Booking (BKNG) 10-K 27 Feb 19 2018 FY Annual report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Feb. 20, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Booking Holdings Inc.
Entity Central Index Key	1,075,531
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		45,012,725
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 96.6

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 2,624	$ 2,542
Short-term investments in marketable securities	3,660	4,860
Accounts receivable, net of allowance for doubtful accounts of $61 and $39, respectively	1,523	1,218
Prepaid expenses and other current assets	600	415
Total current assets	8,407	9,035
Property and equipment, net	656	480
Intangible assets, net	2,125	2,177
Goodwill	2,910	2,738
Long-term investments	8,408	10,873
Other assets	181	148
Total assets	22,687	25,451
Current liabilities:
Accounts payable	1,134	668
Accrued expenses and other current liabilities	1,399	1,139
Deferred merchant bookings	1,022	980
Convertible debt	0	711
Total current liabilities	3,555	3,498
Deferred income taxes	370	481
Long-term U.S. transition tax liability	1,166	1,251
Other long-term liabilities	162	147
Long-term debt	8,649	8,810
Total liabilities	13,902	14,187
Commitments and Contingencies (See Note 14)
Convertible debt	0	3
Stockholders' equity:
Common stock, $0.008 par value, authorized 1,000,000,000 shares, 62,948,762 and 62,689,097 shares issued, respectively	0	0
Treasury stock, 17,317,126 and 14,216,819 shares, respectively	(14,711)	(8,699)
Additional paid-in capital	5,445	5,783
Retained earnings	18,367	13,939
Accumulated other comprehensive income (loss)	(316)	238
Total stockholders' equity	8,785	11,261
Total liabilities and stockholders' equity	$ 22,687	$ 25,451

CONSOLIDATED BALANCE SHEETS (PA

CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 61	$ 39
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)	62,948,762	62,689,097
Treasury stock, shares (in shares)	17,317,126	14,216,819

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Income Statement [Abstract]
Agency revenues	$ 10,480
Agency revenues		$ 9,714		$ 7,982
Merchant revenues	2,987
Merchant revenues		2,133		2,048
Advertising and other revenues	1,060	834		713
Total revenues	14,527	12,681		10,743
Cost of revenues		242		415
Gross profit		12,439		10,328
Operating expenses:
Performance marketing	4,447	4,161		3,479
Brand marketing	509	435		327
Sales and other expenses	830	517		422
Personnel, including stock-based compensation of $317, $261 and $250, respectively	2,042	1,660		1,350
General and administrative	699	576		452
Information technology	233	189		142
Depreciation and amortization	426	363		309
Impairment of goodwill	0	0		941
Total operating expenses	9,186	7,901		7,422
Operating income	5,341	4,538		2,906
Other (expense) income:
Interest income	187	157		95
Interest expense	(269)	(254)		(208)
Net unrealized losses on marketable equity securities	(367)	0		0
Impairment of investments	0
Impairment of investments		(8)		(63)
Foreign currency transactions and other	(57)	(34)		(17)
Total other expense	(506)	(139)		(193)
Earnings before income taxes	4,835	4,399		2,713
Income tax expense	837	2,058		578
Net income	$ 3,998	$ 2,341	[1]	$ 2,135	[1]
Net income applicable to common stockholders per basic common share	$ 84.26	$ 47.78		$ 43.14
Weighted-average number of basic common shares outstanding (in 000's)	47,446	48,994		49,491
Net income applicable to common stockholders per diluted common share	$ 83.26	$ 46.86		$ 42.65
Weighted-average number of diluted common shares outstanding (in 000's)	48,017	49,954		50,063
[1]	The Company realized net gains of $1 million related to investments in debt securities sold for both years ended December 31, 2017 and 2016.

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (PARENTHETICAL) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Stock-based compensation	$ 317	$ 261	$ 250

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Other comprehensive income (loss), net of tax
Net income		$ 3,998		$ 2,341	[1]	$ 2,135	[1]
Foreign currency translation adjustments	[2]	(114)		297		(95)
Net unrealized gain (loss) on marketable securities	[4]	(199)	[3]	76	[1]	(285)	[1]
Comprehensive income		3,685		2,714		1,755
Other Comprehensive Income (Loss), Equity Securities, Reclassification Adjustments to Retained Earnings (ASU 2016-01), Tax		58		0		0
Net realized gains related to investments				1		1
Tax (benefit) associated with gain (loss) on foreign currency translation		12
Net unrealized gain (loss) on marketable securities which are non-taxable in the Netherlands		(190)		86		(332)
Other Comprehensive Income (Loss), Available-for-sale Securities, Taxable		(7)		71		62
Tax (benefit) associated with gain (loss) on marketable securities		(2)		81		15
The Netherlands
Other comprehensive income (loss), net of tax
Tax (benefit) associated with gain (loss) on marketable securities		(2)		18		15
Domestic Tax Authority
Other comprehensive income (loss), net of tax
Tax (benefit) associated with gain (loss) on marketable securities				63
Currency translation adjustment on deemed repatriation tax liability [Member]
Other comprehensive income (loss), net of tax
Tax (benefit) associated with gain (loss) on foreign currency translation		(41)
Net Investment Hedging [Member]
Other comprehensive income (loss), net of tax
Tax (benefit) associated with gain (loss) on foreign currency translation		$ 53		$ (175)		$ 34
[1]	The Company realized net gains of $1 million related to investments in debt securities sold for both years ended December 31, 2017 and 2016.
[2]	Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar denominated net assets, net of the impact of net investment hedges. During the year ended December 31, 2018, the Company recorded a tax benefit of $41 million related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and current year foreign earnings 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"). Prior to January 1, 2018, foreign currency translation adjustments excluded U.S. federal and state income taxes as a result of the Company's intention to indefinitely reinvest the earnings of its international subsidiaries outside of the United States. Foreign currency translation adjustments also include a tax charge of $53 million, a tax benefit of $175 million and a tax charge of $34 million for the years ended December 31, 2018, 2017 and 2016, respectively, associated with the Company's Euro-denominated debt, which is designated as a net investment hedge against the impact of currency fluctuations of the Company's Euro-denominated net assets (see Note 12).
[3]	For periods beginning after December 31, 2017, marketable equity securities are reported at estimated fair value with changes in fair value recognized in net income rather than accumulated other comprehensive income within stockholders' equity, pursuant to the adoption of the accounting update on financial instruments in 2018 (see Note 2).
[4]	Net unrealized losses before tax on marketable securities of $190 million, net unrealized gains of $86 million and net unrealized losses of $332 million for the years ended December 31, 2018, 2017 and 2016, respectively, were not subject to income tax in the Netherlands. Net unrealized losses before tax of $7 million and gains before tax of $71 million and $62 million for the years ended December 31, 2018, 2017 and 2016, respectively, were taxable at a 25% tax rate in the Netherlands, resulting in a tax benefit of $2 million and tax charges of $18 million and $15 million for the years ended December 31, 2018, 2017 and 2016, respectively. The remaining net unrealized losses on marketable securities and related tax benefits for the year ended December 31, 2018 were associated with marketable debt securities held by a U.S. subsidiary.For the year ended December 31, 2017, the Company also recorded a U.S. deferred tax liability of $63 million related to net cumulative unrealized gains associated with certain international investments.

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total		Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2015	$ 8,795		$ 0	$ (5,827)	$ 5,185	$ 9,192	$ 245
Balance (in shares) at Dec. 31, 2015			62,040,000	(12,428,000)
Increase (Decrease) in Stockholders' Equity
Net income	2,135	[1]				2,135
Foreign currency translation adjustments	(95)	[2]					(95)
Net unrealized gain (loss) on marketable securities	(285)	[1],[3]					(285)
Reclassification adjustment for convertible debt in mezzanine	(29)				(29)
Exercise of stock options and vesting of restricted stock units and performance share units	16		$ 0		16
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			339,000
Repurchase of common stock	$ (1,028)			$ (1,028)
Repurchase of common stock (in shares)	(762,984)			(763,000)
Stock-based compensation and other stock-based payments	$ 250				250
Excess tax benefits on stock-based awards and other equity deductions	61				61
Balance at Dec. 31, 2016	9,820		$ 0	$ (6,855)	5,483	11,327	(135)
Balance (in shares) at Dec. 31, 2016			62,379,000	(13,191,000)
Increase (Decrease) in Stockholders' Equity
Net income	2,341	[1]				2,341
Foreign currency translation adjustments	297	[2]					297
Net unrealized gain (loss) on marketable securities	76	[1],[3]					76
Reclassification adjustment for convertible debt in mezzanine	26				26
Exercise of stock options and vesting of restricted stock units and performance share units	5		$ 0		5
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			160,000
Repurchase of common stock	$ (1,844)			$ (1,844)
Repurchase of common stock (in shares)	(1,025,890)			(1,026,000)
Stock-based compensation and other stock-based payments	$ 261				261
Adjustments to Additional Paid in Capital Senior Convertible Notes Converted	(1)				(1)
Conversion of debt (in shares)			150,000
Conversion of debt			$ 0
Balance at Dec. 31, 2017	11,261		$ 0	$ (8,699)	5,783	13,939	238
Balance (in shares) at Dec. 31, 2017			62,689,000	(14,217,000)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of accounting standard updates	280				9	271
Net income	3,998					3,998
Foreign currency translation adjustments	(114)	[2]					(114)
Net unrealized gain (loss) on marketable securities	(199)	[3],[4]					(199)
Reclassification adjustment for convertible debt in mezzanine	3				3
Exercise of stock options and vesting of restricted stock units and performance share units	2		$ 0		2
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			208,000
Repurchase of common stock	$ (6,012)			$ (6,012)
Repurchase of common stock (in shares)	(3,100,307)			(3,100,000)
Stock-based compensation and other stock-based payments	$ 320				320
Adjustments to Additional Paid in Capital Senior Convertible Notes Converted	(773)				(773)
Stock Issued During Period, Shares, Acquisitions			52,000
Stock Issued During Period, Value, Acquisitions	110				110
Conversion of debt (in shares)			0
Conversion of debt			$ 0
Balance at Dec. 31, 2018	8,785		$ 0	$ (14,711)	$ 5,445	18,367	(316)
Balance (in shares) at Dec. 31, 2018			62,949,000	(17,317,000)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of accounting standard updates	$ 189					$ 430	$ (241)
[1]	The Company realized net gains of $1 million related to investments in debt securities sold for both years ended December 31, 2017 and 2016.
[2]	Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar denominated net assets, net of the impact of net investment hedges. During the year ended December 31, 2018, the Company recorded a tax benefit of $41 million related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and current year foreign earnings 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"). Prior to January 1, 2018, foreign currency translation adjustments excluded U.S. federal and state income taxes as a result of the Company's intention to indefinitely reinvest the earnings of its international subsidiaries outside of the United States. Foreign currency translation adjustments also include a tax charge of $53 million, a tax benefit of $175 million and a tax charge of $34 million for the years ended December 31, 2018, 2017 and 2016, respectively, associated with the Company's Euro-denominated debt, which is designated as a net investment hedge against the impact of currency fluctuations of the Company's Euro-denominated net assets (see Note 12).
[3]	Net unrealized losses before tax on marketable securities of $190 million, net unrealized gains of $86 million and net unrealized losses of $332 million for the years ended December 31, 2018, 2017 and 2016, respectively, were not subject to income tax in the Netherlands. Net unrealized losses before tax of $7 million and gains before tax of $71 million and $62 million for the years ended December 31, 2018, 2017 and 2016, respectively, were taxable at a 25% tax rate in the Netherlands, resulting in a tax benefit of $2 million and tax charges of $18 million and $15 million for the years ended December 31, 2018, 2017 and 2016, respectively. The remaining net unrealized losses on marketable securities and related tax benefits for the year ended December 31, 2018 were associated with marketable debt securities held by a U.S. subsidiary.For the year ended December 31, 2017, the Company also recorded a U.S. deferred tax liability of $63 million related to net cumulative unrealized gains associated with certain international investments.
[4]	For periods beginning after December 31, 2017, marketable equity securities are reported at estimated fair value with changes in fair value recognized in net income rather than accumulated other comprehensive income within stockholders' equity, pursuant to the adoption of the accounting update on financial instruments in 2018 (see Note 2).

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (PARENTHETICAL) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Tax (benefit) associated with gain (loss) on marketable securities	$ (2)	$ 81	$ 15
Tax (benefit) associated with gain (loss) on net investment hedges	$ 12

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Statement of Cash Flows [Abstract]
Net income	$ 3,998	$ 2,341	[1]	$ 2,135	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	248	187		140
Amortization	178	176		169
Provision for uncollectible accounts	163	62		46
Deferred income tax benefit	(150)	(32)		(112)
Net unrealized losses on marketable equity securities	367	0		0
Stock-based compensation expense and other stock-based payments	331	261		250
Amortization of debt issuance costs	7	9		8
Amortization of debt discount	52	70		69
Loss on early extinguishment of debt	0	2		0
Impairment of goodwill	0	0		941
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount	0
Impairment of investments		8		63
Excess tax benefits on stock-based awards and other equity deductions	0	0		61
Contingent consideration fair value adjustment	19	0		0
Changes in assets and liabilities, net of effects of acquisitions:
Accounts receivable	(319)	(270)		(284)
Prepaid expenses and other current assets	(201)	(124)		5
Accounts payable, accrued expenses and other current liabilities	635	687		514
Long-term U.S. transition tax liability	40	1,251		0
Other long-term assets and liabilities	(30)	34		(21)
Net cash provided by operating activities	5,338	4,662		3,984
INVESTING ACTIVITIES:
Purchase of investments	(2,686)	(6,941)		(6,748)
Proceeds from sale of investments	5,616	3,580		3,684
Additions to property and equipment	(442)	(288)		(220)
Acquisitions and other investments, net of cash acquired	(273)	(553)		(1)
Acquisition of land-use rights	0	0		(48)
Net cash provided by (used in) investing activities	2,215	(4,202)		(3,333)
FINANCING ACTIVITIES:
Proceeds from short-term borrowing	25	0		0
Proceeds from the issuance of long-term debt	0	2,045		995
Payments for conversion of senior notes	(1,487)	(286)		0
Repayment of debt	0	(15)		0
Payments for repurchase of common stock	(5,971)	(1,828)		(1,012)
Proceeds from exercise of stock options	2	5		16
Net cash used in financing activities	(7,431)	(79)		(1)
Effect of exchange rate changes on cash, cash equivalents and restricted cash and cash equivalents	(40)	100		(46)
Net increase in cash, cash equivalents and restricted cash and cash equivalents	82	481		604
Total cash and cash equivalents and restricted cash and cash equivalents, beginning of period	2,563	2,082		1,478
Total cash and cash equivalents and restricted cash and cash equivalent, end of period	2,645	2,563		2,082
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the period for income taxes	1,169	702		637
Cash paid during the period for interest	219	155		126
Non-cash operating and financing activity for an acquisition (See Note 18)	51	0		0
Non-cash investing and financing activity for an acquisition (See Note 18)	$ 59	$ 0		$ 0
[1]	The Company realized net gains of $1 million related to investments in debt securities sold for both years ended December 31, 2017 and 2016.

