Booking (BKNG) 10-K24 Feb 212020 FY Annual reportFinancial data

Company Profile

COVER PAGE

COVER PAGE - USD ($) $ in Billions	12 Months Ended
COVER PAGE - USD ($) $ in Billions	Dec. 31, 2020	Feb. 17, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Fiscal Period Focus	FY
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Amendment Flag	false
Document Fiscal Year Focus	2020
Current Fiscal Year End Date	--12-31
Entity File Number	1-36691
Entity Registrant Name	Booking Holdings Inc.
Entity Central Index Key	0001075531
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	06-1528493
Entity Address, Address Line One	800 Connecticut Avenue
Entity Address, City or Town	Norwalk
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06854
City Area Code	203
Local Phone Number	299-8000
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 65
Entity Common Stock, Shares Outstanding		40,961,796
Documents Incorporated by Reference	The information required by Part III of this Annual Report on Form 10-K, to the extent not set forth in this Form 10-K, is incorporated herein by reference from Booking Holdings Inc.'s definitive proxy statement relating to its annual meeting of stockholders to be held on June 3, 2021 , to be filed with the Securities and Exchange Commission within 120 days after the end of Booking Holdings Inc.'s fiscal year ended December 31, 2020.
Common Stock par value $0.008 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock par value $0.008 per share
Trading Symbol	BKNG
Security Exchange Name	NASDAQ
0.800% Senior Notes Due 2022
Document Information [Line Items]
Title of 12(b) Security	0.800% Senior Notes Due 2022
Trading Symbol	BKNG 22A
Security Exchange Name	NASDAQ
2.150% Senior Notes Due 2022
Document Information [Line Items]
Title of 12(b) Security	2.150% Senior Notes Due 2022
Trading Symbol	BKNG 22
Security Exchange Name	NASDAQ
2.375% Senior Notes Due 2024
Document Information [Line Items]
Title of 12(b) Security	2.375% Senior Notes Due 2024
Trading Symbol	BKNG 24
Security Exchange Name	NASDAQ
1.800% Senior Notes Due 2027
Document Information [Line Items]
Title of 12(b) Security	1.800% Senior Notes Due 2027
Trading Symbol	BKNG 27
Security Exchange Name	NASDAQ

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents		$ 10,562	$ 6,312
Short-term investments (Available-for-sale debt securities: Amortized cost of $500 and $998, respectively)		501	998
Accounts receivable, net (Allowance for expected credit losses of $166 and $49, respectively)		529	1,680
Prepaid expenses, net (Allowance for expected credit losses of $22 and $6, respectively)		337	479
Other current assets		277	364
Total current assets		12,206	9,833
Property and equipment, net		756	738
Operating lease assets		529	620
Intangible assets, net		1,812	1,954
Goodwill	[1]	1,895	2,913
Long-term investments (Includes available-for-sale debt securities: Amortized cost of $225 and $2,192, respectively)		3,759	4,477
Other assets, net (Allowance for expected credit losses of $33 at December 31, 2020)		917	867
Total assets		21,874	21,402
Current liabilities:
Accounts payable		735	1,239
Accrued expenses and other current liabilities		1,382	1,578
Deferred merchant bookings		323	1,561
Convertible debt		985	988
Total current liabilities		3,425	5,366
Deferred income taxes		1,127	876
Operating lease liabilities		366	462
Long-term U.S. transition tax liability		923	1,021
Other long-term liabilities		111	104
Long-term debt		11,029	7,640
Total liabilities		16,981	15,469
Commitments and contingencies (see Note 16)
Stockholders' equity:
Common stock, $0.008 par value, Authorized shares: 1,000,000,000 Issued shares: 63,406,451 and 63,179,471, respectively		0	0
Treasury stock, 22,446,897 and 21,762,070 shares, respectively		(24,128)	(22,864)
Additional paid-in capital		5,851	5,756
Retained earnings		23,288	23,232
Accumulated other comprehensive loss		(118)	(191)
Total stockholders' equity		4,893	5,933
Total liabilities and stockholders' equity		$ 21,874	$ 21,402

[1]	The balance of goodwill as of December 31, 2020 and 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively.

CONSOLIDATED BALANCE SHEETS (PA

CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Amortized cost of available-for-sale debt securities, current	$ 500	$ 998
Accounts receivable, net, allowance for expected credit losses, current	166	49
Prepaid expenses, net, allowance for expected credit losses, current	22	6
Amortized cost of available-for-sale debt securities, noncurrent	225	2,192
Prepaid expenses, net, allowance for expected credit losses, noncurrent	$ 33	$ 0
Common stock, par value (in dollars per share)	$ 0.008	$ 0.008
Common stock, authorized shares (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	63,406,451	63,179,471
Treasury stock, shares (in shares)	22,446,897	21,762,070

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total revenues	$ 6,796	$ 15,066	$ 14,527
Operating expenses:
Marketing expenses	2,179	4,967	4,956
Sales and other expenses	755	955	830
Personnel, including stock-based compensation of $233, $308 and $317, respectively	1,944	2,248	2,042
General and administrative	581	797	699
Information technology	299	285	233
Depreciation and amortization	458	469	426
Restructuring and other exit costs	149	0	0
Impairment of goodwill	1,062	0	0
Total operating expenses	7,427	9,721	9,186
Operating (loss) income	(631)	5,345	5,341
Interest expense	(356)	(266)	(269)
Other income (expense), net	1,554	879	(237)
Earnings before income taxes	567	5,958	4,835
Income tax expense	508	1,093	837
Net income	$ 59	$ 4,865	$ 3,998
Net income applicable to common stockholders per basic common share	$ 1.45	$ 112.93	$ 84.26
Weighted-average number of basic common shares outstanding (in 000's)	40,974	43,082	47,446
Net income applicable to common stockholders per diluted common share	$ 1.44	$ 111.82	$ 83.26
Weighted-average number of diluted common shares outstanding (in 000's)	41,160	43,509	48,017
Agency revenues
Total revenues	$ 4,314	$ 10,117	$ 10,480
Merchant revenues
Total revenues	2,117	3,830	2,987
Advertising and other revenues
Total revenues	$ 365	$ 1,119	$ 1,060

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (PARENTHETICAL) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Personnel Expenses
Stock-based compensation	$ 233	$ 308	$ 317

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 59	$ 4,865	$ 3,998
Other comprehensive income (loss), net of tax
Foreign currency translation adjustments, net of tax	50	(10)	(114)
Net unrealized gains (losses) on available-for-sale securities, net of tax	23	135	(199)
Total other comprehensive income (loss), net of tax	73	125	(313)
Comprehensive income	$ 132	$ 4,990	$ 3,685

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Millions	Total	Cumulative effect of adoption of accounting standards updates	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Retained EarningsCumulative effect of adoption of accounting standards updates	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss)Cumulative effect of adoption of accounting standards updates
Balance (in shares) at Dec. 31, 2017			62,689	(14,217)
Balance, beginning of period at Dec. 31, 2017	$ 11,261	$ 189	$ 0	$ (8,699)	$ 5,783	$ 13,939	$ 430	$ 238	$ (241)
Increase (Decrease) in Stockholders' Equity
Net income	3,998					3,998
Foreign currency translation adjustments, net of tax	(114)							(114)
Net unrealized gains (losses) on available-for-sale securities, net of tax	(199)							(199)
Conversion of debt	(770)				(770)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			208
Exercise of stock options and vesting of restricted stock units and performance share units	$ 2		$ 0		2
Repurchase of common stock (in shares)	(3,100)			(3,100)
Repurchase of common stock	$ (6,012)			$ (6,012)
Stock-based compensation and other stock-based payments	320				320
Common stock issued in an acquisition (in shares)			52
Common stock issued in an acquisition	110		$ 0		110
Balance (in shares) at Dec. 31, 2018			62,949	(17,317)
Balance, end of period at Dec. 31, 2018	8,785		$ 0	$ (14,711)	5,445	18,367		(316)
Increase (Decrease) in Stockholders' Equity
Net income	4,865					4,865
Foreign currency translation adjustments, net of tax	(10)							(10)
Net unrealized gains (losses) on available-for-sale securities, net of tax	135							135
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			230
Exercise of stock options and vesting of restricted stock units and performance share units	$ 3		$ 0		3
Repurchase of common stock (in shares)	(4,445)			(4,445)
Repurchase of common stock	$ (8,153)			$ (8,153)
Stock-based compensation and other stock-based payments	308				308
Balance (in shares) at Dec. 31, 2019			63,179	(21,762)
Balance, end of period at Dec. 31, 2019	5,933	$ (3)	$ 0	$ (22,864)	5,756	23,232	$ (3)	(191)
Increase (Decrease) in Stockholders' Equity
Net income	59					59
Foreign currency translation adjustments, net of tax	50							50
Net unrealized gains (losses) on available-for-sale securities, net of tax	23							23
Issuance of convertible senior notes	96				96
Conversion of debt	(245)				(245)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			227
Exercise of stock options and vesting of restricted stock units and performance share units	$ 6		$ 0		6
Repurchase of common stock (in shares)	(685)			(685)
Repurchase of common stock	$ (1,264)			$ (1,264)
Stock-based compensation and other stock-based payments	238				238
Balance (in shares) at Dec. 31, 2020			63,406	(22,447)
Balance, end of period at Dec. 31, 2020	$ 4,893		$ 0	$ (24,128)	$ 5,851	$ 23,288		$ (118)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES:
Net income		$ 59	$ 4,865	$ 3,998
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		458	469	426
Provision for expected credit losses and chargebacks		319	138	163
Deferred income tax expense (benefit)		213	122	(150)
Net (gains) losses on marketable equity securities	[1]	(1,811)	(745)	367
Stock-based compensation expense and other stock-based payments		255	325	331
Amortization of debt discount and debt issuance costs		64	58	59
Operating lease amortization		184	172	0
Unrealized foreign currency transaction losses (gains) on Euro-denominated debt		200	(7)	0
Impairment of goodwill		1,062	0	0
Impairment of investment	[1]	100	0	0
Other		2	9	19
Changes in assets and liabilities, net of effects of acquisitions:
Accounts receivable		891	(323)	(319)
Prepaid expenses and other current assets		161	(263)	(201)
Deferred merchant bookings and other current liabilities		(2,266)	480	635
Long-term assets and liabilities		194	(435)	10
Net cash provided by operating activities		85	4,865	5,338
INVESTING ACTIVITIES:
Purchase of investments		(74)	(672)	(2,686)
Proceeds from sale and maturity of investments		2,997	8,099	5,616
Additions to property and equipment		(286)	(368)	(442)
Acquisitions and other investments, net of cash acquired		0	(9)	(273)
Net cash provided by investing activities		2,637	7,050	2,215
FINANCING ACTIVITIES:
Proceeds from revolving credit facility and short-term borrowings		0	400	25
Repayments of revolving credit facility and short-term borrowings		0	(425)	0
Proceeds from the issuance of long-term debt		4,108	0	0
Payments for conversion of debt		(1,244)	0	(1,487)
Payments for repurchase of common stock		(1,303)	(8,187)	(5,971)
Other financing activities		(33)	(8)	2
Net cash provided by (used in) financing activities		1,528	(8,220)	(7,431)
Effect of exchange rate changes on cash and cash equivalents and restricted cash and cash equivalents		0	(8)	(40)
Net increase in cash and cash equivalents and restricted cash and cash equivalents		4,250	3,687	82
Total cash and cash equivalents and restricted cash and cash equivalents, beginning of period		6,332	2,645	2,563
Total cash and cash equivalents and restricted cash and cash equivalents, end of period		10,582	6,332	2,645
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the period for income taxes (see Note 15)		319	1,074	1,169
Cash paid during the period for interest		278	221	219
Non-cash operating and financing activity for an acquisition (see Note 19)		0	0	51
Non-cash investing and financing activity for an acquisition (see Note 19)		$ 0	$ 0	$ 59

[1]	See Note 5 for additional information related to the net gains (losses) on marketable equity securities and impairment of investment.

