively, and tax benefits of $21 million and $11 million for the three and six months ended June 30, 2018 , 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 benefit of $11 million and a tax charge of $8 million for the three and six months ended June 30, 2019 , respectively, and tax charges of $57 million and $31 million for the three and six months ended June 30, 2018 , respectively, associated with the Company's Euro-denominated debt that is designated as a net investment hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (see Note 9

UNAUDITED CONSOLIDATED STATEM_4

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	$ 10		$ 11	$ (1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	9		10	(1)
Tax (benefit) associated with gain (loss) on components of foreign currency translation	15	$ (36)	7	(20)
Tax (benefit) associated with gain (loss) on components of unrealized gain (loss) on debt securities	15	(1)	(36)	1
Currency translation adjustment on deemed repatriation tax liability
Tax (benefit) associated with gain (loss) on components of foreign currency translation	4	21	15	11
Net Investment Hedging
Tax (benefit) associated with gain (loss) on components of foreign currency translation	$ 11	$ (57)	$ (8)	$ (31)

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	1,585	[1]				1,585
Foreign currency translation adjustments, net of taxes	(68)	[2]					(68)
Net unrealized gains (losses) on marketable securities, net of taxes	(5)						(5)
Reclassification adjustment for convertible debt in mezzanine	(43)				(43)
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)			186,000
Exercise of stock options and vesting of restricted stock units and/or performance share units	$ 1		$ 0		1
Repurchase of common stock (in shares)	(945,693)			(946,000)
Repurchase of common stock	$ (1,931)			$ (1,931)
Stock-based compensation and other stock-based payments	147				147
Conversion of debt	(773)				(773)
Common stock issued in an acquisition (in shares)			52,000
Common stock issued in an acquisition	110				110
Balance (in shares) at Jun. 30, 2018			62,927,000	(15,163,000)
Balance at Jun. 30, 2018	10,473		$ 0	$ (10,630)	5,225	15,954	(76)
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
Increase (Decrease) in Stockholders' Equity
Net income	978	[1]				978
Foreign currency translation adjustments, net of taxes	(129)	[2]					(129)
Net unrealized gains (losses) on marketable securities, net of taxes	(5)						(5)
Reclassification adjustment for convertible debt in mezzanine	5				5
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)			37,000
Exercise of stock options and vesting of restricted stock units and/or performance share units	$ 1		$ 0		1
Repurchase of common stock (in shares)	(572,574)			(573,000)
Repurchase of common stock	$ (1,199)			$ (1,199)
Stock-based compensation and other stock-based payments	76				76
Common stock issued in an acquisition (in shares)			52,000
Common stock issued in an acquisition	110				110
Balance (in shares) at Jun. 30, 2018			62,927,000	(15,163,000)
Balance at Jun. 30, 2018	10,473		$ 0	$ (10,630)	5,225	15,954	(76)
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	1,744	[1]				1,744
Foreign currency translation adjustments, net of taxes	(28)	[2]					(28)
Net unrealized gains (losses) on marketable securities, net of taxes	114						114
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)			195,000
Exercise of stock options and vesting of restricted stock units and/or performance share units	$ 1		$ 0		1
Repurchase of common stock (in shares)	(3,061,228)			(3,061,000)
Repurchase of common stock	$ (5,462)			$ (5,462)
Stock-based compensation and other stock-based payments	153				153
Balance (in shares) at Jun. 30, 2019			63,144,000	(20,378,000)
Balance at Jun. 30, 2019	5,307		$ 0	$ (20,173)	5,599	20,111	(230)
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)
Increase (Decrease) in Stockholders' Equity
Net income	979	[1]				979
Foreign currency translation adjustments, net of taxes	(16)	[2]					(16)
Net unrealized gains (losses) on marketable securities, net of taxes	(45)						(45)
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)			22,000
Exercise of stock options and vesting of restricted stock units and/or performance share units	$ 1		$ 0		1
Repurchase of common stock (in shares)	(1,442,440)			(1,442,000)
Repurchase of common stock	$ (2,606)			$ (2,606)
Stock-based compensation and other stock-based payments	79				79
Balance (in shares) at Jun. 30, 2019			63,144,000	(20,378,000)
Balance at Jun. 30, 2019	$ 5,307		$ 0	$ (20,173)	$ 5,599	$ 20,111	$ (230)
[1]	The Company reclassified from accumulated other comprehensive income net gains of $10 million ( $9 million , net of tax) and $11 million ( $10 million , net of tax) for the three and six months ended June 30, 2019 , respectively, and a net loss of $1 million ( $1 million , net of tax) for the six months ended June 30, 2018 from sales of investments in debt securities. The reclassified net gains (losses) are included in " Foreign currency transactions and other " in the Unaudited Consolidated Statements of Operations.
[2]	Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar functional currency subsidiaries' net assets, net of the impact of net investment hedges. The Company recorded tax benefits of $4 million and $15 million for the three and six months ended June 30, 2019 , respectively, and tax benefits of $21 million and $11 million for the three and six months ended June 30, 2018 , 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 benefit of $11 million and a tax charge of $8 million for the three and six months ended June 30, 2019 , respectively, and tax charges of $57 million and $31 million for the three and six months ended June 30, 2018 , respectively, associated with the Company's Euro-denominated debt that is designated as a net investment hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (see Note 9

UNAUDITED CONSOLIDATED STATEM_6

UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Net income	[1]	$ 1,744	$ 1,585
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		235	210
Provision for uncollectible accounts		74	62
Deferred income tax expense (benefit)		60	(21)
Net unrealized gains on marketable equity securities		(468)	(76)
Stock-based compensation expense and other stock-based payments		162	150
Operating lease amortization		85	0
Amortization of debt discount and debt issuance costs		28	30
Contingent consideration fair value adjustment		9	0
Changes in assets and liabilities, net of effects of acquisitions:
Accounts receivable		(523)	(392)
Prepaid expenses and other current assets		(584)	(574)
Accounts payable, accrued expenses and other current liabilities		1,513	1,329
Other long-term assets and liabilities		(398)	(13)
Net cash provided by operating activities		1,937	2,290
INVESTING ACTIVITIES:
Purchase of investments		(580)	(1,360)
Proceeds from sale and maturity of investments		6,977	3,497
Additions to property and equipment		(199)	(235)
Acquisitions and other investments, net of cash acquired		9	139
Net cash provided by investing activities		6,189	1,763
FINANCING ACTIVITIES:
Proceeds from revolving credit facility and short-term borrowings		437	3
Repayments of revolving credit facility and short-term borrowings		(425)	0
Payments for conversion of senior notes		0	(1,487)
Payments for repurchase of common stock		(5,491)	(1,905)
Other financing activities		(8)	1
Net cash used in financing activities		(5,487)	(3,388)
Effect of exchange rate changes on cash and cash equivalents and restricted cash and cash equivalents		(8)	(20)
Net increase in cash and cash equivalents and restricted cash and cash equivalents		2,631	645
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		5,276	3,208
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the period for income taxes		949	985
Cash paid during the period for interest		101	101
Non-cash operating and financing activity for an acquisition		0	51
Non-cash investing and financing activity for an acquisition		$ 0	$ 59
[1]	The Company reclassified from accumulated other comprehensive income net gains of $10 million ( $9 million , net of tax) and $11 million ( $10 million , net of tax) for the three and six months ended June 30, 2019 , respectively, and a net loss of $1 million ( $1 million , net of tax) for the six months ended June 30, 2018 from sales of investments in debt securities. The reclassified net gains (losses) are included in " Foreign currency transactions and other " in the Unaudited Consolidated Statements of Operations.