BUSINESS DESCRIPTION

BUSINESS DESCRIPTION	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BUSINESS DESCRIPTION	BUSINESS DESCRIPTION Booking Holdings Inc. ("Booking Holdings" or the "Company") helps people experience the world by providing consumers, travel service providers and restaurants with leading travel and restaurant online reservation and related services. Through one or more of the Company's brands, consumers can: book a broad array of accommodations (including hotels, motels, resorts, homes, apartments, bed and breakfasts, hostels and other properties); make a car rental reservation or arrange for an airport taxi; make a dinner reservation; or book a cruise, flight, vacation package, tour or activity. Consumers can also use our meta-search services to easily compare travel reservation information, such as airline ticket, hotel reservation and rental car reservation information, from hundreds of online travel platforms at once. In addition, the Company offers various other services to consumers, such as certain insurance products and restaurant management services to restaurants.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation — The Company's Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries, including acquired businesses from the dates of acquisition. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates — The preparation of financial statements in conformity with accounting principles generally accepted in the United States ("U.S. GAAP") requires management to make estimates and assumptions that affect the amounts reported in the financial statements and footnotes thereto. Actual results may differ significantly from those estimates. The estimates underlying the Company's Consolidated Financial Statements relate to, among other things, the valuation of goodwill, long-lived assets and intangible assets, income taxes, stock-based compensation, the allowance for doubtful accounts and the accrual of obligations for loyalty programs. Reclassifications — Certain amounts from prior periods have been reclassified to conform to the current year presentation. Change in Presentation — In the first quarter of 2018, the Company changed the presentation of "Performance advertising", "Brand advertising", and "Sales and marketing" to "Performance marketing", "Brand marketing" and "Sales and other expenses" in the Consolidated Statements of Operations. The descriptions of these new lines are as follows: "Performance marketing" expenses are marketing expenses generally measured by return on investment or an increase in bookings over a specified time period. These expenses consist primarily of the costs of: (1) search engine keyword purchases; (2) referrals from meta-search and travel research websites; (3) affiliate programs; and (4) other performance-based advertisements, including certain incentive programs. "Brand marketing" expenses are marketing expenses to build brand awareness over a specified time period. These expenses consist primarily of television advertising, online video advertising (including the airing of our television advertising online) and online display advertising, as well as other marketing expenses such as public relations, trade shows and sponsorships. "Sales and other expenses" are generally variable in nature and consist primarily of: (1) credit cards and other payment processing fees associated with merchant transactions; (2) fees paid to third parties that provide call center, website content translations and other services; (3) provisions for customer chargebacks associated with merchant transactions; (4) customer relations costs; (5) provisions for bad debt, primarily related to accommodation commission receivables; and (6) insurance claim costs. In conjunction with the adoption of the current revenue recognition accounting standard ("the current revenue standard") effective January 1, 2018, the Company reclassified certain expenses from "Cost of revenues" to "Sales and other expenses" or "General and administrative" expenses in its Consolidated Statements of Operations for the years ended December 31, 2017 and 2016 to conform to the current period presentation. The change in presentation and the reclassification for the years ended December 31, 2017 and 2016 had no impact on operating income or net income and are summarized below (in millions): Previously Reported 2017 2016 Cost of revenues $ 251 $ 428 Performance advertising 4,142 3,479 Brand advertising 392 296 Sales and marketing 562 435 General and administrative 586 456 Current Presentation 2017 2016 Cost of revenues $ 242 $ 415 Performance marketing 4,161 3,479 Brand marketing 435 327 Sales and other expenses 517 422 General and administrative 576 452 Reclassification of Investments in Private Companies: In 2018, the Company changed the presentation of its equity investments in private companies to include them in "Long-term investments" instead of "Other assets" in the Consolidated Balance Sheets and in "Purchase of investments" instead of "Acquisitions and other investments, net of cash acquired" in the Consolidated Statements of Cash Flows. Therefore, the Company reclassified $451 million of investments in its Consolidated Balance Sheet at December 31, 2017 and cash payments of $450 million and $7 million in its Consolidated Statements of Cash Flows for the years ended December 31, 2017 and 2016, respectively, to conform to this current period presentations. See Note 4 for more detail. Fair Value of Financial Instruments — The Company's financial instruments, including cash, restricted cash, 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 financial instruments. See Notes 4 , 5 and 10 for information on fair value for investments, derivatives, and the Company's outstanding Senior Notes. Cash and Cash Equivalents — Cash and cash equivalents consists primarily of cash and highly liquid investment grade securities with an original maturity of three months or less. Cash equivalents are recognized based on settlement date. Restricted Cash and Cash Equivalents — Restricted cash and cash equivalents are restricted through legal contracts, regulations or by the Company's intention to use the cash for a specific purpose. Restricted cash and cash equivalents at December 31, 2018 and 2017 principally relates to the minimum cash requirement for Rentalcars.com's insurance business established in 2017. Restricted cash at December 31, 2016 collateralizes office leases. The following table reconciles cash, cash equivalents and restricted cash and cash equivalents reported in the Consolidated Balance Sheets to the total amount shown in the Consolidated Statements of Cash Flows (in millions): December 31, 2018 2017 2016 As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 2,624 $ 2,542 $ 2,081 Restricted cash and cash equivalents included in prepaid expenses and other current assets 21 21 1 Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Consolidated Statements of Cash Flows $ 2,645 $ 2,563 $ 2,082 Investments — Investments held by the Company include debt and equity securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is considered a debt security. Investments in debt or equity securities that include embedded features, such as conversion or redemption features, are analyzed by the Company to determine if these features are embedded derivatives that require separate accounting treatment. • Debt Securities. The Company has classified its investments in debt securities as available-for-sale securities. These securities are reported at estimated fair value with the aggregate unrealized gains and losses, net of taxes, reflected as a part of " Accumulated other comprehensive income (loss) " in the Consolidated Balance Sheets. Investments in debt securities are considered to be impaired when a decline in fair value is judged to be other than temporary because the Company either intends to sell or it is more-likely-than not that it will have to sell the impaired security before recovery. Once a decline in fair value is determined to be other than temporary, an impairment charge is recorded and a new cost basis in the investment is established. If the Company does not intend to sell the debt security, but it is probable that the Company will not collect all amounts due, then only the impairment due to the credit risk would be recognized in earnings and the remaining amount of the impairment would be recognized in accumulated other comprehensive income within stockholders' equity. The fair value of these investments is based on the specific quoted market price of the securities or comparable securities at the balance sheet dates. Unobservable inputs are also used when little or no market data is available. See Note 5 for information on fair value measurements. The Company's investments in marketable debt securities are recognized based on trade date and reported as "Short-term investments in marketable securities" or "Long-term investments" in the Consolidated Balance Sheets based on the maturity date of the debt security. 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. • Equity Securities. Equity securities are reported as "Long-term investments" in the Consolidated Balance Sheets and include marketable equity securities and equity investments without readily determinable fair values. For periods beginning after December 31, 2017, marketable equity securities are reported at estimated fair value with changes in fair value recognized in net income rather than accumulated other comprehensive income within stockholders' equity, pursuant to the adoption of the accounting update on financial instruments in 2018. As a result, the Company recognized $367 million , before tax, in " Net unrealized losses on marketable equity securities " in the Consolidated Statement of Operations for the year ended December 31, 2018 . See "Recent Accounting Pronouncements Adopted" later in this footnote for further information on the impact of the adoption of this accounting update. The Company holds investments in equity securities of private companies, over which the Company does not have the ability to exercise significant influence or control. Pursuant to the adoption of the accounting update on financial instruments in 2018 (see "Recent Accounting Pronouncements Adopted" later in this footnote), for periods beginning after December 31, 2017, the Company elected to measure these investments at cost less impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Previously, these investments were carried at cost and adjusted to fair value only for other-than-temporary declines in fair value. See " Reclassification of Investments in Private Companies" in this footnote for the change in the presentation of these investments in 2018. See Note 4 and 5 for further information on investments. Property and Equipment — Property and equipment are stated at cost less accumulated depreciation. Depreciation is computed on a straight-line basis over the estimated useful lives of the assets or, when applicable, the life of the lease related to leasehold improvements, whichever is shorter. Building Construction-in-progress — Building construction-in-progress is associated with the construction of an office building in the Netherlands and is included in “Property and equipment, net” in the Consolidated Balance Sheets. Depreciation of the building and its related components will commence once it is ready for the Company’s use. Land-use rights — Land-use rights represent prepayments for the long-term lease of land where the Company is constructing an office building in the Netherlands. At December 31, 2018 and 2017 , the Company had $47 million and $51 million , respectively, associated with land-use rights recorded in “Other assets” in the Consolidated Balance Sheets. The land-use rights are expensed on a straight-line basis over the lease period. This expense is recorded as rent expense in "General and administrative" expense in the Consolidated Statements of Operations. See Note 14 for further details. Website and Internal-use Software Capitalization — Certain direct development costs associated with website and internal-use software are capitalized and include external direct costs of services and payroll costs for employees devoting time to the software projects principally related to platform development, including support systems, software coding, designing system interfaces and installation and testing of the software. These costs are recorded as property and equipment and are generally amortized over a period of two to five years beginning when the asset is substantially ready for use. Costs incurred for enhancements that are expected to result in additional features or functionalities are capitalized and amortized over the estimated useful life of the enhancements. Costs incurred during the preliminary project stage, as well as maintenance and training costs, are expensed as incurred. Additions to capitalized costs during the years ended December 31, 2018 , 2017 and 2016 were $97 million , $80 million and $54 million , respectively. Goodwill — The Company accounts for acquired businesses using the acquisition method of accounting which requires that the assets acquired and liabilities assumed be recorded at the date of acquisition at their respective fair values. Any excess of the purchase price over the estimated fair values of the net assets acquired is recorded as goodwill. The Company's Consolidated Financial Statements reflect an acquired business starting at the date of the acquisition. Goodwill is not subject to amortization and is reviewed at least annually for impairment, or earlier if an event occurs or circumstances change and there is an indication of impairment. The Company tests goodwill at a reporting unit level. The fair value of the reporting unit is compared to its carrying value, including goodwill. Fair values are determined using a combination of standard valuation techniques, including an income approach (discounted cash flows) and market approaches (EBITDA multiples of comparable publicly-traded companies and precedent transactions) and based on market participant assumptions. An impairment is recorded to the extent that the implied fair value of goodwill is less than the carrying value of goodwill. See Note 9 for further information. Impairment of Long-Lived Assets and Intangible Assets — The Company reviews long-lived tangible assets and amortizable intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the Company's ability to recover the carrying value of the assets from the estimated undiscounted future net cash flows, before interest and taxes, of the related operations. The amount of impairment loss, if any, is measured as the excess of the carrying value of the asset over the present value of estimated future cash flows, using a discount rate commensurate with the risks involved and based on assumptions representative of market participants. Online travel reservation services — For periods beginning after December 31, 2017, the Company recognizes revenue for travel reservation services when the travel begins rather than when the travel is completed. Substantially all of the Company's revenues are generated by providing online travel reservation services, which principally allows travelers to book travel reservations with travel service providers through the Company’s platforms. While the Company generally refers to a consumer that books travel reservation services on the Company's platforms as its customer, for accounting purposes, the Company's customers are the travel service providers and, in certain merchant transactions, the travelers. The Company's contracts with travel service providers give them the ability to market their reservation availability without transferring responsibility to deliver the travel service to the Company, therefore, the Company's revenues are presented on a net basis in the Consolidated Statements of Operations. These contracts include payment terms and establish the consideration to which the Company is entitled, which includes either a commission or a margin on the travel transaction. Revenue is measured based on the expected consideration specified in the contract with the travel service provider, considering the effects of sales incentives, "no show" cancellations (where the traveler has not cancelled the reservation but does not arrive on the scheduled reservation date) and "late" cancellations (where the travel service provider accepts a cancellation after its cancellation cut-off date). Estimates for cancellations and sales incentives are based on historical experience and current trends. Coupons are recorded as a reduction of the transaction price at the time they are redeemed. Online travel reservation services are recorded at a point in time when the Company has completed its post-booking services and the travelers begin using the arranged travel services. These services are classified into two categories: • Agency revenues are derived from travel-related transactions where the Company does not receive payments from travelers for the services provided. The Company invoices the travel service providers for its commissions in the month that travel is completed. Agency revenues consist almost entirely of travel reservation commissions, as well as certain global distribution system ("GDS") reservation booking fees and certain travel insurance fees. Substantially all of the Company's agency revenue is from Booking.com agency accommodation reservations. • Merchant revenues are derived from travel-related transactions where the Company receives payments from travelers for the services provided, generally at the time of booking. The Company records cash collected from travelers, which includes the amounts owed to the travel service providers and the Company’s commission or margin and fees, as deferred merchant bookings until the arranged travel service begins. Merchant revenues include travel reservation commissions and transaction net revenues (i.e., the amount charged to travelers less the amount owed to travel service providers) in connection with the Company's merchant reservations services; ancillary fees, including travel insurance-related revenues and certain GDS reservation booking fees; and credit card processing rebates and customer processing fees. Substantially all merchant revenues are for merchant services derived from transactions where travelers book accommodation reservations or rental car reservations from travel service providers. Pursuant to the terms of the Company's merchant services, travel service providers are permitted to bill the Company for the underlying cost of the services during a specified period of time. If the Company is not billed by the travel service provider within the specified period of time, the Company increases its revenue by the unbilled amount. Tax Recovery Charge, Occupancy Taxes and State and Local Taxes — For merchant transactions, the Company charges the traveler an amount intended to cover the taxes that the Company anticipates the travel service provider will remit to the local taxing authorities ("tax recovery charge"). Tax rate information for calculating the tax recovery charge is provided to the Company by the travel service providers. In certain taxing jurisdictions, the Company is required by statute, regulation or court order to collect and remit certain local occupancy tax, general excise tax, value-added tax and/or sales tax ("travel transaction taxes") and/or service fees. In other taxing jurisdictions, the Company is required to collect from the traveler and remit directly to the taxing jurisdiction transaction-related taxes imposed on the full amount of the transaction, which includes taxes on the margin, service fees and the underlying rate provided by the travel service provider. The rate information for calculating these taxes is provided to the Company directly from the taxing jurisdictions. The taxes collected from travelers are reported on a net basis in revenues in the Consolidated Statements of Operations. Advertising and Other Revenues — Advertising and other revenues are primarily recognized by KAYAK and OpenTable for advertising placements on their websites. KAYAK recognizes advertising revenue primarily by sending referrals to online travel companies ("OTCs") and travel service providers and from advertising placements on its platforms. Revenue related to referrals is recognized when a consumer clicks on a referral placement or upon completion of the travel. Revenue for advertising placements is recognized based upon when a consumer clicks on an advertisement or when KAYAK displays an advertisement. OpenTable recognizes revenues for reservation fees when diners are seated through its online restaurant reservation service and revenues for subscription fees for restaurant management services on a straight-line basis over the contractual period in accordance with how the service is provided. Loyalty Programs — The Company provides various loyalty programs, where participating consumers are awarded loyalty incentives on current transactions that can be redeemed for future qualifying reservations booked through the applicable Company platform or, in the case of OpenTable, at participating restaurants. 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 resulted in a reduction of its loyalty program liability by $27 million . At December 31, 2018 and 2017, liabilities of $73 million and $105 million , respectively, for loyalty program incentives were included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets. 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 owed to the travel service providers as well as the Company's deferred revenue for its commission or margin and fees. At December 31, 2018 and 2017, deferred merchant bookings included deferred revenue of $149 million and $151 million , respectively. The Company expects to complete its service obligation within one year of booking. In the year ended December 31, 2018, the Company recognized revenue of $109 million and cancellations of $10 million related to the deferred revenue balance at December 31, 2017. In addition, the Company reduced the December 31, 2017 balance by $32 million for the impact of the adoption of the current revenue standard on January 1, 2018. The offsetting increase in the deferred revenue balance for the year ended December 31, 2018 is principally driven by payments received from travelers, net of amounts payable to travel service providers, in the current period for those online travel reservations that the Company receives cash payments in advance of completing its service obligations. Advertising expense — Included in "Performance marketing" expenses in the Consolidated Statements of Operations are performance advertising expenses of $4.4 billion , $4.1 billion and $3.5 billion for the years ended December 31, 2018 , 2017 and 2016 , respectively. Included in "Brand marketing" expenses in the Consolidated Statements of Operations are brand advertising expenses of $457 million , $392 million and $296 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets are accrued performance advertising liabilities of $313 million and $284 million at December 31, 2018 and 2017 , respectively. See " Change in Presentation " above within this footnote for the description of "Performance marketing" and "Brand marketing." Personnel — Personnel expenses consist of compensation to the Company's personnel, including salaries, stock-based compensation, bonuses, payroll taxes and employee health benefits. Included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets are accrued compensation liabilities of $348 million and $288 million at December 31, 2018 and 2017 , respectively. Stock-Based Compensation — Stock-based compensation is recognized in the financial statements based upon fair value. The fair value 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 at the grant date or acquisition date. The Company records stock-based compensation expense for the performance-based awards based on its estimate of the probable outcome at the end of the performance period (i.e., the estimated performance against the performance targets). The Company periodically adjusts the cumulative stock-based compensation expense recorded when the probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results. 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. Fair value is recognized as expense on a straight-line basis over the requisite service period, and, beginning January 1, 2017, forfeitures are accounted for when they occur. The benefits of tax deductions in excess of recognized compensation costs are recognized in the income statement as a discrete item in periods beginning on or after January 1, 2017 when an option exercise or a vesting and release of shares occurs. Excess tax benefits are presented as operating cash flows and cash payments for employee statutory tax withholding related to vested stock awards are presented as financing cash flows in the statements of cash flows. See Note 3 for further information on stock-based awards. Information Technology — Information technology expenses consist primarily of: (1) software license and system maintenance fees; (2) data communications and other expenses associated with operating our services; (3) outsourced data center costs; and (4) payments to outside consultants. Income Taxes — The Company accounts for income taxes under the asset and liability method. The Company records the estimated future tax effects of temporary differences between the tax bases of assets and liabilities and amounts reported in the Consolidated Balance Sheets, as well as operating loss and tax credit carryforwards. Deferred taxes are classified as noncurrent in the balance sheet. The Company records deferred tax assets to the extent it believes these assets will more likely than not be realized. The Company regularly reviews its deferred tax assets for recoverability considering historical profitability, projected future taxable income, the expected timing of the reversals of existing temporary differences, the carryforward periods available for tax reporting purposes, and tax planning strategies. 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 ultimate realization of deferred tax assets depends on the generation of future taxable income during the period in which related temporary differences become deductible. In determining the future tax consequences of events that have been recognized in the financial statements or tax returns, significant judgments, estimates, and interpretation of statutes are required. Deferred taxes are measured using the enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred taxes of a change in tax rates is recognized in income in the period that includes the enactment date of such change. The Company recognizes liabilities when it believes that uncertain positions may not be fully sustained upon audit by the tax authorities. Liabilities recognized for uncertain tax positions are based on a two-step approach for recognition and measurement. First, the Company evaluates the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on audit based on its technical merits. Second, the Company measures the tax benefit as the largest amount that is more than 50% likely of being realized upon ultimate settlement. Interest and penalties attributable to uncertain tax positions, if any, are recognized as a component of income tax expense. In 2018 the Company adopted an accounting policy to treat taxes on global intangible low-taxed income ("GILTI") introduced by the Tax Act as period costs. See Note 13 for further details on income taxes. Segment Reporting — The Company determined that its primary brands constitute its operating segments. The Company's Booking.com brand represents a substantial majority of total revenues and operating income. Based on similar economic characteristics and other similar operating factors, the Company has aggregated the operating segments into one reportable segment. For geographic information, see Note 16 . Foreign Currency Translation — The functional currency of the Company's foreign subsidiaries is generally their respective local currency. 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 income (loss) " in the Company's Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Foreign currency transactions and other" in the Company's Consolidated Statements of Operations. Derivative Financial Instruments — As a result of the Company's international operations, it is exposed to various market risks that may affect its consolidated results of operations, cash flows and financial position. These market risks include, but are not limited to, fluctuations in currency exchange rates. The Company's primary foreign currency exposures are in Euros and British Pounds Sterling, in which it conducts a significant portion of its business activities. As a result, the Company faces exposure to adverse movements in currency exchange rates as the financial results of its international operations are translated from local currencies into U.S. Dollars upon consolidation. Additionally, foreign exchange rate fluctuations on transactions denominated in currencies other than the functional currency of an entity result in gains and losses that are reflected in income. The Company may enter into derivative instruments to hedge certain net exposures of nonfunctional currency denominated assets and liabilities and the volatility associated with translating earnings for its international businesses into U.S. Dollars, even though it does not elect to apply hedge accounting or hedge accounting does not apply. Gains and losses resulting from a change in fair value for these derivatives are reflected in income in the period in which the change occurs and are recognized in the Consolidated Statements of Operations in "Foreign currency transactions and other." Cash flows related to these contracts are classified within "Net cash provided by operating activities" on the cash flow statement. The Company, from time to time in the past, has utilized derivative instruments to hedge the impact of changes in currency exchange rates on the net assets of its foreign subsidiaries. These instruments are designated as net investment hedges. Hedge ineffectiveness is assessed and measured based on changes in forward exchange rates. The Company records gains and losses on these derivative instruments as currency translation adjustments, which offset a portion of the translation adjustments related to the foreign subsidiaries' net assets. Gains and losses are recognized in the Consolidated Balance Sheet in " Accumulated other comprehensive income (loss) " and will be realized upon a partial sale or liquidation of the investment. The Company documents all derivatives designated as hedging instruments for accounting purposes, both at hedge inception and on an on-going basis. The Company issued Senior Notes due March 10, 2022 for an aggregate principal amount of 1.0 billion Euros in 2017, Senior Notes due November 25, 2022 for an aggregate principal amount of 750 million Euros and Senior Notes due March 3, 2027 for an aggregate principal amount of 1.0 billion Euros both in 2015 and Senior Notes due September 23, 2024 for an aggregate principal amount of 1.0 billion Euros in 2014. The Company designated the carrying value, plus ac

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The Company's 1999 Omnibus Plan, as amended and restated effective June 7, 2018, (the "1999 Plan") is the primary stock compensation plan from which broad-based employee, non-employee director and consultant equity awards may be made. At December 31, 2018 , there were 2,001,849 shares of common stock available for future grant under the 1999 Plan. In addition, under plans assumed in connection with various acquisitions, there were 93,726 shares of common stock available for future grant at December 31, 2018 . Stock-based compensation issued under the plans generally consists of restricted stock units, performance share units and, to a far lesser extent and only in the context of assuming grants in connection with acquisitions, stock options. Restricted stock units and performance share units generally vest over periods from 1 to 3 years. Assumed stock options generally have a term of 10 years. The Company issues shares of common stock upon the vesting of restricted stock units and performance share units and the exercise of stock options. See Note 2 for the Company's accounting policy on stock-based compensation. Stock-based compensation included in personnel expenses in the Consolidated Statements of Operations was $317 million , $261 million and $250 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Stock-based compensation for the years ended December 31, 2018 , 2017 and 2016 includes charges amounting to $48 million , $11 million and $21 million , respectively, representing the impact of adjusting the estimated probable outcome at the end of the performance period for outstanding unvested performance share units. The related tax benefit for stock-based compensation is $36 million , $46 million and $45 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Stock-based compensation from grants to non-employee directors and consultants was $6 million , $3 million and $3 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 2 for the change in the accounting of stock-based awards granted to non-employee consultants. Restricted Stock Units and Performance Share Units The following table summarizes the activity of restricted stock units and performance share units ("share-based awards") for employees and non-employee directors during the years ended December 31, 2016 , 2017 and 2018 : Share-Based Awards Shares Weighted-Average Grant Date Fair Value Unvested at December 31, 2015 637,257 $ 1,070.10 Granted 202,740 $ 1,314.93 Vested (298,753 ) $ 858.23 Performance Shares Adjustment 52,224 $ 1,294.84 Forfeited/Canceled (77,862 ) $ 1,278.06 Unvested at December 31, 2016 515,606 $ 1,287.88 Granted 174,507 $ 1,740.78 Vested (143,771 ) $ 1,316.26 Performance Shares Adjustment 19,357 $ 1,501.48 Forfeited/Canceled (41,003 ) $ 1,416.09 Unvested at December 31, 2017 524,696 $ 1,431.88 Granted 166,304 $ 2,027.43 Vested (204,242 ) $ 1,297.21 Performance Shares Adjustment 66,245 $ 1,872.06 Forfeited/Canceled (41,441 ) $ 1,713.45 Unvested at December 31, 2018 511,562 $ 1,713.44 Share-based awards granted by the Company during the years ended December 31, 2018 , 2017 and 2016 had aggregate grant-date fair values of $337 million , $304 million and $267 million , respectively. Share-based awards that vested during the years ended December 31, 2018 , 2017 , and 2016 had grant-date fair values of $265 million , $189 million and $256 million , respectively. At December 31, 2018 , there was $420 million of total future compensation cost related to unvested share-based awards to be recognized over a weighted-average period of 1.9 years . During the year ended December 31, 2018 , the Company made broad-based grants of 116,583 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 $236 million based on a weighted-average grant-date fair value per share of $2,024.71 . 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. 2018 Performance Share Units During the year ended December 31, 2018 , the Company granted 49,721 performance share units to executives and certain other employees. The performance share units had a total grant-date fair value of $101 million based upon a grant-date fair value per share of $2,033.79 . 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, 2020, assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. At December 31, 2018 , the estimated number of probable shares to be issued is a total of 86,438 shares, net of performance share units that were forfeited or vested since the grant date, including 34,509 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 91,638 total shares could be issued. 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 grant-date fair value per share of $1,735.10 . The actual number of shares to be issued will be determined based 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 December 31, 2018 , there were 60,963 unvested 2017 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. At December 31, 2018 , the number of shares estimated to be issued pursuant to these performance share units at the end of the performance period is a total of 90,151 shares, including 47,706 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 121,926 total shares could be issued pursuant to these performance share units. 2016 Performance Share Units During the year ended December 31, 2016, the Company granted 85,735 performance share units with a grant-date fair value of $112 million , based on a weighted-average grant-date fair value per share of $ 1,302.25 . At December 31, 2018 , there were 63,230 unvested 2016 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. At December 31, 2018 , the number of shares estimated to be issued pursuant to these performance share units in 2019 is 103,076 shares. Stock Options All outstanding employee stock options were assumed in acquisitions. The following table summarizes the activity for stock options during the years ended December 31, 2016 , 2017 and 2018 : Employee Stock Options Number of Shares Weighted-Average Exercise Price Aggregate Intrinsic Value (in millions) Weighted-Average Remaining Contractual Term (in years) Balance, December 31, 2015 89,104 $ 383.03 $ 79 5.4 Exercised (38,150 ) $ 404.40 Forfeited (1,971 ) $ 241.65 Balance, December 31, 2016 48,983 $ 372.07 $ 54 4.4 Exercised (17,359 ) $ 294.45 Forfeited (949 ) $ 837.09 Balance, December 31, 2017 30,675 $ 401.61 $ 41 3.9 Exercised (3,318 ) $ 494.66 Forfeited (94 ) $ 450.84 Balance, December 31, 2018 27,263 $ 386.97 $ 36 2.8 Vested and exercisable at December 31, 2018 27,190 $ 398.69 $ 36 2.8 Vested and exercisable at December 31, 2018 and expected to vest thereafter 27,263 $ 386.97 $ 36 2.8 The aggregate intrinsic value of employee stock options exercised during the years ended December 31, 2018 , 2017 and 2016 was $5 million , $26 million and $35 million , respectively. During the years ended December 31, 2018 , 2017 and 2016 , stock options vested for 98 , 1,515 and 12,180 shares, respectively.

INVESTMENTS

INVESTMENTS	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	INVESTMENTS Short-term and Long-term Investments in Marketable Securities See Note 2 for the Company's accounting policy related to its investments in marketable debt and equity securities. 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 Certificate 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 Investments in Ctrip: Convertible debt securities 1,275 — (98 ) 1,177 Equity securities 655 2 (72 ) 585 Meituan Dianping equity securities 450 1 — 451 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 December 31, 2018 , the weighted-average life of the Company’s fixed income investment portfolio, excluding the Company's investment in Ctrip convertible debt securities, was approximately 1.2 years with an average credit quality of A+/A1/A+. The Company invests in international government securities with high credit quality. At December 31, 2018 , investments in international government securities principally included debt securities issued by the governments of the Netherlands, France, Belgium, Austria, Germany and Finland. At December 31, 2018 , the Company does not consider any of its investments in marketable debt securities to be other-than-temporarily impaired. The following table summarizes, by major security type, the Company's investments in marketable securities at December 31, 2017 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 725 $ — $ — $ 725 U.S. government securities 996 — (2 ) 994 Corporate debt securities 3,068 1 (5 ) 3,064 U.S. government agency securities 4 — — 4 Commercial paper 73 — — 73 Total $ 4,866 $ 1 $ (7 ) $ 4,860 Long-term investments in marketable securities: Debt securities: International government securities $ 607 $ 2 $ (1 ) $ 608 U.S. government securities 845 — (10 ) 835 Corporate debt securities 6,690 8 (42 ) 6,656 Investments in Ctrip: Convertible debt securities 1,275 103 (9 ) 1,369 Equity securities 655 300 (1 ) 954 Total $ 10,072 $ 413 $ (63 ) $ 10,422 Investments in Ctrip In May 2015 and August 2014, the Company invested $250 million and $500 million , respectively, in five -year senior convertible notes issued at par value by Ctrip. In December 2015, the Company invested $500 million in a Ctrip ten -year senior convertible note issued at par value, which included a put option allowing the Company, at its option, to require a prepayment in cash from Ctrip at the end of the sixth year of the note. In September 2016, the Company invested $25 million in a Ctrip six -year senior convertible note issued at par value, which included a put option allowing the Company, at its option, to require prepayment in cash from Ctrip at the end of the third year of the note. The Company determined that the economic characteristics and risks of the put option are clearly and closely related to the note, and therefore did not meet the requirement for separate accounting as embedded derivatives. The Company evaluated the conversion features for all Ctrip senior convertible notes and only the conversion feature associated with the September 2016 investment met the definition of an embedded derivative (see Note 5 ). The Company monitors the conversion features of these notes to determine whether they meet the definition of an embedded derivative during each reporting period. The Ctrip convertible notes have been marked-to-market in accordance with the accounting guidance for available-for-sale securities. At December 31, 2018 , the Company had also invested $655 million in Ctrip American Depositary Shares ("ADSs"). At December 31, 2018 , 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. As a result of Meituan Dianping's initial public offering in September 2018, the Company classified its investment as a marketable equity security (see the table above that summarizes the Company's investments in marketable securities at December 31, 2018 ) and recognized an unrealized gain of $1 million for the year ended December 31, 2018 , which was included in "Net unrealized losses on marketable equity securities" in the Consolidated Statement of Operations. At December 31, 2018 , 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 and $451 million at December 31, 2018 and 2017 , respectively. The investments of $451 million at December 31, 2017 principally related to the Company's investment in Meituan Dianping prior to its initial public offering in September 2018. In July 2018, the Company invested $500 million 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 changes were required to the carrying value of these investments at December 31, 2018 . For the years ended December 31, 2017 and 2016, the Company recognized an impairment of $8 million and $63 million , respectively, to write off its investments in certain private companies. Other Long-term Investments The Company held an investment of $200 million in preferred shares of Grab, a leading on-demand transportation and mobile service platform in Southeast Asia, which is included in "Long-term investments" in the Company's Consolidated Balance Sheet at December 31, 2018 . The preferred shares are convertible to ordinary shares at the Company’s option and are mandatorily convertible upon an initial public offering. The preferred shares also contain a redemption feature that can be exercised by the Company after June 2023. These features have been evaluated as embedded derivatives, however, they do not meet the requirements to be accounted for separately. The investment is classified as a debt security for accounting purposes and categorized as available-for-sale. The investment is reported at estimated fair value with the aggregate unrealized gains and losses, net of taxes, reflected as a part of " Accumulated other comprehensive income (loss) " in the Consolidated Balance Sheet.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Financial assets carried at fair value at December 31, 2018 are classified in the categories described in the tables below (in millions): Level 1 Level 2 Level 3 Total ASSETS: 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 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 Certificate 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 Ctrip equity securities 585 — — 585 Meituan Dianping equity securities 451 — — 451 Other long-term investment — — 200 200 Derivatives: Currency exchange derivatives — 4 — 4 Total assets at fair value $ 3,123 $ 10,358 $ 200 $ 13,681 Financial assets carried at fair value at December 31, 2017 are classified in the categories described in the tables below (in millions): Level 1 Level 2 Total ASSETS: Cash and restricted cash equivalents: Money market funds $ 1,895 $ — $ 1,895 U.S. government securities — 22 22 Corporate debt securities — 7 7 Commercial paper — 96 96 Time deposits 18 — 18 Short-term investments in marketable securities: International government securities — 725 725 U.S. government securities — 994 994 Corporate debt securities — 3,064 3,064 U.S. government agency securities — 4 4 Commercial paper — 73 73 Long-term investments in marketable securities: International government securities — 608 608 U.S. government securities — 835 835 Corporate debt securities — 6,656 6,656 Ctrip convertible debt securities — 1,369 1,369 Ctrip equity securities 954 — 954 Derivatives: Currency exchange derivatives — 2 2 Total assets at fair value $ 2,867 $ 14,455 $ 17,322 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 4 for information on the carrying value of the Company's investments in marketable securities. The investment in Grab, reported at a fair value of $200 million at December 31, 2018, is considered a "Level 3" valuation and measured using management's estimates that incorporate current market participant expectations of future cash flows considered alongside other relevant information. The Company's derivative instruments are valued using pricing models. Pricing models take into account the contract terms as well as multiple inputs where applicable, such as interest rate yield curves, option volatility and currency rates. Derivatives are considered "Level 2 " fair value measurements. The Company's derivative instruments are typically short-term in nature. At December 31, 2018 and 2017 , 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 10 for the estimated fair value of the Company's outstanding Senior Notes and Note 18 for the Company's contingent liability associated with a business acquisition. 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. See Note 2 for the Company's accounting policy on derivative financial instruments. 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 December 31, 2018 and 2017 , 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 losses of $44 million , foreign currency gains of $45 million and foreign currency losses of $16 million for the years ended December 31, 2018 , 2017 and 2016 , 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 $47 million , $27 million and $14 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The net impacts related to these derivatives are reported in "Foreign currency transactions and other" in the Consolidated Statements of Operations. The settlement of derivative contracts not designated as hedging instruments resulted in net cash outflow of $56 million for the year ended December 31, 2018 and net cash inflows of $41 million and $5 million for the years ended December 31, 2017 and 2016 , respectively, and are reported within "Net cash provided by operating activities" in the Consolidated Statements of Cash Flows. Embedded Derivative — In September 2016, the Company invested $25 million in a Ctrip convertible note (see Note 4 ). The Company determined that the conversion option for this note met the definition of an embedded derivative that required separate accounting. At December 31, 2018 and 2017 , the embedded derivative had an estimated fair value of $0.1 million and $2 million , respectively, and is reported in the Consolidated Balance Sheets with its host contract in "Long-term investments." The embedded derivative is bifurcated for fair value measurement purposes only. The mark-to-market adjustments are included in "Foreign currency transactions and other" in the Company's Consolidated Statements of Operations.