BUSINESS DESCRIPTION

BUSINESS DESCRIPTION	12 Months Ended
BUSINESS DESCRIPTION	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BUSINESS DESCRIPTION	BUSINESS DESCRIPTION Booking Holdings Inc. ("Booking Holdings" or the "Company") seeks to make it easier for everyone to experience the world by providing consumers, travel service providers and restaurants with leading travel and restaurant online reservation and related services. The Company offers its services through six primary consumer-facing brands: Booking.com, Priceline, agoda, Rentalcars.com, KAYAK and OpenTable. 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 flight, cruise, vacation package, tour or activity. Consumers can also use the Company's 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, travel service providers and restaurants, such as certain travel-related insurance products and restaurant management services.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Dec. 31, 2020
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, other long-lived tangible and intangible assets, the valuation of investments in private companies, income taxes, contingencies, stock-based compensation, the allowance for expected credit losses (also referred to as allowance for doubtful accounts), customer chargeback provisions and the accrual of obligations for loyalty and other incentive programs. Impact of COVID-19 In response to the outbreak of the novel strain of the coronavirus, COVID-19 (the "COVID-19 pandemic") , many governments around the world have implemented, and continue to implement, a variety of measures to reduce the spread of COVID-19, including travel restrictions and bans, instructions to residents to practice social distancing, curfews, quarantine advisories, including quarantine restrictions after travel in certain locations, shelter-in-place orders, required closures of non-essential businesses and additional restrictions on businesses as part of re-opening plans. These government mandates have forced many of the customers on whom the Company’s business relies, including hotels and other accommodation providers, airlines and restaurants, to seek government support in order to continue operating, to curtail drastically their service offerings, to file for bankruptcy protection or to cease operations entirely. Further, these measures have materially adversely affected, and may further adversely affect, consumer sentiment and discretionary spending patterns and economies, and the Company’s workforce, operations and customers. The COVID-19 pandemic and the resulting economic conditions and government orders have resulted in a material decrease in consumer spending and an unprecedented decline in travel and restaurant activities and consumer demand for related services. The Company’s financial results and prospects are almost entirely dependent on the sale of travel-related services. The Company’s results for the year ended December 31, 2020 have been materially and negatively impacted as compared to 2019 and 2018. Due to the uncertain and rapidly evolving nature of current conditions around the world, the Company is unable to predict accurately the impact that the COVID-19 pandemic will have on its business going forward. With the spread of COVID-19 to all major regions and the discovery of new variants of the coronavirus, the Company expects the COVID-19 pandemic and its effects to continue to have a significant adverse impact on its business for the duration of the pandemic, during any resurgence of the pandemic and during the subsequent economic recovery, which could be an extended period of time. Given the severe downturn in the global travel industry and the financial difficulties faced by many of the Company's travel service provider and restaurant customers and marketing affiliates, the Company has increased its provision for expected credit losses (also referred to as provision for bad debt or provision for uncollectible accounts) on receivables from and prepayments to its travel service provider and restaurant customers and marketing affiliates (see Note 7). Moreover, due to the high level of cancellations of existing reservations, the Company has incurred, and may continue to incur, higher than normal cash outlays to refund consumers for prepaid reservations, including certain situations where the Company has already transferred the prepayment to the travel service provider (see Note 3). Any material increase in the Company’s provision for expected credit losses and any material increase in cash outlays to refund consumers would have a corresponding adverse effect on the Company's results of operations and related cash flows. As a result of the deterioration of the Company’s business due to the COVID-19 pandemic, the Company determined that a portion of its goodwill had experienced a decline in value at March 31, 2020 and recorded a significant impairment charge (see Note 11). In addition, the Company recorded a significant impairment charge at March 31, 2020 for one of the Company's long-term investments due to the impact of the COVID-19 pandemic on the business of the investee and the Company's estimate of the resulting decline in the value of the investment (see Notes 5 and 6). At September 30, 2020, the Company recorded an additional significant impairment charge to its goodwill (see Note 11). Even though no additional impairment indicators were identified as of December 31, 2020 for these assets, it is possible that the Company may have to record additional significant impairment charges in future periods. See Note 12 for additional information about the Company’s existing debt arrangements, including $4.1 billion of debt issued in April 2020. The Company’s continued access to sources of liquidity depends on multiple factors, including global economic conditions, the condition of global financial markets, the availability of sufficient amounts of financing, the Company’s ability to meet debt covenant requirements, the Company’s operating performance and the Company's credit ratings. If the Company’s credit ratings were to be downgraded, or financing sources were to ascribe higher risk to the Company's rating levels, the Company or its industry, the Company’s access to capital and the cost of any financing would be negatively impacted. There is no guarantee that additional debt financing will be available in the future to fund the Company’s obligations, or that it will be available on commercially reasonable terms, in which case the Company may need to seek other sources of funding. The extent of the effects of the COVID-19 pandemic on the Company’s business, results of operations, cash flows and growth prospects is highly uncertain and will ultimately depend on future developments. These include, but are not limited to, the severity, extent and duration of the COVID-19 pandemic, including as a result of any new variants of COVID-19 and any resurgences of the pandemic, and its impact on the travel and restaurant industries and consumer spending more broadly. Even if economic and operating conditions for the Company’s business improve, the Company cannot predict the long-term effects of the pandemic on its business or the travel and restaurant industries as a whole. If the travel and restaurant industries are fundamentally changed by the COVID-19 pandemic in ways that are detrimental to the Company’s operating model, the Company’s business may continue to be adversely affected even as the broader global economy recovers. In response to the reduction in the Company's business volumes as a result of the impact of the COVID-19 pandemic, the Company has taken actions to reduce the size of its workforce to optimize efficiency and reduce costs. See Note 20 for additional information. Certain governments have passed or are considering legislation to help businesses during the COVID-19 pandemic through loans, wage subsidies, tax relief or other financial aid, and some of these governments have extended or are considering extending these programs. The Company has participated in several of these programs, including the Netherlands' wage subsidy program and the United Kingdom's job retention scheme. See Note 21 for additional information. Change in Presentation and Reclassification Certain amounts from prior periods have been reclassified to conform to the current year presentation, including the change in the presentation of marketing expenses disclosed later in this Note. Fair Value of Financial Instruments The Company's financial instruments, including cash, restricted cash, 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. Accounts receivable and other financial assets measured at amortized cost are carried at cost less an allowance for expected credit losses to present the net amount expected to be collected (see Note 7). See Notes 5, 6 and 12 for information related to 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 or regulations. Restricted cash and cash equivalents at December 31, 2020, 2019 and 2018 principally relates to the minimum cash requirement for the Company's travel-related insurance business. The following table reconciles cash and cash equivalents and restricted cash and cash equivalents reported in the Consolidated Balance Sheets to the total amount shown in the Consolidated Statements of Cash Flows (in millions): December 31, 2020 2019 2018 As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 10,562 $ 6,312 $ 2,624 Restricted cash and cash equivalents included in "Other current assets" 20 20 21 Total cash and cash equivalents and restricted cash and cash equivalents as $ 10,582 $ 6,332 $ 2,645 Investments Investments held by the Company include debt securities and equity securities. 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. Payments made for investments are reported in "Purchase of investments" and proceeds received from sales or maturities of investments are reported in "Proceeds from sale and maturity of investments" in the Consolidated Statements of Cash Flows. Debt Securities The Company has classified its investments in debt securities as available-for-sale securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is considered a debt security for accounting purposes. These securities are reported at estimated fair value with the aggregate unrealized gains and losses, net of tax, reflected in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. For periods prior to January 1, 2020, investments in debt securities were considered to be impaired when a decline in fair value was judged to be other than temporary because the Company either intended to sell or it was more-likely-than not that it would be required to sell the impaired security before recovery. Once a decline in fair value was determined to be other than temporary, an impairment charge was recorded and a new cost basis in the investment was established. If the Company did not intend to sell the debt security, but it was probable that the Company would not collect all amounts due, then only the impairment due to the credit risk would be recognized in net income and the remaining amount of the impairment would be recognized in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. On January 1, 2020, the Company adopted the accounting standards update on the measurement of credit losses on financial instruments. Under the current accounting standard, if the amortized cost basis of an available-for-sale security exceeds its fair value and if the Company has the intention to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis, an impairment is recognized in the Consolidated Statements of Operations. If the Company does not have the intention to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis and the Company determines that the decline in fair value below the amortized cost basis of an available-for-sale security is entirely or partially due to credit-related factors, the credit loss is measured and recognized as an allowance for expected credit losses along with the related expense in the Consolidated Statements of Operations. The allowance is measured as the amount by which the debt security’s amortized cost basis exceeds the Company’s best estimate of the present value of cash flows expected to be collected. The fair 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 6 for information related to fair value measurements. The Company's investments in marketable debt securities are recognized based on the trade date. The marketable debt securities generally have a term of less than five years and are assessed for classification in the Consolidated Balance Sheets as short-term or long-term at the individual security level. Classification as short-term or long-term is based on the maturities of the securities, as applicable, and the Company's expectations regarding the timing of sales and redemptions. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage or in connection with a commercial relationship are included in "Long-term investments" in the Consolidated Balance Sheets, except in situations where the Company expects the investment to be realized in cash, redeemed or sold within one year. The cost of marketable debt securities sold is determined using a first-in and first-out method. 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. Marketable equity securities are reported at estimated fair value with changes in fair value recognized in "Other income (expense), net" in the Consolidated Statements of Operations. 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. 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. See Notes 5 and 6 for further information related to investments. Accounts Receivable from Customers and Allowance for Expected Credit Losses For periods prior to January 1, 2020, receivables from customers are recorded at the original invoiced amounts net of an allowance for doubtful accounts. The allowance for doubtful accounts was estimated based on historical experience, aging of the receivable, credit quality of the customers, economic trends and other factors that may affect the Company's ability to collect from customers. On January 1, 2020, the Company adopted the accounting standards update on the measurement of expected credit losses, which requires the Company to estimate lifetime expected credit losses upon recognition of the financial assets. The Company has identified the relevant risk characteristics, of its customers and the related receivables and prepayments, which include the following: size, type (alternative accommodations vs. hotels) or geographic location of the customer, or a combination of these characteristics. Receivables with similar risk characteristics have been grouped into pools. For each pool, the Company considers the historical credit loss experience, current economic conditions, supportable forecasts of future economic conditions, and any recoveries in assessing the lifetime expected credit losses. Other key factors that influence the expected credit loss analysis include customer demographics, payment terms offered in the normal course of business to customers, the nature of competition, and industry-specific factors that could impact the Company's receivables. Additionally, external data and macroeconomic factors are considered. This is assessed at each quarter based on the Company’s specific facts and circumstances. See Note 7 for additional information. Property and Equipment, Net 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 term of the lease related to leasehold improvements, whichever is shorter. Building Construction-in-progress Building construction-in-progress is associated with the construction of Booking.com's future headquarters 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 Acquisition costs and 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 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. Cloud Computing Arrangements The Company utilizes various third-party computer systems and third-party service providers, including global distribution systems ("GDSs") serving the accommodation, rental car and airline industries. The Company uses both internally-developed systems and third-party systems to operate its services, including transaction processing, order management and financial and accounting systems. For periods beginning after December 31, 2018, implementation costs incurred in a hosting arrangement that is a service contract are capitalized and amortized over the term of the hosting arrangement. The capitalized implementation costs are reported as "Prepaid expenses, net" or "Other assets, net" in the Company's Consolidated Balance Sheets, as appropriate. The related amortization expenses are reported as "Information technology" in the Company's Consolidated Statements of Operations. Leases On January 1, 2019, the Company adopted Accounting Standards Codification ("ASC") 842, Leases , using a modified retrospective method applied to all contracts as of January 1, 2019. Therefore, for reporting periods beginning after December 31, 2018, the financial statements are prepared in accordance with the current lease standard and the financial statements for all periods prior to January 1, 2019 are presented under the previous lease standard ("ASC 840"). Under the current lease standard, the Company determines if an arrangement is a lease, or contains a lease, when a contract is signed. The Company determines if a lease is an operating or finance lease and records a lease asset and a lease liability upon lease commencement, which is the date when the underlying asset is made available for use by the lessor. The Company has operating leases for office space, data centers and land for Booking.com's future headquarters. For office space, data centers and land, the Company has elected to combine the fixed payments to lease the asset and any fixed non-lease payments (such as maintenance or utility charges) when determining its lease payments. The Company uses its incremental borrowing rate as its discount rate to determine the present value of its remaining lease payments to calculate its lease assets and lease liabilities because the rate implicit in the lease is not readily determinable. The incremental borrowing rate approximates the rate the Company would pay to borrow in the currency of the lease payments on a collateralized basis for the weighted-average life of the lease. Operating lease assets also include any prepaid lease payments and lease incentives received prior to lease commencement. The Company recognizes lease expense on a straight-line basis over the lease term. Certain of the Company's lease agreements include rent payments which are adjusted periodically for inflation. Any change in payments due to changes in inflation rates are recognized as variable lease expense as they are incurred. Variable lease expense also includes costs for property taxes, insurance and services provided by the lessor which are charged based on usage or performance (such as maintenance or utility charges). Most leases have one or more options to renew, with renewal terms that can extend the initial lease term for various periods up to 9 years. The exercise of renewal options for office space and data centers is at the Company’s discretion and are included if they are reasonably certain to be exercised. The land lease for Booking.com's future headquarters has an initial term which expires in 2065, at which time the lease payments will be adjusted based on the value of the land on the reassessment date. The Company considered the initial term of the land lease to be its expected period of use. "Operating lease assets" in the Consolidated Balance Sheets includes the land-use rights related to payment in 2016 for the land lease for Booking.com's future headquarters as described above. The land-use rights are amortized on a straight-line basis over its expected period of use. This expense is recorded as lease expense in "General and administrative" expense in the Consolidated Statements of Operations. See Notes 10 and 16 for further information. 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 tested annually for impairment and when an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The Company tests goodwill at a reporting unit level. The 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 (e.g., earnings before interest, taxes, depreciation, and amortization ("EBITDA") multiples of comparable publicly traded companies) and based on market participant assumptions. For periods prior to January 1, 2020, an impairment was recorded to the extent that the implied fair value of goodwill is less than the carrying value of goodwill. The Company adopted the accounting standards update on goodwill impairment in the first quarter of 2020, under which a goodwill impairment loss is measured at the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the carrying amount of goodwill. See Note 11 for further information. Impairment of Long-lived Assets The Company reviews long-lived assets, including intangible assets and operating lease assets, whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the 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 asset group. 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. Foreign Currency Translation The functional currency of the Company's subsidiaries is generally the respective local currency. For international operations, assets and liabilities are translated into U.S. Dollars at the rate of exchange existing at the balance sheet date. Income statement amounts are translated at monthly average exchange rates applicable for the period. Translation gains and losses are included as a component of "Accumulated other comprehensive loss" in the Company's Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Other income (expense), net" 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 foreign currency exchange rates. For the Company's international operations, the primary foreign currency exposures are in Euros and British Pounds Sterling, in which the Company conducts a significant portion of its business activities. As a result, the Company faces exposure to adverse movements in foreign currency exchange rates as the financial results of its international operations are translated from local currencies into U.S. Dollars upon consolidation. Additionally, foreign currency 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 net 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 operations into U.S. Dollars, even though it does not elect to apply hedge accounting or hedge accounting does not apply. These contracts are generally short-term in duration. Certain of the Company's derivative instruments have master netting arrangements, which reduce credit risk by permitting net settlement of transactions with the same counterparty. The Company reports the fair value of its derivative assets and liabilities on a gross basis in the Consolidated Balance Sheets in "Other current assets" and "Accrued expenses and other current liabilities," respectively. Unless designated as hedges for accounting purposes, gains and losses resulting from changes in the fair value of derivative instruments are recognized in "Other income (expense), net" in the Consolidated Statements of Operations in the period that the changes occur and are classified within "Net cash provided by operating activities" in the Consolidated Statements of Cash Flows. See Note 6 for further information related to these derivative instruments. The Company, from time to time in the past, has utilized derivative instruments to hedge the impact of changes in foreign currency exchange rates on the net assets of its foreign subsidiaries. These derivative instruments were designated as net investment hedges. Hedge ineffectiveness was assessed and measured based on changes in forward exchange rates. The Company recorded gains and losses on these derivative instruments as foreign currency translation adjustments, which offset a portion of the foreign currency translation adjustments related to the foreign subsidiaries' net assets. Gains and losses on these derivative instruments were recognized in the Consolidated Balance Sheets in "Accumulated other comprehensive loss" and will be realized upon a partial sale or liquidation of the investment. 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 and assesses the creditworthiness of its counterparties. Non-derivative Instrument Designated as Net Investment Hedge The foreign currency transaction gains or losses on the Company's Euro-denominated debt are measured based upon changes in spot rates. The foreign currency transaction gains or losses on the Euro-denominated debt that is designated as a hedging instrument for accounting purposes are recorded in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. The foreign currency transaction gains or losses on the Euro-denominated debt that is not designated as a hedging instrument are recognized in "Other income (expense), net" in the Consolidated Statement of Operations. See Notes 12 and 14 for further information related to the net investment hedge. Revenue Recognition 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. 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 recognition standard, with substantially all of the impact related to the Company’s online travel reservation services. Under the current revenue recognition standard, the Company recognizes revenue for travel reservation services when the travel begins rather than when the travel is completed. Online travel reservation services 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, generally at the time they are redeemed. The local occupancy taxes, general excise taxes, value-added taxes, sales taxes and other similar taxes ("travel transaction taxes"), if any, collected from travelers are reported on a net basis in revenues in the Consolidated Statements of Operations. Revenues for online travel reservation services are recognized 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 facilitate payments from travelers for the s

REVENUE

REVENUE	12 Months Ended
REVENUE	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE Disaggregation of Revenue Revenue by Type of Service Approximately 88%, 87% and 87% of the Company's revenues for each of the years ended December 31, 2020, 2019 and 2018, respectively, relates to online accommodation reservation services. Revenue from all other sources of online travel reservation services and advertising and other revenues each individually represent less than 10% of the Company's total revenues for each year. Revenue by Geographic Area See Note 18 for the information related to revenue by geographic area. Deferred Revenue Cash payments received from travelers in advance of the Company completing its performance obligations are included in "Deferred merchant bookings" in the Company's Consolidated Balance Sheets and are comprised principally of amounts estimated to be payable to the travel service providers as well as the Company's estimated deferred revenue for its commission or margin and fees. The Company expects to complete its performance obligations within one year from the reservation date. The amounts are subject to refunds for cancellations. The following table summarizes the activity of deferred revenue for online travel reservation services for the years ended December 31, 2020 and 2019 (in millions): Year Ended December 31, 2020 2019 Balance, beginning of year $ 220 $ 149 Revenues recognized from the beginning balance (154) (134) Cancellations (66) (15) Payments received from travelers net of amounts estimated to be payable to travel 50 220 Balance, end of year $ 50 $ 220 Loyalty and Other Incentive Programs The Company provides loyalty programs where participating consumers are awarded loyalty points on current transactions that can be redeemed in the future. At December 31, 2020 and 2019, liabilities for loyalty program incentives of $21 million and $80 million, respectively, were included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets. The Company’s largest loyalty program is at OpenTable, where points can be redeemed for rewards such as qualifying reservations at participating restaurants, third-party gift cards and accommodation reservations booked through some of the Company’s other platforms. The estimated fair value of the loyalty points that are expected to be redeemed is recognized as a reduction of revenue at the time the incentives are granted. In March 2018, OpenTable introduced a three-year time-based expiration for points earned by diners, which reduced its loyalty program liability by $27 million , with a corresponding increase to revenue . Unredeemed loyalty points existing as of the date of introduction of the expiration provision will expire during the three months ending March 31, 2021. Unredeemed loyalty points earned after the date of introduction of the expiration provision expire three In addition to the loyalty programs, at December 31, 2020 and 2019 , liabilities of $60 million and $22 million, respectively, for other incentive programs, such as referral bonuses, rebates, credits and discounts, were included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets. During 2020, the Company offered additional rebates to customers meeting certain eligibility requirements under an incentive program at Booking.com. The eligibility requirements include the customer's enrollment in Booking.com's Genius Program (program features include special discounts offered by customers to frequent travelers) and Preferred Partner Program (program features include greater visibility for customers in search results for payment of higher commission) and timely payment of invoices. The additional rebates resulted in a reduction of revenue of $100 million during the year ended December 31, 2020 and a liability of $25 million at December 31, 2020. Refunds to Travelers Due to the high level of cancellations of existing reservations as a result of the COVID-19 pandemic (see Note 2), the Company has incurred, and may continue to incur, higher than normal cash outlays to refund travelers for prepaid reservations, including certain situations where the Company has already transferred the prepayment to the travel service provider. For the year ended December 31, 2020, the Company recorded a reduction in revenue of $44 million for refunds paid or estimated to be