BASIS OF PRESENTATION

BASIS OF PRESENTATION	6 Months Ended
	Jun. 30, 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 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 six months ended June 30, 2018 in this Form 10-Q. As a result of this correction, total comprehensive income in the Company’s previously reported Unaudited Consolidated Statement of Comprehensive Income increased from $1.3 billion to $1.5 billion for the six months ended June 30, 2018. The correction of this error had no effect on the Company’s previously reported 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 presented the correction in the Unaudited Consolidated Statement of Comprehensive Income for the three months ended March 31, 2018 included in the Form 10-Q for the first quarter of 2019 and will present the correction in the Unaudited Consolidated Statement of Comprehensive Income for the nine months ended September 30, 2018 to be included in the Form 10-Q for the third quarter 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 June 30, 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 Consolidated Balance Sheets to the total amount shown in the Unaudited Consolidated Statements of Cash Flows (in millions): June 30, December 31, As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 5,256 $ 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 $ 5,276 $ 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. Step 2 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	6 Months Ended
	Jun. 30, 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 United States The Netherlands Other Total Total revenues for the three months ended June 30, 2019 $ 403 $ 2,954 $ 493 $ 3,850 2018 423 2,706 408 3,537 Total revenues for the six months ended June 30, 2019 $ 783 $ 4,959 $ 945 $ 6,687 2018 802 4,829 834 6,465 Revenue by Type of Service Approximately 87% and 86% of the Company's revenue for the three and six months ended June 30, 2019 , respectively, and 86% for both the three and six months ended June 30, 2018 , 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 Consolidated Balance Sheets and are comprised principally of amounts estimated to be payable to the travel service providers as well as the Company's deferred revenue for its commission or margin and fees. At June 30, 2019 and December 31, 2018 , deferred merchant bookings included deferred revenue of $345 million and $149 million , respectively. The Company expects to complete its service obligation within one year of booking. In the six months ended June 30, 2019 , the Company recognized revenue of $120 million and cancellations of $13 million related to the deferred revenue balance at December 31, 2018 . The offsetting increase of $329 million in the deferred revenue balance for the six months ended June 30, 2019 was principally driven by payments received from travelers, net of estimated 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 expected 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 June 30, 2019 and December 31, 2018 , liabilities of $87 million and $73 million , respectively, for loyalty program incentives were included in "Accrued expenses and other current liabilities" in the 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	6 Months Ended
	Jun. 30, 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 $79 million and $75 million for the three months ended June 30, 2019 and 2018 , respectively, and $153 million and $146 million for the six months ended June 30, 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 six months ended June 30, 2019 : Share-Based Awards Shares Weighted-average Grant Date Fair Value Unvested at December 31, 2018 511,562 $ 1,713 Granted 204,292 $ 1,719 Vested (195,371 ) $ 1,447 Performance shares adjustment 2,635 $ 1,540 Forfeited/Canceled (24,929 ) $ 1,778 Unvested at June 30, 2019 498,189 $ 1,816 At June 30, 2019 , there was $578 million of total future compensation cost related to unvested share-based awards to be recognized over a weighted-average period of 2.1 years. During the six months ended June 30, 2019 , the Company made broad-based grants of 142,380 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 $245 million based on a weighted-average grant-date fair value per share of $1,721 . 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 six months ended June 30, 2019 , the Company granted 61,912 performance share units to executives and certain other employees. The performance share units had a total grant-date fair value of $106 million based on a weighted-average grant-date fair value per share of $1,716 . 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 June 30, 2019 , the estimated number of probable shares to be issued was a total of 61,037 shares, net of performance share units that were forfeited or vested since the grant date, including 47,619 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 122,074 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 June 30, 2019 , there were 43,178 unvested 2018 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. At June 30, 2019 , the number of shares estimated to be issued pursuant to these performance share units at the end of the performance period was a total of 82,778 shares, including 31,868 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 86,356 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 June 30, 2019 , there were 54,110 unvested 2017 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. At June 30, 2019 , the number of shares estimated to be issued pursuant to these performance share units at the end of the performance period was a total of 83,653 shares, including 43,447 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 108,220 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 six months ended June 30, 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 (1,396 ) $ 313 Balance, June 30, 2019 25,867 $ 391 $ 38 2.2 Vested and exercisable at June 30, 2019 25,867 $ 391 $ 38 2.2 The aggregate intrinsic value of employee stock options exercised during the six months ended June 30, 2019 and 2018 was $2 million and $4 million

NET INCOME PER SHARE

NET INCOME PER SHARE	6 Months Ended
	Jun. 30, 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 Six Months Ended 2019 2018 2019 2018 Weighted-average number of basic common shares outstanding 43,251 48,055 44,124 48,202 Weighted-average dilutive stock options, restricted stock units and performance share units 146 198 188 240 Assumed conversion of Convertible Senior Notes 204 297 202 435 Weighted-average number of diluted common and common equivalent shares outstanding 43,601 48,550 44,514 48,877 Anti-dilutive potential common shares 1,304 1,431 1,265 1,410 Anti-dilutive potential common shares for both the three and six months ended June 30, 2019 included 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	6 Months Ended
	Jun. 30, 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 Consolidated Balance Sheets. Classification as short-term or long-term investments is based upon the maturities of the debt securities and the Company's expectations regarding the timing of sales and redemptions. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage are included in "Long-term investments" in the Consolidated Balance Sheets. As of June 30, 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 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 June 30, 2019 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 145 $ — $ — $ 145 U.S. government securities 209 — (1 ) 208 Corporate debt securities 702 — (2 ) 700 Ctrip convertible debt securities 500 — — 500 Total $ 1,556 $ — $ (3 ) $ 1,553 Long-term investments in marketable securities: Debt securities: International government securities $ 29 $ 1 $ — $ 30 U.S. government securities 208 — (2 ) 206 Corporate debt securities 1,357 3 (8 ) 1,352 Ctrip convertible debt securities 775 3 (3 ) 775 Marketable equity securities 1,105 404 (5 ) 1,504 Total $ 3,474 $ 411 $ (18 ) $ 3,867 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 The Company's investment policy seeks to preserve capital and maintain sufficient liquidity to meet operational and other needs of the business. At June 30, 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 1.3 years with an average credit quality of A+/A1/A+. The Company invests in international government securities with high credit quality. At June 30, 2019 , investments in international government securities principally included debt securities issued by the governments of the Netherlands, France, Finland, Austria, and Belgium. Investments in Ctrip As of June 30, 2019 , the Company had invested $1.3 billion in senior convertible notes issued at par value by Ctrip with maturity dates ranging from 2019 to 2025. The investments included $500 million of convertible notes that were repaid on maturity in August 2019 and therefore classified as " Short-term investments in marketable securities " in the Consolidated Balance Sheet at June 30, 2019 . Other strategic investments in Ctrip, including $250 million of convertible notes due May 2020, were classified as " Long-term investments " in the Consolidated Balance Sheet at June 30, 2019 . The Ctrip convertible notes have been marked-to-market in accordance with the accounting guidance for available-for-sale securities, with the aggregate unrealized gains and losses, net of taxes, reflected as a part of " Accumulated other comprehensive loss " in the Consolidated Balance Sheets. The Company had also invested $655 million in Ctrip American Depositary Shares ("ADSs"), which had a fair value of $798 million and $585 million at June 30, 2019 and December 31, 2018 , respectively. " Net unrealized gains on marketable equity securities " in the Unaudited Consolidated Statements of Operations included a net unrealized loss of $147 million and a net unrealized gain of $213 million for the three and six months ended June 30, 2019 , respectively, and net unrealized gains of $21 million and $76 million for the three and six months ended June 30, 2018 , respectively, related to Ctrip ADSs. Certain Ctrip convertible notes include a put option allowing the Company, at its option, to require a prepayment in cash from Ctrip at certain points of time. 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 monitors the conversion features of these notes to determine whether they meet the definition of an embedded derivative during each reporting period. The conversion feature associated with the $25 million convertible notes issued in 2016 meets the definition of an embedded derivative that requires separate accounting. The embedded derivative is bifurcated for fair value measurement purposes only and is reported in the Consolidated Balance Sheets with its host contract in "Long-term investments." The mark-to-market adjustments of the embedded derivative are included in "Foreign currency transactions and other" in the Company's Unaudited Consolidated Statements of Operations. In connection with the Company's investments in Ctrip's convertible notes in August 2014, the Company and Ctrip entered into a 5-year commercial agreement and a standstill agreement whereby Ctrip granted the Company permission to acquire its shares so that the Company could hold up to an aggregate of approximately 15% of Ctrip's outstanding equity plus any ADSs issuable upon the conversion of convertible notes issued in December 2015. The standstill agreement terminated in August 2019, and the Company is evaluating the future commercial relationship. At June 30, 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. The investment had a fair value of $706 million and $451 million at June 30, 2019 and December 31, 2018 , respectively. For the three and six months ended June 30, 2019 , " Net unrealized gains on marketable equity securities " in the Unaudited Consolidated Statement of Operations included unrealized gains of $164 million and $255 million , respectively, related to this investment. At June 30, 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 June 30, 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 Consolidated Balance Sheets. The Company determined that no adjustments were required to the carrying value of these investments at June 30, 2019 . Other Long-term Investments The Company held investments in preferred shares of private companies of $250 million and $200 million at June 30, 2019 and December 31, 2018 , respectively. These investments are classified as debt securities for accounting purposes and categorized as available-for-sale. 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 certain points of time. These features have been evaluated as embedded derivatives, however, they do not meet the requirements to be accounted for separately. The investments are reported at estimated fair value in "Long-term investments" in the Company's Consolidated Balance Sheets, with the aggregate unrealized gains and losses, net of taxes, reflected as a part of " Accumulated other comprehensive loss