ACCOUNTS RECEIVABLE RESERVES

ACCOUNTS RECEIVABLE RESERVES	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
ACCOUNTS RECEIVABLE RESERVES	ACCOUNTS RECEIVABLE RESERVES The Company records a provision for uncollectible commissions and chargebacks related to disputed credit card payments. Changes in accounts receivable reserves consisted of the following (in millions): For the Year Ended December 31, 2018 2017 2016 Balance, beginning of year $ 39 $ 26 $ 15 Provision charged to expense 163 62 46 Charge-offs and adjustments (139 ) (52 ) (35 ) Currency translation adjustments (2 ) 3 — Balance, end of year $ 61 $ 39 $ 26

NET INCOME PER SHARE

NET INCOME PER SHARE	12 Months Ended
	Dec. 31, 2018
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): For the Year Ended December 31, 2018 2017 2016 Weighted-average number of basic common shares outstanding 47,446 48,994 49,491 Weighted-average dilutive stock options, restricted stock units and performance share units 236 295 238 Assumed conversion of Convertible Senior Notes 335 665 334 Weighted-average number of diluted common and common equivalent shares outstanding 48,017 49,954 50,063 Anti-dilutive potential common shares 1,411 1,864 2,443 Anti-dilutive potential common shares for the years ended December 31, 2018 , 2017 and 2016 include approximately 1 million shares, 1 million shares and 2 million shares, respectively, 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.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment at December 31, 2018 and 2017 consisted of the following (in millions): 2018 2017 Estimated Computer equipment and software $ 964 $ 769 2 to 5 years Leasehold improvements 242 199 1 to 13 years Office equipment, furniture and fixtures 55 47 2 to 7 years Building construction-in-progress 88 8 Total 1,349 1,023 Less: accumulated depreciation (693 ) (543 ) Property and equipment, net $ 656 $ 480 Depreciation expense was $248 million , $187 million and $140 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS AND GOODWILL	INTANGIBLE ASSETS AND GOODWILL The Company's intangible assets at December 31, 2018 and 2017 consisted of the following (in millions): December 31, 2018 December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Amortization Supply and distribution agreements $ 1,099 $ (408 ) $ 691 $ 1,057 $ (355 ) $ 702 3 - 20 years Technology 173 (121 ) 52 137 (104 ) 33 1 - 7 years Patents 2 (2 ) — 2 (2 ) — 15 years Internet domain names 41 (30 ) 11 42 (29 ) 13 5 - 20 years Trade names 1,810 (439 ) 1,371 1,779 (350 ) 1,429 4 - 20 years Non-compete agreements 1 (1 ) — 22 (22 ) — 4 years Total intangible assets $ 3,126 $ (1,001 ) $ 2,125 $ 3,039 $ (862 ) $ 2,177 Intangible assets are amortized on a straight-line basis. Amortization expense was $178 million , $176 million and $169 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The annual estimated amortization expense for intangible assets for the next five years and thereafter is expected to be as follows (in millions): 2019 $ 174 2020 166 2021 158 2022 156 2023 154 Thereafter 1,317 $ 2,125 A roll-forward of goodwill for the years ended December 31, 2018 and 2017 consisted of the following (in millions): 2018 2017 Balance, beginning of year $ 2,738 $ 2,397 Acquisitions 212 294 Currency translation adjustments (40 ) 47 Balance, end of year $ 2,910 $ 2,738 A substantial portion of the Company's intangibles and goodwill relates to the acquisition of OpenTable in July 2014 and KAYAK in May 2013. At September 30, 2018 , the Company performed its annual goodwill impairment testing and concluded that there was no impairment of goodwill. Since the annual impairment test, there have been no events or changes in circumstances to indicate a potential impairment to the Company's goodwill. In addition, the Company did not identify an impairment indicator for the Company's other long-lived assets and intangible assets at December 31, 2018 . For the year ended December 31, 2016 , the Company recognized a non-cash impairment charge for goodwill related to OpenTable of $941 million , which was not tax deductible.

DEBT

DEBT	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Short-term Borrowing On December 31, 2018 , the Company had a bank overdraft of $25 million which was reported in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheet at December 31, 2018 and was repaid in January 2019. Revolving Credit Facility In June 2015, the Company entered into a $2.0 billion five -year unsecured revolving credit facility with a group of lenders. Borrowings under the revolving credit facility will bear interest, at the Company’s option, at a rate per annum equal to either (i) the adjusted London Inter-bank Offered Rate ("LIBOR") for the interest period in effect for such borrowing plus an applicable margin ranging from 0.875% to 1.50% ; or (ii) the greatest of (a) Bank of America, N.A.'s prime lending rate, (b) the federal funds rate plus 0.50% , and (c) an adjusted LIBOR for an interest period of one month plus 1.00% , plus an applicable margin ranging from 0.00% to 0.50% . Undrawn balances available under the revolving credit facility are subject to commitment fees at the applicable rate ranging from 0.085% to 0.20% . The revolving credit facility provides for the issuance of up to $70 million of letters of credit as well as borrowings of up to $50 million on same-day notice, referred to as swingline loans. Borrowings under the revolving credit facility may be made in U.S. Dollars, Euros, British Pounds Sterling and any other foreign currency agreed to by the lenders. The proceeds of loans made under the facility would be used for working capital and general corporate purposes, which could include acquisitions, share repurchases or debt repayments. There were no borrowings outstanding and $5 million and $4 million of letters of credit issued under the facility, respectively, at December 31, 2018 and December 31, 2017 . In January 2019, the Company borrowed $100 million , which is due on March 29, 2019 with an interest rate of 3.5% , under this revolving credit facility. Outstanding Debt Outstanding debt at December 31, 2018 consisted of the following (in millions): December 31, 2018 Outstanding Principal Amount Unamortized Debt 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 Outstanding debt at December 31, 2017 consisted of the following (in millions): December 31, 2017 Outstanding Principal Amount Unamortized Debt Carrying Value Short-term debt: 1.0% Convertible Senior Notes due March 2018 $ 714 $ (3 ) $ 711 Long-term debt: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (65 ) $ 935 0.9% Convertible Senior Notes due September 2021 1,000 (83 ) 917 0.8% (€1 Billion) Senior Notes due March 2022 1,201 (6 ) 1,195 2.15% (€750 Million) Senior Notes due November 2022 900 (5 ) 895 2.75% Senior Notes due March 2023 500 (3 ) 497 2.375% (€1 Billion) Senior Notes due September 2024 1,201 (12 ) 1,189 3.65% Senior Notes due March 2025 500 (3 ) 497 3.6% Senior Notes due June 2026 1,000 (7 ) 993 1.8% (€1 Billion) Senior Notes due March 2027 1,201 (5 ) 1,196 3.55% Senior Notes due March 2028 500 (4 ) 496 Total long-term debt $ 9,003 $ (193 ) $ 8,810 Based on the closing price of the Company's common stock for the prescribed measurement periods for the three months ended December 31, 2018 and 2017 , the contingent conversion thresholds on the 2020 Notes (as defined below) and 2021 Notes (as defined below) were not exceeded; therefore, these notes were not convertible at the option of the holder and were reported as non-current liabilities in the Consolidated Balance Sheets. The 2018 Notes (as defined below) became convertible on December 15, 2017, at the option of the holders, and remained convertible until the scheduled trading day immediately preceding the maturity date of March 15, 2018. Therefore, at December 31, 2017, the Company reported the carrying value of the 2018 Notes as a current liability and reclassified the unamortized debt discount for the 2018 Notes in the amount of $3 million before tax from additional paid-in-capital to convertible debt in the mezzanine section in the Consolidated Balance Sheet at that date. Fair Value of Debt At December 31, 2018 and 2017 , the estimated fair value of the outstanding Senior Notes was approximately $9.3 billion and $11.1 billion , respectively, and was considered a "Level 2 " fair value measurement (see Note 5 ). Fair value was estimated based upon actual trades at the end of the reporting period or the most recent trade available as well as the Company's stock price at the end of the reporting period. A substantial portion of the market value of the Company's debt in excess of the outstanding principal amount relates to the conversion premium on the Convertible Senior Notes. Convertible Debt 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 estimated its straight debt borrowing rate, considering its credit rating and straight debt of comparable corporate issuers. Description of Convertible Senior Notes In August 2014, the Company issued in a private placement $1.0 billion aggregate principal amount of Convertible Senior Notes due September 15, 2021, with an interest rate of 0.9% (the "2021 Notes"). The Company paid $11 million in debt issuance costs during the year ended December 31, 2014, related to this offering. The 2021 Notes are convertible, subject to certain conditions, into the Company's common stock at a conversion price of $2,055.50 per share. The 2021 Notes are convertible, at the option of the holder, prior to September 15, 2021, upon the occurrence of specific events, including but not limited to a change in control, or if the closing sales price of the Company's common stock for at least 20 trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is more than 150% of the conversion price in effect for the notes on the last trading day of the immediately preceding quarter. In the event that all or substantially all of the Company's common stock is acquired on or prior to the maturity of the 2021 Notes in a transaction in which the consideration paid to holders of the Company's common stock consists of all or substantially all cash, the Company would be required to make additional payments in the form of additional shares of common stock to the holders of the 2021 Notes in an aggregate value ranging from $0 to $375 million depending upon the date of the transaction and the then current stock price of the Company. At June 15, 2021, holders will have the right to convert all or any portion of the 2021 Notes, regardless of the Company's stock price. The 2021 Notes may not be redeemed by the Company prior to maturity. The holders may require the Company to repurchase the 2021 Notes for cash in certain circumstances. Interest on the 2021 Notes is payable on March 15 and September 15 of each year. In May 2013, the Company issued in a private placement $1.0 billion aggregate principal amount of Convertible Senior Notes due June 15, 2020, with an interest rate of 0.35% (the "2020 Notes"). The 2020 Notes were issued with an initial discount of $20 million . The Company paid $1 million in debt issuance costs during the year ended December 31, 2013, related to this offering. The 2020 Notes are convertible, subject to certain conditions, into the Company's common stock at a conversion price of $1,315.10 per share. The 2020 Notes are convertible, at the option of the holder, prior to June 15, 2020, upon the occurrence of specific events, including but not limited to a change in control, or if the closing sales price of the Company's common stock for at least 20 trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is more than 150% of the conversion price in effect for the notes on the last trading day of the immediately preceding quarter. In the event that all or substantially all of the Company's common stock is acquired on or prior to the maturity of the 2020 Notes in a transaction in which the consideration paid to holders of the Company's common stock consists of all or substantially all cash, the Company would be required to make additional payments in the form of additional shares of common stock to the holders of the 2020 Notes in an aggregate value ranging from $0 to $397 million depending upon the date of the transaction and the then current stock price of the Company. At March 15, 2020, holders will have the right to convert all or any portion of the 2020 Notes, regardless of the Company's stock price. The 2020 Notes may not be redeemed by the Company prior to maturity. The holders may require the Company to repurchase the 2020 Notes for cash in certain circumstances. Interest on the 2020 Notes is payable on June 15 and December 15 of each year. In March 2012, the Company issued in a private placement $1.0 billion aggregate principal amount of Convertible Senior Notes due March 15, 2018, with an interest rate of 1.0% (the "2018 Notes"). The 2018 Notes were convertible, subject to certain conditions, into the Company's common stock at a conversion price of $944.61 per share. In March 2018, in connection with the maturity of the remaining outstanding 2018 Notes, the Company paid $714 million to satisfy the aggregate principal amount due and paid an additional $773 million in satisfaction of the conversion value in excess of the principal amount. Cash-settled convertible debt, such as the Company's Convertible Senior Notes, is separated into debt and equity components at issuance and each component is assigned a value. The value assigned to the debt component is the estimated fair value, at the issuance date, of a similar bond without the conversion feature. The difference between the bond cash proceeds and this estimated fair value, representing the value assigned to the equity component, is recorded as a debt discount. Debt discount is amortized using the effective interest rate method over the period from the origination date through the stated maturity date. The Company estimated the straight debt borrowing rates at debt origination to be 3.18% for the 2021 Notes, 3.13% for the 2020 Notes and 3.50% for the 2018 Notes. The yield to maturity was estimated at an at-market coupon priced at par. Debt discount after tax of $83 million ( $143 million before tax) related to the 2021 Notes, $92 million ( $154 million before tax) related to the 2020 Notes and $81 million ( $135 million before tax) related to the 2018 Notes less financing costs associated with the equity component of the respective convertible notes was recorded in additional paid-in capital in the Consolidated Balance Sheets at debt origination. For the years ended December 31, 2018 , 2017 and 2016 , the Company recognized interest expense of $66 million , $94 million and $95 million , respectively, related to convertible notes, which was comprised of $14 million , $21 million and $22 million , respectively, related to the contractual coupon interest, $50 million , $68 million and $68 million , respectively, related to the amortization of debt discount and $2 million , $5 million and $5 million , respectively, related to the amortization of debt issuance costs. For the years ended December 31, 2018 , 2017 and 2016 , included in the amortization of debt discount mentioned above was $3 million of original issuance discount related to the 2020 Notes for each period. The remaining period for amortization of debt discount and debt issuance costs is the period until the stated maturity date for the respective debt. The weighted-average effective interest rates for the years ended December 31, 2018 , 2017 and 2016 are 3.2% , 3.4% and 3.4% , respectively. Other Long-term Debt In August 2017, the Company issued Senior Notes due March 15, 2023, with an interest rate of 2.75% (the "2023 Notes") for an aggregate principal amount of $500 million . The 2023 Notes were issued with an initial discount of $1 million . In addition, the Company paid $3 million in debt issuance costs during the year ended December 31, 2017. Interest on the 2023 Notes is payable semi-annually on March 15 and September 15. In August 2017, the Company issued Senior Notes due March 15, 2028, with an interest rate of 3.55% (the "2028 Notes") for an aggregate principal amount of $500 million . The 2028 Notes were issued with an initial discount of $0.4 million . In addition, the Company paid $3 million in debt issuance costs during the year ended December 31, 2017. Interest on the 2028 Notes is payable semi-annually on March 15 and September 15. In March 2017, the Company issued Senior Notes due March 10, 2022, with an interest rate of 0.8% (the "March 2022 Notes") for an aggregate principal amount of 1.0 billion Euros. The March 2022 Notes were issued with an initial discount of 2 million Euros. In addition, the Company paid $5 million in debt issuance costs during the year ended December 31, 2017. Interest on the March 2022 Notes is payable annually on March 10. Subject to certain limited exceptions, all payments of interest and principal for the March 2022 Notes will be made in Euros. In May 2016, the Company issued Senior Notes due June 1, 2026, with an interest rate of 3.6% (the "2026 Notes") for an aggregate principal amount of $1.0 billion . The 2026 Notes were issued with an initial discount of $2 million . In addition, the Company paid $6 million in debt issuance costs during the year ended December 31, 2016. Interest on the 2026 Notes is payable semi-annually on June 1 and December 1. In November 2015, the Company issued Senior Notes due November 25, 2022, with an interest rate of 2.15% (the "November 2022 Notes") for an aggregate principal amount of 750 million Euros. The November 2022 Notes were issued with an initial discount of 2 million Euros. In addition, the Company paid $4 million in debt issuance costs during the year ended December 31, 2015. Interest on the November 2022 Notes is payable annually on November 25. Subject to certain limited exceptions, all payments of interest and principal, including payments made upon any redemption of the November 2022 Notes will be made in Euros. In March 2015, the Company issued Senior Notes due March 15, 2025, with an interest rate of 3.65% (the "2025 Notes") for an aggregate principal amount of $500 million . The 2025 Notes were issued with an initial discount of $1 million . In addition, the Company paid $3 million in debt issuance costs during the year ended December 31, 2015. Interest on the 2025 Notes is payable semi-annually on March 15 and September 15. In March 2015, the Company issued Senior Notes due March 3, 2027, with an interest rate of 1.8% (the "2027 Notes") for an aggregate principal amount of 1.0 billion Euros. The 2027 Notes were issued with an initial discount of 0.3 million Euros. In addition, the Company paid $6 million in debt issuance costs during the year ended December 31, 2015. Interest on the 2027 Notes is payable annually on March 3. Subject to certain limited exceptions, all payments of interest and principal for the 2027 Notes will be made in Euros. In September 2014, the Company issued Senior Notes due September 23, 2024, with an interest rate of 2.375% (the "2024 Notes") for an aggregate principal amount of 1.0 billion Euros. The 2024 Notes were issued with an initial discount of 9 million Euros. In addition, the Company paid $7 million in debt issuance costs during the year ended December 31, 2014. Interest on the 2024 Notes is payable annually on September 23. Subject to certain limited exceptions, all payments of interest and principal, including payments made upon any redemption of the 2024 Notes, will be made in Euros. The aggregate principal value of the March 2022 Notes, November 2022 Notes, 2024 Notes and 2027 Notes and accrued interest thereon are designated as a hedge of the Company's net investment in certain Euro functional currency subsidiaries. The foreign currency transaction gains or losses on these liabilities are measured based upon changes in spot rates and are recorded in " Accumulated other comprehensive income (loss) " in the Consolidated Balance Sheets. The Euro-denominated net assets of these subsidiaries are translated into U.S. Dollars at each balance sheet date, with the effects of foreign currency changes also reported in " Accumulated other comprehensive income (loss) " in the Consolidated Balance Sheets. Since the notional amount of Euro-denominated debt and related interest are not greater than the notional amount of the Company's net investment, the Company does not expect to incur any ineffectiveness on this hedge. 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 2.78% for the 2023 Notes, 3.56% for the 2028 Notes, 0.84% for the March 2022 Notes, 3.62% for the 2026 Notes, 2.20% for the November 2022 Notes, 3.68% for the 2025 Notes, 1.80% for the 2027 Notes and 2.48% for the 2024 Notes. For the years ended December 31, 2018 , 2017 and 2016 , the Company recognized interest expense of $170 million , $145 million and $108 million , respectively, related to other long-term debt, which was almost entirely comprised of $163 million , $139 million and $104 million , respectively, related to the contractual coupon interest. The remaining interest expense relates to the amortization of debt discount and debt issuance costs. The remaining period for amortization of debt discount and debt issuance costs is the period until the stated maturity dates for the respective debt. On July 24, 2017, the Company assumed third-party senior debt of $15 million associated with the acquisition of the Momondo Group. The debt was repaid by the Company in July 2017.

TREASURY STOCK

TREASURY STOCK	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
TREASURY STOCK	TREASURY STOCK At December 31, 2017 , the Company had a total remaining authorization of $2.4 billion to repurchase its common stock related to programs authorized by the Company's Board of Directors in 2016 and 2017 for $3.0 billion and $2.0 billion , respectively. In the first quarter of 2018, the Company's Board of Directors authorized an additional program to repurchase up to $8.0 billion of the Company's common stock. At December 31, 2018 , the Company had a remaining authorization of $4.5 billion to repurchase its common stock. In 2019, the Company has continued to make repurchases of its common stock and the Company may continue to make repurchases of shares under its stock repurchase programs, 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 years ended December 31, 2018, 2017 and 2016, respectively (in millions, except for shares): 2018 2017 2016 Shares Amount Shares Amount Shares Amount Authorized stock repurchase programs 3,020,561 $ 5,850 968,521 $ 1,744 635,877 $ 861 General authorization for shares withheld on stock award vesting 79,746 162 57,369 100 127,107 167 Total 3,100,307 $ 6,012 1,025,890 $ 1,844 762,984 $ 1,028 Shares repurchased in December and settled in following January 42,939 $ 74 18,217 $ 32 10,215 $ 15 For the years ended December 31, 2018 , 2017 and 2016 , the Company remitted $163 million , $101 million and $166 million of employee withholding taxes, respectively, to the tax authorities, which is different from the aggregate cost of the shares withheld for taxes for each year due to the timing in remitting the taxes. The cash remitted to the tax authorities is included in financing activities in the Consolidated Statements of Cash Flows. At December 31, 2018 , there were 17,317,126 shares of the Company's common stock held in treasury.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	12 Months Ended
	Dec. 31, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The table below provides the balances for each classification of accumulated other comprehensive income (loss) at December 31, 2018 and 2017 (in millions): December 31, 2018 December 31, 2017 Foreign currency translation adjustments, net of tax (1) $ (129 ) $ (15 ) Net unrealized gains on marketable securities, net of tax: Net unrealized gains on marketable equity securities, net of tax (2) — 241 Net unrealized (losses) gains on marketable debt securities, net of tax (3) (187 ) 12 Accumulated other comprehensive income (loss) $ (316 ) $ 238 (1) Foreign currency translation adjustments, net of tax, at December 31, 2018 and 2017 , include accumulated net losses from fair value adjustments of $35 million after tax ( $53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. Foreign currency translation adjustments, net of tax, include foreign currency transaction losses of $26 million after tax ( $20 million before tax) and $190 million after tax ( $237 million before tax) at December 31, 2018 and 2017 , respectively, associated with the Company's Euro-denominated debt. The Company's Euro-denominated debt is designated as a hedge against the impact of currency fluctuations on its Euro-denominated net assets (see Note 10 ). The remaining balance in foreign currency translation adjustments relates to the cumulative impacts of currency fluctuations on the Company's non-U.S. Dollar denominated net assets. During the year ended December 31, 2018 , the Company recorded a tax benefit of $41 million related to its one-time deemed repatriation tax liability recorded at December 31, 2017 and current year foreign earnings subject to U.S. federal and state income tax, resulting from the introduction of the Tax Act. Prior to January 1, 2018, foreign currency translation adjustments excluded U.S. federal and state income taxes as a result of the Company's intention to indefinitely reinvest the earnings of its international subsidiaries outside of the United States. (2) Net unrealized gains on marketable equity securities, net of tax, at December 31, 2017 related to changes in the fair value of the Company's investment in Ctrip equity securities (see Note 4 ). Net unrealized gains before tax on equity securities at December 31, 2017 were $299 million , of which unrealized gains of $320 million were not subject to income tax in the Netherlands. Unrealized losses of $21 million were taxable at a 25% tax rate in the Netherlands, which resulted in a tax benefit of $5 million at December 31, 2017. The Company also recorded U.S. tax charges of $63 million at December 31, 2017 related to these investments. The Company reclassified the net unrealized gains, net of tax, on its investment in Ctrip equity securities at December 31, 2017 from accumulated other comprehensive income to retained earnings upon the adoption of the accounting update on financial instruments as of January 1, 2018. Changes in fair value subsequent to January 1, 2018 are recognized in net income (see Note 2 ). (3) Net unrealized losses before tax on marketable debt securities of $276 million and $86 million at December 31, 2018 and 2017 , respectively, were not subject to income tax in the Netherlands. Unrealized gains before tax of $123 million and $130 million at December 31, 2018 and 2017, respectively, were taxable at a 25% tax rate in the Netherlands, resulting in tax charges of $30 million and $32 million at December 31, 2018 and 2017 , respectively. The remaining net unrealized losses on marketable securities and related tax benefits at December 31, 2018 were associated with marketable debt securities held by a U.S. subsidiary.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES International pre-tax income was $4.8 billion , $4.5 billion and $3.7 billion for the years ended December 31, 2018 , 2017 and 2016 , respectively. U.S. pre-tax income was $47 million for the year ended December 31, 2018 , and U.S. pre-tax losses were $122 million and $983 million for the years ended December 31, 2017 and 2016 , respectively. Provision for Income Taxes The income tax expense (benefit) for the year ended December 31, 2018 is as follows (in millions): Current Deferred Total International $ 887 $ (3 ) $ 884 U.S. Federal 45 (107 ) (62 ) U.S. State 55 (40 ) 15 Total $ 987 $ (150 ) $ 837 The income tax expense (benefit) for the year ended December 31, 2017 is as follows (in millions): Current Deferred Total International $ 756 $ (10 ) $ 746 U.S. Federal 1,327 (57 ) 1,270 U.S. State 7 35 42 Total $ 2,090 $ (32 ) $ 2,058 The income tax expense (benefit) for the year ended December 31, 2016 is as follows (in millions): Current Deferred Total International $ 627 $ (14 ) $ 613 U.S. Federal 64 (33 ) 31 U.S. State (1 ) (65 ) (66 ) Total $ 690 $ (112 ) $ 578 The U.S. pre-tax loss is lower for the year ended December 31, 2017 compared to the year ended December 31, 2016 primarily due to the impairment charge for goodwill related to OpenTable of $941 million (see Note 9 ) recognized in 2016. Income tax expense on the Company's U.S. pre-tax loss for the year ended December 31, 2017 includes the impact of the Tax Act as disclosed below. U.S. Tax Reform In December 2017, the Tax Act was enacted into law in the United States. The Tax Act made significant changes to U.S. federal tax law, including a reduction in the U.S. federal statutory tax rate from 35% to 21% , effective January 1, 2018. The Tax Act imposed a one-time deemed repatriation tax on accumulated unremitted international earnings, to be paid over eight years. The Company recorded provisional income tax expense of approximately $1.6 billion during the year ended December 31, 2017 in accordance with Staff Accounting Bulletin No. 118 ("SAB 118"), which included U.S. state income taxes and international withholding taxes, related to the mandatory deemed repatriation of estimated accumulated international earnings of approximately $16.5 billion . The Company also recorded a provisional net income tax benefit of $217 million during the year ended December 31, 2017 related to the remeasurement of the Company’s U.S. deferred tax assets and liabilities due to the reduction of the U.S. federal statutory rate from 35% to 21% . The Company expected to use approximately $204 million of deferred tax assets related to federal net operating loss carryforwards ("NOLs") and approximately $46 million of other tax credit carryforwards, and accordingly, reduced the transition tax liability to approximately $1.3 billion , which is presented as "Long-term U.S. transition tax liability" in the Consolidated Balance Sheet as of December 31, 2017. In 2018, the Company completed its accounting for the income tax effects of the Tax Act. The Company recorded an income tax benefit of $46 million to adjust its provisional income tax expense that was recorded during the year ended December 31, 2017 relating to the federal one-time deemed repatriation liability, as well as U.S. state income taxes and international withholding taxes associated with the mandatory deemed repatriation. In addition, the Company recorded an income tax benefit of $2 million in 2018 to adjust the remeasurement of its U.S. deferred tax assets and liabilities due to the reduction of the U.S. federal statutory tax rate that resulted from the Tax Act. The Company utilized $133 million of deferred tax assets related to federal NOLs and $23 million of other tax credit carryforwards to reduce its transition tax liability. Under the Tax Act, the Company's international cash and investments as of December 31, 2017, amounting to $16.2 billion , as well as future cash generated by our international operations, generally can be repatriated without further U.S. federal income tax, but will be subject to U.S. state income taxes and international withholding taxes, which have been accrued by the Company. The Tax Act also introduced in 2018 a tax on 50% of GILTI, which is income determined to be in excess of a specified routine rate of return, and a base erosion and anti-abuse tax (“BEAT”) aimed at preventing the erosion of the U.S. tax base. The Company has adopted an accounting policy to treat taxes on GILTI as period costs. Deferred Income Taxes The Company utilized $379 million of its U.S. NOLs available at December 31, 2016 to reduce its federal tax liability for the deemed repatriation tax. After utilization of available NOLs, at December 31, 2018, the Company had U.S. federal NOLs of $136 million , which are subject to an annual limitation and mainly expire from December 31, 2020 to December 31, 2021, and U.S. state NOLs of $484 million , which mainly expire between December 31, 2020 and December 31, 2034. In addition, at December 31, 2018 , the Company has $132 million of non-U.S. NOLs, of which $50 million expires between December 31, 2020 and December 31, 2024 , and $51 million of U.S. research tax credit and alternative minimum tax carryforwards available to reduce future tax liabilities, the majority of which do not have an expiration date. The utilization of these NOLs, allowances and credits is dependent upon the Company's ability to generate sufficient future taxable income and the tax laws in the jurisdictions where the losses were generated. The Company periodically evaluates the likelihood of the realization of deferred tax assets, and reduces the carrying amount of these deferred tax assets by a valuation allowance to the extent it believes a portion 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 tax effects of temporary differences that give rise to significant portions of deferred tax assets and liabilities at December 31, 2018 and 2017 are as follows (in millions): 2018 2017 Deferred tax assets/(liabilities): Net operating loss carryforward — U.S. $ 59 $ 71 Net operating loss carryforward — International 20 28 Accrued expenses 50 57 Stock-based compensation and other stock based payments 51 48 Currency translation adjustment 27 — Tax credits 46 15 Euro-denominated debt 5 58 Property and equipment 6 9 Subtotal - deferred tax assets 264 286 Discount on convertible notes (22 ) (33 ) Intangible assets and other (482 ) (517 ) State income tax on accumulated unremitted international earnings (25 ) (37 ) Unrealized gain on investments (2 ) (70 ) Other (15 ) (25 ) Subtotal - deferred tax liabilities (546 ) (682 ) Valuation allowance on deferred tax assets (36 ) (44 ) Net deferred tax liabilities (1) $ (318 ) $ (440 ) (1) Includes deferred tax assets of $51 million and $41 million at December 31, 2018 and 2017 , respectively, reported in "Other assets" in the Consolidated Balance Sheets. The valuation allowance on deferred tax assets of $36 million at December 31, 2018 includes $20 million related to international operations and $16 million related to U.S. research credits, capital loss carryforwards and Connecticut NOLs. The valuation allowance on deferred tax assets of $44 million at December 31, 2017 includes $27 million related to international operations and $17 million related to U.S. research credits, capital loss carryforwards and Connecticut NOLs. Pursuant to the adoption of an accounting update on January 1, 2017 related to share-based compensation, the Company recorded a deferred tax asset of $301 million related to previously unrecognized U.S. equity tax deductions, with an offsetting cumulative-effect adjustment to retained earnings, the majority of which was utilized during the year ended December 31, 2017. The Company does not intend to indefinitely reinvest its international earnings that were subject to U.S. taxation pursuant to the mandatory deemed repatriation or subject to U.S. taxation as GILTI. Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate A significant portion of the Company's taxable earnings are generated in the Netherlands. According to Dutch corporate income tax law, income generated from qualifying innovative activities is taxed at a rate of 7% ("Innovation Box Tax") for periods beginning on or after January 1, 2018 rather than the Dutch statutory rate of 25% . Previously, the Innovation Box Tax rate had been 5%. A portion of Booking.com's earnings during the years ended December 31, 2018 , 2017 and 2016 qualifies for Innovation Box Tax treatment, which had a significant beneficial impact on the Company's effective tax rate for those years. The effective income tax rate of the Company is different from the amount computed using the expected U.S. statutory federal rate of 21% in 2018 and 35% in 2017 and 2016 as a result of the following items (in millions): 2018 2017 2016 Income tax expense at federal statutory rate $ 1,015 $ 1,539 $ 950 Adjustment due to: Foreign rate differential 210 (458 ) (378 ) Innovation Box Tax benefit (435 ) (397 ) (325 ) Impairment of goodwill and cost-method investment — — 344 Tax Act - Remeasurement of deferred tax balances (2 ) (217 ) — Tax Act - U.S. transition tax and other transition impacts (46 ) 1,563 — Other 95 28 (13 ) Income tax expense $ 837 $ 2,058 $ 578 Uncertain Tax Positions See Note 2 for the Company's accounting policy on uncertain tax positions. The following is a reconciliation of the total beginning and ending amount of unrecognized tax benefits (in millions): 2018 2017 2016 Unrecognized tax benefit — January 1 $ 32 $ 33 $ 43 Gross increases — tax positions in current period 1 5 2 Gross increases — tax positions in prior periods 19 5 1 Gross decreases — tax positions in prior periods (3 ) (9 ) — Reduction due to lapse in statute of limitations (2 ) (1 ) (9 ) Reduction due to settlements during the current period (2 ) (1 ) (4 ) Unrecognized tax benefit — December 31 $ 45 $ 32 $ 33 The unrecognized tax benefits are included in "Other long-term liabilities" and "Deferred income taxes" in the Consolidated Balance Sheets for the years ended December 31, 2018 and 2017 . The Company does not expect further significant changes in the amount of unrecognized tax benefits during the next twelve months. The Company's major taxing jurisdictions include: Netherlands, U.S. federal, Connecticut, California, New York, Massachusetts, Singapore and U.K. The statute of limitations that remain open related to these major tax jurisdictions are: the Company's Netherlands returns from 2014 and forward; the Company's Singapore returns from 2015 and forward; the Company's U.S. federal returns for 2012, 2013, 2015 and forward; the Company's Connecticut returns from 2011 to 2013 and from 2015 and forward; the Company's California returns for 2011 and forward; the Company's New York returns for 2011 to 2013 and from 2015 and forward; the Company's Massachusetts returns from 2012 to 2013, and from 2015 and forward and the Company's U.K. returns for the tax years 2015 and 2016. No income tax waivers have been executed that would extend the period subject to examination beyond the period prescribed by statute or for the periods just stated above in the major taxing jurisdictions in which the Company is a taxpayer. The Company’s 2015 U.S. federal income tax return is currently under audit by the Internal Revenue Service. See Note 14 for more information regarding tax contingencies.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES