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
STOCK-BASED COMPENSATION	Dec. 31, 2020
Share-based Payment Arrangement [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, 2020, there were 1,614,570 shares of common stock available for future grant under the 1999 Plan. In addition, under plans assumed in connection with various acquisitions, there were 52,192 shares of common stock available for future grant at December 31, 2020. Stock-based compensation issued under the plans generally consists of restricted stock units, performance share units and stock options. Performance share units and restricted stock units are payable in shares of the Company's common stock upon vesting. The Company issues shares of its common stock upon the exercise of stock options. Stock-based compensation expense included in "Personnel" expenses in the Consolidated Statements of Operations was $233 million, $308 million and $317 million for the years ended December 31, 2020, 2019 and 2018, respectively. The related tax benefit for stock-based compensation was $30 million, $38 million and $36 million for the years ended December 31, 2020, 2019 and 2018, respectively. Stock-based compensation for the years ended December 31, 2020, 2019 and 2018 includes benefits of $71 million and $4 million, and a charge of $48 million, respectively, representing the impact of adjusting the estimated probable outcome at the end of the performance period for outstanding unvested performance share units. Due to the impact of the COVID-19 pandemic (see Note 2), there was a significant decline in the estimated performance over the performance periods against the performance targets and consequently, a significant reduction in the number of shares that were probable to be issued as compared to December 31, 2019. As a result, the Company recognized a reduction in stock-based compensation expense of $73 million, which is included in "Personnel" expense in the Consolidated Statement of Operations for the year ended December 31, 2020. In 2020, considering pre-COVID-19 performance and the significant effect of the COVID-19 pandemic on Company performance and consequently on the number of shares that were probable to be issued to employees, the Company modified the performance-based awards granted in 2018 (other than the performance-based awards granted to executive officers and certain other employees) to fix the number of shares to be issued, subject to other vesting conditions. As a result, the Company incurred an additional stock-based compensation expense of $11 million to be recognized over the remaining requisite service period. In January 2021, the Company modified the performance-based awards granted in 2018 and 2019 to its executive officers, to fix the number of shares to be issued, subject to other vesting conditions. The modification, in the aggregate, will result in additional stock-based compensation expense of approximately $40 million, to be recognized over the remaining requisite service periods for the performance-based awards. Restricted stock units and performance share units granted by the Company during the years ended December 31, 2020, 2019 and 2018 had aggregate grant-date fair values of $392 million, $380 million and $337 million, respectively. Restricted stock units and performance share units that vested during the years ended December 31, 2020, 2019, and 2018 had aggregate fair values at vesting of $358 million, $373 million and $415 million, respectively. At December 31, 2020, there was $384 million of estimated total future stock-based compensation expense related to unvested restricted stock units and performance share units to be recognized over a weighted-average period of 1.9 years. Stock options granted by the Company during the year ended December 31, 2020 had an aggregate grant-date fair value of $79 million. At December 31, 2020, there was $57 million of estimated total future stock-based compensation expense related to unvested stock options to be recognized over a weighted-average period of 2.2 years. Restricted Stock Units The Company makes broad-based grants of restricted stock units that generally vest during a period of one The following table summarizes the activity of restricted stock units for employees and non-employee directors during the year ended December 31, 2020: Restricted Stock Units Shares Weighted-average Grant-date Fair Value Unvested at December 31, 2019 256,745 $ 1,801 Granted 222,977 $ 1,659 Vested (130,684) $ 1,822 Forfeited (43,079) $ 1,737 Unvested at December 31, 2020 305,959 $ 1,697 Performance Share Units The Company grants performance share units to executives and certain other employees, which generally vest at the end of a three-year period, subject to certain exceptions for terminations other than for "cause," for "good reason" or on account of death or disability. The number of shares that ultimately vest depends on achieving certain performance metrics or performance goals, as applicable, by the end of the performance period, assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. The following table summarizes the activity of performance share units for employees during the year ended December 31, 2020: Performance Share Units Shares Weighted-average Grant-date Fair Value Unvested at December 31, 2019 216,083 $ 1,835 Granted 9,040 $ 2,498 Vested (82,023) $ 1,741 Performance Shares Adjustment * (49,775) $ 1,944 Forfeited (8,847) $ 1,829 Unvested at December 31, 2020 84,478 $ 1,930 Probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable, and the impact of modifications. The following table summarizes the estimated vesting, as of December 31, 2020, of performance share units granted in 2020, 2019 and 2018, net of forfeiture and vesting since the respective grant dates: Performance Share Units, by grant year 2020 2019 2018 Shares probable to be issued 9,040 40,843 34,595 Shares not subject to the achievement of minimum performance thresholds — 40,843 N/A Shares that could be issued if maximum performance thresholds are met 18,080 108,522 N/A* * The performance period for the performance share units granted in 2018 ended on December 31, 2020. Stock Options In May 2020, the Company granted stock options that vest in March 2023, subject to certain exceptions for terminations other than for "cause," for "good reason" or on account of death or disability. No stock options were granted to the executive officers of the Company. Stock options granted or assumed in acquisitions generally have a term of 10 years from the grant date. The fair value of stock options granted is estimated on the grant date using the Black-Scholes option pricing model and is affected by assumptions regarding a number of complex and subjective variables. The use of an option pricing model requires the use of several assumptions including expected volatility, risk-free interest rate, expected dividends, and expected term. Expected volatility is based on the Company’s historical volatility over the expected term of the option and implied volatility of publicly traded options of the Company’s common stock. The expected term of the options represents the estimated period of time until option exercise. Since the Company has limited historical stock option exercise experience, the Company used the simplified method in estimating the expected term, which is calculated as the average of the sum of the vesting term and the original contractual term of the options. The risk-free interest rate is based on U.S. Treasury zero-coupon issues at the time of grant for the expected term of the option. The following table summarizes the assumptions used to value option grants granted during the year ended December 31, 2020 using the Black-Scholes options pricing model: Black-Scholes assumptions Risk-free interest rate 0.56 % Expected term in years 6.4 Expected stock price volatility 33.8 % Expected dividend yield 0 % The following table summarizes the activity for stock options during the year ended December 31, 2020: Employee Stock Options Number of Shares Weighted-average Aggregate Weighted-average Remaining Contractual Term (in years) Balance, December 31, 2019 15,122 $ 484 $ 24 2.6 Granted 163,494 $ 1,411 Exercised (13,217) $ 466 Forfeited (12,653) $ 1,411 Balance, December 31, 2020 152,746 $ 1,401 $ 126 9.3 Exercisable at December 31, 2020 1,954 $ 660 $ 3 2.1 Stock options granted by the Company during the year ended December 31, 2020 had a weighted-average grant-date fair value per option of $485

INVESTMENTS

INVESTMENTS	12 Months Ended
INVESTMENTS	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	INVESTMENTS The following table summarizes, by major security type, the Company's investments at December 31, 2020 (in millions): Cost Gross Gross Carrying Value Short-term investments: Debt securities: Trip.com Group convertible debt securities $ 500 $ 1 $ — $ 501 Long-term investments: Investments in private companies: Debt securities $ 200 $ — $ — $ 200 Equity securities 552 3 (100) 455 Other long-term investments: Debt securities: Trip.com Group convertible debt securities 25 — (1) 24 Equity securities 463 2,617 — 3,080 Total $ 1,240 $ 2,620 $ (101) $ 3,759 The following table summarizes, by major security type, the Company's investments at December 31, 2019 (in millions): prv Cost Gross Gross Carrying Value Short-term investments: Debt securities: International government securities $ 109 $ — $ — $ 109 U.S. government securities 138 — — 138 Corporate debt securities 751 1 (1) 751 Total $ 998 $ 1 $ (1) $ 998 Long-term investments: Investments in private companies: Debt securities $ 250 $ — $ — $ 250 Equity securities 501 — — 501 Other long-term investments: Debt securities: International government securities 68 — — 68 U.S. government securities 136 — (1) 135 Corporate debt securities 963 2 (2) 963 Trip.com Group convertible debt securities 775 — (8) 767 Equity securities 1,117 684 (8) 1,793 Total $ 3,810 $ 686 $ (19) $ 4,477 Investments in Government and Corporate Debt Securities The Company has classified its investments in international government securities, U.S. government securities and corporate debt securities as available-for-sale securities. During the year ended December 31, 2020, the Company realized $2.2 billion in cash from sales and maturities of its investments in government and corporate debt securities. Investments in Trip.com Group At December 31, 2020, the Company had $525 million invested in convertible senior notes issued at par value by Trip.com Group including $25 million six-year convertible senior notes issued in September 2016 and $500 million ten-year convertible senior notes issued in December 2015. The $500 million convertible senior notes include a put option allowing the Company, at its option, to require a prepayment in cash from Trip.com Group at the end of the sixth year of the note. The $500 million convertible senior notes were classified as "Short-term investments" in the Consolidated Balance Sheet at December 31, 2020 as the Company expects to exercise the put option and redeem the investment. In May 2020, the Company's May 2015 investment of $250 million in Trip.com Group's convertible senior notes was repaid upon maturity. The Company determined that the economic characteristics and risks of the put option related to the $500 million convertible senior notes are clearly and closely related to the notes, and therefore did not meet the requirement for separate accounting as embedded derivatives. The Company monitors the conversion features of these notes to determine whether they meet the definition of an embedded derivative during each reporting period. The conversion feature associated with the $25 million convertible senior notes meets the definition of an embedded derivative that requires separate accounting. The embedded derivative is bifurcated for fair value measurement purposes only and is reported in the Consolidated Balance Sheets with its host contract in "Long-term investments." The mark-to-market adjustments of the embedded derivative are included in "Other income (expense), net" in the Company's Consolidated Statements of Operations. At December 31, 2019, the Company had $655 million invested in Trip.com Group American Depositary Shares ("ADSs") with a fair value of $726 million, which is reported in "Long-term investments" in the Consolidated Balance Sheet. During the year ended December 31, 2020, the Company sold its entire investment in these ADSs for $525 million. "Other income (expense), net" in the Consolidated Statements of Operations includes a net realized loss of $201 million, a net unrealized gain of $141 million and a net unrealized loss of $368 million for the years ended December 31, 2020, 2019 and 2018, respectively, related to these ADSs. Investment in Meituan In 2017, the Company invested $450 million in preferred shares of Meituan, the leading e-commerce platform for local services in China. The investment has been converted to ordinary shares and classified as a marketable equity security since Meituan's initial public offering in 2018. The investment had a fair value of $3.1 billion and $1.1 billion at December 31, 2020 and 2019, respectively, which is included in "Long-term investments" in the Consolidated Balance Sheets. Net unrealized gains of $2.0 billion, $602 million and $1 million for the years ended December 31, 2020, 2019 and 2018, respectively, related to this investment, are included in "Other income (expense), net" in the Consolidated Statements of Operations. Investments in Private Companies Equity Securities without Readily Determinable Fair Values The Company had $501 million invested in equity securities of private companies at December 31, 2019, including $500 million invested in Didi Chuxing. Considering the impact of the COVID-19 pandemic (see Note 2) , the Company performed an impairment analysis, as of March 31, 2020, on the investment in Didi Chuxing. The Company recognized an impairment charge of $100 million during the three months ended March 31, 2020, resulting in an adjusted carrying value of $400 million at March 31, 2020 and December 31, 2020 (see Note 6). No additional impairment indicators were identified as of December 31, 2020. In 2020, the Company changed its classification as a debt security of an investment in the preferred shares of a private company due to changes in the redemption features of the preferred shares. As of December 31, 2020, the investment is classified as an equity security and had a carrying value of $51 million. These equity 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. Debt Securities The Company had $200 million and $250 million invested in preferred shares of private companies, including Grab Holdings Inc. ("Grab"), with an aggregate estimated fair value of $200 million and $250 million at December 31, 2020 and 2019, respectively. The investment in Grab is classified as a debt security for accounting purposes and categorized as available-for-sale. The preferred shares are convertible to ordinary shares at the Company’s option and are mandatorily convertible upon an initial public offering. The preferred shares also contain a redemption feature that can be exercised by the Company after certain points of time. The investment is reported at estimated fair value in "Long-term investments" in the Company's Consolidated Balance Sheets, with the aggregate unrealized gains and losses, net of tax, reflected in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. As discussed above in "Equity Securities without Readily Determinable Fair Values", in 2020, the Company changed its classification of an investment that was previously accounted as a debt security.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
FAIR VALUE MEASUREMENTS	Dec. 31, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Financial assets and liabilities carried at fair value at December 31, 2020 and nonrecurring fair value measurements are classified in the categories described in the tables below (in millions): Level 1 Level 2 Level 3 Total Recurring fair value measurements ASSETS: Cash equivalents and restricted cash equivalents: Money market fund investments $ 10,208 $ — $ — $ 10,208 Time deposits and certificates of deposit 32 — — 32 Short-term investments: Trip.com Group convertible debt securities — 501 — 501 Long-term investments: Investments in private companies: Debt securities — — 200 200 Other long-term investments: Trip.com Group convertible debt securities — 24 — 24 Equity securities 3,080 — — 3,080 Derivatives: Foreign currency exchange derivatives — 9 — 9 Total assets at fair value $ 13,320 $ 534 $ 200 $ 14,054 LIABILITIES Foreign currency exchange derivatives $ — $ 7 $ — $ 7 Nonrecurring fair value measurements Investments in equity securities of private companies (1) $ — $ — $ 404 $ 404 Goodwill of the OpenTable and KAYAK reporting unit (2) — — 1,000 1,000 Total nonrecurring fair value measurements $ — $ — $ 1,404 $ 1,404 (1) At March 31, 2020, the investment in Didi Chuxing was written down to its estimated fair value of $400 million, resulting in an impairment charge of $100 million (see Note 5). (2) At March 31, 2020, the goodwill of the OpenTable and KAYAK reporting unit was written down to its estimated fair value of $1.5 billion, resulting in an impairment charge of $489 million. At September 30, 2020, th e goodwill was further written down to its estimated fair value of $1.0 billion, resulting in an additional impairment charge of $573 million (see Note 11). Financial assets and liabilities carried at fair value at December 31, 2019 are classified in the categories described in the tables below (in millions): Level 1 Level 2 Level 3 Total Recurring fair value measurements ASSETS: Cash equivalents and restricted cash equivalents: Money market fund investments $ 5,734 $ — $ — $ 5,734 Corporate debt securities — 2 — 2 Time deposits and certificates of deposit 29 — — 29 Short-term investments: International government securities — 109 — 109 U.S. government securities — 138 — 138 Corporate debt securities — 751 — 751 Long-term investments: Investments in private companies: Debt securities — — 250 250 Other long-term investments: International government securities — 68 — 68 U.S. government securities — 135 — 135 Corporate debt securities — 963 — 963 Trip.com Group convertible debt securities — 767 — 767 Equity securities 1,793 — — 1,793 Derivatives: Foreign currency exchange derivatives — 12 — 12 Total assets at fair value $ 7,556 $ 2,945 $ 250 $ 10,751 LIABILITIES Foreign currency exchange derivatives $ — $ 5 $ — $ 5 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 See Note 5 for additional information related to the Company's investments. The valuation of investments in corporate debt securities, U.S. and international government securities and Trip.com Group convertible debt securities are considered "Level 2" valuations because the Company has access to quoted prices, but does not have visibility into the volume and frequency of trading for these investments. A market approach is used for recurring fair value measurements and the valuation techniques use inputs that are observable, or can be corroborated by observable data, in an active marketplace. Investments in private companies measured using Level 3 inputs The Company’s investments measured using Level 3 inputs primarily consist of preferred stock investments in privately-held companies that are classified as either debt securities or equity securities without readily determinable fair values. Fair values of privately held securities are estimated using a variety of valuation methodologies, including both market and income approaches. The Company has used valuation techniques appropriate for the type of investment and the information available about the investee as of the valuation date to determine fair value. Recent financing transactions in the investee, such as new investments in preferred stock, are generally considered the best indication of the enterprise value and therefore used as a basis to estimate fair value. However, based on a number of factors, such as the proximity in timing to the valuation date or the volume or other terms of these financing transactions, the Company may also use other valuation techniques to supplement this data, including the income approach. In addition, an option-pricing model (“OPM”) is utilized to allocate value to the various classes of securities of the investee, including the class owned by the Company. The model includes assumptions around the investees' expected time to liquidity and volatility. The Company's investment in Grab, which is classified as a debt security for accounting purposes, had an aggregate estimated fair value of $200 million at December 31, 2020 and 2019. The Company measured this investment using Level 3 inputs and management's estimates that incorporate current market participant expectations of future cash flows considered alongside recent financing transactions of the investee and other relevant information. For the investment in equity securities of Didi Chuxing, considering the impact of the COVID-19 pandemic, the Company performed an impairment analysis as of March 31, 2020 resulting in an adjusted carrying value of $400 million at March 31, 2020 and December 31, 2020. No additional impairment indicators were identified as of December 31, 2020. As discussed below, the Company used unobservable inputs in order to determine fair value. The Company used an income approach in estimating the fair value of Didi Chuxing as of March 31, 2020. The income approach estimates value based on the expectation of future cash flows that a company will generate. These future cash flows are discounted to their present values using a discount rate based on a company’s weighted-average cost of capital, and is adjusted to reflect the risks inherent in its cash flows. The key unobservable inputs and ranges used include the weighted average cost of capit al (12%-14%), terminal EBITDA multiple (13x-15x), volatility (60%-70%) and an estimated time to liquidity of 4 years. Significant changes in any of these inputs in isolation would result in significantly different fair value measurements. Generally, a change in the assumption used for terminal EBITDA multiples would result in a directionally similar change in the fair value and a change in the assumption used for weighted average cost of capital or volatility would result in a directionally opposite change in the fair value. The determination of the fair values of investments, where the Company is a minority shareholder and has access to limited information from the investee, reflects numerous assumptions that are subject to various risks and uncertainties, including key assumptions regarding the investee’s expected growth rates and operating margin, expected length and severity of the impact of the COVID-19 pandemic on the investee and the shape and timing of the subsequent recovery, as well as other key assumptions with respect to matters outside of the Company's control, such as discount rates and market comparables. It requires significant judgments and estimates and actual results could be materially different than those judgments and estimates utilized in the fair value estimate. Future events and changing market conditions may lead the Company to re-evaluate the assumptions reflected in the valuation, particularly the assumptions related to the length and severity of the COVID-19 pandemic and the shape and timing of the subsequent recovery and the overall impact on the investee’s business, which may result in a need to recognize an additional impairment charge that could have a material adverse effect on the Company's results of operations. Derivatives 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 foreign currency exchange rates. The valuation of derivatives are considered "Level 2" fair value measurements. The Company's derivative instruments are typically short-term in nature. In the normal course of business, the Company is exposed to the impact of foreign currency fluctuations. The Company mitigates these risks by following established risk management policies and procedures, including the use of derivatives. The Company enters into foreign currency forward contracts to hedge its exposure to the impact of movements in foreign currency exchange rates on its transactional balances denominated in currencies other than the functional currency. In periods prior to the second quarter of 2020, the Company also entered into foreign currency derivative contracts to hedge translation risks from short-term foreign currency exchange rate fluctuations for the Euro, British Pound Sterling and certain other currencies versus the U.S. Dollar. Since the first quarter of 2020, the Company has not entered into such derivative instruments as the impact of the COVID-19 pandemic on the Company’s operating results are highly uncertain. The Company does not use derivatives for trading or speculative purposes. The Company reports the fair values of its derivative assets and liabilities on a gross basis in the Consolidated Balance Sheets in "Other current assets" and "Accrued expenses and other current liabilities," respectively. Unless designated as hedges for accounting purposes, gains and losses resulting from changes in the fair values of derivative instruments are recognized in "Other income (expense), net" in the Consolidated Statements of Operations in the period that the changes occur and cash flow impacts, if any, are classified within "Net cash provided by operating activities" in the Consolidated Statements of Cash Flows. As of December 31, 2020 and 2019, the Company did not designate any derivatives as hedges for accounting purposes. The table below provides estimated fair values and notional amounts of foreign currency exchange derivatives outstanding at December 31, 2020 and 2019 (in millions). The notional amount of a foreign currency forward contract is the contracted amount of foreign currency to be exchanged and is not recorded in the balance sheet. December 31, 2020 December 31, 2019 Estimated fair value of derivative assets $ 9 $ 12 Estimated fair value of derivative liabilities 7 5 Notional amount: Foreign currency purchases 898 1,770 Foreign currency sales 839 901 The effect of foreign currency exchange derivatives recorded in "Other income (expense), net" in the Consolidated Statements of Operations for the years ended December 31, 2020, 2019, and 2018 is as follows (in millions): For the Year Ended December 31, 2020 2019 2018 Losses on foreign currency exchange derivatives $ 31 $ 19 $ 44 Other Financial Assets and Liabilities At December 31, 2020 and 2019, the Company's cash consisted of bank deposits. Cash equivalents principally include money market fund investments, time deposits and certificates of deposit. Other financial assets and liabilities, including restricted cash, 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. Accounts receivable and other financial assets measured at amortized cost are carried at cost less an allowance for expected credit losses to present the net amount expected to be collected (see Note 7). See Note 12 for the estimated fair value of the Company's outstanding senior notes and Note 5 for information related to an embedded derivative associated with the $25 million Trip.com Group convertible notes issued in 2016. Goodwill