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Financial assets carried at fair value at June 30, 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 $ 4,693 $ — $ — $ 4,693 Time deposits and certificates of deposit 8 — — 8 Short-term investments in marketable securities: International government securities — 145 — 145 U.S. government securities — 208 — 208 Corporate debt securities — 700 — 700 Ctrip convertible debt securities — 500 — 500 Long-term investments in marketable securities: International government securities — 30 — 30 U.S. government securities — 206 — 206 Corporate debt securities — 1,352 — 1,352 Ctrip convertible debt securities — 775 — 775 Marketable equity securities 1,504 — — 1,504 Other long-term investments — — 250 250 Derivatives: Currency exchange derivatives — 1 — 1 Total assets at fair value $ 6,205 $ 3,917 $ 250 $ 10,372 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 related to the carrying value of the Company's investments in marketable securities. Other long-term investments reported at an aggregate fair value of $250 million and $200 million at June 30, 2019 and December 31, 2018, respectively, were 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. See Note 5 for further information related to these investments. 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 June 30, 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 and Note 5 for information related to an embedded derivative associated with the $25 million Ctrip convertible notes issued in 2016. 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 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. 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 June 30, 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 Consolidated Balance Sheets. Derivatives associated with these transaction risks resulted in foreign currency gains of $8 million and foreign currency losses of $5 million for the three and six months ended June 30, 2019 , respectively, and foreign currency losses of $51 million and $30 million for the three and six months ended June 30, 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 $13 million and $21 million for the three and six months ended June 30, 2019 , respectively, and net losses of $12 million and $17 million for the three and six months ended June 30, 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 a net cash inflow of $3 million and a net cash outflow of $30 million for the six months ended June 30, 2019 and 2018 , respectively, which are reported within " Net cash provided by operating activities

LEASES

LEASES	6 Months Ended
	Jun. 30, 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 financing leases as of June 30, 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 the Company's 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 June 30, 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 June 30, 2019 , the Company’s weighted-average discount rate was approximately 2.1% . The Company recognized the following related to leases in its Consolidated Balance Sheet at June 30, 2019 (in millions): Classification in Consolidated Balance Sheet June 30, 2019 Operating lease assets Operating lease assets $ 639 Lease Liabilities: Current operating lease liabilities Accrued expenses and other current liabilities $ 154 Non-current operating lease liabilities Operating lease liabilities 495 Total operating lease liabilities $ 649 As of June 30, 2019 , the operating lease liabilities will mature over the following periods (in millions): Remainder of 2019 $ 83 2020 158 2021 129 2022 83 2023 61 2024 42 Thereafter 164 Total remaining lease payments $ 720 Less: Imputed interest (71 ) Total operating lease liabilities $ 649 As of June 30, 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 leases will commence by 2020 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 Statements of Operations (in millions): Classification in Unaudited Consolidated Statement of Operations Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Lease expense General and administrative and Information technology $ 46 $ 91 Variable lease expense General and administrative and Information technology 15 28 Less: Sublease income General and administrative — (1 ) Total lease expense, net of sublease income $ 61 $ 118 Supplemental cash flow information related to operating leases are as follows (in millions): Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 87 Operating lease assets obtained in exchange for operating lease liabilities 86

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	6 Months Ended
	Jun. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at June 30, 2019 and December 31, 2018 consisted of the following (in millions): June 30, 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 $ 1,100 $ (440 ) $ 660 $ 1,099 $ (408 ) $ 691 3 - 20 years Technology 176 (129 ) 47 173 (121 ) 52 1 - 7 years Internet domain names 41 (31 ) 10 41 (30 ) 11 5 - 20 years Trade names 1,810 (486 ) 1,324 1,810 (439 ) 1,371 4 - 20 years Other intangible assets 2 (2 ) — 3 (3 ) — Up to 15 years Total intangible assets $ 3,129 $ (1,088 ) $ 2,041 $ 3,126 $ (1,001 ) $ 2,125 Intangible assets are amortized on a straight-line basis. Amortization expense was $44 million and $89 million for the three and six months ended June 30, 2019 , respectively, and $45 million and $92 million for the three and six months ended June 30, 2018 , respectively. A substantial portion of the Company's intangible assets and goodwill relates to the acquisitions of OpenTable and KAYAK. There were no events or changes in circumstances to indicate a potential impairment to goodwill or intangible assets at June 30, 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. In April 2018, the Company paid $139 million , net of cash acquired, and issued shares of the Company's common stock in the amount of $110 million in connection with the acquisition of FareHarbor, a leading provider of business-to-business activities distribution services. In respect of the shares issued, as presented in the supplemental disclosure in the Unaudited Consolidated Statement of Cash Flows, $59 million relates to purchase price consideration and $51 million relates to shares restricted for trading purposes until certain conditions are met.

DEBT

DEBT	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
DEBT	DEBT Short-term Borrowing On June 30, 2019 , the Company had a bank overdraft of $37 million , which was repaid in July 2019. On December 31, 2018 , the Company had a bank overdraft of $25 million , which was repaid in January 2019. These bank overdrafts are reported in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets at June 30, 2019 and December 31, 2018 . 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 June 30, 2019 and December 31, 2018 . There were no borrowings outstanding under this revolving credit facility at June 30, 2019 and December 31, 2018 . During the six months ended June 30, 2019 , the Company made several short-term borrowings under this revolving credit facility totaling $400 million with a weighted-average interest rate of 3.5% , all of which were repaid prior to June 30, 2019 . Outstanding Debt Outstanding debt at June 30, 2019 consisted of the following (in millions): June 30, 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 $ (25 ) $ 975 Long-term debt: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (50 ) $ 950 0.8% (€1 Billion) Senior Notes due March 2022 1,139 (4 ) 1,135 2.15% (€750 Million) Senior Notes due November 2022 854 (3 ) 851 2.75% Senior Notes due March 2023 500 (2 ) 498 2.375% (€1 Billion) Senior Notes due September 2024 1,139 (10 ) 1,129 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 1,139 (4 ) 1,135 3.55% Senior Notes due March 2028 500 (3 ) 497 Total long-term debt $ 7,771 $ (85 ) $ 7,686 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 June 30, 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, and therefore, these notes were not convertible at the option of the holder. Fair Value of Debt At June 30, 2019 and December 31, 2018 , the estimated fair value of the outstanding Senior Notes was approximately $9.8 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 fair 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 the straight debt borrowing rate, considering the 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 June 30, 2019 and 2018 , the Company recognized interest expense of $16 million and $15 million , respectively, related to convertible notes, which was almost entirely comprised of the amortization of debt discount of $12 million and the contractual coupon interest of $3 million for each period. For the three months ended June 30, 2019 , included in the amortization of debt discount mentioned above was $1 million of original issuance discount related to the 2020 Notes. The remaining interest expense related to the amortization of debt issuance costs. The weighted-average effective interest rates for both the three months ended June 30, 2019 and 2018 were 3.2% . For the six months ended June 30, 2019 and 2018 , the Company recognized interest expense of $31 million and $35 million , respectively, related to convertible notes, which was almost entirely comprised of the amortization of debt discount of $24 million and $26 million , respectively, and the contractual coupon interest of $6 million and $8 million , respectively. For the six months ended June 30, 2019 and 2018 , included in the amortization of debt discount mentioned above was $2 million and $1 million , respectively, of original issuance discount related to the 2020 Notes. The remaining interest expense related to the amortization of debt issuance costs. 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 both the six months ended June 30, 2019 and 2018 were 3.2% . Other Long-term Debt Other long-term debt had a total carrying value of $6.7 billion at both June 30, 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 June 30, 2019 and 2018 , the Company recognized interest expense of $41 million and $43 million , respectively, related to other long-term debt, which was almost entirely comprised of $40 million and $41 million , respectively, related to the contractual coupon interest. The remaining interest expense relates to the amortization of debt discount and debt issuance costs. For the six months ended June 30, 2019 and 2018 , the Company recognized interest expense of $83 million and $86 million , respectively, related to other long-term debt, which was almost entirely comprised of $80 million and $83 million , respectively, related to the contractual coupon interest. The remaining interest expense related 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 (collectively "Euro-denominated debt") and accrued interest thereon had historically been designated as a hedge of the Company's net investment in a Euro functional currency subsidiary. The Company dedesignated a portion of this hedge in the second quarter of 2019. For the six months ended June 30, 2019 , the carrying value of the portion of Euro-denominated debt, including accrued interest, designated as a net investment hedge, ranged from $3.4 billion to $4.3 billion . The foreign currency transaction gains or losses on these Euro-denominated liabilities are measured based upon changes in spot rates. The foreign currency transaction gains or losses on the Euro-denominated debt that is designated as hedging instruments are recorded in " Accumulated other comprehensive loss " in the Consolidated Balance Sheets. The net assets of this subsidiary 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 Consolidated Balance Sheets. The foreign currency transaction gains or losses on the Euro-denominated debt that is not designated as hedging instruments for accounting purposes are recognized in " Foreign currency transactions and other