BENEFIT PLANS

BENEFIT PLANS	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
BENEFIT PLANS	BENEFIT PLANS The Company maintains a defined contribution 401(k) savings plan (the "Plan") covering certain U.S. employees. In connection with acquisitions, effective at the date of such acquisitions, the Company assumed defined contribution plans covering the U.S. employees of the acquired companies. The Company also maintains certain other defined contribution plans outside of the United States for which it provides contributions for participating employees. The Company's matching contributions during the years ended December 31, 2018 , 2017 and 2016 were $22 million , $15 million and $10 million , respectively.

GEOGRAPHIC INFORMATION

GEOGRAPHIC INFORMATION	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
GEOGRAPHIC INFORMATION	GEOGRAPHIC AND DISAGGREGATED REVENUE INFORMATION 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 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): United States International Total Company The Netherlands Other 2018 Total Revenues (1) $ 1,626 (2) $ 11,094 $ 1,807 $ 14,527 (2) Intangible assets, net 1,747 30 348 2,125 Goodwill 1,938 246 726 2,910 Other long-lived assets 159 365 260 784 2017 Total Revenues $ 1,620 (3) $ 9,540 $ 1,521 $ 12,681 (3) Intangible assets, net 1,790 44 343 2,177 Goodwill 1,807 254 677 2,738 Other long-lived assets 124 254 208 586 2016 Total Revenues $ 1,680 (3) $ 7,783 $ 1,280 $ 10,743 (3) Intangible assets, net 1,918 51 25 1,994 Goodwill 1,802 229 366 2,397 Other long-lived assets 102 196 124 422 (1) Approximately 87% of the Company's revenues for the years ended December 31, 2018 relates to online accommodation reservation services. Revenues from all other sources of online travel reservation services or advertising and other revenues each represents less than 10% of the Company's total revenues. (2) Total revenues are reported on a net basis for Name Your Own Price ® transactions, which have been reduced for cost of revenues of $170 million (see Note 2). (3) Total revenues are reported on a gross basis for Name Your Own Price ® transactions, which were not reduced for cost of revenues of $242 million and $415 million in 2017 and 2016, respectively.

SELECTED QUARTERLY FINANCIAL DA

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) 2018 Total revenues (1) $ 2,928 $ 3,537 $ 4,849 $ 3,213 Net income (2) 607 977 1,768 646 Net income applicable to common stockholders per basic common share $ 12.56 $ 20.34 $ 37.39 $ 14.00 Net income applicable to common stockholders per diluted common share $ 12.34 $ 20.13 $ 37.02 $ 13.86 First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) 2017 Total revenues (1) $ 2,419 $ 3,025 $ 4,434 $ 2,803 Gross profit (1) 2,339 2,957 4,380 2,763 Net income (loss) (2) 456 720 1,720 (555 ) Net income (loss) applicable to common stockholders per basic common share (2) $ 9.26 $ 14.66 $ 35.12 $ (11.41 ) Net income (loss) applicable to common stockholders per diluted common share (2) $ 9.11 $ 14.39 $ 34.43 $ (11.41 ) (1) For periods beginning after December 31, 2017, the Company reports revenues in accordance with the current revenue standard and no longer presents "Cost of revenues" or "Gross profit" in its Consolidated Statement of Operations. For all periods prior to January 1, 2018, the Company reported under the previous revenue standard. See Note 2 for further information. (2) Includes, for the fourth quarter of 2018, an income tax benefit of $46 million to adjust the 2017 provisional tax expense related to a one-time transitional tax on mandatory deemed repatriation of accumulated unremitted international earnings as a result of the Tax Act. The income tax provision for the fourth quarter of 2017 includes a provisional tax expense of approximately $1.6 billion related to the transition tax mentioned above and a provisional tax benefit of $217 million related to the remeasurement of the Company’s U.S. deferred tax assets and liabilities as a result of the Tax Act.

ACQUISITIONS

ACQUISITIONS	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS Acquisition activities in 2018 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 to the shares issued, as shown in the supplemental disclosure in the Consolidated Statement of Cash Flows, $59 million relates to purchase price consideration and $51 million relates to shares restricted for trading purposes until the required post-acquisition services are completed by certain employees. At December 31, 2018, the Company's Consolidated Balance Sheet includes $17 million in "Prepaid expenses and other current assets" and $23 million in "Other assets" related to this deferred compensation charge associated with these restricted shares. The purchase price allocation was completed at September 30, 2018. In November 2018, the Company paid $134 million , net of cash acquired, to complete the acquisition of HotelsCombined, a hotel meta-search company. The purchase price allocation has not been completed at December 31, 2018. The Company's Consolidated Financial Statements include the accounts of these businesses starting at their respective acquisition dates. Revenues and earnings of these businesses since their respective acquisition dates and pro forma results of operations have not been presented separately as such financial information is not material to the Company's results of operations. Acquisition activity in 2017 In July 2017, the Company completed the acquisition of the Momondo Group, which operates the travel meta-search websites Momondo and Cheapflights, for $556 million , and which is managed as part of the Company's KAYAK business. The purchase price allocations were completed at December 31, 2017. The aggregate purchase price was allocated to the assets acquired and liabilities assumed as follows (in millions): Current assets (1) $ 50 Identifiable intangible assets (2) 333 Goodwill (3) 288 Property and equipment 1 Total liabilities (4) (116 ) Total consideration $ 556 (1) Includes cash acquired of $15 million . (2) Acquired definite-lived intangible assets, consisted of distribution agreements of $214 million with a weighted-average useful life of 15 years, trade names of $104 million with a weighted-average useful life of 13 years and technology of $15 million with a weighted-average life of 4 years. (3) Goodwill is not tax deductible. (4) Includes deferred tax liabilities of $70 million and third-party senior debt of $15 million . The Company's Consolidated Financial Statements include the accounts of the Momondo Group beginning July 24, 2017. Revenues and earnings of this business since the acquisition date and pro forma results of operations have not been presented separately as such financial information is not material to the Company's results of operations. The Company incurred $5 million of professional fees for the year ended December 31, 2017 related to this acquisition. The acquisition-related expenses were included in general and administrative expenses in the Company's Consolidated Statement of Operations. Contingent Consideration for Business Acquisition At December 31, 2018 and December 31, 2017 , the Company's Consolidated Balance Sheets included a liability of $28 million and $9 million , respectively, for estimated contingent payments for a business acquired in 2015. At December 31, 2018 , based on current forecasts, the estimated fair value of the liability increased by $19 million and the associated expense was included in "General and administrative" expense in the Company's Consolidated Statement of Operations for the year ended December 31, 2018 . The fair value of the liability, which is considered a "Level 3" fair value measurement (see Note 5 ), was based upon probability-weighted average payments for specific performance factors from the acquisition date through the performance period which ends on March 31, 2019. The range of undiscounted outcomes for the estimated contingent payments is $0 million to $90 million .