ACCOUNTS RECEIVABLE AND OTHER F

ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS	12 Months Ended
ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS	Dec. 31, 2020
Receivables [Abstract]
ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS	ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS Accounts receivable in the Consolidated Balance Sheets at December 31, 2020 and 2019 includes receivables from customers of $510 million and $1.2 billion, respectively, and receivables from marketing affiliates of $32 million and $110 million, respectively. The remaining balance principally relates to receivables from third-party payment processors. In addition, the Company had prepayments to certain customers of $107 million and $232 million at December 31, 2020 and 2019, respectively, which are included in "Prepaid expenses, net," and $45 million at December 31, 2020, which is included in "Other assets, net" in the Consolidated Balance Sheets. The amounts mentioned above are stated on a gross basis, before deducting the allowance for expected credit losses. For periods prior to January 1, 2020, receivables from customers were recorded at the original invoiced amounts net of an allowance for doubtful accounts. On January 1, 2020, the Company adopted the accounting standards update on the measurement of expected credit losses, which requires the Company to estimate lifetime expected credit losses upon recognition of the financial assets. The Company records a provision for expected credit losses on receivables from customers and marketing affiliates. The following table summarizes the activity of the allowance for expected credit losses on receivables (in millions): For the Year Ended December 31, 2020 2019 2018 Balance, beginning of year $ 49 $ 51 $ 35 Provision charged to earnings 216 69 79 Write-offs and adjustments (116) (70) (62) Foreign currency translation adjustments 17 (1) (1) Balance, end of year $ 166 $ 49 $ 51 The allowance for expected credit losses on receivables as of December 31, 2020 includes a portion of the amounts related to refunds paid or payable to certain travelers without a corresponding estimated expected recovery from the travel service providers, primarily due to the impact of the COVID-19 pandemic (see Note 3). For the year ended December 31, 2020, the Company recorded a reduction in revenue of $37 million for such refunds, which is included in "Provision charged to earnings" in the table above. In addition, the Company recorded an allowance for expected credit losses on prepayments to certain customers of $55 million and $6 million at December 31, 2020 and 2019, respectively, which are included in "Prepaid expenses, net" and "Other assets, net", as applicable, in the Consolidated Balance Sheets. For the year ended December 31, 2020, the Company recorded expected credit loss expenses of $51 million for the prepayments, which is included in "Sales and other expenses" in the Consolidated Statement of Operations.

NET INCOME PER SHARE

NET INCOME PER SHARE	12 Months Ended
NET INCOME PER SHARE	Dec. 31, 2020
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. Under the treasury stock method, if the conversion prices for the convertible notes exceed the Company's average stock price for the period, the convertible notes generally have no impact on diluted net income per share. The convertible notes are included in the calculation of diluted net income per share if their inclusion is dilutive under the treasury stock method. A reconciliation of the weighted-average number of shares outstanding used in calculating diluted net income per share is as follows (in thousands): For the Year Ended December 31, 2020 2019 2018 Weighted-average number of basic common shares outstanding 40,974 43,082 47,446 Weighted-average dilutive stock options, restricted stock units and performance share units 158 203 236 Assumed conversion of convertible senior notes 28 224 335 Weighted-average number of diluted common and common equivalent shares outstanding 41,160 43,509 48,017 For the year ended December 31, 2020, 125,000 potential common shares related to stock options and restricted stock units were excluded from the calculation of diluted net income per share because their effect would have been anti-dilutive for the year.

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	12 Months Ended
PROPERTY AND EQUIPMENT, NET	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Property and equipment, net at December 31, 2020 and 2019 consist of the following (in millions): 2020 2019 Estimated Computer equipment $ 746 $ 736 2 to 6 years Capitalized software 565 442 2 to 5 years Leasehold improvements 278 265 1 to 15 years Office equipment, furniture and fixtures 63 61 2 to 8 years Building construction-in-progress 257 161 Total 1,909 1,665 Less: Accumulated depreciation (1,153) (927) Property and equipment, net $ 756 $ 738

LEASES

LEASES	12 Months Ended
LEASES	Dec. 31, 2020
Leases [Abstract]
LEASES	LEASESThe Company has operating leases for office space, data centers and the land for Booking.com's future headquarters (see Note 16). The Company’s weighted-average discount rate was approximately 2.2% and 2.0% as of December 31, 2020 and 2019, respectively. The weighted-average remaining lease terms were approximately 8.1 years and 7.8 years as of December 31, 2020 and 2019, respectively. The Company recognized the following related to operating leases in its Consolidated Balance Sheets at December 31, 2020 and 2019 (in millions): December 31, Classification in Consolidated Balance Sheet 2020 2019 Operating lease assets Operating lease assets $ 529 $ 620 Lease Liabilities: Current operating lease liabilities Accrued expenses and other current liabilities $ 159 $ 161 Non-current operating lease liabilities Operating lease liabilities 366 462 Total operating lease liabilities $ 525 $ 623 The Company recognized the following related to operating leases in its Consolidated Statements of Operations (in millions): Year Ended December 31, Classification in Consolidated Statement of Operations 2020 2019 Lease expense General and administrative and Information technology $ 194 $ 183 Variable lease expense General and administrative and Information technology 46 56 Less: Sublease income General and administrative (2) (2) Total lease expense, net of sublease income $ 238 $ 237 For the year ended December 31, 2018, the Company recognized lease expense of $149 million under ASC 840. As of December 31, 2020, the operating lease liabilities will mature over the following periods (in millions): 2021 $ 168 2022 122 2023 74 2024 50 2025 35 Thereafter 136 Total remaining lease payments $ 585 Less: Imputed interest (60) Total operating lease liabilities $ 525 As of December 31, 2020, the Company has entered into leases that have not yet commenced with future lease payments of approximately $7 million which are not reflected in the table above. These leases will commence in 2021 with lease terms of up to 7.5 years and will be recognized upon lease commencement. In addition, the Company entered into an agreement to sign a future lease in the city of Manchester in the United Kingdom for the future headquarters of Rentalcars.com (see Note 16). Supplemental cash flow information related to operating leases is as follows (in millions): Year Ended December 31, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities $ 200 $ 189 Operating lease assets obtained in exchange for lease liabilities 67 155 "Operating lease amortization" presented in the operating activities section of the Consolidated Statements of Cash Flows reflects the portion of the operating lease expense from the amortization of the operating lease assets.

GOODWILL, INTANGIBLE ASSETS AND

GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS	12 Months Ended
GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS	GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS A substantial portion of the Company's intangible assets and goodwill relates to the acquisitions of OpenTable and KAYAK. Goodwill The changes in the balance of goodwill for the years ended December 31, 2020 and 2019 consist of the following (in millions): 2020 2019 Balance, beginning of year $ 2,913 $ 2,910 Acquisitions — 7 Impairments (1,062) — Foreign currency translation adjustments 44 (4) Balance, end of year (1) $ 1,895 $ 2,913 (1) The balance of goodwill as of December 31, 2020 and 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively. Interim Goodwill Impairment Test Due to the significant and negative financial impact of the COVID-19 pandemic (see Note 2), the Company performed an interim period goodwill impairment test at March 31, 2020. Under the current goodwill impairment standard adopted in the first quarter of 2020, a goodwill impairment loss is measured at the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the carrying amount of goodwill (see Note 2). As of March 31, 2020, the estimated fair value of each of the Company’s reporting units, except the OpenTable and KAYAK reporting unit, exceeded its respective carrying value. For the OpenTable and KAYAK reporting unit, the Company recognized a goodwill impairment charge of $489 million for the three months ended March 31, 2020, which is not tax-deductible, resulting in an adjusted carrying value of goodwill for OpenTable and KAYAK of $1.5 billion at March 31, 2020. The goodwill impairment was primarily driven by a significant reduction in the forecasted near-term cash flows of OpenTable and KAYAK as well as the significant decline in comparable companies' market values as a result of the COVID-19 pandemic. The estimated fair value of OpenTable and KAYAK was determined using a combination of standard valuation techniques, including an income approach (discounted cash flows) and a market approach (applying the recent decline in enterprise values of comparable publicly-traded companies to the recently calculated fair value for OpenTable and KAYAK, as well as applying comparable company multiples). The income approach estimates fair value utilizing long-term growth rates and discount rates applied to the cash flow projections. In the cash flow projections, the Company assumed that OpenTable and KAYAK will experience a significant decline in near-term cash flows with a recovery to 2019 levels of financial performance (including profitability) oc curring in 2023. The shape and timing of the recovery was a key assumption in the fair value calculation (both in the income and market approaches). Annual Goodwill Impairment Test As of September 30, 2020, the Company performed its annual goodwill impairment test. Other than the OpenTable and KAYAK reporting unit, the fair values of the Company’s reporting units exceeded their respective carrying values. For the OpenTable and KAYAK reporting unit, the Company recognized a goodwill impairment charge of $573 million for the three months ended September 30, 2020, which is not tax-deductible, resulting in an adjusted carrying value of goodwill for OpenTable and KAYAK of $1.0 billion at September 30, 2020. The goodwill impairment was primarily driven by a significant reduction in the forecasted cash flows of OpenTable and KAYAK, reflecting a longer assumed recovery period to 2019 levels of profitability, mainly due to the continued material adverse impact of the COVID-19 pandemic, including its impact on the flight vertical at KAYAK, and the lowered outlook for monetization opportunities in restaurant reservation services. The estimated fair value of OpenTable and KAYAK was determined using a combination of standard valuation techniques, including an income approach (discounted cash flows) and a market approach (applying comparable company multiples). The income approach estimates fair value utilizing long-term growth rates and discount rates applied to the cash flow projections. The income approach, applied as of September 30, 2020, reflected a reduction in the forecasted cash flows of OpenTable and KAYAK and a longer assumed recovery period to 2019 levels of profitability, driven primarily by a lowered outlook for monetization opportunities in restaurant reservation services and slower than previously expected recovery trends for airline travel, which is a key vertical for KAYAK. For the interim goodwill impairment test at March 31, 2020, the Company expected a recovery to 2019 levels of financial performance occurring in 2023 for OpenTable and KAYAK. Based on the Company's evaluation of all relevant information available as of September 30, 2020 for the annual goodwill impairment test, the Company expected that OpenTable and KAYAK would not return to the 2019 level of profitability within the next five years, and that it was uncertain whether the shape of the recovery would ultimately match the Company’s expectations. An increase or decrease of one percentage point to the profitability growth rates used in the cash flow projections would result in an increase or decrease of approximately $100 million to the estimated fair value of OpenTable and KAYAK as of September 30, 2020. The discount rate is determined based on t he reporting unit’s estimated weighted- average cost of capital and adjusted to reflect the risks inherent in its cash flows, which requires significant judgments. The discount rate used for the annual goodwill impairment test as of September 30, 2020 is higher than the discount rate used for the interim goodwill impairment test as of March 31, 2020. If the discount rate used in the income approach increases or decreases by 0.5%, the impact to the estimated fair value of OpenTable and KAYAK, at September 30, 2020, ranges from a decrease of approximately $65 million to an increase of approximately $70 million. The estimation of fair value reflects numerous assumptions that are subject to various risks and uncertainties, including key assumptions regarding OpenTable and KAYAK’s expected growth rates and operating margin, expected length and severity of the impact from the COVID-19 pandemic, the shape and timing of the subsequent recovery and the competitive environment, as well as other key assumptions with respect to matters outside of the Company's control, such as discount rates and market comparables. It requires significant judgments and estimates and actual results could be materially different than the judgments and estimates used to estimate fair value. Future events and changing market conditions may lead the Company to re-evaluate the assumptions reflected in the current forecast disclosed above, particularly the assumptions related to the length and severity of the COVID-19 pandemic and the shape and timing of the subsequent recovery, which may result in a need to recognize an additional goodwill impairment charge that could have a material adverse effect on the Company's results of operations. No additional impairment indicators were identified as of December 31, 2020. Intangible Assets and Other Long-lived Assets The Company's intangible assets at December 31, 2020 and 2019 consist of the following (in millions): December 31, 2020 December 31, 2019 Gross Carrying Accumulated Net Carrying Gross Carrying Accumulated Net Carrying Amortization Supply and distribution $ 1,136 $ (552) $ 584 $ 1,100 $ (472) $ 628 3 - 20 years Technology 174 (144) 30 170 (129) 41 2 - 7 years Internet domain names 44 (37) 7 40 (32) 8 5 - 20 years Trade names 1,824 (633) 1,191 1,811 (534) 1,277 4 -20 years Other intangible assets 2 (2) — 2 (2) — Up to 15 years Total intangible assets $ 3,180 $ (1,368) $ 1,812 $ 3,123 $ (1,169) $ 1,954 Intangible assets are amortized on a straight-line basis. Amortization expense was $167 million, $175 million and $178 million for the years ended December 31, 2020, 2019 and 2018, respectively. The estimate d annual amortization expense for intangible assets for the next five years and thereafter is expected to be as follows (in millions): 2021 $ 163 2022 160 2023 158 2024 157 2025 152 Thereafter 1,022 $ 1,812 The Company reviews long-lived assets, including intangible assets and operating lease assets, whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the ability to recover the carrying value of the assets from the estimated undiscounted future net cash flows, before interest and taxes, of the related asset group. Due to the significant and negative financial impact of the COVID-19 pandemic (see Note 2), at March 31, 2020, the Company performed the recoverability test of its long-lived assets and concluded that there was no impairment. At September 30, 2020, for OpenTable and KAYAK, the Company performed the recoverability test of its long-lived assets due to additional impairment indicators and concluded that there was no impairment. At December 31, 2020, no additional impairment indicators were identified for the Company's long-lived assets.