TREASURY STOCK

TREASURY STOCK	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
TREASURY STOCK	TREASURY STOCK At December 31, 2018, the Company had a total remaining authorization of $4.5 billion 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. At June 30, 2019 , the Company had a total remaining authorization of $14.2 billion to repurchase its common stock. The Company has continued to make repurchases of its common stock in the third 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 and six months ended June 30, 2019 and 2018 , respectively (in millions, except for shares): Three Months Ended Six Months Ended 2019 2018 2019 2018 Shares Amount Shares Amount Shares Amount Shares Amount Authorized stock repurchase programs 1,433,726 $ 2,590 559,910 $ 1,173 2,981,809 $ 5,325 873,986 $ 1,785 General authorization for shares withheld on stock award vesting 8,714 16 12,664 26 79,419 137 71,707 146 Total 1,442,440 $ 2,606 572,574 $ 1,199 3,061,228 $ 5,462 945,693 $ 1,931 Stock repurchases of $44 million in June 2019 were settled in July 2019. Stock repurchases of $74 million in December 2018 were settled in January 2019. For the six months ended June 30, 2019 and 2018 , the Company remitted employee withholding taxes of $136 million and $145 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 June 30, 2019 , there were 20,378,354 shares of the Company's common stock held in treasury.

INCOME TAXES

INCOME TAXES	6 Months Ended
	Jun. 30, 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 rates for the three and six months ended June 30, 2019 were 18.9% and 19.8% , respectively, compared to 19.2% for both the three and six months ended June 30, 2018 . The Company's 2019 effective tax rates differ from the U.S. federal statutory tax rate of 21% , primarily due to the benefit of the Netherlands Innovation Box Tax (discussed below), partially offset by the effect of higher international tax rates. The Company's 2018 effective tax rates differ from the U.S. federal statutory tax rate of 21% , primarily due to the benefit of the Netherlands Innovation Box Tax, U.S. state tax rate changes that resulted in a net decrease to deferred tax liabilities associated with acquired intangible assets, and 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 international earnings resulting from the introduction of the Tax Act. The Company's effective tax rate was lower for the three months ended June 30, 2019 , compared to the three months ended June 30, 2018 , primarily as a result of lower U.S. federal and state tax associated with the Company’s current year international earnings resulting from the introduction of the Tax Act and lower discrete tax charges related to unrealized gains on equity securities, partially offset by lower U.S. state tax rate change benefits on deferred tax liabilities associated with acquired intangible assets. The Company's effective tax rate was higher for the six months ended June 30, 2019 , compared to the six months ended June 30, 2018 , primarily as a result of higher discrete tax charges related to unrealized gains on equity securities and lower excess tax benefits recognized from the vesting of equity awards, 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 and six months ended June 30, 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 and six months ended June 30, 2019 and 2018 qualified for Innovation Box Tax treatment, which had a significant beneficial impact on the Company's effective tax rates for those periods.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME	6 Months Ended
	Jun. 30, 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 June 30, 2019 and December 31, 2018 (in millions): June 30, December 31, Foreign currency translation adjustments, net of tax (1) $ (157 ) $ (129 ) Net unrealized losses on debt securities, net of tax (2) (73 ) (187 ) Accumulated other comprehensive loss $ (230 ) $ (316 ) (1) Foreign currency translation adjustments, net of tax, at June 30, 2019 and December 31, 2018 , included 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, included foreign currency transaction gains of $1 million after tax ( $15 million before tax) and foreign currency transaction losses of $26 million after tax ( $20 million before tax) at June 30, 2019 and December 31, 2018 , respectively, associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (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 functional currency subsidiaries' net assets. At June 30, 2019 and December 31, 2018 , the Company had deferred tax benefits of $56 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 $66 million and $30 million at June 30, 2019 and December 31, 2018

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES

BASIS OF PRESENTATION (Policies

BASIS OF PRESENTATION (Policies)	6 Months Ended
	Jun. 30, 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 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	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 six months ended June 30, 2018 in this Form 10-Q. As a result of this correction, total comprehensive income in the Company’s previously reported Unaudited Consolidated Statement of Comprehensive Income increased from $1.3 billion to $1.5 billion for the six months ended June 30, 2018. The correction of this error had no effect on the Company’s previously reported 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 presented the correction in the Unaudited Consolidated Statement of Comprehensive Income for the three months ended March 31, 2018 included in the Form 10-Q for the first quarter of 2019 and will present the correction in the Unaudited Consolidated Statement of Comprehensive Income for the nine months ended September 30, 2018 to be included in the Form 10-Q for the third quarter 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 June 30, 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 Consolidated Balance Sheets to the total amount shown in the Unaudited Consolidated Statements of Cash Flows (in millions): June 30, December 31, As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 5,256 $ 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 $ 5,276 $ 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. Step 2 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)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Leases	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 financing leases as of June 30, 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 the Company's 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 June 30, 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 June 30, 2019 , the Company’s weighted-average discount rate was approximately 2.1% .

BASIS OF PRESENTATION (Tables)

BASIS OF PRESENTATION (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 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 Consolidated Balance Sheets to the total amount shown in the Unaudited Consolidated Statements of Cash Flows (in millions): June 30, December 31, As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 5,256 $ 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 $ 5,276 $ 2,645

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	6 Months Ended
	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Geographic Information	The Company's geographic information is as follows (in millions): International United States The Netherlands Other Total Total revenues for the three months ended June 30, 2019 $ 403 $ 2,954 $ 493 $ 3,850 2018 423 2,706 408 3,537 Total revenues for the six months ended June 30, 2019 $ 783 $ 4,959 $ 945 $ 6,687 2018 802 4,829 834 6,465

STOCK-BASED EMPLOYEE COMPENSA_2

STOCK-BASED EMPLOYEE COMPENSATION (Tables)	6 Months Ended
	Jun. 30, 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 six months ended June 30, 2019 : Share-Based Awards Shares Weighted-average Grant Date Fair Value Unvested at December 31, 2018 511,562 $ 1,713 Granted 204,292 $ 1,719 Vested (195,371 ) $ 1,447 Performance shares adjustment 2,635 $ 1,540 Forfeited/Canceled (24,929 ) $ 1,778 Unvested at June 30, 2019 498,189 $ 1,816
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 six months ended June 30, 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 (1,396 ) $ 313 Balance, June 30, 2019 25,867 $ 391 $ 38 2.2 Vested and exercisable at June 30, 2019 25,867 $ 391 $ 38 2.2

NET INCOME PER SHARE (Tables)