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation — The Company's Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries, including acquired businesses from the dates of acquisition. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates — The preparation of financial statements in conformity with accounting principles generally accepted in the United States ("U.S. GAAP") requires management to make estimates and assumptions that affect the amounts reported in the financial statements and footnotes thereto. Actual results may differ significantly from those estimates. The estimates underlying the Company's Consolidated Financial Statements relate to, among other things, the valuation of goodwill, long-lived assets and intangible assets, income taxes, stock-based compensation, the allowance for doubtful accounts and the accrual of obligations for loyalty programs.
Reclassifications	Reclassifications — Certain amounts from prior periods have been reclassified to conform to the current year presentation. Change in Presentation — In the first quarter of 2018, the Company changed the presentation of "Performance advertising", "Brand advertising", and "Sales and marketing" to "Performance marketing", "Brand marketing" and "Sales and other expenses" in the Consolidated Statements of Operations. The descriptions of these new lines are as follows: "Performance marketing" expenses are marketing expenses generally measured by return on investment or an increase in bookings over a specified time period. These expenses consist primarily of the costs of: (1) search engine keyword purchases; (2) referrals from meta-search and travel research websites; (3) affiliate programs; and (4) other performance-based advertisements, including certain incentive programs. "Brand marketing" expenses are marketing expenses to build brand awareness over a specified time period. These expenses consist primarily of television advertising, online video advertising (including the airing of our television advertising online) and online display advertising, as well as other marketing expenses such as public relations, trade shows and sponsorships. "Sales and other expenses" are generally variable in nature and consist primarily of: (1) credit cards and other payment processing fees associated with merchant transactions; (2) fees paid to third parties that provide call center, website content translations and other services; (3) provisions for customer chargebacks associated with merchant transactions; (4) customer relations costs; (5) provisions for bad debt, primarily related to accommodation commission receivables; and (6) insurance claim costs. In conjunction with the adoption of the current revenue recognition accounting standard ("the current revenue standard") effective January 1, 2018, the Company reclassified certain expenses from "Cost of revenues" to "Sales and other expenses" or "General and administrative" expenses in its Consolidated Statements of Operations for the years ended December 31, 2017 and 2016 to conform to the current period presentation. The change in presentation and the reclassification for the years ended December 31, 2017 and 2016 had no impact on operating income or net income and are summarized below (in millions): Previously Reported 2017 2016 Cost of revenues $ 251 $ 428 Performance advertising 4,142 3,479 Brand advertising 392 296 Sales and marketing 562 435 General and administrative 586 456 Current Presentation 2017 2016 Cost of revenues $ 242 $ 415 Performance marketing 4,161 3,479 Brand marketing 435 327 Sales and other expenses 517 422 General and administrative 576 452 Reclassification of Investments in Private Companies: In 2018, the Company changed the presentation of its equity investments in private companies to include them in "Long-term investments" instead of "Other assets" in the Consolidated Balance Sheets and in "Purchase of investments" instead of "Acquisitions and other investments, net of cash acquired" in the Consolidated Statements of Cash Flows. Therefore, the Company reclassified $451 million of investments in its Consolidated Balance Sheet at December 31, 2017 and cash payments of $450 million and $7 million in its Consolidated Statements of Cash Flows for the years ended December 31, 2017 and 2016, respectively, to conform to this current period presentations. See Note 4 for more detail.
Fair Value of Financial Instruments	Fair Value of Financial Instruments — The Company's financial instruments, including cash, restricted cash, 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 financial instruments. See Notes 4 , 5 and 10 for information on fair value for investments, derivatives, and the Company's outstanding Senior Notes.
Cash and Cash Equivalents	Cash and Cash Equivalents — Cash and cash equivalents consists primarily of cash and highly liquid investment grade securities with an original maturity of three months or less. Cash equivalents are recognized based on settlement date.
Restricted Cash and Cash Equivalents	Restricted Cash and Cash Equivalents — Restricted cash and cash equivalents are restricted through legal contracts, regulations or by the Company's intention to use the cash for a specific purpose. Restricted cash and cash equivalents at December 31, 2018 and 2017 principally relates to the minimum cash requirement for Rentalcars.com's insurance business established in 2017. Restricted cash at December 31, 2016 collateralizes office leases.
Investments	Investments — Investments held by the Company include debt and equity securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is considered a debt security. Investments in debt or equity securities that include embedded features, such as conversion or redemption features, are analyzed by the Company to determine if these features are embedded derivatives that require separate accounting treatment. • Debt Securities. The Company has classified its investments in debt securities as available-for-sale securities. These securities are reported at estimated fair value with the aggregate unrealized gains and losses, net of taxes, reflected as a part of " Accumulated other comprehensive income (loss) " in the Consolidated Balance Sheets. Investments in debt securities are considered to be impaired when a decline in fair value is judged to be other than temporary because the Company either intends to sell or it is more-likely-than not that it will have to sell the impaired security before recovery. Once a decline in fair value is determined to be other than temporary, an impairment charge is recorded and a new cost basis in the investment is established. If the Company does not intend to sell the debt security, but it is probable that the Company will not collect all amounts due, then only the impairment due to the credit risk would be recognized in earnings and the remaining amount of the impairment would be recognized in accumulated other comprehensive income within stockholders' equity. The fair value of these investments is based on the specific quoted market price of the securities or comparable securities at the balance sheet dates. Unobservable inputs are also used when little or no market data is available. See Note 5 for information on fair value measurements. The Company's investments in marketable debt securities are recognized based on trade date and reported as "Short-term investments in marketable securities" or "Long-term investments" in the Consolidated Balance Sheets based on the maturity date of the debt security. 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. • Equity Securities. Equity securities are reported as "Long-term investments" in the Consolidated Balance Sheets and include marketable equity securities and equity investments without readily determinable fair values. For periods beginning after December 31, 2017, marketable equity securities are reported at estimated fair value with changes in fair value recognized in net income rather than accumulated other comprehensive income within stockholders' equity, pursuant to the adoption of the accounting update on financial instruments in 2018. As a result, the Company recognized $367 million , before tax, in " Net unrealized losses on marketable equity securities " in the Consolidated Statement of Operations for the year ended December 31, 2018 . See "Recent Accounting Pronouncements Adopted" later in this footnote for further information on the impact of the adoption of this accounting update. The Company holds investments in equity securities of private companies, over which the Company does not have the ability to exercise significant influence or control. Pursuant to the adoption of the accounting update on financial instruments in 2018 (see "Recent Accounting Pronouncements Adopted" later in this footnote), for periods beginning after December 31, 2017, the Company elected to measure these investments at cost less impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Previously, these investments were carried at cost and adjusted to fair value only for other-than-temporary declines in fair value. See " Reclassification of Investments in Private Companies" in this footnote for the change in the presentation of these investments in 2018. See Note 4 and 5 for further information on investments.
Property and Equipment	Property and Equipment — Property and equipment are stated at cost less accumulated depreciation. Depreciation is computed on a straight-line basis over the estimated useful lives of the assets or, when applicable, the life of the lease related to leasehold improvements, whichever is shorter. Building Construction-in-progress — Building construction-in-progress is associated with the construction of an office building in the Netherlands and is included in “Property and equipment, net” in the Consolidated Balance Sheets. Depreciation of the building and its related components will commence once it is ready for the Company’s use.
Website and Internal-use Software Capitalization	Website and Internal-use Software Capitalization — Certain direct development costs associated with website and internal-use software are capitalized and include external direct costs of services and payroll costs for employees devoting time to the software projects principally related to platform development, including support systems, software coding, designing system interfaces and installation and testing of the software. These costs are recorded as property and equipment and are generally amortized over a period of two to five years beginning when the asset is substantially ready for use. Costs incurred for enhancements that are expected to result in additional features or functionalities are capitalized and amortized over the estimated useful life of the enhancements. Costs incurred during the preliminary project stage, as well as maintenance and training costs, are expensed as incurred. Additions to capitalized costs during the years ended December 31, 2018 , 2017 and 2016 were $97 million , $80 million and $54 million , respectively.
Land-use rights	Land-use rights — Land-use rights represent prepayments for the long-term lease of land where the Company is constructing an office building in the Netherlands. At December 31, 2018 and 2017 , the Company had $47 million and $51 million , respectively, associated with land-use rights recorded in “Other assets” in the Consolidated Balance Sheets. The land-use rights are expensed on a straight-line basis over the lease period. This expense is recorded as rent expense in "General and administrative" expense in the Consolidated Statements of Operations. See Note 14 for further details.
Goodwill	Goodwill — The Company accounts for acquired businesses using the acquisition method of accounting which requires that the assets acquired and liabilities assumed be recorded at the date of acquisition at their respective fair values. Any excess of the purchase price over the estimated fair values of the net assets acquired is recorded as goodwill. The Company's Consolidated Financial Statements reflect an acquired business starting at the date of the acquisition. Goodwill is not subject to amortization and is reviewed at least annually for impairment, or earlier if an event occurs or circumstances change and there is an indication of impairment. The Company tests goodwill at a reporting unit level. The fair value of the reporting unit is compared to its carrying value, including goodwill. Fair values are determined using a combination of standard valuation techniques, including an income approach (discounted cash flows) and market approaches (EBITDA multiples of comparable publicly-traded companies and precedent transactions) and based on market participant assumptions. An impairment is recorded to the extent that the implied fair value of goodwill is less than the carrying value of goodwill. See Note 9 for further information.
Impairment of Long-Lived Assets and Intangible Assets	Impairment of Long-Lived Assets and Intangible Assets — The Company reviews long-lived tangible assets and amortizable intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the Company's ability to recover the carrying value of the assets from the estimated undiscounted future net cash flows, before interest and taxes, of the related operations. The amount of impairment loss, if any, is measured as the excess of the carrying value of the asset over the present value of estimated future cash flows, using a discount rate commensurate with the risks involved and based on assumptions representative of market participants.
Revenue Recognition	Advertising and Other Revenues — Advertising and other revenues are primarily recognized by KAYAK and OpenTable for advertising placements on their websites. KAYAK recognizes advertising revenue primarily by sending referrals to online travel companies ("OTCs") and travel service providers and from advertising placements on its platforms. Revenue related to referrals is recognized when a consumer clicks on a referral placement or upon completion of the travel. Revenue for advertising placements is recognized based upon when a consumer clicks on an advertisement or when KAYAK displays an advertisement. OpenTable recognizes revenues for reservation fees when diners are seated through its online restaurant reservation service and revenues for subscription fees for restaurant management services on a straight-line basis over the contractual period in accordance with how the service is provided. Online travel reservation services — For periods beginning after December 31, 2017, the Company recognizes revenue for travel reservation services when the travel begins rather than when the travel is completed. Substantially all of the Company's revenues are generated by providing online travel reservation services, which principally allows travelers to book travel reservations with travel service providers through the Company’s platforms. While the Company generally refers to a consumer that books travel reservation services on the Company's platforms as its customer, for accounting purposes, the Company's customers are the travel service providers and, in certain merchant transactions, the travelers. The Company's contracts with travel service providers give them the ability to market their reservation availability without transferring responsibility to deliver the travel service to the Company, therefore, the Company's revenues are presented on a net basis in the Consolidated Statements of Operations. These contracts include payment terms and establish the consideration to which the Company is entitled, which includes either a commission or a margin on the travel transaction. Revenue is measured based on the expected consideration specified in the contract with the travel service provider, considering the effects of sales incentives, "no show" cancellations (where the traveler has not cancelled the reservation but does not arrive on the scheduled reservation date) and "late" cancellations (where the travel service provider accepts a cancellation after its cancellation cut-off date). Estimates for cancellations and sales incentives are based on historical experience and current trends. Coupons are recorded as a reduction of the transaction price at the time they are redeemed. Online travel reservation services are recorded at a point in time when the Company has completed its post-booking services and the travelers begin using the arranged travel services. These services are classified into two categories: • Agency revenues are derived from travel-related transactions where the Company does not receive payments from travelers for the services provided. The Company invoices the travel service providers for its commissions in the month that travel is completed. Agency revenues consist almost entirely of travel reservation commissions, as well as certain global distribution system ("GDS") reservation booking fees and certain travel insurance fees. Substantially all of the Company's agency revenue is from Booking.com agency accommodation reservations. • Merchant revenues are derived from travel-related transactions where the Company receives payments from travelers for the services provided, generally at the time of booking. The Company records cash collected from travelers, which includes the amounts owed to the travel service providers and the Company’s commission or margin and fees, as deferred merchant bookings until the arranged travel service begins. Merchant revenues include travel reservation commissions and transaction net revenues (i.e., the amount charged to travelers less the amount owed to travel service providers) in connection with the Company's merchant reservations services; ancillary fees, including travel insurance-related revenues and certain GDS reservation booking fees; and credit card processing rebates and customer processing fees. Substantially all merchant revenues are for merchant services derived from transactions where travelers book accommodation reservations or rental car reservations from travel service providers. Pursuant to the terms of the Company's merchant services, travel service providers are permitted to bill the Company for the underlying cost of the services during a specified period of time. If the Company is not billed by the travel service provider within the specified period of time, the Company increases its revenue by the unbilled amount. 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 owed to the travel service providers as well as the Company's deferred revenue for its commission or margin and fees. At December 31, 2018 and 2017, deferred merchant bookings included deferred revenue of $149 million and $151 million , respectively. The Company expects to complete its service obligation within one year of booking. In the year ended December 31, 2018, the Company recognized revenue of $109 million and cancellations of $10 million related to the deferred revenue balance at December 31, 2017. In addition, the Company reduced the December 31, 2017 balance by $32 million for the impact of the adoption of the current revenue standard on January 1, 2018. The offsetting increase in the deferred revenue balance for the year ended December 31, 2018 is principally driven by payments received from travelers, net of amounts payable to travel service providers, in the current period for those online travel reservations that the Company receives cash payments in advance of completing its service obligations.
Loyalty Programs	Loyalty Programs — The Company provides various loyalty programs, where participating consumers are awarded loyalty incentives on current transactions that can be redeemed for future qualifying reservations booked through the applicable Company platform or, in the case of OpenTable, at participating restaurants. 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 resulted in a reduction of its loyalty program liability by $27 million . At December 31, 2018 and 2017, liabilities of $73 million and $105 million , respectively, for loyalty program incentives were included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets.
Tax Recovery Charge, Occupancy Taxes and State and Local Taxes	Tax Recovery Charge, Occupancy Taxes and State and Local Taxes — For merchant transactions, the Company charges the traveler an amount intended to cover the taxes that the Company anticipates the travel service provider will remit to the local taxing authorities ("tax recovery charge"). Tax rate information for calculating the tax recovery charge is provided to the Company by the travel service providers. In certain taxing jurisdictions, the Company is required by statute, regulation or court order to collect and remit certain local occupancy tax, general excise tax, value-added tax and/or sales tax ("travel transaction taxes") and/or service fees. In other taxing jurisdictions, the Company is required to collect from the traveler and remit directly to the taxing jurisdiction transaction-related taxes imposed on the full amount of the transaction, which includes taxes on the margin, service fees and the underlying rate provided by the travel service provider. The rate information for calculating these taxes is provided to the Company directly from the taxing jurisdictions. The taxes collected from travelers are reported on a net basis in revenues in the Consolidated Statements of Operations.
Advertising Expense	Advertising expense — Included in "Performance marketing" expenses in the Consolidated Statements of Operations are performance advertising expenses of $4.4 billion , $4.1 billion and $3.5 billion for the years ended December 31, 2018 , 2017 and 2016 , respectively. Included in "Brand marketing" expenses in the Consolidated Statements of Operations are brand advertising expenses of $457 million , $392 million and $296 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets are accrued performance advertising liabilities of $313 million and $284 million at December 31, 2018 and 2017 , respectively. See " Change in Presentation " above within this footnote for the description of "Performance marketing" and "Brand marketing."
Personnel	Personnel — Personnel expenses consist of compensation to the Company's personnel, including salaries, stock-based compensation, bonuses, payroll taxes and employee health benefits. Included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets are accrued compensation liabilities of $348 million and $288 million at December 31, 2018 and 2017 , respectively.
Share-based Compensation	Stock-Based Compensation — Stock-based compensation is recognized in the financial statements based upon fair value. The fair value 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 at the grant date or acquisition date. The Company records stock-based compensation expense for the performance-based awards based on its estimate of the probable outcome at the end of the performance period (i.e., the estimated performance against the performance targets). The Company periodically adjusts the cumulative stock-based compensation expense recorded when the probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results. 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. Fair value is recognized as expense on a straight-line basis over the requisite service period, and, beginning January 1, 2017, forfeitures are accounted for when they occur. The benefits of tax deductions in excess of recognized compensation costs are recognized in the income statement as a discrete item in periods beginning on or after January 1, 2017 when an option exercise or a vesting and release of shares occurs. Excess tax benefits are presented as operating cash flows and cash payments for employee statutory tax withholding related to vested stock awards are presented as financing cash flows in the statements of cash flows. See Note 3 for further information on stock-based awards.
Information Technology	Information Technology — Information technology expenses consist primarily of: (1) software license and system maintenance fees; (2) data communications and other expenses associated with operating our services; (3) outsourced data center costs; and (4) payments to outside consultants.
Income Taxes	Income Taxes — The Company accounts for income taxes under the asset and liability method. The Company records the estimated future tax effects of temporary differences between the tax bases of assets and liabilities and amounts reported in the Consolidated Balance Sheets, as well as operating loss and tax credit carryforwards. Deferred taxes are classified as noncurrent in the balance sheet. The Company records deferred tax assets to the extent it believes these assets will more likely than not be realized. The Company regularly reviews its deferred tax assets for recoverability considering historical profitability, projected future taxable income, the expected timing of the reversals of existing temporary differences, the carryforward periods available for tax reporting purposes, and tax planning strategies. 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 ultimate realization of deferred tax assets depends on the generation of future taxable income during the period in which related temporary differences become deductible. In determining the future tax consequences of events that have been recognized in the financial statements or tax returns, significant judgments, estimates, and interpretation of statutes are required. Deferred taxes are measured using the enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred taxes of a change in tax rates is recognized in income in the period that includes the enactment date of such change. The Company recognizes liabilities when it believes that uncertain positions may not be fully sustained upon audit by the tax authorities. Liabilities recognized for uncertain tax positions are based on a two-step approach for recognition and measurement. First, the Company evaluates the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on audit based on its technical merits. Second, the Company measures the tax benefit as the largest amount that is more than 50% likely of being realized upon ultimate settlement. Interest and penalties attributable to uncertain tax positions, if any, are recognized as a component of income tax expense. In 2018 the Company adopted an accounting policy to treat taxes on global intangible low-taxed income ("GILTI") introduced by the Tax Act as period costs. See Note 13 for further details on income taxes.
Segment Reporting	Segment Reporting — The Company determined that its primary brands constitute its operating segments. The Company's Booking.com brand represents a substantial majority of total revenues and operating income. Based on similar economic characteristics and other similar operating factors, the Company has aggregated the operating segments into one reportable segment. For geographic information, see Note 16 .
Foreign Currency Translation	Foreign Currency Translation — The functional currency of the Company's foreign subsidiaries is generally their respective local currency. 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 income (loss) " in the Company's Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Foreign currency transactions and other" in the Company's Consolidated Statements of Operations.
Derivative Financial Instruments	Derivative Financial Instruments — As a result of the Company's international operations, it is exposed to various market risks that may affect its consolidated results of operations, cash flows and financial position. These market risks include, but are not limited to, fluctuations in currency exchange rates. The Company's primary foreign currency exposures are in Euros and British Pounds Sterling, in which it conducts a significant portion of its business activities. As a result, the Company faces exposure to adverse movements in currency exchange rates as the financial results of its international operations are translated from local currencies into U.S. Dollars upon consolidation. Additionally, foreign exchange rate fluctuations on transactions denominated in currencies other than the functional currency of an entity result in gains and losses that are reflected in income. The Company may enter into derivative instruments to hedge certain net exposures of nonfunctional currency denominated assets and liabilities and the volatility associated with translating earnings for its international businesses into U.S. Dollars, even though it does not elect to apply hedge accounting or hedge accounting does not apply. Gains and losses resulting from a change in fair value for these derivatives are reflected in income in the period in which the change occurs and are recognized in the Consolidated Statements of Operations in "Foreign currency transactions and other." Cash flows related to these contracts are classified within "Net cash provided by operating activities" on the cash flow statement. The Company, from time to time in the past, has utilized derivative instruments to hedge the impact of changes in currency exchange rates on the net assets of its foreign subsidiaries. These instruments are designated as net investment hedges. Hedge ineffectiveness is assessed and measured based on changes in forward exchange rates. The Company records gains and losses on these derivative instruments as currency translation adjustments, which offset a portion of the translation adjustments related to the foreign subsidiaries' net assets. Gains and losses are recognized in the Consolidated Balance Sheet in " Accumulated other comprehensive income (loss) " and will be realized upon a partial sale or liquidation of the investment. The Company documents all derivatives designated as hedging instruments for accounting purposes, both at hedge inception and on an on-going basis. The Company issued Senior Notes due March 10, 2022 for an aggregate principal amount of 1.0 billion Euros in 2017, Senior Notes due November 25, 2022 for an aggregate principal amount of 750 million Euros and Senior Notes due March 3, 2027 for an aggregate principal amount of 1.0 billion Euros both in 2015 and Senior Notes due September 23, 2024 for an aggregate principal amount of 1.0 billion Euros in 2014. The Company designated the carrying value, plus accrued interest, of these Euro-denominated Senior Notes as a hedge of the Company's net investment in Euro functional currency subsidiaries. The foreign currency transaction gains or losses on these liabilities and the foreign currency translation gains or losses from translating the Euro-denominated net assets of these subsidiaries into U.S. Dollars are included as a component of " Accumulated other comprehensive income (loss) " in the Company's Consolidated Balance Sheets (see Notes 10 and 12 ). The Company does not use derivative instruments for trading or speculative purposes. The Company recognizes all derivative instruments on the balance sheet at fair value and its derivative instruments are generally short-term in duration. The derivative instruments do not contain leverage features. The Company is exposed to the risk that counterparties to derivative instruments may fail to meet their contractual obligations. The Company regularly reviews its credit exposure as well as assessing the creditworthiness of its counterparties. See Note 5 for further detail on derivatives.
New Accounting Pronouncements and Changes in Accounting Principles Not Yet Adopted	Recent Accounting Pronouncements Adopted Premium Amortization on Purchased Callable Debt Securities In March 2017, the Financial Accounting Standards Board (“FASB”) issued a new accounting update to shorten the premium amortization period of purchased callable debt securities with non-contingent call features that are callable at fixed prices and on preset dates from their contractual maturity to the earliest call date. For public business entities, this update is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption allowed. The Company early adopted this new standard in the third quarter of 2018. The adoption of this update did not have an impact to the Consolidated Financial Statements. Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued a new accounting update to make targeted improvement to the disclosure requirement for fair value measurements as part of its disclosure framework project. This update eliminates, adds and modifies certain disclosure requirements primarily related to Level 3 fair value measurements. For public business entities, this update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years, with early adoption allowed. The Company early adopted this new standard in the third quarter of 2018. The adoption of this update did not have a material impact to the Consolidated Financial Statements. Improvements to Non-employee Share-Based Payment Accounting In June 2018, the FASB issued a new accounting update which amends the guidance on share-based payments granted to non-employees for goods and services to align it with the guidance for share-based payments to employees. Under this new guidance, share-based awards to non-employees will be generally measured at fair value on the grant date of the awards and entities will need to assess the probability of satisfying performance conditions, if any are present, to determine the amount of expense to be recognized. This update is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption allowed. The Company early adopted this new standard in the second quarter of 2018 and applied this update as of January 1, 2018. The adoption of this update did not have a material impact to the Consolidated Financial Statements. Recognition and Measurement of Financial Instruments In January 2016, the FASB issued a new accounting update which amends the guidance on the recognition and measurement of financial instruments. The update (1) requires an entity to measure equity investments (except those accounted for under the equity method or those that result in consolidation of the investee) at fair value with changes in fair value recognized in net income rather than accumulated other comprehensive income, (2) allows an entity to elect to measure those equity investments that do not have a readily determinable fair value 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, (3) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment, and (4) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity’s evaluation of its other deferred tax assets. This update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company adopted this update in the first quarter of 2018. The Company recorded an increase of $241 million to retained earnings for the net unrealized gain, net of tax, related to its investment in Ctrip.com International Ltd. ("Ctrip") equity securities, with an offsetting adjustment to accumulated other comprehensive income as of January 1, 2018. Changes in fair value of the Company's investments in marketable equity securities subsequent to January 1, 2018 are recognized in net income. In addition, the Company elected to measure equity investments without readily determinable fair value 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. Revenue from Contracts with Customers In May 2014, the FASB issued a new accounting standard on the recognition of revenue from contracts with customers that was designed to create greater comparability for financial statement users across industries. The core principle of this new standard is that an "entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services." This new standard also requires enhanced disclosures on the nature, amount, timing and uncertainty of revenue from contracts with customers. On January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers , using a modified retrospective method applied to all contracts as of January 1, 2018. Therefore, for reporting periods beginning after December 31, 2017, the financial statements are prepared in accordance with the current revenue standard and the financial statements for all periods prior to January 1, 2018 are presented under the previous revenue recognition accounting standard ("the previous revenue standard"). For periods beginning after December 31, 2017, the Company recognizes revenue for travel reservation services when the travel begins rather than when the travel is completed. For example, revenues for accommodation reservation services, which were principally recognized at check-out under the previous revenue standard, are now recognized at check-in under the current revenue standard. This timing change did not have a significant impact to the Company's annual revenues and net income. In addition, revenues from priceline's Name Your Own Price ® transactions were previously presented on a gross basis with the amount remitted to the travel service providers reported as cost of revenues. Under the current revenue standard, Name Your Own Price ® revenues are reported on a net basis with the amount remitted to the travel service providers recorded as an offset in merchant revenues. Therefore, for periods beginning after December 31, 2017, the Company no longer presents "Cost of revenues" or "Gross profit" in its Consolidated Statements of Operations. Total revenues reported in 2018 are comparable to gross profit reported in previous years. Billing and cash collections remain unchanged and, therefore, "Net cash provided by operating activities" as presented in the Consolidated Statements of Cash Flows is not impacted. The Company recorded a net increase to its retained earnings of $189 million , net of tax, as of January 1, 2018, due to the cumulative impact of adopting the current revenue standard, with substantially all of the impact related to the Company’s travel reservation services. In addition, since the Company is using the modified retrospective method of adopting the current revenue standard, the Company is required to disclose the financial impacts to its Consolidated Balance Sheets and Consolidated Statements of Operations for all 2018 reporting periods (refer to the disclosures below for this additional information). The cumulative effects of adopting the current revenue standard on the Company's Consolidated Balance Sheet as of January 1, 2018 were as follows (in millions): Balance at December 31, 2017 Adjustments Balance at January 1, 2018 ASSETS Current assets: Accounts receivable, net $ 1,218 $ 205 $ 1,423 LIABILITIES AND STOCKHOLDERS' EQUITY Current liabilities: Accounts payable $ 668 $ 172 $ 840 Accrued expenses and other current liabilities 1,139 44 1,183 Deferred merchant bookings 980 (202 ) 778 Deferred income taxes 481 2 483 Stockholders' equity: Retained earnings 13,939 189 14,128 The following tables summarize the impacts of adopting the current revenue standard (in millions, except per share data): Consolidated Balance Sheet at December 31, 2018 : As reported (current revenue standard) Adjustments As adjusted (previous revenue standard) ASSETS Current assets: Accounts receivable, net $ 1,523 $ (216 ) $ 1,307 Prepaid expenses and other current assets 600 10 610 LIABILITIES AND STOCKHOLDERS' EQUITY Current liabilities: Accounts payable $ 1,134 $ (234 ) $ 900 Accrued expenses and other current liabilities 1,399 (47 ) 1,352 Deferred merchant bookings 1,022 280 1,302 Deferred income taxes 370 (3 ) 367 Stockholders' equity: Retained earnings 18,367 (205 ) 18,162 Accumulated other comprehensive income (loss) (316 ) 3 (313 ) Consolidated Statement of Operations for the Year Ended December 31, 2018 : As reported (current revenue standard) Current year adjustments As adjusted (previous revenue standard) Agency revenues $ 10,480 $ (10 ) $ 10,470 Merchant revenues 2,987 157 3,144 Cost of revenues — 170 170 Operating expenses: Performance marketing 4,447 (2 ) 4,445 Foreign currency transactions and other (57 ) 2 (55 ) Income tax expense 837 (3 ) 834 Net income 3,998 (16 ) (1) 3,982 Net income applicable to common stockholders per basic common share $ 84.26 $ (0.34 ) $ 83.92 Net income applicable to common stockholders per diluted common share $ 83.26 $ (0.34 ) $ 82.92 (1) The current year adjustment represents the net income recorded directly to retained earnings on January 1, 2018 of $189 million that would have been recognized in the first quarter of 2018 under the previous revenue standard, partially offset by $205 million that would have been recognized in the first quarter of 2019 under the previous revenue standard. Other Recent Accounting Pronouncements Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In August 2018, the 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 adds 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). For public business entities, this update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years, with early adoption permitted. The Company adopted this update on January 1, 2019 and will apply it on a prospective basis. The Company does not expect a material impact to the Consolidated Financial Statements as a result of the adoption. Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued a new accounting update to simplify the test for goodwill impairment by eliminating Step 2, which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill, which requires a hypothetical purchase price allocation, with the carrying amount of that reporting unit's goodwill. Under this update, an entity would perform its quantitative annual or interim goodwill impairment test using the current Step 1 test and recognize an impairment charge for the excess of the carrying value of a reporting unit over its fair value. For public business entities, this update is effective for their annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests occurring after January 1, 2017. The update will be applied prospectively. The Company has not early adopted this update. In the third quarter of 2018, the Company performed its annual quantitative goodwill impairment test (see Note 9 ). 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 to have a material impact. Leases In February 2016, the FASB issued a new accounting standard intended to improve the financial reporting of lease transactions. The new accounting standard requires lessees to recognize an asset and a liability on the balance sheet for the rights and obligations created by entering into a lease transaction. The new standard retains the dual-model concept by requiring entities to determine if a lease is an operating or financing lease. The lessor accounting model remains largely unchanged. The new standard also expands qualitative and quantitative disclosures for lessees. The standard is effective for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018 using a modified retrospective approach applied to the earliest comparative period in the financial statements. In July 2018, the FASB approved a new transition method ("new transition method") that would permit issuers to apply the standard as of January 1, 2019 and not restate comparable periods. Early adoption is permitted. In preparation for adoption of the standard, the Company has implemented internal controls and a software solution to manage and account for its leases. The Company elected the new transition method and 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, as permitted under this standard. The Company also elected to combine lease and non-lease components. The associated lease payments will be recognized in the Consolidated Statement of Operations on a straight-line basis over the lease period. The Company expects to recognize right-of-use assets of approximately $640 million and lease liabilities of approximately $650 million in the Consolidated Balance Sheet based on leases which have commenced before January 1, 2019. The difference between the right-of-use asset and lease liability primarily relates to the classification of land-use rights (refer to Land-use rights above) and the impact of the timing differences between the recognition of rent expense and when rent payments are made and incentives are received on existing leases. There is no impact to retained earnings. The Company does not expect a material impact to its Consolidated Statement of Operations and Statement of Cash Flows resulting from the adoption.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Reclassifications [Table Text Block]	The change in presentation and the reclassification for the years ended December 31, 2017 and 2016 had no impact on operating income or net income and are summarized below (in millions): Previously Reported 2017 2016 Cost of revenues $ 251 $ 428 Performance advertising 4,142 3,479 Brand advertising 392 296 Sales and marketing 562 435 General and administrative 586 456 Current Presentation 2017 2016 Cost of revenues $ 242 $ 415 Performance marketing 4,161 3,479 Brand marketing 435 327 Sales and other expenses 517 422 General and administrative 576 452
Summary of the Impacts of Adopting the Current Revenue Standard	The cumulative effects of adopting the current revenue standard on the Company's Consolidated Balance Sheet as of January 1, 2018 were as follows (in millions): Balance at December 31, 2017 Adjustments Balance at January 1, 2018 ASSETS Current assets: Accounts receivable, net $ 1,218 $ 205 $ 1,423 LIABILITIES AND STOCKHOLDERS' EQUITY Current liabilities: Accounts payable $ 668 $ 172 $ 840 Accrued expenses and other current liabilities 1,139 44 1,183 Deferred merchant bookings 980 (202 ) 778 Deferred income taxes 481 2 483 Stockholders' equity: Retained earnings 13,939 189 14,128 The following tables summarize the impacts of adopting the current revenue standard (in millions, except per share data): Consolidated Balance Sheet at December 31, 2018 : As reported (current revenue standard) Adjustments As adjusted (previous revenue standard) ASSETS Current assets: Accounts receivable, net $ 1,523 $ (216 ) $ 1,307 Prepaid expenses and other current assets 600 10 610 LIABILITIES AND STOCKHOLDERS' EQUITY Current liabilities: Accounts payable $ 1,134 $ (234 ) $ 900 Accrued expenses and other current liabilities 1,399 (47 ) 1,352 Deferred merchant bookings 1,022 280 1,302 Deferred income taxes 370 (3 ) 367 Stockholders' equity: Retained earnings 18,367 (205 ) 18,162 Accumulated other comprehensive income (loss) (316 ) 3 (313 ) Consolidated Statement of Operations for the Year Ended December 31, 2018 : As reported (current revenue standard) Current year adjustments As adjusted (previous revenue standard) Agency revenues $ 10,480 $ (10 ) $ 10,470 Merchant revenues 2,987 157 3,144 Cost of revenues — 170 170 Operating expenses: Performance marketing 4,447 (2 ) 4,445 Foreign currency transactions and other (57 ) 2 (55 ) Income tax expense 837 (3 ) 834 Net income 3,998 (16 ) (1) 3,982 Net income applicable to common stockholders per basic common share $ 84.26 $ (0.34 ) $ 83.92 Net income applicable to common stockholders per diluted common share $ 83.26 $ (0.34 ) $ 82.92 (1) The current year adjustment represents the net income recorded directly to retained earnings on January 1, 2018 of $189 million that would have been recognized in the first quarter of 2018 under the previous revenue standard, partially offset by $205 million that would have been recognized in the first quarter of 2019 under the previous revenue standard.
Reconciliation of Cash, Cash Equivalents and Restricted Cash and Cash Equivalents	The following table reconciles cash, cash equivalents and restricted cash and cash equivalents reported in the Consolidated Balance Sheets to the total amount shown in the Consolidated Statements of Cash Flows (in millions): December 31, 2018 2017 2016 As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 2,624 $ 2,542 $ 2,081 Restricted cash and cash equivalents included in prepaid expenses and other current assets 21 21 1 Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Consolidated Statements of Cash Flows $ 2,645 $ 2,563 $ 2,082

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Activity of unvested restricted stock units and performance share units	The following table summarizes the activity of restricted stock units and performance share units ("share-based awards") for employees and non-employee directors during the years ended December 31, 2016 , 2017 and 2018 : Share-Based Awards Shares Weighted-Average Grant Date Fair Value Unvested at December 31, 2015 637,257 $ 1,070.10 Granted 202,740 $ 1,314.93 Vested (298,753 ) $ 858.23 Performance Shares Adjustment 52,224 $ 1,294.84 Forfeited/Canceled (77,862 ) $ 1,278.06 Unvested at December 31, 2016 515,606 $ 1,287.88 Granted 174,507 $ 1,740.78 Vested (143,771 ) $ 1,316.26 Performance Shares Adjustment 19,357 $ 1,501.48 Forfeited/Canceled (41,003 ) $ 1,416.09 Unvested at December 31, 2017 524,696 $ 1,431.88 Granted 166,304 $ 2,027.43 Vested (204,242 ) $ 1,297.21 Performance Shares Adjustment 66,245 $ 1,872.06 Forfeited/Canceled (41,441 ) $ 1,713.45 Unvested at December 31, 2018 511,562 $ 1,713.44
Schedule of share-based compensation, stock options, activity	The following table summarizes the activity for stock options during the years ended December 31, 2016 , 2017 and 2018 : Employee Stock Options Number of Shares Weighted-Average Exercise Price Aggregate Intrinsic Value (in millions) Weighted-Average Remaining Contractual Term (in years) Balance, December 31, 2015 89,104 $ 383.03 $ 79 5.4 Exercised (38,150 ) $ 404.40 Forfeited (1,971 ) $ 241.65 Balance, December 31, 2016 48,983 $ 372.07 $ 54 4.4 Exercised (17,359 ) $ 294.45 Forfeited (949 ) $ 837.09 Balance, December 31, 2017 30,675 $ 401.61 $ 41 3.9 Exercised (3,318 ) $ 494.66 Forfeited (94 ) $ 450.84 Balance, December 31, 2018 27,263 $ 386.97 $ 36 2.8 Vested and exercisable at December 31, 2018 27,190 $ 398.69 $ 36 2.8 Vested and exercisable at December 31, 2018 and expected to vest thereafter 27,263 $ 386.97 $ 36 2.8

INVESTMENTS (Tables)

INVESTMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	The following table summarizes, by major security type, the Company's investments in marketable securities at December 31, 2017 (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Short-term investments in marketable securities: Debt securities: International government securities $ 725 $ — $ — $ 725 U.S. government securities 996 — (2 ) 994 Corporate debt securities 3,068 1 (5 ) 3,064 U.S. government agency securities 4 — — 4 Commercial paper 73 — — 73 Total $ 4,866 $ 1 $ (7 ) $ 4,860 Long-term investments in marketable securities: Debt securities: International government securities $ 607 $ 2 $ (1 ) $ 608 U.S. government securities 845 — (10 ) 835 Corporate debt securities 6,690 8 (42 ) 6,656 Investments in Ctrip: Convertible debt securities 1,275 103 (9 ) 1,369 Equity securities 655 300 (1 ) 954 Total $ 10,072 $ 413 $ (63 ) $ 10,422 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 Certificate 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 Investments in Ctrip: Convertible debt securities 1,275 — (98 ) 1,177 Equity securities 655 2 (72 ) 585 Meituan Dianping equity securities 450 1 — 451 Total $ 7,921 $ 10 $ (224 ) $ 7,707