DEBT

DEBT	12 Months Ended
DEBT	Dec. 31, 2020
Debt Disclosure [Abstract]
DEBT	DEBT Revolving Credit Facility In August 2019, 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 London Inter-bank Offer Rate, or if such London Inter-bank Offer Rate is no longer available, the agreed alternate rate of interest ("LIBOR") (but no less than 0%) for the interest period in effect for such borrowing plus an applicable margin ranging from 0.875% to 1.50%; or (ii) for U.S. Dollar-denominated loans only, the sum of (x) the greatest of (a) JPMorgan Chase Bank, N.A.'s prime lending rate, (b) the U.S. federal funds rate plus 0.50% and (c) LIBOR (but no less than 0%) for an interest period of one month plus 1.00%, plus (y) an applicable margin ranging from 0% to 0.50%. Undrawn balances available under the revolving credit facility are subject to commitment fees at the applicable rate ranging from 0.07% to 0.20%. The revolving credit facility provides for the issuance of up to $80 million of letters of credit as well as borrowings of up to $100 million on same-day notice, referred to as swingline loans. Other than swingline loans, which are available only in U.S. Dollars, borrowings and letters of credit 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 can be used for working capital and general corporate purposes, including acquisitions, share repurchases and debt repayments. At December 31, 2020 and 2019, there were no borrowings outstanding and $4 million and $5 million of letters of credit issued under this revolving credit facility, respectively. Upon entering into this revolving credit facility, the Company terminated its prior $2.0 billion five-year revolving credit facility entered into in June 2015. During the six months ended June 30, 2019, the Company made short-term borrowings under the prior revolving credit facility totaling $400 million with a weighted-average interest rate of 3.5%, which were repaid prior to June 30, 2019. The current revolving credit facility contains a maximum leverage ratio covenant, compliance with which is a condition to the Company's ability to borrow thereunder. In April 2020, the Company amended the revolving credit facility, pursuant to which the maximum leverage ratio covenant was suspended through and including the three months ending March 31, 2021, and was replaced with a $4.5 billion minimum liquidity covenant based on unrestricted cash, cash equivalents, short-term investments and unused capacity under this revolving credit facility. In October 2020, the Company further amended the revolving credit facility to extend the suspension of the maximum leverage ratio covenant and the related replacement with the minimum liquidity covenant through and including the three months ending March 31, 2022 and increase the permitted maximum leverage ratio from and including the three months ending June 30, 2022 through and including the three months ending March 31, 2023. The Company agreed not to declare or make any cash distribution and not to repurchase any of its shares (with certain exceptions including in connection with tax withholding related to shares issued to employees) unless (i) prior to the delivery of financial statements for the three months ending June 30, 2022, it has at least $6.0 billion of liquidity on a pro forma basis, based on unrestricted cash, cash equivalents, short-term investments and unused capacity under this revolving credit facility and (ii) after the delivery of financial statements for the three months ending June 30, 2022, it is in compliance on a pro forma basis with the maximum leverage ratio covenant then in effect. Such restriction ends upon delivery of financial statements required for the three months ending June 30, 2023, or the Company has the ability to terminate this restriction earlier if it demonstrates compliance with the original maximum leverage ratio covenant in the revolving credit facility. Beginning with the three months ending June 30, 2022, the minimum liquidity covenant will cease to apply and the maximum leverage ratio covenant, as increased, will again be in effect. Outstanding Debt Outstanding debt at December 31, 2020 consists of the following (in millions): December 31, 2020 Outstanding Unamortized Debt Carrying Current Liabilities: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (15) $ 985 Long-term debt: 0.8% (€1 Billion) Senior Notes due March 2022 $ 1,223 $ (1) $ 1,222 2.15% (€750 Million) Senior Notes due November 2022 919 (4) 915 2.75% Senior Notes due March 2023 500 (1) 499 2.375% (€1 Billion) Senior Notes due September 2024 1,223 (7) 1,216 3.65% Senior Notes due March 2025 500 (2) 498 4.1% Senior Notes due April 2025 1,000 (5) 995 0.75% Convertible Senior Notes due May 2025 863 (128) 735 3.6% Senior Notes due June 2026 1,000 (4) 996 1.8% (€1 Billion) Senior Notes due March 2027 1,223 (2) 1,221 4.5% Senior Notes due April 2027 750 (5) 745 3.55% Senior Notes due March 2028 500 (2) 498 4.625% Senior Notes due April 2030 1,500 (11) 1,489 Total long-term debt $ 11,201 $ (172) $ 11,029 Outstanding debt at December 31, 2019 consists of the following (in millions): December 31, 2019 Outstanding Unamortized Debt Carrying Current Liabilities: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (12) $ 988 Long-term debt: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (39) $ 961 0.8% (€1 Billion) Senior Notes due March 2022 1,123 (3) 1,120 2.15% (€750 Million) Senior Notes due November 2022 842 (3) 839 2.75% Senior Notes due March 2023 500 (2) 498 2.375% (€1 Billion) Senior Notes due September 2024 1,123 (9) 1,114 3.65% Senior Notes due March 2025 500 (2) 498 3.6% Senior Notes due June 2026 1,000 (5) 995 1.8% (€1 Billion) Senior Notes due March 2027 1,123 (5) 1,118 3.55% Senior Notes due March 2028 500 (3) 497 Total long-term debt $ 7,711 $ (71) $ 7,640 Based on the closing price of the Company's common stock for the prescribed measurement periods for the three months ended December 31, 2020 and 2019, as applicable, the contingent conversion thresholds on the 2021 Notes (as defined below) and the May 2025 Notes (as defined below) were not exceeded; and therefore, the notes were not convertible at the option of the holders. Fair Value of Debt At December 31, 2020 and 2019, the estimated fair value of the outstanding debt was approximately $14.0 billion and $9.8 billion, respectively, and was considered a "Level 2" fair value measurement (see Note 6). Fair value was estimated based upon actual trades at the end of the reporting period or the most recent trade available as well as the Company's stock price at the end of the reporting period. The estimated fair value of the Company's debt in excess of the outstanding principal amount at December 31, 2020 primarily relates to the Senior Notes and the Convertible Senior Notes issued in April 2020. The estimated fair value of the Company's debt in excess of the outstanding principal amount at December 31, 2019 primarily relates to the conversion premium on the convertible senior notes. Convertible Senior Notes If the note holders exercise their option to convert, the Company delivers cash to repay the principal amount of the notes and delivers shares of common stock or cash, at its option, to satisfy the conversion value in excess of the principal amount. If the Company's convertible debt is redeemed or converted prior to maturity, a gain or loss on extinguishment is recognized. The gain or loss is the difference between the fair value of the debt component immediately prior to extinguishment and its carrying value. To estimate the fair value of the debt at the conversion date, the Company estimates the borrowing rate, considering the credit rating and similar debt of comparable corporate issuers without the conversion feature. Description of Convertible Senior Notes In April 2020, the Company issued $863 million aggregate principal amount of Convertible Senior Notes due May 1, 2025 with an interest rate of 0.75% (the "May 2025 Notes"). The Company paid $19 million in debt issuance costs during the year ended December 31, 2020 related to this offering. The May 2025 Notes are convertible, subject to certain conditions, into the Company's common stock at a conversion price of $1,886.44 per share. The May 2025 Notes are convertible, at the option of the holder, prior to November 1, 2024, 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 130% 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 May 2025 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 May 2025 Notes in an aggregate value ranging from $0 to $235 million depending upon the date of the transaction and the then current stock price of the Company. Starting on November 1, 2024, holders will have the right to convert all or any portion of the May 2025 Notes, regardless of the Company's stock price. The May 2025 Notes may not be redeemed by the Company prior to maturity. The holders may require the Company to repurchase the May 2025 Notes for cash in certain circumstances. Interest on the May 2025 Notes is payable on May 1 and November 1 of each year. At December 31, 2020, the if-converted value of the May 2025 Notes exceeded the aggregate principal amount by $97 million. The proceeds from the issuance of the Convertible Senior Notes can be used for general corporate purposes, which may include repayment of debt, including the repayment, at maturity or upon conversion prior thereto, of the Company’s outstanding Convertible Senior Notes. In August 2014, the Company issued $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. Starting on 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. At December 31, 2020, the if-converted value of the 2021 Notes exceeded the aggregate principal amount by $17 million. In May 2013, the Company issued $1.0 billion aggregate principal amount of Convertible Senior Notes due June 15, 2020, with an interest rate of 0.35% (the "2020 Notes"). In June 2020, in connection with the maturity of the outstanding 2020 Notes, the Company paid $1.0 billion to satisfy the aggregate principal amount due and paid an additional $245 million in satisfaction of the conversion value in excess of the principal amount. 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"). 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 borrowing rates at debt origination to be 4.10% for the May 2025 Notes, 3.18% for the 2021 Notes and 3.13% for the 2020 Notes, considering its credit rating and similar debt of the Company or comparable corporate issuers without the conversion feature. The yield to maturity was estimated at an at-market coupon priced at par. Debt discount after tax of $100 million ($130 million before tax) related to the May 2025 Notes, $83 million ($143 million before tax) related to the 2021 Notes and $92 million ($154 million before tax) related to the 2020 Notes less financing costs allocated to the equity component of the respective convertible notes was recorded in "Additional paid-in capital" in the balance sheet at debt origination. The following table summarizes the interest expenses and weighted-average effective interest rates related to the convertible senior notes (in millions, except for interest rates). The remaining period for amortization of debt discount and debt issuance costs is the period until the stated maturity date for the respective debt. For the Year Ended December 31, 2020 2019 2018 Coupon interest expense $ 15 $ 12 14 Amortization of debt discount and debt issuance costs 54 50 52 Total interest expenses $ 69 $ 62 $ 66 Weighted-average effective interest rate 3.5 % 3.2 % 3.2 % Other Long-term Debt In April 2020, the Company issued Senior Notes due April 13, 2025 with an interest rate of 4.10% for an aggregate principal amount of $1.0 billion, Senior Notes due April 13, 2027 with an interest rate of 4.50% for an aggregate principal amount of $750 million and Senior Notes due April 13, 2030 with an interest rate of 4.625% for an aggregate principal amount of $1.5 billion. The Company paid $19 million in debt issuance costs during the year ended December 31, 2020 related to issuance of these senior notes. The proceeds from the issuance of the Senior Notes can be used for general corporate purposes, which may include repayment of debt, including the repayment, at maturity or upon conversion prior thereto, of the Company’s outstanding Convertible Senior Notes. Other long-term debt, including the Senior Notes issued in April 2020, had a total carrying value of $10.3 billion and $6.7 billion at December 31, 2020 and 2019, respectively. Debt discount and debt issuance costs are amortized using the effective interest rate method over the period from the origination date through the stated maturity date. The following table summarizes the information related to other long-term debt outstanding at December 31, 2020: Other Long-term Debt Date of Issuance Effective Interest Rate (1) Timing of Interest Payments 0.8% Senior Notes due March 2022 March 2017 0.94 % Annually in March 2.15% Senior Notes due November 2022 November 2015 2.27 % Annually in November 2.75% Senior Notes due March 2023 August 2017 2.88 % Semi-annually in March and September 2.375% Senior Notes due September 2024 September 2014 2.54 % Annually in September 3.65% Senior Notes due March 2025 March 2015 3.76 % Semi-annually in March and September 4.1% Senior Notes due April 2025 April 2020 4.22 % Semi-annually in April and October 3.6% Senior Notes due June 2026 May 2016 3.70 % Semi-annually in June and December 1.8% Senior Notes due March 2027 March 2015 1.86 % Annually in March 4.5% Senior Notes due April 2027 April 2020 4.63 % Semi-annually in April and October 3.55% Senior Notes due March 2028 August 2017 3.63 % Semi-annually in March and September 4.625% Senior Notes due April 2030 April 2020 4.72 % Semi-annually in April and October (1) Represents the coupon interest rate adjusted for deferred debt issuance costs, premiums or discounts existing at the origination of the debt. The following table summarizes the interest expenses related to other long-term debt (in millions): For the Year Ended December 31, 2020 2019 2018 Coupon interest expense $ 264 $ 160 $ 163 Amortization of debt discount and debt issuance costs 9 6 7 Total interest expenses $ 273 $ 166 $ 170 Historically, the aggregate principal value of the Euro-denominated Senior Notes maturing in March 2022, November 2022, September 2024 and March 2027 (collectively the "Euro-denominated debt") and accrued interest thereon had been designated as a hedge of the Company's net investment in a Euro functional currency subsidiary. Beginning in the second quarter of 2019, the Company has only designated certain portions of the aggregated principal value of the Euro-denominated debt as a hedge. For the years ended December 31, 2020 and 2019, the carrying value of the portion of Euro-denominated debt, designated as a net investment hedge, ranged from $1.8 billion to $3.2 billion and from $2.4 billion to $4.3 billion, respectively. The foreign currency transaction gains or losses on the Euro-denominated debt that is designated as a hedging instrument for accounting purposes are recorded in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets.

TREASURY STOCK

TREASURY STOCK	12 Months Ended
TREASURY STOCK	Dec. 31, 2020
Equity [Abstract]
TREASURY STOCK	TREASURY STOCK At December 31, 2019, the Company had a total remaining authorization of $11.5 billion to repurchase its common stock under a program authorized by the Company's Board of Directors in 2019 to repurchase up to $15.0 billion of the Company's common stock. At December 31, 2020, the Company had a total remaining authorization of $10.4 billion to repurchase its common stock. The Company has no t repurchased any shares since March 2020 under this authorization and does not intend to initiate any repurchases under this authorization until it has better visibility into the shape and timing of a recovery from the COVID-19 pandemic. See Note 12 for a description of the impact of the October 2020 credit facility amendment on the Company's ability to repurchase shares. 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, 2020, 2019 and 2018 (in millions, except for shares, which are reflected in thousands): 2020 2019 2018 Shares Amount Shares Amount Shares Amount Authorized stock repurchase programs 601 $ 1,122 4,358 $ 8,002 3,020 $ 5,850 General authorization for shares withheld on stock award vesting 84 142 87 151 80 162 Total 685 $ 1,264 4,445 $ 8,153 3,100 $ 6,012 Shares repurchased in December and settled in following January — $ — 19 $ 40 43 $ 74 For the years ended December 31, 2020, 2019 and 2018, the Company remitted employee withholding taxes of $141 million, $151 million and $163 million, 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, 2020, there were 22,446,897 shares of the Company's common stock held in treasury.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT	12 Months Ended
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT	Dec. 31, 2020
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT	CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT The table below presents the changes in the balances of accumulated other comprehensive income (loss) ("AOCI") by component for the years ended December 31, 2018, 2019 and 2020 (in millions): Foreign currency translation adjustments, net of tax Net unrealized gains (losses) on available-for-sale securities, net of tax (1) Total AOCI, net of tax Foreign currency translation Net investment hedges (2) Total, net of tax Before tax Tax (expense) benefit Total, net of tax Before tax Tax benefit (expense) (3) Before tax Tax benefit (expense) Balance, December 31, 2017 $ 210 $ — $ (290) $ 65 $ (15) $ 343 $ (90) $ 253 $ 238 Other Comprehensive Income (Loss) ("OCI") before (319) 41 217 (53) (114) (201) 2 (199) (313) OCI for the period (319) 41 217 (53) (114) (201) 2 (199) (313) Amounts reclassified to retained earnings (1) — — — — — (299) 58 (241) (241) Balance, December 31, 2018 $ (109) $ 41 $ (73) $ 12 $ (129) $ (157) $ (30) $ (187) $ (316) OCI before reclassifications (77) 13 71 (17) (10) 161 (37) 124 114 Amounts reclassified to net income (4) — — — — — (11) 22 11 11 OCI for the period (77) 13 71 (17) (10) 150 (15) 135 125 Balance, December 31, 2019 $ (186) $ 54 $ (2) $ (5) $ (139) $ (7) $ (45) $ (52) $ (191) OCI before reclassifications 197 (7) (182) 42 50 6 (1) 5 55 Amounts reclassified to net income (4) — — — — — 4 14 18 18 OCI for the period 197 (7) (182) 42 50 10 13 23 73 Balance, December 31, 2020 $ 11 $ 47 $ (184) $ 37 $ (89) $ 3 $ (32) $ (29) $ (118) (1) Upon the adoption of the accounting update on financial instruments on January 1, 2018, the Company reclassified net unrealized gains, net of tax, of $241 million ($299 million before tax) related to marketable equity securities from AOCI to retained earnings. Changes in fair value of marketable equity securities subsequent to January 1, 2018 are recognized in net income rather than "Accumulated other comprehensive loss" in the Consolidated Balance Sheets (see Note 2). (2) Net investment hedges balance, net of tax, at December 31, 2020 and earlier dates presented above, includes accumulated net losses from fair value adjustments of $35 million ($53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. The remaining balances relate to foreign currency transaction gains (losses) and related tax benefits (expenses) associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (see Notes 2 and 12). (3) The tax benefits relate to foreign currency translation adjustments to the Company's one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the enactment of the Tax Act. (4) The reclassified net gains (losses) on available-for-sale securities, before tax, are included in "Other income (expense), net" and the reclassified tax (expenses) benefits are included in "Income tax expense" in the Consolidated Statements of Operations. For the year ended December 31, 2020, the reclassified tax expenses include a tax expense of $15 million related to the maturity in May 2020 of the Company's investment of $250 million in Trip.com Group convertible senior notes (see Note 5). For the year ended December 31, 2019, the reclassified tax expenses include a tax expense of $21 million related to the maturity in August 2019 of the Company's investment of $500 million in Trip.com Group convertible senior notes.