NET INCOME PER SHARE (Tables)	6 Months Ended
	Jun. 30, 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 Six Months Ended 2019 2018 2019 2018 Weighted-average number of basic common shares outstanding 43,251 48,055 44,124 48,202 Weighted-average dilutive stock options, restricted stock units and performance share units 146 198 188 240 Assumed conversion of Convertible Senior Notes 204 297 202 435 Weighted-average number of diluted common and common equivalent shares outstanding 43,601 48,550 44,514 48,877 Anti-dilutive potential common shares 1,304 1,431 1,265 1,410

INVESTMENTS (Tables)

INVESTMENTS (Tables)	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	The following table summarizes, by major security type, the Company's investments in marketable securities at June 30, 2019 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 145 $ — $ — $ 145 U.S. government securities 209 — (1 ) 208 Corporate debt securities 702 — (2 ) 700 Ctrip convertible debt securities 500 — — 500 Total $ 1,556 $ — $ (3 ) $ 1,553 Long-term investments in marketable securities: Debt securities: International government securities $ 29 $ 1 $ — $ 30 U.S. government securities 208 — (2 ) 206 Corporate debt securities 1,357 3 (8 ) 1,352 Ctrip convertible debt securities 775 3 (3 ) 775 Marketable equity securities 1,105 404 (5 ) 1,504 Total $ 3,474 $ 411 $ (18 ) $ 3,867 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)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Financial instruments carried at fair value	Financial assets carried at fair value at June 30, 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 $ 4,693 $ — $ — $ 4,693 Time deposits and certificates of deposit 8 — — 8 Short-term investments in marketable securities: International government securities — 145 — 145 U.S. government securities — 208 — 208 Corporate debt securities — 700 — 700 Ctrip convertible debt securities — 500 — 500 Long-term investments in marketable securities: International government securities — 30 — 30 U.S. government securities — 206 — 206 Corporate debt securities — 1,352 — 1,352 Ctrip convertible debt securities — 775 — 775 Marketable equity securities 1,504 — — 1,504 Other long-term investments — — 250 250 Derivatives: Currency exchange derivatives — 1 — 1 Total assets at fair value $ 6,205 $ 3,917 $ 250 $ 10,372 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)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Operating leases	The Company recognized the following related to leases in its Consolidated Balance Sheet at June 30, 2019 (in millions): Classification in Consolidated Balance Sheet June 30, 2019 Operating lease assets Operating lease assets $ 639 Lease Liabilities: Current operating lease liabilities Accrued expenses and other current liabilities $ 154 Non-current operating lease liabilities Operating lease liabilities 495 Total operating lease liabilities $ 649
Operating lease liability maturity	As of June 30, 2019 , the operating lease liabilities will mature over the following periods (in millions): Remainder of 2019 $ 83 2020 158 2021 129 2022 83 2023 61 2024 42 Thereafter 164 Total remaining lease payments $ 720 Less: Imputed interest (71 ) Total operating lease liabilities $ 649
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 Statements of Operations (in millions): Classification in Unaudited Consolidated Statement of Operations Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Lease expense General and administrative and Information technology $ 46 $ 91 Variable lease expense General and administrative and Information technology 15 28 Less: Sublease income General and administrative — (1 ) Total lease expense, net of sublease income $ 61 $ 118
Operating lease supplemental cash flow	Supplemental cash flow information related to operating leases are as follows (in millions): Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 87 Operating lease assets obtained in exchange for operating lease liabilities 86

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	6 Months Ended
	Jun. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible assets	The Company's intangible assets at June 30, 2019 and December 31, 2018 consisted of the following (in millions): June 30, 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 $ 1,100 $ (440 ) $ 660 $ 1,099 $ (408 ) $ 691 3 - 20 years Technology 176 (129 ) 47 173 (121 ) 52 1 - 7 years Internet domain names 41 (31 ) 10 41 (30 ) 11 5 - 20 years Trade names 1,810 (486 ) 1,324 1,810 (439 ) 1,371 4 - 20 years Other intangible assets 2 (2 ) — 3 (3 ) — Up to 15 years Total intangible assets $ 3,129 $ (1,088 ) $ 2,041 $ 3,126 $ (1,001 ) $ 2,125

DEBT (Tables)

DEBT (Tables)	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Schedule of Debt	Outstanding Debt Outstanding debt at June 30, 2019 consisted of the following (in millions): June 30, 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 $ (25 ) $ 975 Long-term debt: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (50 ) $ 950 0.8% (€1 Billion) Senior Notes due March 2022 1,139 (4 ) 1,135 2.15% (€750 Million) Senior Notes due November 2022 854 (3 ) 851 2.75% Senior Notes due March 2023 500 (2 ) 498 2.375% (€1 Billion) Senior Notes due September 2024 1,139 (10 ) 1,129 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 1,139 (4 ) 1,135 3.55% Senior Notes due March 2028 500 (3 ) 497 Total long-term debt $ 7,771 $ (85 ) $ 7,686 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)	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Schedule of Stock Repurchase Activity	The following table summarizes the Company's stock repurchase activities during the three and six months ended June 30, 2019 and 2018 , respectively (in millions, except for shares): Three Months Ended Six Months Ended 2019 2018 2019 2018 Shares Amount Shares Amount Shares Amount Shares Amount Authorized stock repurchase programs 1,433,726 $ 2,590 559,910 $ 1,173 2,981,809 $ 5,325 873,986 $ 1,785 General authorization for shares withheld on stock award vesting 8,714 16 12,664 26 79,419 137 71,707 146 Total 1,442,440 $ 2,606 572,574 $ 1,199 3,061,228 $ 5,462 945,693 $ 1,931

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 and December 31, 2018 (in millions): June 30, December 31, Foreign currency translation adjustments, net of tax (1) $ (157 ) $ (129 ) Net unrealized losses on debt securities, net of tax (2) (73 ) (187 ) Accumulated other comprehensive loss $ (230 ) $ (316 ) (1) Foreign currency translation adjustments, net of tax, at June 30, 2019 and December 31, 2018 , included 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, included foreign currency transaction gains of $1 million after tax ( $15 million before tax) and foreign currency transaction losses of $26 million after tax ( $20 million before tax) at June 30, 2019 and December 31, 2018 , respectively, associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (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 functional currency subsidiaries' net assets. At June 30, 2019 and December 31, 2018 , the Company had deferred tax benefits of $56 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 $66 million and $30 million at June 30, 2019 and December 31, 2018

BASIS OF PRESENTATION Basis of

BASIS OF PRESENTATION Basis of Presentation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Cumulative effect of adoption of accounting standards updates								$ 189
Comprehensive income	$ 918	$ 844	$ 1,830	$ 1,512
Cash and cash equivalents	5,256		5,256			$ 2,624
Restricted cash included in prepaid expenses and other current assets	20		20			21
Total cash, cash equivalents and restricted cash as shown in the Unaudited Consolidated Statements of Cash Flows	5,276	$ 3,208	5,276	3,208		2,645		2,563
Operating lease assets	639		639			0
Total operating lease liabilities	649		649
Current operating lease liabilities	154		154
Non-current operating lease liabilities	$ 495		$ 495			$ 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				$ 1,300
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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 3,850	$ 3,537	$ 6,687	$ 6,465
United States
Disaggregation of Revenue [Line Items]
Revenues	403	423	783	802
The Netherlands
Disaggregation of Revenue [Line Items]
Revenues	2,954	2,706	4,959	4,829
Other
Disaggregation of Revenue [Line Items]
Revenues	$ 493	$ 408	$ 945	$ 834
Online accommodation reservation services [Member] | Product Concentration Risk | Sales Revenue, Net [Member]
Disaggregation of Revenue [Line Items]
Concentration risk percentage	87.00%	86.00%	86.00%	86.00%
Maximum | Other sources of online travel reservation services or advertising and other revenues [Member] | Product Concentration Risk | Sales Revenue, Net [Member]
Disaggregation of Revenue [Line Items]
Concentration risk percentage				10.00%

REVENUE RECOGNITION - Narrative

REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue recognized	$ 120
Deferred revenue refund payments	13
Payments received from travelers	329
Liabilities for loyalty program incentives	87		$ 73
Reduction in loyalty program liability		$ (27)
Deferred Merchant Bookings
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue in deferred merchant bookings	$ 345		$ 149

STOCK-BASED EMPLOYEE COMPENSA_3

STOCK-BASED EMPLOYEE COMPENSATION (Stock-based Employee Compensation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense	$ 79	$ 75	$ 153	$ 146