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Financial instruments carried at fair value	Financial assets carried at fair value at December 31, 2018 are classified in the categories described in the tables below (in millions): Level 1 Level 2 Level 3 Total ASSETS: 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 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 Certificate 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 Ctrip equity securities 585 — — 585 Meituan Dianping equity securities 451 — — 451 Other long-term investment — — 200 200 Derivatives: Currency exchange derivatives — 4 — 4 Total assets at fair value $ 3,123 $ 10,358 $ 200 $ 13,681 Financial assets carried at fair value at December 31, 2017 are classified in the categories described in the tables below (in millions): Level 1 Level 2 Total ASSETS: Cash and restricted cash equivalents: Money market funds $ 1,895 $ — $ 1,895 U.S. government securities — 22 22 Corporate debt securities — 7 7 Commercial paper — 96 96 Time deposits 18 — 18 Short-term investments in marketable securities: International government securities — 725 725 U.S. government securities — 994 994 Corporate debt securities — 3,064 3,064 U.S. government agency securities — 4 4 Commercial paper — 73 73 Long-term investments in marketable securities: International government securities — 608 608 U.S. government securities — 835 835 Corporate debt securities — 6,656 6,656 Ctrip convertible debt securities — 1,369 1,369 Ctrip equity securities 954 — 954 Derivatives: Currency exchange derivatives — 2 2 Total assets at fair value $ 2,867 $ 14,455 $ 17,322

ACCOUNTS RECEIVABLE RESERVES (T

ACCOUNTS RECEIVABLE RESERVES (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Changes in accounts receivable reserves	Changes in accounts receivable reserves consisted of the following (in millions): For the Year Ended December 31, 2018 2017 2016 Balance, beginning of year $ 39 $ 26 $ 15 Provision charged to expense 163 62 46 Charge-offs and adjustments (139 ) (52 ) (35 ) Currency translation adjustments (2 ) 3 — Balance, end of year $ 61 $ 39 $ 26

NET INCOME PER SHARE (Tables)

NET INCOME PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
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): For the Year Ended December 31, 2018 2017 2016 Weighted-average number of basic common shares outstanding 47,446 48,994 49,491 Weighted-average dilutive stock options, restricted stock units and performance share units 236 295 238 Assumed conversion of Convertible Senior Notes 335 665 334 Weighted-average number of diluted common and common equivalent shares outstanding 48,017 49,954 50,063 Anti-dilutive potential common shares 1,411 1,864 2,443

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and equipment	Property and equipment at December 31, 2018 and 2017 consisted of the following (in millions): 2018 2017 Estimated Computer equipment and software $ 964 $ 769 2 to 5 years Leasehold improvements 242 199 1 to 13 years Office equipment, furniture and fixtures 55 47 2 to 7 years Building construction-in-progress 88 8 Total 1,349 1,023 Less: accumulated depreciation (693 ) (543 ) Property and equipment, net $ 656 $ 480

INTANGIBLE ASSETS AND GOODWILL

INTANGIBLE ASSETS AND GOODWILL (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible assets	The Company's intangible assets at December 31, 2018 and 2017 consisted of the following (in millions): December 31, 2018 December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Amortization Supply and distribution agreements $ 1,099 $ (408 ) $ 691 $ 1,057 $ (355 ) $ 702 3 - 20 years Technology 173 (121 ) 52 137 (104 ) 33 1 - 7 years Patents 2 (2 ) — 2 (2 ) — 15 years Internet domain names 41 (30 ) 11 42 (29 ) 13 5 - 20 years Trade names 1,810 (439 ) 1,371 1,779 (350 ) 1,429 4 - 20 years Non-compete agreements 1 (1 ) — 22 (22 ) — 4 years Total intangible assets $ 3,126 $ (1,001 ) $ 2,125 $ 3,039 $ (862 ) $ 2,177
Annual estimated amortization expense for intangible assets for the next five years and thereafter	The annual estimated amortization expense for intangible assets for the next five years and thereafter is expected to be as follows (in millions): 2019 $ 174 2020 166 2021 158 2022 156 2023 154 Thereafter 1,317 $ 2,125
Goodwill	A roll-forward of goodwill for the years ended December 31, 2018 and 2017 consisted of the following (in millions): 2018 2017 Balance, beginning of year $ 2,738 $ 2,397 Acquisitions 212 294 Currency translation adjustments (40 ) 47 Balance, end of year $ 2,910 $ 2,738

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Debt	Outstanding debt at December 31, 2018 consisted of the following (in millions): December 31, 2018 Outstanding Principal Amount Unamortized Debt 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 Outstanding debt at December 31, 2017 consisted of the following (in millions): December 31, 2017 Outstanding Principal Amount Unamortized Debt Carrying Value Short-term debt: 1.0% Convertible Senior Notes due March 2018 $ 714 $ (3 ) $ 711 Long-term debt: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (65 ) $ 935 0.9% Convertible Senior Notes due September 2021 1,000 (83 ) 917 0.8% (€1 Billion) Senior Notes due March 2022 1,201 (6 ) 1,195 2.15% (€750 Million) Senior Notes due November 2022 900 (5 ) 895 2.75% Senior Notes due March 2023 500 (3 ) 497 2.375% (€1 Billion) Senior Notes due September 2024 1,201 (12 ) 1,189 3.65% Senior Notes due March 2025 500 (3 ) 497 3.6% Senior Notes due June 2026 1,000 (7 ) 993 1.8% (€1 Billion) Senior Notes due March 2027 1,201 (5 ) 1,196 3.55% Senior Notes due March 2028 500 (4 ) 496 Total long-term debt $ 9,003 $ (193 ) $ 8,810

TREASURY STOCK - (Tables)

TREASURY STOCK - (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Summary of Repurchase Activity	The following table summarizes the Company's stock repurchase activities during the years ended December 31, 2018, 2017 and 2016, respectively (in millions, except for shares): 2018 2017 2016 Shares Amount Shares Amount Shares Amount Authorized stock repurchase programs 3,020,561 $ 5,850 968,521 $ 1,744 635,877 $ 861 General authorization for shares withheld on stock award vesting 79,746 162 57,369 100 127,107 167 Total 3,100,307 $ 6,012 1,025,890 $ 1,844 762,984 $ 1,028 Shares repurchased in December and settled in following January 42,939 $ 74 18,217 $ 32 10,215 $ 15

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)	12 Months Ended
	Dec. 31, 2018
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 income (loss) at December 31, 2018 and 2017 (in millions): December 31, 2018 December 31, 2017 Foreign currency translation adjustments, net of tax (1) $ (129 ) $ (15 ) Net unrealized gains on marketable securities, net of tax: Net unrealized gains on marketable equity securities, net of tax (2) — 241 Net unrealized (losses) gains on marketable debt securities, net of tax (3) (187 ) 12 Accumulated other comprehensive income (loss) $ (316 ) $ 238 (1) Foreign currency translation adjustments, net of tax, at December 31, 2018 and 2017 , include accumulated net losses from fair value adjustments of $35 million after tax ( $53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. Foreign currency translation adjustments, net of tax, include foreign currency transaction losses of $26 million after tax ( $20 million before tax) and $190 million after tax ( $237 million before tax) at December 31, 2018 and 2017 , respectively, associated with the Company's Euro-denominated debt. The Company's Euro-denominated debt is designated as a hedge against the impact of currency fluctuations on its Euro-denominated net assets (see Note 10 ). The remaining balance in foreign currency translation adjustments relates to the cumulative impacts of currency fluctuations on the Company's non-U.S. Dollar denominated net assets. During the year ended December 31, 2018 , the Company recorded a tax benefit of $41 million related to its one-time deemed repatriation tax liability recorded at December 31, 2017 and current year foreign earnings subject to U.S. federal and state income tax, resulting from the introduction of the Tax Act. Prior to January 1, 2018, foreign currency translation adjustments excluded U.S. federal and state income taxes as a result of the Company's intention to indefinitely reinvest the earnings of its international subsidiaries outside of the United States. (2) Net unrealized gains on marketable equity securities, net of tax, at December 31, 2017 related to changes in the fair value of the Company's investment in Ctrip equity securities (see Note 4 ). Net unrealized gains before tax on equity securities at December 31, 2017 were $299 million , of which unrealized gains of $320 million were not subject to income tax in the Netherlands. Unrealized losses of $21 million were taxable at a 25% tax rate in the Netherlands, which resulted in a tax benefit of $5 million at December 31, 2017. The Company also recorded U.S. tax charges of $63 million at December 31, 2017 related to these investments. The Company reclassified the net unrealized gains, net of tax, on its investment in Ctrip equity securities at December 31, 2017 from accumulated other comprehensive income to retained earnings upon the adoption of the accounting update on financial instruments as of January 1, 2018. Changes in fair value subsequent to January 1, 2018 are recognized in net income (see Note 2 ). (3) Net unrealized losses before tax on marketable debt securities of $276 million and $86 million at December 31, 2018 and 2017 , respectively, were not subject to income tax in the Netherlands. Unrealized gains before tax of $123 million and $130 million at December 31, 2018 and 2017, respectively, were taxable at a 25% tax rate in the Netherlands, resulting in tax charges of $30 million and $32 million at December 31, 2018 and 2017 , respectively. The remaining net unrealized losses on marketable securities and related tax benefits at December 31, 2018 were associated with marketable debt securities held by a U.S. subsidiary.

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	The income tax expense (benefit) for the year ended December 31, 2018 is as follows (in millions): Current Deferred Total International $ 887 $ (3 ) $ 884 U.S. Federal 45 (107 ) (62 ) U.S. State 55 (40 ) 15 Total $ 987 $ (150 ) $ 837 The income tax expense (benefit) for the year ended December 31, 2017 is as follows (in millions): Current Deferred Total International $ 756 $ (10 ) $ 746 U.S. Federal 1,327 (57 ) 1,270 U.S. State 7 35 42 Total $ 2,090 $ (32 ) $ 2,058 The income tax expense (benefit) for the year ended December 31, 2016 is as follows (in millions): Current Deferred Total International $ 627 $ (14 ) $ 613 U.S. Federal 64 (33 ) 31 U.S. State (1 ) (65 ) (66 ) Total $ 690 $ (112 ) $ 578
Tax effects of temporary differences that give rise to significant portions of deterred tax assets and liabilities	The tax effects of temporary differences that give rise to significant portions of deferred tax assets and liabilities at December 31, 2018 and 2017 are as follows (in millions): 2018 2017 Deferred tax assets/(liabilities): Net operating loss carryforward — U.S. $ 59 $ 71 Net operating loss carryforward — International 20 28 Accrued expenses 50 57 Stock-based compensation and other stock based payments 51 48 Currency translation adjustment 27 — Tax credits 46 15 Euro-denominated debt 5 58 Property and equipment 6 9 Subtotal - deferred tax assets 264 286 Discount on convertible notes (22 ) (33 ) Intangible assets and other (482 ) (517 ) State income tax on accumulated unremitted international earnings (25 ) (37 ) Unrealized gain on investments (2 ) (70 ) Other (15 ) (25 ) Subtotal - deferred tax liabilities (546 ) (682 ) Valuation allowance on deferred tax assets (36 ) (44 ) Net deferred tax liabilities (1) $ (318 ) $ (440 ) (1) Includes deferred tax assets of $51 million and $41 million at December 31, 2018 and 2017 , respectively, reported in "Other assets" in the Consolidated Balance Sheets.
Schedule of effective income tax rate reconciliation	The effective income tax rate of the Company is different from the amount computed using the expected U.S. statutory federal rate of 21% in 2018 and 35% in 2017 and 2016 as a result of the following items (in millions): 2018 2017 2016 Income tax expense at federal statutory rate $ 1,015 $ 1,539 $ 950 Adjustment due to: Foreign rate differential 210 (458 ) (378 ) Innovation Box Tax benefit (435 ) (397 ) (325 ) Impairment of goodwill and cost-method investment — — 344 Tax Act - Remeasurement of deferred tax balances (2 ) (217 ) — Tax Act - U.S. transition tax and other transition impacts (46 ) 1,563 — Other 95 28 (13 ) Income tax expense $ 837 $ 2,058 $ 578
Reconciliation of unrecognized tax benefits	The following is a reconciliation of the total beginning and ending amount of unrecognized tax benefits (in millions): 2018 2017 2016 Unrecognized tax benefit — January 1 $ 32 $ 33 $ 43 Gross increases — tax positions in current period 1 5 2 Gross increases — tax positions in prior periods 19 5 1 Gross decreases — tax positions in prior periods (3 ) (9 ) — Reduction due to lapse in statute of limitations (2 ) (1 ) (9 ) Reduction due to settlements during the current period (2 ) (1 ) (4 ) Unrecognized tax benefit — December 31 $ 45 $ 32 $ 33

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Minimum payments for operating leases	Minimum payments for operating leases having initial or remaining non-cancellable terms in excess of one year and the land lease associated with an office buildings in the Netherlands discussed above have been translated into U.S. Dollars at the December 31, 2018 spot exchange rates, as applicable, and are as follows (in millions): 2019 2020 2021 2022 2023 After 2023 Total Operating lease obligations $ 163 $ 140 $ 108 $ 64 $ 50 $ 118 $ 643 Land lease obligation 1 2 2 2 2 72 81

GEOGRAPHIC INFORMATION (Tables)

GEOGRAPHIC INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Geographic Information	The Company's geographic information is as follows (in millions): United States International Total Company The Netherlands Other 2018 Total Revenues (1) $ 1,626 (2) $ 11,094 $ 1,807 $ 14,527 (2) Intangible assets, net 1,747 30 348 2,125 Goodwill 1,938 246 726 2,910 Other long-lived assets 159 365 260 784 2017 Total Revenues $ 1,620 (3) $ 9,540 $ 1,521 $ 12,681 (3) Intangible assets, net 1,790 44 343 2,177 Goodwill 1,807 254 677 2,738 Other long-lived assets 124 254 208 586 2016 Total Revenues $ 1,680 (3) $ 7,783 $ 1,280 $ 10,743 (3) Intangible assets, net 1,918 51 25 1,994 Goodwill 1,802 229 366 2,397 Other long-lived assets 102 196 124 422 (1) Approximately 87% of the Company's revenues for the years ended December 31, 2018 relates to online accommodation reservation services. Revenues from all other sources of online travel reservation services or advertising and other revenues each represents less than 10% of the Company's total revenues. (2) Total revenues are reported on a net basis for Name Your Own Price ® transactions, which have been reduced for cost of revenues of $170 million (see Note 2). (3) Total revenues are reported on a gross basis for Name Your Own Price ® transactions, which were not reduced for cost of revenues of $242 million and $415 million in 2017 and 2016, respectively.

SELECTED QUARTERLY FINANCIAL _2

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected quarterly financial data (unaudited)	First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) 2018 Total revenues (1) $ 2,928 $ 3,537 $ 4,849 $ 3,213 Net income (2) 607 977 1,768 646 Net income applicable to common stockholders per basic common share $ 12.56 $ 20.34 $ 37.39 $ 14.00 Net income applicable to common stockholders per diluted common share $ 12.34 $ 20.13 $ 37.02 $ 13.86 First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) 2017 Total revenues (1) $ 2,419 $ 3,025 $ 4,434 $ 2,803 Gross profit (1) 2,339 2,957 4,380 2,763 Net income (loss) (2) 456 720 1,720 (555 ) Net income (loss) applicable to common stockholders per basic common share (2) $ 9.26 $ 14.66 $ 35.12 $ (11.41 ) Net income (loss) applicable to common stockholders per diluted common share (2) $ 9.11 $ 14.39 $ 34.43 $ (11.41 ) (1) For periods beginning after December 31, 2017, the Company reports revenues in accordance with the current revenue standard and no longer presents "Cost of revenues" or "Gross profit" in its Consolidated Statement of Operations. For all periods prior to January 1, 2018, the Company reported under the previous revenue standard. See Note 2 for further information. (2) Includes, for the fourth quarter of 2018, an income tax benefit of $46 million to adjust the 2017 provisional tax expense related to a one-time transitional tax on mandatory deemed repatriation of accumulated unremitted international earnings as a result of the Tax Act. The income tax provision for the fourth quarter of 2017 includes a provisional tax expense of approximately $1.6 billion related to the transition tax mentioned above and a provisional tax benefit of $217 million related to the remeasurement of the Company’s U.S. deferred tax assets and liabilities as a result of the Tax Act.

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Purchase Price Allocation	The purchase price allocations were completed at December 31, 2017. The aggregate purchase price was allocated to the assets acquired and liabilities assumed as follows (in millions): Current assets (1) $ 50 Identifiable intangible assets (2) 333 Goodwill (3) 288 Property and equipment 1 Total liabilities (4) (116 ) Total consideration $ 556 (1) Includes cash acquired of $15 million . (2) Acquired definite-lived intangible assets, consisted of distribution agreements of $214 million with a weighted-average useful life of 15 years, trade names of $104 million with a weighted-average useful life of 13 years and technology of $15 million with a weighted-average life of 4 years. (3) Goodwill is not tax deductible. (4) Includes deferred tax liabilities of $70 million and third-party senior debt of $15 million .

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) € in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2018USD ($)	Jan. 01, 2018USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2017USD ($)	Mar. 10, 2017EUR (€)	Nov. 25, 2015EUR (€)	Mar. 03, 2015EUR (€)	Sep. 23, 2014EUR (€)
Accounting Policies [Line Items]
Equity securities without readily determinable fair value reclassified from other assets to long-term investments										$ 451
Purchase of investments		$ 2,686	$ 6,941	$ 6,748
Investments in equity securities							$ 501
Net unrealized losses on marketable equity securities		(367)	0	0
Land-use rights							47			51
Reduction in loyalty liability estimate	$ 27
Deferred revenue recognized		109
Cancellation refunds		$ 10
Accrued online advertising liabilities							313			284
Accrued compensation liabilities							348			288
Number of reportable segments | segment		1
Cumulative effect of adoption of accounting standard updates							189			280
Acquisitions and other investments, net of cash acquired		$ 273	553	1
Software Development
Accounting Policies [Line Items]
Estimated useful life		5 years
Additions to capitalized website development		$ 97	80	54
0.8% Senior Notes Due March 2022
Accounting Policies [Line Items]
Senior notes face amount | €						€ 1,000			€ 1,000		€ 1,000
2.15% Senior Notes Due November 2022
Accounting Policies [Line Items]
Senior notes face amount | €						750			750			€ 750
1.8% Senior Notes Due March 2027
Accounting Policies [Line Items]
Senior notes face amount | €						1,000			1,000				€ 1,000
2.375% Senior Notes Due September 2024
Accounting Policies [Line Items]
Senior notes face amount | €						€ 1,000			€ 1,000					€ 1,000
Accrued Expenses and Other Current Liabilities
Accounting Policies [Line Items]
Contract liability, current							73
Loyalty program incentive liabilities										105
Deferred Merchant Bookings
Accounting Policies [Line Items]
Contract liability, current							149
Deferred revenue										151
Performance Marketing Expense
Accounting Policies [Line Items]
Advertising expense		4,400	4,100	3,500
Brand Marketing Expense
Accounting Policies [Line Items]
Advertising expense		$ 457	392	296
Retained Earnings
Accounting Policies [Line Items]
Cumulative effect of adoption of accounting standard updates							$ 430			$ 271
Retained Earnings | Accounting Standards Update 2016-01
Accounting Policies [Line Items]
Cumulative effect of adoption of accounting standard updates								$ 241
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Accounting Policies [Line Items]
Contract liability, current								$ (32)
Restatement Adjustment
Accounting Policies [Line Items]
Purchase of investments			450	7
Acquisitions and other investments, net of cash acquired			$ (450)	$ (7)
Minimum | Software Development
Accounting Policies [Line Items]
Estimated useful life		2 years
Scenario, Forecast | Accounting Standards Update 2016-02
Accounting Policies [Line Items]
Operating lease right-of-use assets					$ 640
Operating lease liability					$ 650

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Change in Presentation and Reclassification) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Prior Period Presentation Adjustments [Line Items]
Cost of revenues		$ 242	$ 415
Performance marketing	$ 4,447	4,161	3,479
Brand marketing	509	435	327
Sales and other expenses	830	517	422
General and administrative	$ 699	576	452
Previously Reported
Prior Period Presentation Adjustments [Line Items]
Cost of revenues		251	428
Performance advertising		4,142	3,479
Brand advertising		392	296
Sales and marketing		562	435
General and administrative		$ 586	$ 456

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Balance Sheet Impacts of Adopting Revenue Standard) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 1,523	$ 1,423	$ 1,218
Prepaid expenses and other current assets	600		415
Other Assets	181		148
Accounts payable	1,134	840	668
Accrued expenses and other current liabilities	1,399	1,183	1,139
Deferred merchant bookings	1,022	778	980
Deferred income taxes	370	483	481
Retained earnings	18,367	14,128	13,939
Accumulated other comprehensive income (loss)	(316)		238
As adjusted (previous revenue standard)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	1,307		1,218
Prepaid expenses and other current assets	610
Accounts payable	900		668
Accrued expenses and other current liabilities	1,352		1,139
Deferred merchant bookings	1,302		980
Deferred income taxes	367		481
Retained earnings	18,162		$ 13,939
Accumulated other comprehensive income (loss)	(313)
Accounting Standards Update 2014-09 | Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	(216)	205
Prepaid expenses and other current assets	10
Accounts payable	(234)	172
Accrued expenses and other current liabilities	(47)	44
Deferred merchant bookings	280	(202)
Deferred income taxes	(3)	2
Retained earnings	(205)	$ 189
Accumulated other comprehensive income (loss)	$ 3

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Statement of Operations Impacts of Adopting Revenue Standard) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Agency revenues											$ 10,480
Agency revenues												$ 9,714		$ 7,982
Merchant revenues											2,987
Merchant revenues												2,133		2,048
Advertising and other revenues											1,060	834		713
Cost of revenues												242		415
Performance marketing											4,447	4,161		3,479
Sales and other expenses											830	517		422
General and administrative											699	576		452
Foreign currency transactions and other											(57)	(34)		(17)
Income tax expense											837	2,058		578
Net income	$ 646	[1]	$ 1,768	$ 977	$ 607	$ (555)		$ 1,720	$ 720	$ 456	$ 3,998	$ 2,341	[2]	$ 2,135	[2]
Net income applicable to common stockholders per basic common share	$ 14		$ 37.39	$ 20.34	$ 12.56	$ (11.41)		$ 35.12	$ 14.66	$ 9.26	$ 84.26	$ 47.78		$ 43.14
Net income applicable to common stockholders per diluted common share	$ 13.86		$ 37.02	$ 20.13	$ 12.34	$ (11.41)		$ 34.43	$ 14.39	$ 9.11	$ 83.26	$ 46.86		$ 42.65
As adjusted (previous revenue standard)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Agency revenues											$ 10,470
Merchant revenues											3,144
Cost of revenues											170
Performance marketing											4,445
Foreign currency transactions and other											(55)
Income tax expense											834
Net income											$ 3,982
Net income applicable to common stockholders per basic common share											$ 83.92
Net income applicable to common stockholders per diluted common share											$ 82.92
Accounting Standards Update 2014-09 | Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Agency revenues											$ (10)
Merchant revenues											157
Cost of revenues											170
Performance marketing											(2)
Foreign currency transactions and other											2
Income tax expense											(3)
Net income											$ (16)
Net income applicable to common stockholders per basic common share											$ (0.34)
Net income applicable to common stockholders per diluted common share											$ (0.34)
[1]	Includes, for the fourth quarter of 2018, an income tax benefit of $46 million to adjust the 2017 provisional tax expense related to a one-time transitional tax on mandatory deemed repatriation of accumulated unremitted international earnings as a result of the Tax Act. The income tax provision for the fourth quarter of 2017 includes a provisional tax expense of approximately $1.6 billion related to the transition tax mentioned above and a provisional tax benefit of $217 million related to the remeasurement of the Company’s U.S. deferred tax assets and liabilities as a result of the Tax Act.
[2]	The Company realized net gains of $1 million related to investments in debt securities sold for both years ended December 31, 2017 and 2016.