INCOME TAXES

INCOME TAXES	12 Months Ended
INCOME TAXES	Dec. 31, 2020
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES International pre-tax income was $2.6 billion, $5.7 billion and $4.8 billion for the years ended December 31, 2020, 2019 and 2018, respectively. U.S. pre-tax loss was $2.0 billion for the year ended December 31, 2020, and U.S. pre-tax income was $213 million and $47 million for the years ended December 31, 2019 and 2018, respectively. Provision for Income Taxes The income tax expense (benefit) for the year ended December 31, 2020 is as follows (in millions): Current Deferred Total International $ 320 $ (62) $ 258 U.S. Federal (9) 296 287 U.S. State (16) (21) (37) Total $ 295 $ 213 $ 508 The income tax expense (benefit) for the year ended December 31, 2019 is as follows (in millions): Current Deferred Total International $ 915 $ (12) $ 903 U.S. Federal 22 166 188 U.S. State 34 (32) 2 Total $ 971 $ 122 $ 1,093 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 Income tax liabilities of $174 million and $158 million are included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets at December 31, 2020 and 2019, respectively. In the first quarter of 2020, the Company made a prepayment of the Netherlands income taxes of 660 million Euros ($717 million) to earn prepayment discounts. The Company requested a refund of this amount from the Dutch tax authorities and it was received in April 2020. 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. In 2018, 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. In 2019, as a result of additional technical guidance issued by U.S. federal and state tax authorities with respect to the Tax Act, the Company recorded an income tax benefit of $17 million to adjust its 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 associated with the mandatory deemed repatriation. In 2020, the Company recorded an income tax benefit of $8 million to adjust its income tax expense that was recorded during the year ended December 31, 2017 relating to the federal one-time deemed repatriation liability. This benefit was primarily due to additional tax credits. The Company utilized $108 million of deferred tax assets related to U.S. federal NOLs and $115 million of other tax credit carryforwards to reduce its transition tax liability as of December 31, 2020. Under the Tax Act, the Company's future cash generated by the Company's international operations can generally 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 $309 million of its U.S. NOLs to reduce its U.S. federal tax liability for the deemed repatriation tax. After utilization of available NOLs, at December 31, 2020, the Company had U.S. federal NOLs of $179 million, the majority of which do not have an expiration date, and U.S. state NOLs of $457 million, which mainly begin to expire in years December 31, 2032 and forward. In addition, at December 31, 2020, the Company had $488 million of non-U.S. NOLs, and $14 million of U.S. research tax credit carryforwards available to reduce future tax liabilities and the majority of both 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, 2020 and 2019 are as follows (in millions): 2020 2019 Deferred tax assets/(liabilities): Net operating loss carryforward — U.S. $ 67 $ 37 Net operating loss carryforward — International 81 15 Accrued expenses 47 35 Stock-based compensation and other stock based payments 40 49 Foreign currency translation adjustment 29 36 Tax credits 9 14 Euro-denominated debt 77 — Operating lease liabilities 43 38 Property and equipment 11 31 Subtotal - deferred tax assets 404 255 Discount on convertible notes (29) (10) Intangible assets and other (119) (133) Euro-denominated debt — (14) State income tax on accumulated unremitted international earnings (5) (8) Unrealized gains on investments (550) (191) Operating lease assets (38) (35) Installment sale liability (263) (284) Other (14) (11) Subtotal - deferred tax liabilities (1,018) (686) Valuation allowance on deferred tax assets (58) (45) Net deferred tax liabilities (1) $ (672) $ (476) (1) Includes deferred tax assets of $455 million and $400 million at December 31, 2020 and 2019, respectively, reported in "Other assets, net" in the Consolidated Balance Sheets. During the year ended December 31, 2019, the Company recorded a deferred tax asset of $335 million, which is included in "Other Assets, net" in the Consolidated Balance Sheet, and a deferred tax liability of $325 million, both related to an internal legal entity reorganization. The valuation allowance on deferred tax assets of $58 million at December 31, 2020 includes $18 million related to international operations and $40 million primarily related to certain U.S. federal NOLs, research credits and Connecticut NOLs. The valuation allowance on deferred tax assets of $45 million at December 31, 2019 includes $30 million related to international operations and $15 million primarily related to U.S. research credits, capital loss carryforwards and Connecticut NOLs. 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 is 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") rather than the Dutch statutory rate of 25%. A portion of Booking.com's earnings during the years ended December 31, 2020, 2019 and 2018 qualified 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% for the years ended December 31, 2020, 2019 and 2018 as a result of the following items (in millions): 2020 2019 2018 Income tax expense at U.S. federal statutory rate $ 119 $ 1,251 $ 1,015 Adjustment due to: Foreign rate differential 55 210 210 Innovation Box Tax benefit (79) (443) (435) Goodwill impairment 228 — — Stock-based compensation 32 23 12 Federal GILTI 73 36 35 State income tax (benefit) expense (31) 9 1 Valuation allowance 36 1 (3) Uncertain tax positions 64 11 (4) Tax Act - Remeasurement of deferred tax balances — — (2) Tax Act - U.S. transition tax benefit and other transition impacts (8) (17) (46) Other 19 12 54 Income tax expense $ 508 $ 1,093 $ 837 Uncertain Tax Positions The following is a reconciliation of the total beginning and ending amount of unrecognized tax benefits (in millions): 2020 2019 2018 Unrecognized tax benefit — January 1 $ 56 $ 45 $ 32 Gross increases — tax positions in current period 2 3 1 Gross increases — tax positions in prior periods 48 11 19 Gross decreases — tax positions in prior periods (11) (3) (3) Reduction due to lapse in statute of limitations — — (2) Reduction due to settlements during the current period (11) — (2) Unrecognized tax benefit — December 31 $ 84 $ 56 $ 45 The increase in unrecognized tax benefits is principally related to Booking.com’s French tax disputes (see Note 16), the majority of which is included as a partial reduction to the French tax payment recorded in “Other Assets, net” in the Consolidated Balance Sheets for the years ended December 31, 2020 and 2019. The remaining unrecognized tax benefits are primarily included in "Other long-term liabilities" and "Deferred income taxes" in the Consolidated Balance Sheets for the years ended December 31, 2020 and 2019. The unrecognized tax benefits, if recognized, would affect the effective tax rate. The Company does not expect further significant changes in the amount of unrecognized tax benefits during the next twelve months. As of December 31, 2020 and 2019, total gross interest and penalties accrued was $31 million and $10 million, respectively.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Competition and Consumer Protection Reviews At times, online platforms, including online travel platforms, have been the subject of investigations or inquiries by various national competition authorities ("NCAs") or other governmental authorities regarding competition law matters, consumer protection issues or other areas of concern. The Company is or has been involved in many such investigations. For example, the Company has been and continues to be involved in investigations related to whether Booking.com's contractual parity arrangements with accommodation providers, sometimes also referred to as "most favored nation" or "MFN" provisions, are anti-competitive because they require accommodation providers to provide Booking.com with room rates, conditions or availability that are at least as favorable as those offered to other OTCs or through the accommodation provider's website. To resolve and close certain of the investigations, the Company has from time to time made commitments to the investigating authorities regarding future business practices or activities. For example, Booking.com has made commitments to several NCAs, including agreeing to narrow the scope of its parity clauses, in order to resolve parity-related investigations. These investigations can also result in fines and the Company recorded a liability of $23 million during the year ended December 31, 2020 for potential fines associated with its contractual parity arrangements. In addition, in September 2017, the Swiss Price Surveillance Office opened an investigation into the level of commissions of Booking.com in Switzerland and the investigation is ongoing. If there is an adverse outcome and Booking.com is unsuccessful in any appeal, Booking.com could be required to reduce its commissions in Switzerland. Some authorities are reviewing the online hotel booking sector more generally through market inquiries and the Company cannot predict the outcome of such inquiries or any resulting impact on its business, results of operations, cash flows or financial condition. NCAs or other governmental authorities are continuing to review the activities of online platforms, including through the use of consumer protection powers. For example, the United Kingdom's NCA (the Competition and Markets Authority, or CMA) conducted a consumer protection law investigation into the clarity, accuracy and presentation of information on hotel booking sites. In connection with this investigation, in 2019 Booking.com, agoda and KAYAK, along with a number of other OTCs, voluntarily agreed to certain commitments with the CMA, which resolved the CMA's investigation without a finding by the CMA of an infringement or an admission of wrongdoing by the OTCs involved. Among other things, the commitments provided to the CMA included showing prices inclusive of all mandatory taxes and charges, providing information about the effect of money earned on search result rankings on or before the search results page and making certain adjustments to how discounts and statements concerning popularity or availability are shown to consumers. The CMA has stated that it expects all participants in the online travel market to adhere to the same standards, regardless of whether they formally signed the commitments. As a result of additional inquiries from other NCAs in the European Union, Booking.com has made similar commitments with the Consumer Protection Cooperation Network that became applicable in the European Union in June 2020. In the future, it is possible other jurisdictions could engage Booking.com in discussions to implement similar changes to its business in those countries. The Company is unable to predict what, if any, effect any future similar commitments will have on its business, industry practices or online commerce more generally. To the extent that any other investigations or inquiries result in additional commitments, fines, damages or other remedies, the Company's business, financial condition and results of operations could be harmed. The Company is involved in multiple litigations in Israel claiming that it has violated Israeli consumer protection and competition laws. For example, one such lawsuit alleges that the Company violated Israeli consumer protection laws by failing to properly display Israeli local taxes in the total prices shown to Israeli residents on its platform. Another lawsuit claims that the Company's parity contractual terms with partners violate Israeli competition laws because they are anti-competitive. A third lawsuit claims Israeli consumer protection laws prohibit the Company from facilitating non-refundable bookings to Israeli residents. Each of the plaintiffs in these matters is requesting certification of a class and the Company is defending against class certification. If the court were to grant class certification for any of these matters and if the plaintiffs were successful on the merits of the claims, the Company could be required to pay damages. However, it is not reasonably possible to estimate the amount of such damages because the likelihood of class certification and the success of the merits of these cases are both too speculative at this stage in the litigation and also because a reasonable assessment of the size of any potential class is not possible at this time. Although Booking.com has not been sued, a German hotel association has threatened Booking.com with a class action lawsuit on behalf of a group of German hotels that alleges that the hotels overpaid commissions to Booking.com because of wide parity terms in the contracts between the hotels and Booking.com between 2006 and 2015. Booking.com is pursuing court proceedings in the Netherlands to declare that the Netherlands is the proper forum for this matter. If the hotel association follows through and files the lawsuit, the class were to be certified and there were to be an adverse outcome, the Company could be required to pay damages. Although the Company believes the claim to be without merit and intends to defend against the claim, if the hotel association were successful in any litigation and the Company were required to pay damages, the amount could be significant. The Company cannot reasonably estimate an amount of potential loss because there are several unknown variables at this early stage, including that the plaintiff has not yet filed a lawsuit. The Company is unable to predict how any current or future investigations or litigation may be resolved or the long-term impact of any such resolution on its business. For example, competition and consumer-law-related investigations, legislation or issues have and could in the future result in private litigation. More immediate results could include, among other things, the imposition of fines, commitments to change certain business practices or reputational damage, any of which could harm the Company's business, results of operations, brands or competitive position. Tax Matters French tax authorities conducted audits of Booking.com for the years 2003 through 2012 and years 2013 through 2015 and currently are conducting an audit for the years 2016 through 2018. In December 2015, the French tax authorities issued Booking.com assessments for unpaid income and value added taxes ("VAT") related to tax years 2006 through 2012 for approximately 356 million Euros ($403 million), the majority of which represents penalties and interest. The assessments assert that Booking.com had a permanent establishment in France. In December 2019, the French tax authorities issued an additional assessment of 70 million Euros ($86 million), including interest and penalties, for the 2013 year asserting that Booking.com had taxable income attributable to a permanent establishment in France. The French tax authorities also have issued assessments totaling 39 million Euros ($48 million), including interest and penalties, for certain tax years between 2011 and 2015 on Booking.com's French subsidiary asserting that the subsidiary did not receive sufficient compensation for the services it rendered to Booking.com in the Netherlands. As a result of a formal demand from the French tax authorities for payment of the amounts assessed against Booking.com for the years 2006 through 2012, in January 2019, the Company paid the assessments of approximately 356 million Euros ($403 million) in order to preserve its right to contest those assessments in court. The payment, which is included in "Other assets, net" in the Consolidated Balance Sheets at December 31, 2020 and 2019, does not constitute an admission that the Company owes the taxes and will be refunded (with interest) to the Company to the extent the Company prevails. In December 2019 and October 2020, the Company initiated court proceedings with respect to certain of the assessments. Although the Company believes that Booking.com has been, and continues to be, in compliance with French tax law, and the Company is contesting the assessments, during the three months ended September 30, 2020, the Company contacted the French tax authorities regarding the potential to achieve resolution of the matter through a settlement. After assessing several potential outcomes and potential settlement amounts and terms, an unrecognized tax benefit in the amount of 50 million Euros ($61 million) has been recorded during the year ended December 31, 2020, of which the majority has been included as a partial reduction to the tax payment recorded in “Other Assets, net” in the Consolidated Balance Sheet at December 31, 2020. In December 2020, the French Administrative Court (Conseil d’Etat) delivered a decision in the "ValueClick" case that could have an impact on the outcome in the Company's case. After considering the potential impact of the new decision on the potential outcomes for the Booking.com assessments, the Company currently estimates that the reasonably possible loss related to VAT is approximately 20 million Euros ($24 million). Additional assessments could result when the French tax authorities complete the outstanding audits. Italian authorities are reviewing Booking.com's activities for the years 2011 through 2019. They are reviewing whether Booking.com has a permanent establishment in Italy, Booking.com's transfer pricing policies in Italy, and for the years 2013 through 2019, whether Booking.com is subject to VAT. The Company is cooperating with the investigation but intends to contest any allegation that Booking.com has a permanent establishment in Italy or that its transfer pricing policies are inappropriate. In December 2018 and 2019, the Italian tax authorities issued assessments on Booking.com's Italian subsidiary for approximately 48 million Euros ($58 million) for the 2013 tax year and 58 million Euros ($71 million) for the 2014 tax year, respectively, asserting that its transfer pricing policies were inadequate. The Company believes that Booking.com has been, and continues to be, in compliance with Italian tax law. The Company paid 10 million Euros ($11 million) in December 2019 as a partial prepayment of the 2013 assessment to avoid any collection enforcement from the Italian tax authorities pending the appeal phase of this case. The payment, which is included in "Other assets, net" in the Consolidated Balance Sheets at December 31, 2020 and 2019, does not constitute an admission that the Company owes the taxes and will be refunded (with interest) to the Company to the extent the Company prevails. In September 2020, the Italian tax authorities approved the opening of a Mutual Agreement Procedure (“MAP”) between Italy and the Netherlands for the 2013 tax year and the Company expects to request that the 2014 tax year be added to the MAP. Based on the possibility of the 2013 and 2014 Italian assessments being settled through the MAP process, and, after considering potential resolution amounts, a net unrecognized tax benefit amount of 4 million Euros ($5 million) has been recorded during the year ended December 31, 2020, of which the majority has been included as a partial reduction to the tax payment recorded in "Other Assets, net" in the Consolidated Balance Sheet at December 31, 2020. It is unclear what further actions, if any, the Italian authorities will take. Such actions could include closing the investigation, assessing Booking.com additional taxes and/or imposing interest, fines and penalties. In addition, Turkish tax authorities have asserted that Booking.com has a permanent establishment in Turkey and have issued tax assessments for the years 2012 through 2018 for approximately 766 million Turkish Lira ($103 million), which includes interest and penalties through December 31, 2020. The Company believes that Booking.com has been, and continues to be, in compliance with Turkish tax law, and the Company is contesting these assessments. The Company has not recorded a liability in connection with these assessments. As a result of an internal review of tax policies and positions at one of the Company's smaller subsidiaries in 2018, the Company identified two issues related to the application of certain non-income-based tax laws to that subsidiary's business. At December 31, 2020 and 2019, the Company had accrued $59 million and $67 million, respectively, related to these travel transaction taxes, based on the Company's estimate of the probable travel transaction tax owed for the prior periods, including interest and penalties, as applicable. The related expenses are included in "General and administrative" expense in the Consolidated Statements of Operations. The Company currently estimates that the reasonably possible loss related to these matters in excess of the amount accrued is approximately $25 million. To the extent the Company determines that the probable taxes owed related to these matters exceed what has already been accrued or new issues are identified, the Company may need to accrue additional amounts, which could adversely affect the Company’s business, results of operations, financial condition and cash flows. During the second quarter of 2019, the Company identified the nonpayment in prior periods of a wage-related tax under Netherlands' law on compensation paid to certain highly-compensated former employees in the year of their separation from employment with Booking.com. The Company has informed the Dutch tax authorities of the nonpayment and, to correct this immaterial error, has paid an amount of $61 million based on the Company's estimate of the probable tax owed for prior tax years, including interest. This expense is recorded in "Personnel" expenses in the Consolidated Statement of Operations for the year ended December 31, 2019. From time to time, the Company is involved in other tax-related audits, investigations or proceedings, which could relate to income taxes, value-added taxes, sales taxes, employment taxes, etc. For example, the Company is subject to legal proceedings in the United States related to travel transaction taxes (e.g., hotel occupancy taxes, sales taxes, etc.). Any taxes or other assessments in excess of the Company's current tax provisions, whether in connection with the foregoing or otherwise (including the resolution of any tax proceedings), could have a materially adverse impact on the Company's results of operations, cash flows and financial condition. Other Matters Beginning in 2014, Booking.com received several letters from the Netherlands Pension Fund for the Travel Industry (Reiswerk) (“BPF”) claiming that Booking.com is required to participate in the mandatory pension scheme of the BPF with retroactive effect to 1999, which has a higher contribution rate than the pension scheme in which Booking.com is currently participating. BPF instituted legal proceedings against Booking.com and in 2016 the District Court of Amsterdam rejected all of BPF’s claims. BPF appealed the decision to the Court of Appeal, and, in May 2019, the Court of Appeal also rejected all of BPF’s claims, in each case by ruling that Booking.com does not meet the definition of a travel intermediary for purposes of the mandatory pension scheme. BPF has appealed to the Netherlands Supreme Court. In October 2020, the Dutch Advocate General issued an opinion to the Supreme Court stating that the Dutch Advocate General believes the decision of the Court of Appeal to be incorrect based on her interpretation of the pension scheme requirements. The Company has submitted to the Supreme Court a response to the Advocate General's opinion. While the Company continues to believe that Booking.com is in compliance with its pension obligations and that the Dutch Supreme Court should uphold the ruling of the Court of Appeal, based on the significant influence the Dutch Advocate General’s opinion typically has on the Supreme Court, the Company has reevaluated the probability of a loss and believes it is probable that it has incurred a loss related to this matter. The Company expects the Dutch Supreme Court to rule in the first quarter of 2021. In the event the Supreme Court overturns the decision of the Court of Appeal and remands the case to a lower court, the Company intends to pursue a number of defenses in any subsequent proceedings and may ultimately prevail in whole or in part. The Company is not able to reasonably estimate a loss or a range of loss because the litigation is ongoing and there are significant factual and legal questions yet to be determined. As a result, as of December 31, 2020, the Company has not recorded a liability in connection with a potential adverse outcome to this litigation. However, if Booking.com were to ultimately lose and all of BPF’s claims were to be accepted (including with retroactive effect to 1999), the Company estimates that as of December 31, 2020, the maximum loss, not including any potential interest or penalties, would be approximately $290 million. Such estimated potential loss increases as Booking.com continues not to contribute to the BPF and depends on Booking.com's applicable employee compensation after December 31, 2020. From time to time the Company notifies the Dutch data protection authority in accordance with its obligations under the E.U. General Data Protection Regulation of certain incidental and accidental personal data security incidents. Although the Company believes it has fulfilled its data protection regulatory obligations, should the Dutch data protection authority decide these incidents were the result of inadequate technical and organizational security measures, it could decide to impose a fine. While the Company believes that any fine imposed on it would be immaterial, the Company estimates that if a fine were imposed, it could range from a de minimis amount to 20 million Euros ($24 million) per incident, depending on the Dutch data protection authority’s evaluation of the facts and circumstances associated with the incident after investigation. The Company accrues for certain legal contingencies where it is probable that a loss has been incurred and the amount can be reasonably estimated. Such accrued amounts are not material to the Company's balance sheets and provisions recorded have not been material to the Company's results of operations or cash flows. From time to time, the Company has been, and expects to continue to be, subject to legal proceedings and claims in the ordinary course of business, including claims of alleged infringement of third-party intellectual property rights. Such claims, even if not meritorious, could result in the expenditure of significant financial and managerial resources, divert management's attention from the Company's business objectives and adversely affect the Company's business, results of operations, financial condition and cash flows. Building Construction In September 2016, the Company signed a turnkey agreement to construct an office building for Booking.com's future headquarters in the Netherlands for 270 million Euros ($331 million). Upon signing this agreement, the Company paid 43 million Euros ($48 million) for the acquired land-use rights, which was included in "Operating lease assets" in the Consolidated Balance Sheets. In addition, since signing the turnkey agreement the Company has made several progress payments principally related to the construction of the building, which are included in "Property and equipment, net" in the Consolidated Balance Sheets. As of December 31, 2020, the Company had a remaining obligation of 56 million Euros ($68 million) related to the turnkey agreement. The Company's contractual obligation was reduced by 9 million Euros ($11 million) during 2020. The remaining obligation will be paid through 2022, when the Company anticipates construction will be complete. In addition to the turnkey agreement, the Company has a remaining obligation at December 31, 2020 to pay 70 million Euros ($86 million) over the remaining initial term of the acquired land lease, which expires in 2065. The Company has made and will continue to make additional capital expenditures to fit out and furnish the office space. At December 31, 2020, the Company had 29 million Euros ($35 million) of outstanding commitments to vendors to fit out and furnish the office space. Lease obligations See Note 10 for information about the Company's lease obligations. Other Contractual Obligations and Commitments In 2018, the Company entered into an agreement to sign a future lease related to approximately 222,000 square feet of office space in the city of Manchester in the United Kingdom for the future headquarters of Rentalcars.com. The Company's obligation to execute the lease is conditional upon the lessor completing certain activities, which are expected to be completed in 2021. If these activities are completed, the lease will commence for a term of approximately 13 years and the Company will have a lease obligation of approximately 65 million British Pounds Sterling ($88 million), excluding lease incentives. The Company will also make capital expenditures to fit out and furnish the office space.