STOCK-BASED EMPLOYEE COMPENSA_4

STOCK-BASED EMPLOYEE COMPENSATION (Restricted Stock Units and Performance Share Units) (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 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)	204,292
Vested (in shares)	(195,371)
Performance share units adjustment (in shares)	2,635
Forfeited/Canceled (in shares)	(24,929)
Unvested at June 30, 2019	498,189	511,562
Share-Based Awards - Weighted Average Grant Date Fair Value
Unvested (in dollars per share)	$ 1,713
Granted (in dollars per share)	1,719
Vested (in dollars per share)	1,447
Performance share units adjustment (in dollars per share)	1,540
Forfeited/Canceled (in dollars per share)	1,778
Unvested (in dollars per share)	$ 1,816	$ 1,713
Total unrecognized estimated compensation expense, unvested share-based awards	$ 578
Total future compensation cost related to unvested share-based awards, expected period of recognition	2 years 1 month 6 days
Restricted Stock Units (RSUs)
Share-Based Awards - Shares
Granted (in shares)	142,380
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 1,721
Vesting period (in years)	3 years
Grant date fair value	$ 245
Performance Share Units 2019 Grants
Share-Based Awards - Shares
Granted (in shares)	61,912
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 1,716
Grant date fair value	$ 106
Estimated number of probable shares to be issued (in shares)	61,037
Maximum shares that could be issued (in shares)	122,074
Minimum shares that could be issued (in shares)	47,619
Performance Share Units 2018 Grants
Share-Based Awards - Shares
Granted (in shares)		49,721
Unvested at June 30, 2019	43,178
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)	82,778
Maximum shares that could be issued (in shares)	86,356
Minimum shares that could be issued (in shares)	31,868
Performance Share Units 2017 Grants
Share-Based Awards - Shares
Granted (in shares)			73,893
Unvested at June 30, 2019	54,110
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)	83,653
Maximum shares that could be issued (in shares)	108,220
Minimum shares that could be issued (in shares)	43,447

STOCK-BASED EMPLOYEE COMPENSA_5

STOCK-BASED EMPLOYEE COMPENSATION (Stock Options) (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Number of Shares
Beginning balance (in shares)	27,263
Exercised (in shares)	(1,396)
Ending balance (in shares)	25,867		27,263
Weighted-average Exercise Price
Beginning balance (in dollars per share)	$ 387
Exercised (in dollars per share)	313
Ending balance (in dollars per share)	$ 391		$ 387
Aggregate Intrinsic Value	$ 38		$ 36
Weighted Average Remaining Contractual Term	2 years 2 months 12 days		2 years 9 months 18 days
Vested and exercisable at June 30, 2019
Number of Shares	25,867
Weighted Average Exercise Price (in dollars per share)	$ 391
Aggregate Intrinsic Value	$ 38
Weighted Average Remaining Contractual Term, Exercisable	2 years 2 months 12 days
Stock options exercised, total intrinsic value	$ 2	$ 4

NET INCOME PER SHARE (Details)

NET INCOME PER SHARE (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Weighted-average number of basic common shares outstanding (in shares)	43,251	48,055	44,124	48,202
Weighted-average dilutive stock options, restricted stock units and performance share units (in shares)	146	198	188	240
Assumed conversion of Convertible Senior Notes (in shares)	204	297	202	435
Weighted-average number of diluted common and common equivalent shares outstanding (in shares)	43,601	48,550	44,514	48,877
Unvested Stock Awards Outstanding and Convertible Debt Securities
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive potential common shares (in shares)	1,304	1,431	1,265	1,410
Convertible Debt
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	Aug. 06, 2014	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Jul. 17, 2018	Oct. 31, 2017	Sep. 12, 2016	May 26, 2015
Schedule of Investments [Line Items]
Debt Investment, Term	5 years
Net unrealized gains on marketable equity securities		$ 17	$ 21	$ 468	$ 76
Debt securities:
Maximum Ownership Percentage in Ctrip										15.00%
Marketable securities:
Short-term investments in marketable securities		1,553		$ 1,553		$ 3,660
Investments [Abstract]
Weighted average life of all fixed income investments, excluding the Company's investment in Ctrip convertible debt securities				1 year 3 months 18 days
Investment in equity securities without readily determinable FV		501		$ 501		501
Ctrip.com International, Ltd.
Schedule of Investments [Line Items]
Net unrealized gains on marketable equity securities		(147)	$ 21	213	$ 76
Meituan-Dianping
Schedule of Investments [Line Items]
Net unrealized gains on marketable equity securities		164		255
Investments in Equity securities:
Cost Method Investments								$ 450
Fair Value		706		706		451
Didi Chuxing
Investments [Abstract]
Investment in equity securities without readily determinable FV							$ 500
Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost		1,300		1,300
Short-term Investments
Marketable securities:
Cost		1,556		1,556		3,674
Gross Unrealized Gains		0		0		0
Gross Unrealized Losses		(3)		(3)		(14)
Short-term investments in marketable securities		1,553		1,553		3,660
Short-term Investments | International government securities
Debt securities:
Cost		145		145		314
Gross Unrealized Gains		0		0		0
Gross Unrealized Losses		0		0		0
Fair Value		145		145		314
Short-term Investments | U.S. government securities
Debt securities:
Cost		209		209		658
Gross Unrealized Gains		0		0		0
Gross Unrealized Losses		(1)		(1)		(2)
Fair Value		208		208		656
Short-term Investments | Corporate debt securities
Debt securities:
Cost		702		702		2,693
Gross Unrealized Gains		0		0		0
Gross Unrealized Losses		(2)		(2)		(12)
Fair Value		700		700		2,681
Short-term Investments | U.S. government agency securities
Debt securities:
Cost						1
Gross Unrealized Gains						0
Gross Unrealized Losses						0
Fair Value						1
Short-term Investments | Commercial paper
Debt securities:
Cost						7
Gross Unrealized Gains						0
Gross Unrealized Losses						0
Fair Value						7
Short-term Investments | Time deposits and certificates of deposit
Debt securities:
Cost						1
Gross Unrealized Gains						0
Gross Unrealized Losses						0
Fair Value						1
Short-term Investments | Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost		500		500
Gross Unrealized Gains		0		0
Gross Unrealized Losses		0		0
Fair Value		500		500
Long-term Investments
Investments in Equity securities:
Cost		1,105		1,105		1,105
Gross Unrealized Gains		404		404		3
Gross Unrealized Losses		(5)		(5)		(72)
Fair Value		1,504		1,504		1,036
Marketable securities:
Cost		3,474		3,474		7,921
Gross Unrealized Gains		411		411		10
Gross Unrealized Losses		(18)		(18)		(224)
Long-term investments		3,867		3,867		7,707
Long-term Investments | Ctrip.com International, Ltd.
Investments in Equity securities:
Cost		655		655		655
Fair Value		798		798		585
Long-term Investments | International government securities
Debt securities:
Cost		29		29		797
Gross Unrealized Gains		1		1		3
Gross Unrealized Losses		0		0		0
Fair Value		30		30		800
Long-term Investments | U.S. government securities
Debt securities:
Cost		208		208		299
Gross Unrealized Gains		0		0		0
Gross Unrealized Losses		(2)		(2)		(6)
Fair Value		206		206		293
Long-term Investments | Corporate debt securities
Debt securities:
Cost		1,357		1,357		4,445
Gross Unrealized Gains		3		3		4
Gross Unrealized Losses		(8)		(8)		(48)
Fair Value		1,352		1,352		4,401
Long-term Investments | Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost		775		775		1,275
Gross Unrealized Gains		3		3		0
Gross Unrealized Losses		(3)		(3)		(98)
Fair Value		775		775		1,177
Other Long-term Investments | Redeemable Convertible Preferred Stock [Member]
Debt securities:
Cost		250		250		$ 200
Ctrip 1% Notes due 2019 [Member] | Short-term Investments | Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost		500		500
Ctrip 1% Note Due 2020 [Member] | Long-term Investments | Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost		$ 250		$ 250
Ctrip 1% Notes due 2019 [Member] | Long-term Investments | Ctrip convertible debt securities | Ctrip.com International, Ltd.
Debt securities:
Cost									$ 25