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Reconciliation of Cash, Cash Equivalents and Restricted Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 2,624	$ 2,542
Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Consolidated Statements of Cash Flows	2,645	2,563	$ 2,082	$ 1,478
Accounting Standards Update 2016-18
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	2,624	2,542	2,081
Restricted cash and cash equivalents included in prepaid expenses and other current assets	21	21	1
Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Consolidated Statements of Cash Flows	$ 2,645	$ 2,563	$ 2,082

STOCK-BASED COMPENSATION (Narra

STOCK-BASED COMPENSATION (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 317	$ 261	$ 250
Share-based compensation, cumulative charges for adjustment of the estimated probable outcome on unvested performance awards	48	11	21
Stock-based compensation cost, non-employee directors	6	3	3
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$ 36	$ 46	$ 45
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant term (in years)	10 years
1999 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available to be issued under the plan (in shares)	2,001,849
Other plans assumed in acquisitions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available to be issued under the plan (in shares)	93,726
Minimum | Awards Other Than Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	1 year
Maximum | Awards Other Than Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years

STOCK-BASED COMPENSATION (Restr

STOCK-BASED COMPENSATION (Restricted Stock Units and Performance Share Units) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Awards Other Than Options
Share-Based Awards - Shares
Unvested, beginning of period (in shares)	524,696	515,606	637,257
Granted (in shares)	166,304	174,507	202,740
Vested (in shares)	(204,242)	(143,771)	(298,753)
Performance Shares Adjustment (in shares)	66,245	19,357	52,224
Forfeited (in shares)	(41,441)	(41,003)	(77,862)
Unvested, end of period (in shares)	511,562	524,696	515,606
Share-Based Awards - Weighted Average Grant Date Fair Value
Unvested at (in dollars per share)	$ 1,431.88	$ 1,287.88	$ 1,070.10
Granted (in dollars per share)	2,027.43	1,740.78	1,314.93
Vested (in dollars per share)	1,297.21	1,316.26	858.23
Performance Shares Adjustment (in dollars per share)	1,872.06	1,501.48	1,294.84
Forfeited (in dollars per share)	1,713.45	1,416.09	1,278.06
Unvested at (in dollars per share)	$ 1,713.44	$ 1,431.88	$ 1,287.88
Restricted stock units and performance share units aggregate grant-date fair value	$ 337	$ 304	$ 267
Aggregate grant-date fair value of restricted shares, performance share units and restricted stock units vested during the period	265	$ 189	$ 256
Total future compensation cost related to unvested share-based awards	$ 420
Total future compensation cost related to unvested share-based awards, expected period of recognition	1 year 11 months
Restricted Stock Units (RSUs)
Share-Based Awards - Shares
Granted (in shares)	116,583
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 2,024.71
Vesting period (in years)	3 years
Grant date fair value	$ 236
Performance Share Units 2018 Grants [Member]
Share-Based Awards - Shares
Granted (in shares)	49,721
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 2,033.79
Grant date fair value	$ 101
Estimated number of probable shares to be issued (in shares)	86,438
Maximum shares that could be issued (in shares)	91,638
Minimum shares that could be issued (in shares)	34,509
Performance Share Units 2017 Grants
Share-Based Awards - Shares
Granted (in shares)		73,893
Unvested, end of period (in shares)	60,963
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)		$ 1,735.10
Grant date fair value		$ 128
Estimated number of probable shares to be issued (in shares)	90,151
Maximum shares that could be issued (in shares)	121,926
Minimum shares that could be issued (in shares)	47,706
Performance Share Units 2016 Grants
Share-Based Awards - Shares
Granted (in shares)			85,735
Unvested, end of period (in shares)	63,230
Share-Based Awards - Weighted Average Grant Date Fair Value
Granted (in dollars per share)			$ 1,302.25
Grant date fair value			$ 112
Estimated number of probable shares to be issued (in shares)	103,076

STOCK-BASED COMPENSATION (Sched

STOCK-BASED COMPENSATION (Schedule of Assumed Stock Options) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Vested and exercisable and expected to vest thereafter, net of estimated forfeitures
Stock-based compensation	$ 317	$ 261	$ 250
Employee Stock Option
Number of Shares
Balance, (in shares)	30,675	48,983	89,104
Exercised (in shares)	(3,318)	(17,359)	(38,150)
Forfeited (in shares)	(94)	(949)	(1,971)
Balance, (in shares)	27,263	30,675	48,983	89,104
Weighted-Average Exercise Price
Balance, (in dollars per share)	$ 401.61	$ 372.07	$ 383.03
Exercised (in dollars per share)	494.66	294.45	404.40
Forfeited (in dollars per share)	450.84	837.09	241.65
Balance, (in dollars per share)	$ 386.97	$ 401.61	$ 372.07	$ 383.03
Aggregate Intrinsic Value (in millions)
Aggregate Intrinsic Value	$ 36	$ 41	$ 54	$ 79
Weighted Average Remaining Contractual Term	2 years 10 months	3 years 11 months	4 years 5 months	5 years 5 months
Vested and exercisable
Number of Shares	27,190
Weighted Average Exercise Price (in dollars per share)	$ 398.69
Aggregate Intrinsic Value	$ 36
Weighted Average Remaining Contractual Term	2 years 10 months
Vested and exercisable and expected to vest thereafter, net of estimated forfeitures
Number of Shares	27,263
Weighted Average Exercise Price (in dollars per share)	$ 386.97
Aggregate Intrinsic Value	$ 36
Weighted Average Remaining Contractual Term	2 years 10 months
Stock options exercised, total intrinsic value	$ 5	$ 26	$ 35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	98	1,515	12,180

INVESTMENTS (Details)

INVESTMENTS (Details) - USD ($) $ in Millions	Sep. 12, 2016	Dec. 11, 2015	May 26, 2015	Aug. 07, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 17, 2018	Oct. 31, 2017
Investments
Weighted maturity of investments					1 year 2 months
Cost Method Investments						$ 451
Equity Securities without Readily Determinable Fair Value, Amount					$ 501
Impairment of investments						8	$ 63
Short-term Investments
Investments
Cost						4,866
Gross Unrealized Gains						1
Gross Unrealized Losses						(7)
Fair Value						4,860
Marketable Securities, Cost					3,674
Marketable Securities, Gross Unrealized Gain					0
Marketable Securities, Gross Unrealized Losses					(14)
Marketable Securities, Current					3,660
Short-term Investments | International government securities
Investments
Cost						725
Gross Unrealized Gains						0
Gross Unrealized Losses						0
Fair Value						725
Debt Securities, Available-for-sale, Amortized Cost					314
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					0
Debt Securities, Available-for-sale					314
Short-term Investments | U.S. government securities
Investments
Cost						996
Gross Unrealized Gains						0
Gross Unrealized Losses						(2)
Fair Value						994
Debt Securities, Available-for-sale, Amortized Cost					658
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					(2)
Debt Securities, Available-for-sale					656
Short-term Investments | Corporate debt securities
Investments
Cost						3,068
Gross Unrealized Gains						1
Gross Unrealized Losses						(5)
Fair Value						3,064
Debt Securities, Available-for-sale, Amortized Cost					2,693
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					(12)
Debt Securities, Available-for-sale					2,681
Short-term Investments | U.S. government agency securities
Investments
Cost						4
Gross Unrealized Gains						0
Gross Unrealized Losses						0
Fair Value						4
Debt Securities, Available-for-sale, Amortized Cost					1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					0
Debt Securities, Available-for-sale					1
Short-term Investments | Commercial paper
Investments
Cost						73
Gross Unrealized Gains						0
Gross Unrealized Losses						0
Fair Value						73
Debt Securities, Available-for-sale, Amortized Cost					7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					0
Debt Securities, Available-for-sale					7
Short-term Investments | Certificates of Deposit [Member]
Investments
Debt Securities, Available-for-sale, Amortized Cost					1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					0
Debt Securities, Available-for-sale					1
Long-term Investments
Investments
Cost						10,072
Gross Unrealized Gains						413
Gross Unrealized Losses						(63)
Fair Value						10,422
Marketable Securities, Cost					7,921
Marketable Securities, Gross Unrealized Gain					10
Marketable Securities, Gross Unrealized Losses					(224)
Marketable Securities, Noncurrent					7,707
Long-term Investments | International government securities
Investments
Cost						607
Gross Unrealized Gains						2
Gross Unrealized Losses						(1)
Fair Value						608
Debt Securities, Available-for-sale, Amortized Cost					797
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					0
Debt Securities, Available-for-sale					800
Long-term Investments | U.S. government securities
Investments
Cost						845
Gross Unrealized Gains						0
Gross Unrealized Losses						(10)
Fair Value						835
Debt Securities, Available-for-sale, Amortized Cost					299
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					(6)
Debt Securities, Available-for-sale					293
Long-term Investments | Corporate debt securities
Investments
Cost						6,690
Gross Unrealized Gains						8
Gross Unrealized Losses						(42)
Fair Value						6,656
Debt Securities, Available-for-sale, Amortized Cost					4,445
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					4
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					(48)
Debt Securities, Available-for-sale					4,401
Ctrip.com International, Ltd.
Investments
Debt Investment, Term	6 years	10 years	5 years	5 years
Ctrip.com International, Ltd. | Long-term Investments | Convertible debt securities
Investments
Cost	$ 25	$ 500	$ 250	$ 500		1,275
Gross Unrealized Gains						103
Gross Unrealized Losses						(9)
Fair Value						1,369
Debt Securities, Available-for-sale, Amortized Cost					1,275
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax					0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax					(98)
Debt Securities, Available-for-sale					1,177
Ctrip.com International, Ltd. | Long-term Investments | Equity securities
Investments
Cost						655
Gross Unrealized Gains						300
Gross Unrealized Losses						(1)
Fair Value						$ 954
Equity Securities, FV-NI, Cost					655
Net unrealized losses on marketable equity securities					2
Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, Before Tax					(72)
Assets, Fair Value Disclosure					585
Meituan-Dianping [Member]
Investments
Cost Method Investments									$ 450
Meituan-Dianping [Member] | Long-term Investments | Equity securities
Investments
Equity Securities, FV-NI, Cost					450
Net unrealized losses on marketable equity securities					1
Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, Before Tax					0
Assets, Fair Value Disclosure					451
Didi Chuxing [Member]
Investments
Equity Securities without Readily Determinable Fair Value, Amount								$ 500
Grab
Investments
Debt Securities, Available-for-sale, Noncurrent					$ 200

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Recurring Basis
ASSETS:
Total assets at fair value	$ 13,681	$ 17,322
Recurring Basis | Level 1
ASSETS:
Total assets at fair value	3,123	2,867
Recurring Basis | Level 2
ASSETS:
Total assets at fair value	10,358	14,455
Recurring Basis | Level 3
ASSETS:
Total assets at fair value	200
Cash equivalents | Recurring Basis | Money market funds
ASSETS:
Total assets at fair value	2,061	1,895
Cash equivalents | Recurring Basis | International government securities
ASSETS:
Total assets at fair value	21
Cash equivalents | Recurring Basis | U.S. government securities
ASSETS:
Total assets at fair value	1	22
Cash equivalents | Recurring Basis | Corporate debt securities
ASSETS:
Total assets at fair value		7
Cash equivalents | Recurring Basis | Commercial paper
ASSETS:
Total assets at fair value	2	96
Cash equivalents | Recurring Basis | Time deposits
ASSETS:
Total assets at fair value	25	18
Cash equivalents | Recurring Basis | Level 1 | Money market funds
ASSETS:
Total assets at fair value	2,061	1,895
Cash equivalents | Recurring Basis | Level 1 | International government securities
ASSETS:
Total assets at fair value	0
Cash equivalents | Recurring Basis | Level 1 | U.S. government securities
ASSETS:
Total assets at fair value	0	0
Cash equivalents | Recurring Basis | Level 1 | Corporate debt securities
ASSETS:
Total assets at fair value		0
Cash equivalents | Recurring Basis | Level 1 | Commercial paper
ASSETS:
Total assets at fair value	0	0
Cash equivalents | Recurring Basis | Level 1 | Time deposits
ASSETS:
Total assets at fair value	25	18
Cash equivalents | Recurring Basis | Level 2 | Money market funds
ASSETS:
Total assets at fair value	0	0
Cash equivalents | Recurring Basis | Level 2 | International government securities
ASSETS:
Total assets at fair value	21
Cash equivalents | Recurring Basis | Level 2 | U.S. government securities
ASSETS:
Total assets at fair value	1	22
Cash equivalents | Recurring Basis | Level 2 | Corporate debt securities
ASSETS:
Total assets at fair value		7
Cash equivalents | Recurring Basis | Level 2 | Commercial paper
ASSETS:
Total assets at fair value	2	96
Cash equivalents | Recurring Basis | Level 2 | Time deposits
ASSETS:
Total assets at fair value	0	0
Cash equivalents | Recurring Basis | Level 3 | Money market funds
ASSETS:
Total assets at fair value	0
Cash equivalents | Recurring Basis | Level 3 | International government securities
ASSETS:
Total assets at fair value	0
Cash equivalents | Recurring Basis | Level 3 | U.S. government securities
ASSETS:
Total assets at fair value	0
Cash equivalents | Recurring Basis | Level 3 | Commercial paper
ASSETS:
Total assets at fair value	0
Cash equivalents | Recurring Basis | Level 3 | Time deposits
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | International government securities
ASSETS:
Total assets at fair value	314	725
Short-term Investments | Recurring Basis | U.S. government securities
ASSETS:
Total assets at fair value	656	994
Short-term Investments | Recurring Basis | Corporate debt securities
ASSETS:
Total assets at fair value	2,681	3,064
Short-term Investments | Recurring Basis | Commercial paper
ASSETS:
Total assets at fair value	7	73
Short-term Investments | Recurring Basis | Certificates of Deposit [Member]
ASSETS:
Total assets at fair value	1
Short-term Investments | Recurring Basis | U.S. government agency securities
ASSETS:
Total assets at fair value	1	4
Short-term Investments | Recurring Basis | Level 1 | International government securities
ASSETS:
Total assets at fair value	0	0
Short-term Investments | Recurring Basis | Level 1 | U.S. government securities
ASSETS:
Total assets at fair value	0	0
Short-term Investments | Recurring Basis | Level 1 | Corporate debt securities
ASSETS:
Total assets at fair value	0	0
Short-term Investments | Recurring Basis | Level 1 | Commercial paper
ASSETS:
Total assets at fair value	0	0
Short-term Investments | Recurring Basis | Level 1 | Certificates of Deposit [Member]
ASSETS:
Total assets at fair value	1
Short-term Investments | Recurring Basis | Level 1 | U.S. government agency securities
ASSETS:
Total assets at fair value	0	0
Short-term Investments | Recurring Basis | Level 2 | International government securities
ASSETS:
Total assets at fair value	314	725
Short-term Investments | Recurring Basis | Level 2 | U.S. government securities
ASSETS:
Total assets at fair value	656	994
Short-term Investments | Recurring Basis | Level 2 | Corporate debt securities
ASSETS:
Total assets at fair value	2,681	3,064
Short-term Investments | Recurring Basis | Level 2 | Commercial paper
ASSETS:
Total assets at fair value	7	73
Short-term Investments | Recurring Basis | Level 2 | Certificates of Deposit [Member]
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | Level 2 | U.S. government agency securities
ASSETS:
Total assets at fair value	1	4
Short-term Investments | Recurring Basis | Level 3 | International government securities
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | Level 3 | U.S. government securities
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | Level 3 | Corporate debt securities
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | Level 3 | Commercial paper
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | Level 3 | Certificates of Deposit [Member]
ASSETS:
Total assets at fair value	0
Short-term Investments | Recurring Basis | Level 3 | U.S. government agency securities
ASSETS:
Total assets at fair value	0
Long-term Investments | Recurring Basis | International government securities
ASSETS:
Total assets at fair value	800	608
Long-term Investments | Recurring Basis | U.S. government securities
ASSETS:
Total assets at fair value	293	835
Long-term Investments | Recurring Basis | Corporate debt securities
ASSETS:
Total assets at fair value	4,401	6,656
Long-term Investments | Recurring Basis | Level 1 | International government securities
ASSETS:
Total assets at fair value	0	0
Long-term Investments | Recurring Basis | Level 1 | U.S. government securities
ASSETS:
Total assets at fair value	0	0
Long-term Investments | Recurring Basis | Level 1 | Corporate debt securities
ASSETS:
Total assets at fair value	0	0
Long-term Investments | Recurring Basis | Level 2 | International government securities
ASSETS:
Total assets at fair value	800	608
Long-term Investments | Recurring Basis | Level 2 | U.S. government securities
ASSETS:
Total assets at fair value	293	835
Long-term Investments | Recurring Basis | Level 2 | Corporate debt securities
ASSETS:
Total assets at fair value	4,401	6,656
Long-term Investments | Recurring Basis | Level 3 | International government securities
ASSETS:
Total assets at fair value	0
Long-term Investments | Recurring Basis | Level 3 | U.S. government securities
ASSETS:
Total assets at fair value	0
Long-term Investments | Recurring Basis | Level 3 | Corporate debt securities
ASSETS:
Total assets at fair value	0
Other Long-term Investment | Recurring Basis
ASSETS:
Total assets at fair value	200
Other Long-term Investment | Recurring Basis | Level 1
ASSETS:
Total assets at fair value	0
Other Long-term Investment | Recurring Basis | Level 2
ASSETS:
Total assets at fair value	0
Other Long-term Investment | Recurring Basis | Level 3
ASSETS:
Total assets at fair value	200
Foreign exchange derivatives | Recurring Basis
ASSETS:
Total assets at fair value	4	2
Foreign exchange derivatives | Recurring Basis | Level 1
ASSETS:
Total assets at fair value	0	0
Foreign exchange derivatives | Recurring Basis | Level 2
ASSETS:
Total assets at fair value	4	2
Foreign exchange derivatives | Recurring Basis | Level 3
ASSETS:
Total assets at fair value	0
Meituan-Dianping [Member] | Long-term Investments | Equity securities
ASSETS:
Total assets at fair value	451
Meituan-Dianping [Member] | Long-term Investments | Recurring Basis | Equity securities
ASSETS:
Total assets at fair value	451
Meituan-Dianping [Member] | Long-term Investments | Recurring Basis | Level 1 | Equity securities
ASSETS:
Total assets at fair value	451
Meituan-Dianping [Member] | Long-term Investments | Recurring Basis | Level 2 | Equity securities
ASSETS:
Total assets at fair value	0
Meituan-Dianping [Member] | Long-term Investments | Recurring Basis | Level 3 | Equity securities
ASSETS:
Total assets at fair value	0
Ctrip.com International, Ltd. | Long-term Investments | Equity securities
ASSETS:
Total assets at fair value	585
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Convertible debt securities
ASSETS:
Total assets at fair value	1,177	1,369
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Equity securities
ASSETS:
Total assets at fair value	585	954
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Level 1 | Convertible debt securities
ASSETS:
Total assets at fair value	0	0
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Level 1 | Equity securities
ASSETS:
Total assets at fair value	585	954
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Level 2 | Convertible debt securities
ASSETS:
Total assets at fair value	1,177	1,369
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Level 2 | Equity securities
ASSETS:
Total assets at fair value	0	$ 0
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Level 3 | Convertible debt securities
ASSETS:
Total assets at fair value	0
Ctrip.com International, Ltd. | Long-term Investments | Recurring Basis | Level 3 | Equity securities
ASSETS:
Total assets at fair value	$ 0

FAIR VALUE MEASUREMENTS (Narrat

FAIR VALUE MEASUREMENTS (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 12, 2016	Dec. 11, 2015	May 26, 2015	Aug. 07, 2014
Derivatives Not Designated as Hedging Instruments
Foreign exchange gains (losses), net of derivative activity	$ (47)	$ (27)	$ (14)
Derivatives Designated as Hedging Instruments
Equity Securities without Readily Determinable Fair Value, Amount	501
Foreign Exchange Contracts, Translation Risk
Derivatives Not Designated as Hedging Instruments
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	0	0
Foreign Exchange Contracts, Transaction Risk
Derivatives Not Designated as Hedging Instruments
Foreign exchange gains (losses) recorded in "Foreign currency transactions and other"	(44)	45	(16)
Foreign exchange derivatives
Derivatives Not Designated as Hedging Instruments
Proceeds for Derivative Instrument Operating Activities		41	$ 5
Payments for Derivative Instrument Operating Activities	56
Long-term Investments
Derivatives Designated as Hedging Instruments
Ctrip convertible notes		10,072
Grab
Foreign Currency Derivatives
Debt Securities, Available-for-sale, Noncurrent	200
Ctrip.com International, Ltd. | Convertible debt securities | Long-term Investments
Derivatives Designated as Hedging Instruments
Ctrip convertible notes		1,275		$ 25	$ 500	$ 250	$ 500
Embedded derivative fair value	0.1	$ 2
Level 3 | Grab
Foreign Currency Derivatives
Debt Securities, Available-for-sale, Noncurrent	$ 200

ACCOUNTS RECEIVABLE RESERVES (D

ACCOUNTS RECEIVABLE RESERVES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Balance, beginning of year	$ 39	$ 26	$ 15
Provision charged to expense	163	62	46
Charge-offs and adjustments	(139)	(52)	(35)
Currency translation adjustments	(2)	3	0
Balance, end of year	$ 61	$ 39	$ 26

NET INCOME PER SHARE (Details)

NET INCOME PER SHARE (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Anti-dilutive Securities Excluded From Computation Of Earnings Per Share
Weighted-average number of basic common shares outstanding (in 000's)	47,446	48,994	49,491
Weighted-average dilutive stock options, restricted stock units and performance share units	236	295	238
Assumed conversion of Convertible Senior Notes	335	665	334
Weighted-average number of diluted common and common equivalent shares outstanding	48,017	49,954	50,063
Antidultive outstanding stock awards and convertible debt securities
Anti-dilutive Securities Excluded From Computation Of Earnings Per Share
Anti-dilutive potential common shares	1,411	1,864	2,443
Convertible Debt
Anti-dilutive Securities Excluded From Computation Of Earnings Per Share
Anti-dilutive potential common shares	1,000	1,000	2,000

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,349	$ 1,023
Less: accumulated depreciation	(693)	(543)
Property and equipment, net	656	480
Depreciation	248	187	$ 140
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 964	769
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	2 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 242	199
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	1 year
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	13 years
Office equipment, furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 55	47
Office equipment, furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	2 years
Office equipment, furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	7 years
Building construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 88	$ 8

INTANGIBLE ASSETS AND GOODWIL_2

INTANGIBLE ASSETS AND GOODWILL (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-lived intangible assets
Gross Carrying Amount	$ 3,126	$ 3,039
Accumulated Amortization	(1,001)	(862)
Net Carrying Amount	2,125	2,177	$ 1,994
Intangible assets amortization expense	178	176	$ 169
Supply and distribution agreements
Finite-lived intangible assets
Gross Carrying Amount	1,099	1,057
Accumulated Amortization	(408)	(355)
Net Carrying Amount	$ 691	702
Supply and distribution agreements | Minimum
Finite-lived intangible assets
Amortization Period	3 years
Supply and distribution agreements | Maximum
Finite-lived intangible assets
Amortization Period	20 years
Technology
Finite-lived intangible assets
Gross Carrying Amount	$ 173	137
Accumulated Amortization	(121)	(104)
Net Carrying Amount	$ 52	33
Technology | Minimum
Finite-lived intangible assets
Amortization Period	1 year
Technology | Maximum
Finite-lived intangible assets
Amortization Period	7 years
Patents
Finite-lived intangible assets
Gross Carrying Amount	$ 2	2
Accumulated Amortization	(2)	(2)
Net Carrying Amount	$ 0	0
Amortization Period	15 years
Internet domain names
Finite-lived intangible assets
Gross Carrying Amount	$ 41	42
Accumulated Amortization	(30)	(29)
Net Carrying Amount	$ 11	13
Internet domain names | Minimum
Finite-lived intangible assets
Amortization Period	5 years
Internet domain names | Maximum
Finite-lived intangible assets
Amortization Period	20 years
Trade names
Finite-lived intangible assets
Gross Carrying Amount	$ 1,810	1,779
Accumulated Amortization	(439)	(350)
Net Carrying Amount	$ 1,371	1,429
Trade names | Minimum
Finite-lived intangible assets
Amortization Period	4 years
Trade names | Maximum
Finite-lived intangible assets
Amortization Period	20 years
Non-compete agreements
Finite-lived intangible assets
Gross Carrying Amount	$ 1	22
Accumulated Amortization	(1)	(22)
Net Carrying Amount	$ 0	$ 0
Amortization Period	4 years

INTANGIBLE ASSETS AND GOODWIL_3

INTANGIBLE ASSETS AND GOODWILL (Finite-lived intangibles) (Details) $ in Millions	Dec. 31, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,019	$ 174
2,020	166
2,021	158
2,022	156
2,023	154
Thereafter	1,317
Total	$ 2,125

INTANGIBLE ASSETS AND GOODWIL_4

INTANGIBLE ASSETS AND GOODWILL (Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Balance, beginning of year	$ 2,738	$ 2,397
Acquisitions	212	294
Currency translation adjustments	(40)	47
Balance, end of year	$ 2,910	$ 2,738

INTANGIBLE ASSETS AND GOODWIL_5

INTANGIBLE ASSETS AND GOODWILL (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Impairment of goodwill	$ 0	$ 0	$ 941
OpenTable
Goodwill [Line Items]
Impairment of goodwill			$ 941

DEBT (Short Term Borrowings and

DEBT (Short Term Borrowings and Revolving Credit) (Details) - USD ($) $ in Millions	Jun. 19, 2015	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Bank Overdrafts			$ 25
Letters of Credit Outstanding, Amount			$ 5	$ 4
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	$ 2,000
Line of credit facility, term	5 years
Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Revolving credit facility commitment fee percentage on undrawn balances	0.085%
Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Revolving credit facility commitment fee percentage on undrawn balances	0.20%
Revolving Credit Facility | 3.5% Borrowings - January 2019 [Member] | Subsequent Event
Debt Instrument [Line Items]
Amount borrowed		$ 100
Interest rate stated percentage (as a percent)		3.50%
Revolving Credit Facility | Rate 1 | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Revolving credit facility interest rate	0.875%
Revolving Credit Facility | Rate 1 | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Revolving credit facility interest rate	1.50%
Revolving Credit Facility | Rate 2B | Federal Funds Purchased
Debt Instrument [Line Items]
Revolving credit facility interest rate	0.50%
Revolving Credit Facility | Rate 2C | Minimum
Debt Instrument [Line Items]
Revolving credit facility interest rate	0.00%
Revolving Credit Facility | Rate 2C | Maximum
Debt Instrument [Line Items]
Revolving credit facility interest rate	0.50%
Revolving Credit Facility | Rate 2C | One Month LIBOR
Debt Instrument [Line Items]
Revolving credit facility interest rate	1.00%
Letter of Credit
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	$ 70
Swingline Loans
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	$ 50