BENEFIT PLANS

BENEFIT PLANS	12 Months Ended
BENEFIT PLANS	Dec. 31, 2020
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, 2020, 2019 and 2018 were $33 million, $26 million and $22 million, respectively.

GEOGRAPHIC INFORMATION

GEOGRAPHIC INFORMATION	12 Months Ended
GEOGRAPHIC INFORMATION	Dec. 31, 2020
Segment Reporting [Abstract]
GEOGRAPHIC INFORMATION	GEOGRAPHIC INFORMATION The Company's international revenue information consists of the information of Booking.com, agoda and Rentalcars.com in their entirety and the information of the international businesses of KAYAK and OpenTable. This classification is independent of where the consumer resides, where the consumer is physically located while using the Company's services or the location of the travel service provider or restaurant. For example, a reservation made through Booking.com (which is domiciled in the Netherlands) at a hotel in New York by a consumer in the United States is part of the Company's international results. The Company's geographic information on revenues is as follows (in millions): United States International Total For the year ended: The Netherlands Other December 31, 2020 $ 783 $ 5,264 $ 749 $ 6,796 December 31, 2019 1,537 11,686 1,843 15,066 December 31, 2018 1,536 11,348 1,643 14,527 The following table presents information on the Company's property and equipment (excluding capitalized software) and operating lease assets based on location of the assets at December 31, 2020 and 2019 (in millions): United States International Total The Netherlands United Kingdom Other December 31, 2020 $ 186 $ 499 $ 85 $ 278 $ 1,048 December 31, 2019 216 484 137 327 1,164

ACQUISITIONS

ACQUISITIONS	12 Months Ended
ACQUISITIONS	Dec. 31, 2020
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS 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. In November 2018, the Company paid $134 million, net of cash acquired, to complete the acquisition of HotelsCombined, a hotel meta-search company. 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. In 2019, the Company paid $37 million of contingent consideration for a business acquired in 2015. The contingent payment was dependent on the achievement of certain performance factors.

RESTRUCTURING AND OTHER EXIT CO

RESTRUCTURING AND OTHER EXIT COSTS	12 Months Ended
RESTRUCTURING AND OTHER EXIT COSTS	Dec. 31, 2020
Restructuring and Related Activities [Abstract]
RESTRUCTURING AND OTHER EXIT COSTS	RESTRUCTURING AND OTHER EXIT COSTS In response to the reduction in the Company's business volumes as a result of the impact of the COVID-19 pandemic (see Note 2), during the year ended December 31, 2020, the Company took actions at all of its brands to reduce the size of its workforce across more than 60 countries to optimize efficiency and reduce costs. As part of these actions, the Company engaged in the process of consulting with its employees, works councils, employee representatives and other relevant organizations related to the reductions in force in certain countries (including the Netherlands and the United Kingdom), which have substantially concluded as of December 31, 2020. These consultations resulted in the Company executing either voluntary leaver schemes or involuntary reductions in force, or, in some countries, a combination of the two. The Company completed the vast majority of announcements to affected employees by December 2020. In January 2021, the Company approved and communicated the final portion of workforce reductions in the Netherlands. During the year ended December 31, 2020, the Company recorded expenses of $149 million for the restructuring actions, which are included in “Restructuring and other exit costs” in the Consolidated Statement of Operations. These expenses are primarily cash-based and consist of employee severance and other termination benefits, and other costs. Noncash restructuring expenses recorded during the year ended December 31, 2020 were $7 million. At December 31, 2020, restructuring liabilities of $37 million are included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheet.

GOVERNMENT GRANTS AND OTHER ASS

GOVERNMENT GRANTS AND OTHER ASSISTANCE	12 Months Ended
GOVERNMENT GRANTS AND OTHER ASSISTANCE	Dec. 31, 2020
Unusual or Infrequent Items, or Both [Abstract]
GOVERNMENT GRANTS AND OTHER ASSISTANCE	GOVERNMENT GRANTS AND OTHER ASSISTANCECertain governments have passed or are considering modifying legislation to help businesses during the COVID-19 pandemic through loans, wage subsidies, tax relief or other financial aid, and some of these governments have extended or are considering extending these programs. The Company has participated in several of these programs, including the Netherlands' wage subsidy program and the United Kingdom's job retention scheme. In addition, in certain countries, such as Singapore and China, the Company also participated in programs where the government assistance is in the form of wage subsidies and reductions in wage-related employer taxes paid by the Company. During the year ended December 31, 2020, the Company recognized government grants and other assistance benefits of $127 million. The government grants and other assistance is recorded principally as a reduction of "Personnel" expense in the Consolidated Statement of Operations. At December 31, 2020, the Company has received $99 million and recorded a receivable of $28 million, which is included in “Other current assets” in the Consolidated Balance Sheet, for payments expected to be received for the programs where it has met the qualifying requirements and it is probable that payment will be received. This receivable is expected to be received in 2021. In addition, certain governments have extended support for the travel and tourism industry through special programs whereby discounts are extended to travelers through travel service providers or through travel agents for reservations facilitated by them. The Company has participated in Japan's Go To Travel program and Thailand's We Travel Together program.

OTHER INCOME (EXPENSE), NET

OTHER INCOME (EXPENSE), NET	12 Months Ended
OTHER INCOME (EXPENSE), NET	Dec. 31, 2020
Other Income and Expenses [Abstract]
OTHER INCOME (EXPENSE), NET	OTHER INCOME (EXPENSE), NET The components of other income (expense), net included the following (in millions): Year Ended December 31, 2020 2019 2018 Interest and dividend income $ 54 $ 152 $ 187 Net gains (losses) on marketable equity securities (1) 1,811 745 (367) Impairment of investment (1) (100) — — Foreign currency transaction losses (207) (31) (53) Other (4) 13 (4) Other income (expense), net $ 1,554 $ 879 $ (237)