FAIR VALUE MEASUREMENTS Fair va

FAIR VALUE MEASUREMENTS Fair value measurements (Details) - Recurring Basis - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 10,372	$ 13,681
Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	1	4
Other Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		200
Money market funds | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	4,693	2,061
International government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		21
International government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	145	314
International government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	30	800
U.S. government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1
U.S. government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	208	656
U.S. government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	206	293
Corporate debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	700	2,681
Corporate debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	1,352	4,401
U.S. government agency securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1
Commercial paper | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		2
Commercial paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		7
Time deposits and certificates of deposit | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	8	25
Time deposits and certificates of deposit | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1
Marketable equity securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	1,504	1,036
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	6,205	3,123
Level 1 | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | Other Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | Money market funds | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	4,693	2,061
Level 1 | International government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 1 | International government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | International government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | U.S. government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 1 | U.S. government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | U.S. government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | Corporate debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | Corporate debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 1 | U.S. government agency securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 1 | Commercial paper | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 1 | Commercial paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 1 | Time deposits and certificates of deposit | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	8	25
Level 1 | Time deposits and certificates of deposit | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1
Level 1 | Marketable equity securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	1,504	1,036
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	3,917	10,358
Level 2 | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	1	4
Level 2 | Other Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 2 | Money market funds | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 2 | International government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		21
Level 2 | International government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	145	314
Level 2 | International government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	30	800
Level 2 | U.S. government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1
Level 2 | U.S. government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	208	656
Level 2 | U.S. government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	206	293
Level 2 | Corporate debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	700	2,681
Level 2 | Corporate debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	1,352	4,401
Level 2 | U.S. government agency securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1
Level 2 | Commercial paper | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		2
Level 2 | Commercial paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		7
Level 2 | Time deposits and certificates of deposit | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 2 | Time deposits and certificates of deposit | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 2 | Marketable equity securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	250	200
Level 3 | Foreign Currency Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | Other Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	250	200
Level 3 | Money market funds | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | International government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 3 | International government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | International government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | U.S. government securities | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 3 | U.S. government securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | U.S. government securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | Corporate debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | Corporate debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | U.S. government agency securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 3 | Commercial paper | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 3 | Commercial paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 3 | Time deposits and certificates of deposit | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Level 3 | Time deposits and certificates of deposit | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0
Level 3 | Marketable equity securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Ctrip.com International, Ltd. | Ctrip convertible debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	500
Ctrip.com International, Ltd. | Ctrip convertible debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	775	1,177
Ctrip.com International, Ltd. | Level 1 | Ctrip convertible debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0
Ctrip.com International, Ltd. | Level 1 | Ctrip convertible debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Ctrip.com International, Ltd. | Level 2 | Ctrip convertible debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	500
Ctrip.com International, Ltd. | Level 2 | Ctrip convertible debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	775	1,177
Ctrip.com International, Ltd. | Level 3 | Ctrip convertible debt securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0
Ctrip.com International, Ltd. | Level 3 | Ctrip convertible debt securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Derivatives Not Designated as Hedging Instruments
Foreign currency gains (losses), net of derivative activity	$ (13)	$ (12)	$ (21)	$ (17)
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		$ 0
Foreign Currency Contracts, Transaction Risk
Derivatives Not Designated as Hedging Instruments
Foreign currency gains (losses) recorded in foreign currency transactions and other	8	$ (51)	(5)	(30)
Foreign Currency Contracts
Derivatives Not Designated as Hedging Instruments
Net cash inflow from settlement of derivative contracts included in operating activities			3
Net cash outflow from settlement of derivative contracts included in operating activities				$ 30
Ctrip.com International, Ltd. | Ctrip convertible debt securities
Derivatives Not Designated as Hedging Instruments
Cost of Ctrip convertible notes	1,300		1,300
Ctrip.com International, Ltd. | Ctrip convertible debt securities | Long-term Investments
Derivatives Not Designated as Hedging Instruments
Cost of Ctrip convertible notes	$ 775		$ 775		$ 1,275

LEASES Operating lease (Details

LEASES Operating lease (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Finance leases	$ 0	$ 0
Weighted average remaining lease term of operating leases	8 years 2 months 12 days	8 years 2 months 12 days
Weighted average discount rate of operating leases	2.10%	2.10%
Leases, Operating [Abstract]
Operating lease assets	$ 639	$ 639	$ 0
Current operating lease liabilities	154	154
Non-current operating lease liabilities	495	495	0
Total operating lease liabilities	649	649
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019	83	83
2020	158	158
2021	129	129
2022	83	83
2023	61	61
2024	42	42
Thereafter	164	164
Total remaining lease payments	720	720
Less: Imputed interest	(71)	(71)
Total operating lease liabilities	649	649
Lessee, Operating Lease, Not yet Commenced, Description [Abstract]
Minimum lease payments related to operating leases which have not commenced at period end	7	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	46	91
Variable lease expense	15	28
Sublease income	0	(1)
Total lease expense, net of sublease income	$ 61	118
Cash Flow, Operating Activities, Lessee [Abstract]
Cash paid for amounts included in the measurement of lease liabilities		87
Operating lease assets obtained in exchange for operating lease liabilities		$ 86
Maximum
Lessee, Lease, Description [Line Items]
Initial term of renewal options	9 years	9 years
Lessee, Operating Lease, Not yet Commenced, Description [Abstract]
Lease term of operating leases which have not commenced at period end	5 years	5 years

INTANGIBLE ASSETS AND GOODWIL_2

INTANGIBLE ASSETS AND GOODWILL (Details) - USD ($) $ in Millions	Nov. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Finite-lived intangible assets
Gross Carrying Amount		$ 3,129		$ 3,129		$ 3,126
Accumulated Amortization		(1,088)		(1,088)		(1,001)
Net Carrying Amount		2,041		2,041		2,125
Amortization expense		44	$ 45	89	$ 92
Acquisitions and other investments, net of cash acquired				9	139
Common stock issued in an acquisition			$ 110		110
Non-cash operating and financing activity for an acquisition				0	51
Non-cash investing and financing activity for an acquisition				0	59
Supply and distribution agreements
Finite-lived intangible assets
Gross Carrying Amount		1,100		1,100		1,099
Accumulated Amortization		(440)		(440)		(408)
Net Carrying Amount		660		660		691
Technology
Finite-lived intangible assets
Gross Carrying Amount		176		176		173
Accumulated Amortization		(129)		(129)		(121)
Net Carrying Amount		47		47		52
Internet domain names
Finite-lived intangible assets
Gross Carrying Amount		41		41		41
Accumulated Amortization		(31)		(31)		(30)
Net Carrying Amount		10		10		11
Trade Names
Finite-lived intangible assets
Gross Carrying Amount		1,810		1,810		1,810
Accumulated Amortization		(486)		(486)		(439)
Net Carrying Amount		1,324		1,324		1,371
Other Intangible Assets
Finite-lived intangible assets
Gross Carrying Amount		2		2		3
Accumulated Amortization		(2)		(2)		(3)
Net Carrying Amount		$ 0		$ 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
Minimum | Other Intangible Assets
Finite-lived intangible assets
Amortization Period				0 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
Maximum | Other Intangible Assets
Finite-lived intangible assets
Amortization Period				15 years
HotelsCombined
Finite-lived intangible assets
Acquisitions and other investments, net of cash acquired	$ 134
FareHarbor
Finite-lived intangible assets
Acquisitions and other investments, net of cash acquired					139
Common stock issued in an acquisition					110
Non-cash operating and financing activity for an acquisition					59
Non-cash investing and financing activity for an acquisition					$ 51

DEBT Short-term Borrowing (Deta

DEBT Short-term Borrowing (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Bank Overdrafts	$ 37	$ 25

DEBT (Revolving Credit Facility

DEBT (Revolving Credit Facility) (Details) - USD ($)	Jun. 19, 2015	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Line of Credit Facility [Line Items]
Proceeds from revolving credit facility and short-term borrowings		$ 437,000,000	$ 3,000,000
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		$ 0
Proceeds from revolving credit facility and short-term borrowings		$ 400,000,000
Weighted average interest rate		3.50%
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