DEBT (Outstanding Debt) (Detail

DEBT (Outstanding Debt) (Details) $ / shares in Units, € in Millions, $ in Millions	Aug. 20, 2014USD ($)Days$ / shares	May 31, 2013USD ($)Days$ / shares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2018USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2017USD ($)	Aug. 15, 2017USD ($)	Jul. 24, 2017USD ($)	Mar. 10, 2017EUR (€)	May 23, 2016USD ($)	Nov. 25, 2015EUR (€)	Mar. 13, 2015USD ($)	Mar. 03, 2015EUR (€)	Sep. 23, 2014EUR (€)	Jun. 30, 2013USD ($)	Mar. 31, 2012USD ($)$ / shares
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 8,787		$ 9,003
Unamortized Debt Discount and Debt Issuance Cost										(138)		(193)
Long-term Debt										8,649		8,810
Description of Senior Notes
Reclassification of unamortized debt discount from additional paid-in-capital to convertible debt in mezzanine										0		3
Payments for conversion of senior notes			$ 1,487	$ 286	$ 0
Amortization of debt discount			52	70	69
Level 2
Description of Senior Notes
Estimated market value of outstanding senior notes										9,300		11,100
Momondo Group
Description of Senior Notes
Debt assumed in acquisition(s)														$ 15
1.00% Convertible Senior Notes Due March 2018
Debt Instrument [Line Items]
Outstanding Principal Amount												714
Unamortized Debt Discount and Debt Issuance Cost												(3)
Short-term Debt												$ 711
Description of Senior Notes
Reclassification of unamortized debt discount from additional paid-in-capital to convertible debt in mezzanine										3
Senior notes face amount																						$ 1,000
Interest rate stated percentage (as a percent)											1.00%	1.00%										1.00%
Debt Instrument, Convertible, Conversion Price | $ / shares																						$ 944.61
Payments for conversion of senior notes			714
Cash payment of the conversion value in excess of the principal amount			773
Debt Instrument, Interest Rate, Effective Percentage																						3.50%
Debt discount related to convertible notes, net of tax																						$ 81
Debt discount related to convertible notes, before tax																						$ 135
Convertible Notes
Description of Senior Notes
Interest Expense, Debt			66	94	95
Debt Instrument, Coupon Interest Expense			14	21	22
Amortization of debt discount			$ 50	$ 68	$ 68
Weighted-average effective interest rate during the period			3.20%	3.40%	3.40%
Amortization of debt issuance costs included in interest expense			$ 2	$ 5	$ 5
0.35% Senior Convertible Notes Due June 2020
Debt Instrument [Line Items]
Outstanding Principal Amount										1,000		$ 1,000
Unamortized Debt Discount and Debt Issuance Cost										(39)		(65)
Long-term Debt										$ 961		$ 935
Description of Senior Notes
Senior notes face amount		$ 1,000
Interest rate stated percentage (as a percent)		0.35%							0.35%	0.35%	0.35%	0.35%
Unamortized Debt Discount		$ 20
Payments of debt issuance costs								$ 1
Debt Instrument, Convertible, Conversion Price | $ / shares		$ 1,315.10
Ratio of closing share price to conversion price as a condition for conversion of convertible 2015 Senior Notes, minimum (as a percent)		150.00%
Debt Instrument, Interest Rate, Effective Percentage		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			3	3	3
0.35% Senior Convertible Notes Due June 2020 | Minimum
Description of Senior Notes
Debt Instrument, Convertible, Threshold Consecutive Trading Days | Days		20
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares		$ 0
0.35% Senior Convertible Notes Due June 2020 | Maximum
Description of Senior Notes
Debt Instrument, Convertible, Threshold Consecutive Trading Days | Days		30
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares		$ 397
0.9% Senior Convertible Notes Due September 2021
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 1,000		$ 1,000
Unamortized Debt Discount and Debt Issuance Cost										(61)		(83)
Long-term Debt										$ 939		$ 917
Description of Senior Notes
Senior notes face amount	$ 1,000
Interest rate stated percentage (as a percent)	0.90%								0.90%	0.90%	0.90%	0.90%
Payments of debt issuance costs							$ 11
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 2,055.50
Ratio of closing share price to conversion price as a condition for conversion of convertible 2015 Senior Notes, minimum (as a percent)	150.00%
Debt Instrument, Interest Rate, Effective Percentage	3.18%
Debt discount related to convertible notes, net of tax						$ 83
Debt discount related to convertible notes, before tax						143
0.9% Senior Convertible Notes Due September 2021 | Minimum
Description of Senior Notes
Debt Instrument, Convertible, Threshold Consecutive Trading Days | Days	20
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares	$ 0
0.9% Senior Convertible Notes Due September 2021 | Maximum
Description of Senior Notes
Debt Instrument, Convertible, Threshold Consecutive Trading Days | Days	30
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares	$ 375
0.8% Senior Notes Due March 2022
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 1,143		$ 1,201
Unamortized Debt Discount and Debt Issuance Cost										(5)		(6)
Long-term Debt										$ 1,138		$ 1,195
Description of Senior Notes
Senior notes face amount | €									€ 1,000		€ 1,000				€ 1,000
Interest rate stated percentage (as a percent)									0.80%	0.80%	0.80%	0.80%			0.80%
Unamortized Debt Discount | €															€ 2
Payments of debt issuance costs				5
Debt Instrument, Interest Rate, Effective Percentage															0.84%
2.15% Senior Notes Due November 2022
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 858		$ 900
Unamortized Debt Discount and Debt Issuance Cost										(4)		(5)
Long-term Debt										$ 854		$ 895
Description of Senior Notes
Senior notes face amount | €									€ 750		€ 750						€ 750
Interest rate stated percentage (as a percent)									2.15%	2.15%	2.15%	2.15%					2.15%
Unamortized Debt Discount | €																	€ 2
Payments of debt issuance costs						4
Debt Instrument, Interest Rate, Effective Percentage																		2.20%
2.75% Senior Notes Due March 2023
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 500		$ 500
Unamortized Debt Discount and Debt Issuance Cost										(3)		(3)
Long-term Debt										$ 497		$ 497
Description of Senior Notes
Senior notes face amount													$ 500
Interest rate stated percentage (as a percent)									2.75%	2.75%	2.75%	2.75%	2.75%
Unamortized Debt Discount													$ 1
Payments of debt issuance costs				3
Debt Instrument, Interest Rate, Effective Percentage													2.78%
2.375% Senior Notes Due September 2024
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 1,143		$ 1,201
Unamortized Debt Discount and Debt Issuance Cost										(10)		(12)
Long-term Debt										$ 1,133		$ 1,189
Description of Senior Notes
Senior notes face amount | €									€ 1,000		€ 1,000									€ 1,000
Interest rate stated percentage (as a percent)									2.375%	2.375%	2.375%	2.375%								2.375%
Unamortized Debt Discount | €																				€ 9
Payments of debt issuance costs							$ 7
Debt Instrument, Interest Rate, Effective Percentage																				2.48%
3.65% Senior Notes Due March 2025
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 500		$ 500
Unamortized Debt Discount and Debt Issuance Cost										(3)		(3)
Long-term Debt										$ 497		$ 497
Description of Senior Notes
Senior notes face amount																		$ 500
Interest rate stated percentage (as a percent)									3.65%	3.65%	3.65%	3.65%						3.65%
Unamortized Debt Discount																		$ 1
Payments of debt issuance costs						3
Debt Instrument, Interest Rate, Effective Percentage																		3.68%
3.6% Senior Notes Due June 2026
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 1,000		$ 1,000
Unamortized Debt Discount and Debt Issuance Cost										(6)		(7)
Long-term Debt										$ 994		$ 993
Description of Senior Notes
Senior notes face amount																$ 1,000
Interest rate stated percentage (as a percent)									3.60%	3.60%	3.60%	3.60%				3.60%
Unamortized Debt Discount																$ 2
Payments of debt issuance costs					6
Debt Instrument, Interest Rate, Effective Percentage																3.62%
1.8% Senior Notes Due March 2027
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 1,143		$ 1,201
Unamortized Debt Discount and Debt Issuance Cost										(4)		(5)
Long-term Debt										$ 1,139		$ 1,196
Description of Senior Notes
Senior notes face amount | €									€ 1,000		€ 1,000								€ 1,000
Interest rate stated percentage (as a percent)									1.80%	1.80%	1.80%	1.80%							1.80%
Unamortized Debt Discount | €																			€ 0.3
Payments of debt issuance costs						$ 6
Debt Instrument, Interest Rate, Effective Percentage																			1.80%
3.55% Senior Notes Due March 2028
Debt Instrument [Line Items]
Outstanding Principal Amount										$ 500		$ 500
Unamortized Debt Discount and Debt Issuance Cost										(3)		(4)
Long-term Debt										$ 497		$ 496
Description of Senior Notes
Senior notes face amount													$ 500
Interest rate stated percentage (as a percent)									3.55%	3.55%	3.55%	3.55%	3.55%
Unamortized Debt Discount													$ 0.4
Payments of debt issuance costs				3
Debt Instrument, Interest Rate, Effective Percentage													3.56%
Other Long-term Debt
Description of Senior Notes
Interest Expense, Debt			170	145	108
Debt Instrument, Coupon Interest Expense			$ 163	$ 139	$ 104

TREASURY STOCK (Details)

TREASURY STOCK (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Treasury Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 4,500	$ 2,400
Payments Related to Tax Withholding for Share-based Compensation	$ 163	$ 101	$ 166
Treasury stock, shares (in shares)	17,317,126	14,216,819
Repurchase Program (Q12018)
Treasury Stock [Line Items]
Stock repurchase program, authorized amount				$ 8,000
Repurchase Program (Q12016)
Treasury Stock [Line Items]
Stock repurchase program, authorized amount						$ 3,000
Repurchase Program (Q12017)
Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 2,000

TREASURY STOCK (Summary of Repu

TREASURY STOCK (Summary of Repurchase Activity) (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Shares				17,317,126	14,216,819
Repurchases (in shares)				3,100,307	1,025,890	762,984
Repurchases				$ 6,012	$ 1,844	$ 1,028
General authorization for shares withheld for stock award vesting (in shares)				79,746	57,369	127,107
General authorization for shares withheld on stock award vesting				$ 162	$ 100	$ 167
Repurchase Program (Q12017) and (Q12018) [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchases (in shares)				3,020,561
Repurchases				$ 5,850
Repurchase Program (Q12016)
Equity, Class of Treasury Stock [Line Items]
Repurchases (in shares)					968,521	635,877
Repurchases					$ 1,744	$ 861
Shares repurchased in December and settled in following January (in shares)		18,217	10,215
Shares repurchased in December and settled in following January		$ 32	$ 15
Subsequent Event | Repurchase Program (Q12018)
Equity, Class of Treasury Stock [Line Items]
Repurchases (in shares)	42,939
Repurchases	$ 74

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	$ 8,785	$ 11,261	$ 9,820	$ 8,795
Tax (benefit) associated with gain (loss) on net investment hedges	12
Tax (benefit) associated with gain (loss) on marketable securities	(2)	81	15
Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	(129)	(15)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	(316)	238	(135)	$ 245
Net Investment Hedging [Member] | Foreign Currency Adjustment Attributable to Parent [Member] | Euro Senior Notes [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	(26)	(190)
AOCI before Tax, Attributable to Parent	(20)	(237)
Net Investment Hedging [Member] | Foreign Currency Adjustment Attributable to Parent [Member] | Foreign Exchange Forward
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	(35)
AOCI before Tax, Attributable to Parent	$ (53)
The Netherlands
Accumulated Other Comprehensive Income (Loss) [Line Items]
Statutory rate (as a percent)	25.00%
Tax (benefit) associated with gain (loss) on marketable securities	$ (2)	18	$ 15
Domestic Tax Authority
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax (benefit) associated with gain (loss) on marketable securities		63
Ctrip.com International, Ltd. | Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI before Tax, Attributable to Parent		299
Ctrip.com International, Ltd. | The Netherlands | Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI before Tax, Attributable to Parent, Tax-exempt		320
AOCI before Tax, Attributable to Parent, Taxable		(21)
AOCI Tax, Attributable to Parent		(5)
Ctrip.com International, Ltd. | Internal Revenue Service (IRS) [Member] | Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent		63
Debt Securities [Member] | Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	(187)	12
Debt Securities [Member] | The Netherlands | Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI before Tax, Attributable to Parent, Tax-exempt	(276)	(86)
AOCI before Tax, Attributable to Parent, Taxable	123	130
AOCI Tax, Attributable to Parent	30	32
Currency translation adjustment on deemed repatriation tax liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax (benefit) associated with gain (loss) on net investment hedges	(41)
Ctrip.com International, Ltd. | Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders' equity	$ 0	$ 241

INCOME TAXES (Narrative) (Detai

INCOME TAXES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017
Income Tax Contingency [Line Items]
International pre-tax income			$ 4,800	$ 4,500	$ 3,700
Domestic pre-tax income			47	(122)	(983)
Impairment of goodwill			0	0	941
Transition tax for accumulated foreign earnings, provisional income tax expense (benefit)		$ 1,600
Provisional undistributed accumulated earnings of foreign subsidiary		16,500		16,500
Change In tax rate, deferred tax, provisional income tax expense (benefit)		217
Federal net operating loss carryforwards expected to be used		204		204
Other tax credit carryforwards		46		46
Long-term U.S. transition tax liability		1,300		1,300
Income tax benefit to adjust provisional tax expense	$ (46)		(46)	1,563	0
Tax Act - Remeasurement of deferred tax balances			(2)	(217)	0
Operating loss carryforwards used in period	133				379
Tax credit carryforwards used in period	23
Valuation allowance on deferred tax assets	36	44	36	44
Cumulative effect of adoption of accounting standard updates	189	280	189	280
Federal
Income Tax Contingency [Line Items]
Operating loss carryforwards	136		136
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Operating loss carryforwards	484		484
Foreign Tax Authority
Income Tax Contingency [Line Items]
Operating loss carryforwards	132		132
Valuation allowance on deferred tax assets	20	27	$ 20	27
The Netherlands
Income Tax Contingency [Line Items]
Innovation Box Tax rate			7.00%
Statutory rate (as a percent)			25.00%
OpenTable
Income Tax Contingency [Line Items]
Impairment of goodwill					$ 941
Geographic Distribution, Foreign
Income Tax Contingency [Line Items]
International cash and investments		16,200		16,200
Expiration Period between, December 31, 2020 and December 31, 2024 [Member] | Foreign Tax Authority
Income Tax Contingency [Line Items]
Operating loss carryforwards	50		$ 50
Research Tax Credit Carryforward | Domestic Tax Authority
Income Tax Contingency [Line Items]
Tax credit carryforward	51		51
Research credit, capital loss carryforward and state net operating losses [Member] | Domestic Tax Authority
Income Tax Contingency [Line Items]
Valuation allowance on deferred tax assets	16	17	16	17
Retained Earnings
Income Tax Contingency [Line Items]
Cumulative effect of adoption of accounting standard updates	$ 430	$ 271	$ 430	$ 271
Accounting Standards Update 2016-09, Unrecognized Equity Deductions Component | Accounting Standards Update 2016-09 | Retained Earnings
Income Tax Contingency [Line Items]
Cumulative effect of adoption of accounting standard updates						$ 301

INCOME TAXES (Income Tax expens

INCOME TAXES (Income Tax expense (benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current
International	$ 887	$ 756	$ 627
U.S. Federal	45	1,327	64
U.S. State	55	7	(1)
Total	987	2,090	690
Deferred
International	(3)	(10)	(14)
U.S. Federal	(107)	(57)	(33)
U.S. State	(40)	35	(65)
Total	(150)	(32)	(112)
Total
International	884	746	613
U.S. Federal	(62)	1,270	31
U.S. State	15	42	(66)
Income tax expense	$ 837	$ 2,058	$ 578

INCOME TAXES (Net deferred tax

INCOME TAXES (Net deferred tax Assets/(Liabilities)) (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets/(liabilities):
Net operating loss carryforward — U.S.		$ 59	$ 71
Net operating loss carryforward — International		20	28
Accrued expenses		50	57
Stock-based compensation and other stock based payments		51	48
Currency translation adjustment		27	0
Tax credits		46	15
Euro-denominated debt		5	58
Property and equipment		6	9
Subtotal - deferred tax assets		264	286
Discount on convertible notes		(22)	(33)
Intangible assets and other		(482)	(517)
State income tax on accumulated unremitted international earnings		(25)	(37)
Unrealized gain on investments		(2)	(70)
Other		(15)	(25)
Subtotal - deferred tax liabilities		(546)	(682)
Valuation allowance on deferred tax assets		(36)	(44)
Net deferred tax assets (liabilities)	[1]	(318)	(440)
Deferred tax assets		$ 51	$ 41
[1]	(1) Includes deferred tax assets of $51 million and $41 million at December 31, 2018 and 2017, respectively, reported in "Other assets" in the Consolidated Balance Sheets.

INCOME TAXES (Effective Income

INCOME TAXES (Effective Income Tax Rate Reconciliation and Income Tax Contingencies) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of effective income tax rate and amount computed using expected U.S. statutory federal rate
Income tax expense at federal statutory rate		$ 1,015	$ 1,539	$ 950
Adjustment due to:
Foreign rate differential		210	(458)	(378)
Innovation Box Tax benefit		(435)	(397)	(325)
Impairment of goodwill and cost-method investment		0	0	344
Tax Act - Remeasurement of deferred tax balances		(2)	(217)	0
Tax Act - U.S. transition tax and other transition impacts	$ (46)	(46)	1,563	0
Other		95	28	(13)
Income tax expense		837	2,058	578
Unrecognized tax benefits
Unrecognized tax benefit — January 1		32	33	43
Gross increases — tax positions in current period		1	5	2
Gross increases — tax positions in prior periods		19	5	1
Gross decreases — tax positions in prior periods		(3)	(9)	0
Reduction due to lapse in statute of limitations		(2)	(1)	(9)
Reduction due to settlements during the current period		(2)	(1)	(4)
Unrecognized tax benefit — December 31	$ 45	$ 45	$ 32	$ 33
The Netherlands
Operating Loss Carryforwards [Line Items]
Innovation Box Tax rate		7.00%
Statutory rate (as a percent)		25.00%

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES (Narrative) (Details) € in Millions, $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2018EUR (€)	Sep. 30, 2018USD ($)	Dec. 31, 2018EUR (€)country	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of pricing parity working group members | country			10
French Tax Audit
Travel Transaction Taxes
Assessed taxes including interest and penalties			€ 356
Italian Tax Audit
Travel Transaction Taxes
Assessed taxes including interest and penalties	€ 48
Turkish Tax Audit [Member]
Travel Transaction Taxes
Assessed taxes including interest and penalties			€ 71
Taxes Owed For Prior Periods
Travel Transaction Taxes
Loss Contingency, Loss in Period | $		$ 46
Loss Contingency, Range of Possible Loss, Portion Not Accrued | $				$ 20

COMMITMENTS AND CONTINGENCIES B

COMMITMENTS AND CONTINGENCIES Building Construction (Details) € in Millions, $ in Millions	3 Months Ended	12 Months Ended				27 Months Ended	54 Months Ended
	Sep. 30, 2016EUR (€)	Dec. 31, 2018EUR (€)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Mar. 31, 2021EUR (€)	Mar. 31, 2021EUR (€)
Other Commitments [Line Items]
Acquisition of land use rights | $			$ 0	$ 0	$ 48
Payments for building construction | $			$ 442	$ 288	$ 220
Headquarters | Booking.com
Other Commitments [Line Items]
Contractual Obligation	€ 270
Payments to developer for land-use rights and building construction	48
Acquisition of land use rights	43
Payments for building construction	€ 5	€ 66
Ground Lease | Headquarters | Booking.com
Other Commitments [Line Items]
Contractual Obligation		€ 75
Scenario, Forecast | Headquarters | Booking.com
Other Commitments [Line Items]
Payments for building construction						€ 156	€ 222

COMMITMENTS AND CONTINGENCIES O

COMMITMENTS AND CONTINGENCIES Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating lease obligations
Operating lease obligations
2,019	$ 163
2,020	140
2,021	108
2,022	64
2,023	50
After 2,023	118
Total	643
Office Leases [Member]
Operating Lease, Types [Line Items]
Operating Leases, Rent Expense, Net	115	$ 96	$ 77
Data Center Space, Leases [Member]
Operating Lease, Types [Line Items]
Operating Leases, Rent Expense, Net	34	$ 24	$ 22
Land lease obligation
Operating lease obligations
2,019	1
2,020	2
2,021	2
2,022	2
2,023	2
After 2,023	72
Total	$ 81

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES Other Contractual Obligations (Details) - Headquarters - Manchester, England [Member] - Rentalcars.com [Member] £ in Millions	Dec. 31, 2018GBP (£)ft²
Other Commitments [Line Items]
Area of Real Estate Property | ft²	222,000
Lessee, Operating Lease, Term of Contract	13 years
Operating lease obligations
Other Commitments [Line Items]
Contractual Obligation | £	£ 65

BENEFIT PLANS (Details)

BENEFIT PLANS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Defined Contribution Plan, Cost	$ 22	$ 15	$ 10

GEOGRAPHIC INFORMATION (Details

GEOGRAPHIC INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 31, 2017		Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Geographic Information
Cost of Goods and Services Sold																		$ 242	$ 415
Revenues	$ 3,213	[1]	$ 4,849		$ 3,537		$ 2,928		$ 2,803	[1]	$ 4,434		$ 3,025		$ 2,419		$ 14,527	12,681	10,743
Intangible assets, net	2,125								2,177								2,125	2,177	1,994
Goodwill	2,910								2,738								2,910	2,738	2,397
Other long-lived assets	784								586								784	586	422
United States
Geographic Information
Revenues																	1,626	1,620	1,680
Intangible assets, net	1,747								1,790								1,747	1,790	1,918
Goodwill	1,938								1,807								1,938	1,807	1,802
Other long-lived assets	159								124								159	124	102
The Netherlands
Geographic Information
Revenues																	11,094	9,540	7,783
Intangible assets, net	30								44								30	44	51
Goodwill	246								254								246	254	229
Other long-lived assets	365								254								365	254	196
Other
Geographic Information
Revenues																	1,807	1,521	1,280
Intangible assets, net	348								343								348	343	25
Goodwill	726								677								726	677	366
Other long-lived assets	$ 260								$ 208								260	$ 208	$ 124
Accounting Standards Update 2014-09 | Adjustments
Geographic Information
Cost of Goods and Services Sold																	$ 170
Product Concentration Risk [Member] | Sales Revenue, Net [Member]
Geographic Information
Concentration Risk, Percentage																	87.00%
[1]	For periods beginning after December 31, 2017, the Company reports revenues in accordance with the current revenue standard and no longer presents "Cost of revenues" or "Gross profit" in its Consolidated Statement of Operations. For all periods prior to January 1, 2018, the Company reported under the previous revenue standard. See Note 2 for further information.

SELECTED QUARTERLY FINANCIAL _3

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 3,213	[1]	$ 4,849	[1]	$ 3,537	[1]	$ 2,928	[1]	$ 2,803	[1]	$ 4,434	[1]	$ 3,025	[1]	$ 2,419	[1]	$ 14,527	$ 12,681		$ 10,743
Gross profit									2,763	[1]	4,380	[1]	2,957	[1]	2,339	[1]		12,439		10,328
Net income	$ 646	[2]	$ 1,768		$ 977		$ 607		$ (555)	[2]	$ 1,720		$ 720		$ 456		$ 3,998	$ 2,341	[3]	$ 2,135	[3]
Net income applicable to common stockholders per basic common share	$ 14		$ 37.39		$ 20.34		$ 12.56		$ (11.41)	[2]	$ 35.12		$ 14.66		$ 9.26		$ 84.26	$ 47.78		$ 43.14
Net income applicable to common stockholders per diluted common share	$ 13.86		$ 37.02		$ 20.13		$ 12.34		$ (11.41)	[2]	$ 34.43		$ 14.39		$ 9.11		$ 83.26	$ 46.86		$ 42.65
Income tax benefit to adjust provisional tax expense	$ (46)																$ (46)	$ 1,563		$ 0
Transition tax for accumulated foreign earnings, provisional income tax expense (benefit)									$ 1,600
Change In tax rate, deferred tax, provisional income tax expense (benefit)									$ 217
[1]	For periods beginning after December 31, 2017, the Company reports revenues in accordance with the current revenue standard and no longer presents "Cost of revenues" or "Gross profit" in its Consolidated Statement of Operations. For all periods prior to January 1, 2018, the Company reported under the previous revenue standard. See Note 2 for further information.
[2]	Includes, for the fourth quarter of 2018, an income tax benefit of $46 million to adjust the 2017 provisional tax expense related to a one-time transitional tax on mandatory deemed repatriation of accumulated unremitted international earnings as a result of the Tax Act. The income tax provision for the fourth quarter of 2017 includes a provisional tax expense of approximately $1.6 billion related to the transition tax mentioned above and a provisional tax benefit of $217 million related to the remeasurement of the Company’s U.S. deferred tax assets and liabilities as a result of the Tax Act.
[3]	The Company realized net gains of $1 million related to investments in debt securities sold for both years ended December 31, 2017 and 2016.

ACQUISITIONS (Details)

ACQUISITIONS (Details) - USD ($) $ in Millions	Nov. 30, 2018	Apr. 26, 2018	Jul. 24, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Acquisitions and other investments, net of cash acquired				$ 273	$ 553	$ 1
Stock Issued During Period, Value, Acquisitions				110
Non-cash investing and financing activity for an acquisition				59	0	0
Goodwill				2,910	2,738	2,397
Deferred tax liability established as a result of identifiable intangible assets acquired				482	517
Acquisition related costs				5
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				19	0	$ 0
FareHarbor [Member]
Business Acquisition [Line Items]
Acquisitions and other investments, net of cash acquired		$ 139
Restricted Stock, Issued		51
HotelsCombined [Member]
Business Acquisition [Line Items]
Acquisitions and other investments, net of cash acquired	$ 134
Momondo Group
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 556
Current assets			50
Identifiable intangible assets			333
Goodwill			288
Property and equipment			1
Total liabilities			(116)
Purchase price, total consideration			556
Cash Acquired from Acquisition			15
Deferred tax liability established as a result of identifiable intangible assets acquired			70
Debt assumed in acquisition(s)			15
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low				0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High				90
Supply and distribution agreements | Momondo Group
Business Acquisition [Line Items]
Identifiable intangible assets			$ 214
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			15 years
Trade names | Momondo Group
Business Acquisition [Line Items]
Identifiable intangible assets			$ 104
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			13 years
Technology | Momondo Group
Business Acquisition [Line Items]
Identifiable intangible assets			$ 15
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			4 years
Additional Paid-in Capital
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions				110
Additional Paid-in Capital | FareHarbor [Member]
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions		$ 110
Restricted Stock [Member] | Prepaid Expenses and Other Current Assets [Member] | FareHarbor [Member]
Business Acquisition [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options				17
Restricted Stock [Member] | Other Assets [Member] | FareHarbor [Member]
Business Acquisition [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options				23
Level 3 | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability				28	$ 9
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				$ 19