DEBT (Outstanding Debt) (Detail

DEBT (Outstanding Debt) (Details) $ / shares in Units, $ in Millions	Aug. 20, 2014USD ($)Days$ / shares	May 31, 2013USD ($)Days$ / shares	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Jun. 30, 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			$ 7,771		$ 7,771					$ 8,787
Unamortized Debt Discount and Debt Issuance Cost			(85)		(85)					(138)
Carrying Value, Long-Term Debt			7,686		7,686					8,649
Description of Senior Notes
Payments for conversion of senior notes					0	$ (1,487)
0.35% Convertible Senior Notes due June 2020
Debt Instrument
Outstanding Principal Amount, Short-Term Debt			1,000		1,000
Carrying Value, Short-term debt			975		975
Outstanding Principal Amount, Long-Term Debt										1,000
Unamortized Debt Discount and Debt Issuance Cost			$ (25)		$ (25)					(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%	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		3.13%
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		$ 2	1
0.9% Convertible Senior Notes due September 2021
Debt Instrument
Outstanding Principal Amount, Long-Term Debt			1,000		1,000					$ 1,000
Unamortized Debt Discount and Debt Issuance Cost			(50)		(50)					(61)
Carrying Value, Long-Term Debt			$ 950		$ 950					$ 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%	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			$ 1,139		$ 1,139					$ 1,143
Unamortized Debt Discount and Debt Issuance Cost			(4)		(4)					(5)
Carrying Value, Long-Term Debt			$ 1,135		$ 1,135					$ 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%	0.80%
Effective interest rate at debt origination or modification													0.84%
2.15% (€750 Million) Senior Notes due November 2022
Debt Instrument
Outstanding Principal Amount, Long-Term Debt			$ 854		$ 854					$ 858
Unamortized Debt Discount and Debt Issuance Cost			(3)		(3)					(4)
Carrying Value, Long-Term Debt			$ 851		$ 851					$ 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%	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					$ 500
Unamortized Debt Discount and Debt Issuance Cost			(2)		(2)					(3)
Carrying Value, Long-Term Debt			$ 498		$ 498					$ 497
Description of Senior Notes
Interest rate on long-term debt			2.75%		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			$ 1,139		$ 1,139					$ 1,143
Unamortized Debt Discount and Debt Issuance Cost			(10)		(10)					(10)
Carrying Value, Long-Term Debt			$ 1,129		$ 1,129					$ 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%	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					$ 500
Unamortized Debt Discount and Debt Issuance Cost			(3)		(3)					(3)
Carrying Value, Long-Term Debt			$ 497		$ 497					$ 497
Description of Senior Notes
Interest rate on long-term debt			3.65%		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					$ 1,000
Unamortized Debt Discount and Debt Issuance Cost			(6)		(6)					(6)
Carrying Value, Long-Term Debt			$ 994		$ 994					$ 994
Description of Senior Notes
Interest rate on long-term debt			3.60%		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			$ 1,139		$ 1,139					$ 1,143
Unamortized Debt Discount and Debt Issuance Cost			(4)		(4)					(4)
Carrying Value, Long-Term Debt			$ 1,135		$ 1,135					$ 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%	1.80%
Effective interest rate at debt origination or modification																	1.80%
3.55% Senior Notes due March 2028
Debt Instrument
Outstanding Principal Amount, Long-Term Debt			$ 500		$ 500					$ 500
Unamortized Debt Discount and Debt Issuance Cost			(3)		(3)					(3)
Carrying Value, Long-Term Debt			$ 497		$ 497					$ 497
Description of Senior Notes
Interest rate on long-term debt			3.55%		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 for 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			$ 16	$ 15	31	35
Coupon Interest expense			3	3	6	8
Amortization of debt discount included in interest expense			$ 12	$ 12	$ 24	$ 26
Debt, weighted average interest rate			3.20%	3.20%	3.20%	3.20%
Other Long-term Debt
Debt Instrument
Carrying Value, Long-Term Debt			$ 6,700		$ 6,700					$ 6,700
Description of Senior Notes
Interest expense related to debt			41	$ 43	83	$ 86
Coupon Interest expense			40	$ 41	80	$ 83
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			$ 9,800		9,800					$ 9,300
Designated as Hedging Instrument | Minimum | Euro-Denominated Debt
Description of Senior Notes
Notional amount of nonderivative instruments					3,400
Designated as Hedging Instrument | Maximum | Euro-Denominated Debt
Description of Senior Notes
Notional amount of nonderivative instruments					$ 4,300

TREASURY STOCK (Details)

TREASURY STOCK (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Apr. 30, 2019	Mar. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Remaining authorization to repurchase common stock	$ 14,200	$ 4,500		$ 14,200
Authorized stock repurchase programs (in shares)	1,442,440		572,574	3,061,228	945,693
Authorized stock repurchase programs	$ 2,606		$ 1,199	$ 5,462	$ 1,931
General authorization for shares withheld on stock award vesting (in shares)	8,714		12,664	79,419	71,707
General authorization for shares withheld on stock award vesting	$ 16		$ 26	$ 137	$ 146
Payments related to tax withholding for share-based compensation				$ 136	$ 145
Treasury stock, shares (in shares)	20,378,354	17,317,126		20,378,354
Repurchase Program (Q12018) and (Q22019)
Equity, Class of Treasury Stock [Line Items]
Authorized stock repurchase programs (in shares)	1,433,726
Repurchase Program (Q12018)
Equity, Class of Treasury Stock [Line Items]
Amount of common stock repurchases authorized							$ 8,000
Authorized stock repurchase programs (in shares)				2,981,809
Authorized stock repurchase programs	$ 2,590			$ 5,325
Treasury stock repurchased but unsettled by period end, amount	$ 44	$ 74
Repurchase Program (Q12016) and (Q12017)
Equity, Class of Treasury Stock [Line Items]
Authorized stock repurchase programs (in shares)			559,910		873,986
Authorized stock repurchase programs			$ 1,173		$ 1,785
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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Contingency [Line Items]
Effective income tax rate reconciliation, percent	18.90%	19.20%	19.80%	19.20%
Statutory federal rate				21.00%
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		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		$ 5,307	$ 6,915	$ 8,785	$ 10,473	$ 10,636	$ 11,261
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	[1]	(157)		(129)
Foreign currency translation adjustments | Net Investment Hedging | Euro Senior Notes
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		1		(26)
Stockholders' equity, before tax		15		(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]	(73)		(187)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity		(230)	$ (169)	(316)	$ (76)	$ 58	$ 238
Accumulated Net Investment Gain (Loss) Attributable to Parent | Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent		66		30
Currency translation adjustment on deemed repatriation tax liability | Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent		$ (56)		$ (41)
[1]	Foreign currency translation adjustments, net of tax, at June 30, 2019 and December 31, 2018 , included 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, included foreign currency transaction gains of $1 million after tax ( $15 million before tax) and foreign currency transaction losses of $26 million after tax ( $20 million before tax) at June 30, 2019 and December 31, 2018 , respectively, associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (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 functional currency subsidiaries' net assets. At June 30, 2019 and December 31, 2018 , the Company had deferred tax benefits of $56 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 $66 million and $30 million at June 30, 2019 and December 31, 2018

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) ₺ in Millions, € in Millions, £ in Millions, $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended					12 Months Ended
	Dec. 31, 2015EUR (€)	Sep. 30, 2016EUR (€)	Jun. 30, 2019USD ($)	Jun. 30, 2019TRY (₺)	Jun. 30, 2019EUR (€)	Dec. 31, 2018USD ($)ft²	Jun. 30, 2018USD ($)	Dec. 31, 2018EUR (€)	Jun. 30, 2019EUR (€)	Jun. 30, 2019GBP (£)
Commitments and Contingencies
French digital services tax rate			3.00%	3.00%	3.00%
Payment for contingent consideration liability, total			$ 37
Increase in the estimated fair value of contingent consideration liabilities			9				$ 0
Booking.com | Headquarters
Commitments and Contingencies
Contractual obligation		€ 270	159						€ 139
Acquisition of land use rights | €		€ 43
Booking.com | Headquarters | Ground Lease
Commitments and Contingencies
Contractual obligation			83						€ 72
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
Wage-related taxes owed for prior periods, including interest
Commitments and Contingencies
Charge for estimated probable tax owed for prior periods, including applicable interest and penalties			66
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
French Digital Services Tax [Member]
Commitments and Contingencies
Loss contingency, estimate of possible loss			$ 15
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			$ 83							£ 65