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
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, other long-lived tangible and intangible assets, the valuation of investments in private companies, income taxes, contingencies, stock-based compensation, the allowance for expected credit losses (also referred to as allowance for doubtful accounts), customer chargeback provisions and the accrual of obligations for loyalty and other incentive programs.
Impact of COVID-19	Impact of COVID-19 In response to the outbreak of the novel strain of the coronavirus, COVID-19 (the "COVID-19 pandemic") , many governments around the world have implemented, and continue to implement, a variety of measures to reduce the spread of COVID-19, including travel restrictions and bans, instructions to residents to practice social distancing, curfews, quarantine advisories, including quarantine restrictions after travel in certain locations, shelter-in-place orders, required closures of non-essential businesses and additional restrictions on businesses as part of re-opening plans. These government mandates have forced many of the customers on whom the Company’s business relies, including hotels and other accommodation providers, airlines and restaurants, to seek government support in order to continue operating, to curtail drastically their service offerings, to file for bankruptcy protection or to cease operations entirely. Further, these measures have materially adversely affected, and may further adversely affect, consumer sentiment and discretionary spending patterns and economies, and the Company’s workforce, operations and customers. The COVID-19 pandemic and the resulting economic conditions and government orders have resulted in a material decrease in consumer spending and an unprecedented decline in travel and restaurant activities and consumer demand for related services. The Company’s financial results and prospects are almost entirely dependent on the sale of travel-related services. The Company’s results for the year ended December 31, 2020 have been materially and negatively impacted as compared to 2019 and 2018. Due to the uncertain and rapidly evolving nature of current conditions around the world, the Company is unable to predict accurately the impact that the COVID-19 pandemic will have on its business going forward. With the spread of COVID-19 to all major regions and the discovery of new variants of the coronavirus, the Company expects the COVID-19 pandemic and its effects to continue to have a significant adverse impact on its business for the duration of the pandemic, during any resurgence of the pandemic and during the subsequent economic recovery, which could be an extended period of time. Given the severe downturn in the global travel industry and the financial difficulties faced by many of the Company's travel service provider and restaurant customers and marketing affiliates, the Company has increased its provision for expected credit losses (also referred to as provision for bad debt or provision for uncollectible accounts) on receivables from and prepayments to its travel service provider and restaurant customers and marketing affiliates (see Note 7). Moreover, due to the high level of cancellations of existing reservations, the Company has incurred, and may continue to incur, higher than normal cash outlays to refund consumers for prepaid reservations, including certain situations where the Company has already transferred the prepayment to the travel service provider (see Note 3). Any material increase in the Company’s provision for expected credit losses and any material increase in cash outlays to refund consumers would have a corresponding adverse effect on the Company's results of operations and related cash flows. As a result of the deterioration of the Company’s business due to the COVID-19 pandemic, the Company determined that a portion of its goodwill had experienced a decline in value at March 31, 2020 and recorded a significant impairment charge (see Note 11). In addition, the Company recorded a significant impairment charge at March 31, 2020 for one of the Company's long-term investments due to the impact of the COVID-19 pandemic on the business of the investee and the Company's estimate of the resulting decline in the value of the investment (see Notes 5 and 6). At September 30, 2020, the Company recorded an additional significant impairment charge to its goodwill (see Note 11). Even though no additional impairment indicators were identified as of December 31, 2020 for these assets, it is possible that the Company may have to record additional significant impairment charges in future periods. See Note 12 for additional information about the Company’s existing debt arrangements, including $4.1 billion of debt issued in April 2020. The Company’s continued access to sources of liquidity depends on multiple factors, including global economic conditions, the condition of global financial markets, the availability of sufficient amounts of financing, the Company’s ability to meet debt covenant requirements, the Company’s operating performance and the Company's credit ratings. If the Company’s credit ratings were to be downgraded, or financing sources were to ascribe higher risk to the Company's rating levels, the Company or its industry, the Company’s access to capital and the cost of any financing would be negatively impacted. There is no guarantee that additional debt financing will be available in the future to fund the Company’s obligations, or that it will be available on commercially reasonable terms, in which case the Company may need to seek other sources of funding. The extent of the effects of the COVID-19 pandemic on the Company’s business, results of operations, cash flows and growth prospects is highly uncertain and will ultimately depend on future developments. These include, but are not limited to, the severity, extent and duration of the COVID-19 pandemic, including as a result of any new variants of COVID-19 and any resurgences of the pandemic, and its impact on the travel and restaurant industries and consumer spending more broadly. Even if economic and operating conditions for the Company’s business improve, the Company cannot predict the long-term effects of the pandemic on its business or the travel and restaurant industries as a whole. If the travel and restaurant industries are fundamentally changed by the COVID-19 pandemic in ways that are detrimental to the Company’s operating model, the Company’s business may continue to be adversely affected even as the broader global economy recovers. In response to the reduction in the Company's business volumes as a result of the impact of the COVID-19 pandemic, the Company has taken actions to reduce the size of its workforce to optimize efficiency and reduce costs. See Note 20 for additional information.
Change in Presentation and Reclassification	Change in Presentation and ReclassificationCertain amounts from prior periods have been reclassified to conform to the current year presentation, including the change in the presentation of marketing expenses disclosed later in this Note.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company's financial instruments, including cash, restricted cash, 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. Accounts receivable and other financial assets measured at amortized cost are carried at cost less an allowance for expected credit losses to present the net amount expected to be collected (see Note 7). See Notes 5, 6 and 12 for information related to fair value for investments, derivatives and the Company's outstanding senior notes.
Cash and Cash Equivalents	Cash and Cash EquivalentsCash 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 or regulations. Restricted cash and cash equivalents at December 31, 2020, 2019 and 2018 principally relates to the minimum cash requirement for the Company's travel-related insurance business. The following table reconciles cash and cash equivalents and restricted cash and cash equivalents reported in the Consolidated Balance Sheets to the total amount shown in the Consolidated Statements of Cash Flows (in millions): December 31, 2020 2019 2018 As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 10,562 $ 6,312 $ 2,624 Restricted cash and cash equivalents included in "Other current assets" 20 20 21 Total cash and cash equivalents and restricted cash and cash equivalents as $ 10,582 $ 6,332 $ 2,645
Investments	Investments Investments held by the Company include debt securities and equity securities. 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. Payments made for investments are reported in "Purchase of investments" and proceeds received from sales or maturities of investments are reported in "Proceeds from sale and maturity of investments" in the Consolidated Statements of Cash Flows. Debt Securities The Company has classified its investments in debt securities as available-for-sale securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is considered a debt security for accounting purposes. These securities are reported at estimated fair value with the aggregate unrealized gains and losses, net of tax, reflected in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. For periods prior to January 1, 2020, investments in debt securities were considered to be impaired when a decline in fair value was judged to be other than temporary because the Company either intended to sell or it was more-likely-than not that it would be required to sell the impaired security before recovery. Once a decline in fair value was determined to be other than temporary, an impairment charge was recorded and a new cost basis in the investment was established. If the Company did not intend to sell the debt security, but it was probable that the Company would not collect all amounts due, then only the impairment due to the credit risk would be recognized in net income and the remaining amount of the impairment would be recognized in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. On January 1, 2020, the Company adopted the accounting standards update on the measurement of credit losses on financial instruments. Under the current accounting standard, if the amortized cost basis of an available-for-sale security exceeds its fair value and if the Company has the intention to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis, an impairment is recognized in the Consolidated Statements of Operations. If the Company does not have the intention to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis and the Company determines that the decline in fair value below the amortized cost basis of an available-for-sale security is entirely or partially due to credit-related factors, the credit loss is measured and recognized as an allowance for expected credit losses along with the related expense in the Consolidated Statements of Operations. The allowance is measured as the amount by which the debt security’s amortized cost basis exceeds the Company’s best estimate of the present value of cash flows expected to be collected. The fair 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 6 for information related to fair value measurements. The Company's investments in marketable debt securities are recognized based on the trade date. The marketable debt securities generally have a term of less than five years and are assessed for classification in the Consolidated Balance Sheets as short-term or long-term at the individual security level. Classification as short-term or long-term is based on the maturities of the securities, as applicable, and the Company's expectations regarding the timing of sales and redemptions. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage or in connection with a commercial relationship are included in "Long-term investments" in the Consolidated Balance Sheets, except in situations where the Company expects the investment to be realized in cash, redeemed or sold within one year. The cost of marketable debt securities sold is determined using a first-in and first-out method. 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. Marketable equity securities are reported at estimated fair value with changes in fair value recognized in "Other income (expense), net" in the Consolidated Statements of Operations. 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. 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. See Notes 5 and 6 for further information related to investments.
Accounts Receivable from Customers and Allowance for Expected Credit Losses	Accounts Receivable from Customers and Allowance for Expected Credit Losses For periods prior to January 1, 2020, receivables from customers are recorded at the original invoiced amounts net of an allowance for doubtful accounts. The allowance for doubtful accounts was estimated based on historical experience, aging of the receivable, credit quality of the customers, economic trends and other factors that may affect the Company's ability to collect from customers. On January 1, 2020, the Company adopted the accounting standards update on the measurement of expected credit losses, which requires the Company to estimate lifetime expected credit losses upon recognition of the financial assets. The Company has identified the relevant risk characteristics, of its customers and the related receivables and prepayments, which include the following: size, type (alternative accommodations vs. hotels) or geographic location of the customer, or a combination of these characteristics. Receivables with similar risk characteristics have been grouped into pools. For each pool, the Company considers the historical credit loss experience, current economic conditions, supportable forecasts of future economic conditions, and any recoveries in assessing the lifetime expected credit losses. Other key factors that influence the expected credit loss analysis include customer demographics, payment terms offered in the normal course of business to customers, the nature of competition, and industry-specific factors that could impact the Company's receivables. Additionally, external data and macroeconomic factors are considered. This is assessed at each quarter based on the Company’s specific facts and circumstances. See Note 7 for additional information.
Property and Equipment, Net	Property and Equipment, Net 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 term of the lease related to leasehold improvements, whichever is shorter. Building Construction-in-progress Building construction-in-progress is associated with the construction of Booking.com's future headquarters 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 Acquisition costs and 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 beginning when the asset is substantially ready for use. Costs incurred for enhancements that are expected to result in
Cloud Computing Arrangements	Cloud Computing ArrangementsThe Company utilizes various third-party computer systems and third-party service providers, including global distribution systems ("GDSs") serving the accommodation, rental car and airline industries. The Company uses both internally-developed systems and third-party systems to operate its services, including transaction processing, order management and financial and accounting systems. For periods beginning after December 31, 2018, implementation costs incurred in a hosting arrangement that is a service contract are capitalized and amortized over the term of the hosting arrangement. The capitalized implementation costs are reported as "Prepaid expenses, net" or "Other assets, net" in the Company's Consolidated Balance Sheets, as appropriate. The related amortization expenses are reported as "Information technology" in the Company's Consolidated Statements of Operations.
Leases	Leases On January 1, 2019, the Company adopted Accounting Standards Codification ("ASC") 842, Leases , using a modified retrospective method applied to all contracts as of January 1, 2019. Therefore, for reporting periods beginning after December 31, 2018, the financial statements are prepared in accordance with the current lease standard and the financial statements for all periods prior to January 1, 2019 are presented under the previous lease standard ("ASC 840"). Under the current lease standard, the Company determines if an arrangement is a lease, or contains a lease, when a contract is signed. The Company determines if a lease is an operating or finance lease and records a lease asset and a lease liability upon lease commencement, which is the date when the underlying asset is made available for use by the lessor. The Company has operating leases for office space, data centers and land for Booking.com's future headquarters. For office space, data centers and land, the Company has elected to combine the fixed payments to lease the asset and any fixed non-lease payments (such as maintenance or utility charges) when determining its lease payments. The Company uses its incremental borrowing rate as its discount rate to determine the present value of its remaining lease payments to calculate its lease assets and lease liabilities because the rate implicit in the lease is not readily determinable. The incremental borrowing rate approximates the rate the Company would pay to borrow in the currency of the lease payments on a collateralized basis for the weighted-average life of the lease. Operating lease assets also include any prepaid lease payments and lease incentives received prior to lease commencement. The Company recognizes lease expense on a straight-line basis over the lease term. Certain of the Company's lease agreements include rent payments which are adjusted periodically for inflation. Any change in payments due to changes in inflation rates are recognized as variable lease expense as they are incurred. Variable lease expense also includes costs for property taxes, insurance and services provided by the lessor which are charged based on usage or performance (such as maintenance or utility charges). Most leases have one or more options to renew, with renewal terms that can extend the initial lease term for various periods up to 9 years. The exercise of renewal options for office space and data centers is at the Company’s discretion and are included if they are reasonably certain to be exercised. The land lease for Booking.com's future headquarters has an initial term which expires in 2065, at which time the lease payments will be adjusted based on the value of the land on the reassessment date. The Company considered the initial term of the land lease to be its expected period of use.
Land-use rights	"Operating lease assets" in the Consolidated Balance Sheets includes the land-use rights related to payment in 2016 for the land lease for Booking.com's future headquarters as described above. The land-use rights are amortized on a straight-line basis over its expected period of use. This expense is recorded as lease expense in "General and administrative" expense in the Consolidated Statements of Operations. See Notes 10 and 16 for further information.
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 tested annually for impairment and when an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. The Company tests goodwill at a reporting unit level. The fair value of the reporting unit is compared to its carrying value,
Impairment of Long-Lived Assets	Impairment of Long-lived Assets The Company reviews long-lived assets, including intangible assets and operating lease assets, whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the 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 asset group. 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.
Foreign Currency Translation	Foreign Currency Translation The functional currency of the Company's subsidiaries is generally the respective local currency. For international operations, assets and liabilities are translated into U.S. Dollars at the rate of exchange existing at the balance sheet date. Income statement amounts are translated at monthly average exchange rates applicable for the period. Translation gains and losses are included as a component of "Accumulated other comprehensive loss" in the Company's Consolidated Balance Sheets. Foreign currency transaction gains and losses are included in "Other income (expense), net" 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 foreign currency exchange rates. For the Company's international operations, the primary foreign currency exposures are in Euros and British Pounds Sterling, in which the Company conducts a significant portion of its business activities. As a result, the Company faces exposure to adverse movements in foreign currency exchange rates as the financial results of its international operations are translated from local currencies into U.S. Dollars upon consolidation. Additionally, foreign currency 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 net 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 operations into U.S. Dollars, even though it does not elect to apply hedge accounting or hedge accounting does not apply. These contracts are generally short-term in duration. Certain of the Company's derivative instruments have master netting arrangements, which reduce credit risk by permitting net settlement of transactions with the same counterparty. The Company reports the fair value of its derivative assets and liabilities on a gross basis in the Consolidated Balance Sheets in "Other current assets" and "Accrued expenses and other current liabilities," respectively. Unless designated as hedges for accounting purposes, gains and losses resulting from changes in the fair value of derivative instruments are recognized in "Other income (expense), net" in the Consolidated Statements of Operations in the period that the changes occur and are classified within "Net cash provided by operating activities" in the Consolidated Statements of Cash Flows. See Note 6 for further information related to these derivative instruments. The Company, from time to time in the past, has utilized derivative instruments to hedge the impact of changes in foreign currency exchange rates on the net assets of its foreign subsidiaries. These derivative instruments were designated as net investment hedges. Hedge ineffectiveness was assessed and measured based on changes in forward exchange rates. The Company recorded gains and losses on these derivative instruments as foreign currency translation adjustments, which offset a portion of the foreign currency translation adjustments related to the foreign subsidiaries' net assets. Gains and losses on these derivative instruments were recognized in the Consolidated Balance Sheets in "Accumulated other comprehensive loss" and will be realized upon a partial sale or liquidation of the investment.
Non-derivative Instrument Designated as Net Investment Hedge	Non-derivative Instrument Designated as Net Investment HedgeThe foreign currency transaction gains or losses on the Company's Euro-denominated debt are measured based upon changes in spot rates. The foreign currency transaction gains or losses on the Euro-denominated debt that is designated as a hedging instrument for accounting purposes are recorded in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. The foreign currency transaction gains or losses on the Euro-denominated debt that is not designated as a hedging instrument are recognized in "Other income (expense), net" in the Consolidated Statement of Operations. See Notes 12 and 14 for further information related to the net investment hedge.
Revenue Recognition	Revenue Recognition 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. 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 recognition standard, with substantially all of the impact related to the Company’s online travel reservation services. Under the current revenue recognition standard, the Company recognizes revenue for travel reservation services when the travel begins rather than when the travel is completed. Online travel reservation services 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, generally at the time they are redeemed. The local occupancy taxes, general excise taxes, value-added taxes, sales taxes and other similar taxes ("travel transaction taxes"), if any, collected from travelers are reported on a net basis in revenues in the Consolidated Statements of Operations. Revenues for online travel reservation services are recognized 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 facilitate 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. 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 facilitates 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; credit card processing rebates and customer processing fees; and ancillary fees, including travel-related insurance revenues. Substantially all merchant revenues are derived from transactions where travelers book accommodation reservations or rental car reservations. Advertising and Other Revenues Advertising and other revenues are primarily recognized by KAYAK and OpenTable. 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. Accrued Liabilities for Loyalty and Other Incentive Programs See Note 3 for information related to accrued liabilities for loyalty and other incentive programs. Deferred Revenue See Note 3 for information related to deferred revenue.
Advertising Expenses	Advertising Expenses Marketing Expenses The Company's advertising expenses are reported in "Marketing expenses" in the Consolidated Statements of Operations. Marketing expenses consist of performance marketing expenses and brand marketing expenses. Performance marketing expenses are 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 marketing and incentives. Performance marketing expenses are recognized as incurred. Included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets are accrued performance marketing liabilities of $156 million and $333 million at December 31, 2020 and 2019, respectively. Brand marketing expenses are expenses incurred to build brand awareness over a specified time period. These expenses consist primarily of television advertising and online video and display advertising (including the airing of the Company's television advertising online), as well as other marketing expenses such as public relations and sponsorships. Brand marketing expenses are generally recognized as incurred with the exception of advertising production costs, which are deferred and expensed the first time the advertisement is displayed or broadcast. In the year ended December 31, 2019 and prior periods, the Company's marketing expenses were presented in the Consolidated Statements of Operations as "Performance marketing" and "Brand marketing" expenses. In 2020, the Company changed the presentation of marketing expenses by combining "Performance marketing" and "Brand marketing" into "Marketing expenses" in the Consolidated Statement of Operations because of the increased convergence of performance marketing and brand marketing channels in areas including digital marketing and the Company's view of overall marketing expenditure as its investment in customer acquisition and retention. The change in presentation had no impact on operating income or net income.
Sales and Other Expenses	Sales and Other Expenses 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) provisions for expected credit losses, primarily related to accommodation commission receivables and prepayments to certain customers; (3) fees paid to third parties that provide call center, website content translations and other services; (4) customer relations costs; (5) customer chargeback provisions and fraud prevention expenses associated with merchant transactions; and (6) insurance claim costs for the Company's travel-related insurance business.
Personnel	Personnel Personnel expenses consist of compensation to the Company's personnel, including salaries, stock-based compensation, bonuses, payroll taxes and employee health and other benefits. Included in "Accrued expenses and other current liabilities" in the Consolidated Balance Sheets are accrued compensation liabilities of $333 million and $344 million at December 31, 2020 and 2019, respectively.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense related to performance share units, restricted stock units and stock options is recognized based on fair value on a straight-line basis over the respective requisite service periods and forfeitures are accounted for when they occur. The fair value on the grant date of performance share units and restricted stock units is determined based on the number of units granted and the quoted price of the Company's common stock. For performance share units with market conditions, the effect of the market condition is also considered in the determination of fair value on the grant date using Monte Carlo simulations. The fair value of employee stock options is determined using the Black-Scholes model. The Company records stock-based compensation expense for performance-based awards using its estimate of the probable outcome at the end of the performance period (i.e., the estimated performance against the performance targets). The Company periodically adjusts the cumulative stock-based compensation expense recorded when the probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable. The benefits of tax deductions in excess of recognized compensation costs are recognized in the income statement as a discrete item 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 Consolidated Statements of Cash Flows.
Government Grants and Other Assistance	Government Grants and Other AssistanceThe Company recognizes government grants in the financial statements when it is probable that the grant will be received and the Company will comply with the conditions of the grant. Government grants are recorded as a reduction in the related operating expense or the cost of the asset that they are intended to defray. The government grants received by the Company have principally been granted to defray personnel costs.
Information Technology	Information Technology Information technology expenses consist primarily of: (1) software license and system maintenance fees; (2) outsourced data center and cloud computing costs; (3) payments to contractors; and (4) data communications and other expenses associated with operating the Company's services.
Restructuring and Other Exit Costs	Restructuring and Other Exit Costs The Company records employee severance and other termination costs that meet the requirements for recognition in accordance with the relevant guidance of ASC 420, Exit or Disposal Cost Obligations, or ASC 712, Compensation - Nonretirement Postemployment Benefits
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.
Contingencies	Contingencies Loss contingencies (other than income tax-related contingencies) arise from actual or possible claims and assessments and pending or threatened litigation that may be brought against the Company by individuals, governments or other entities. Based on the Company's assessment of loss contingencies at each balance sheet date, a loss is recorded in the financial statements if it is probable that an asset has been impaired or a liability has been incurred and the amount of the loss can be reasonably estimated.
Segment Reporting	Segment Reporting The Company historically determined that its primary brands constituted its operating segments. In 2019, reflecting changes to the management structure, the Company reorganized its operating segments from six to four operating segments by combining Booking.com with Rentalcars.com and KAYAK with OpenTable. The Company's Booking.com and Rentalcars.com operating segment represents a substantial majority of the Company's total revenues and operating income. The Company's operating segments continue to be aggregated into one reportable segment based on the similarity in economic characteristics, other qualitative factors and the objectives and principles of ASC 280, Segment Reporting. For geographic information, see Note 18.
Recent Accounting Pronouncements Adopted and Other Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted Simplifying the Test for Goodwill Impairment The Financial Accounting Standards Board ("FASB") issued an accounting update to simplify the test for goodwill impairment. The revised guidance eliminates the previously required step two of the goodwill impairment test, which required a hypothetical purchase price allocation to measure goodwill impairment. Under the revised guidance, a goodwill impairment loss will be measured at the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the carrying amount of goodwill. The Company adopted this update in the first quarter of 2020 and applied it on a prospective basis (see Note 11 for additional information on the goodwill impairment tests performed in 2020). Measurement of Credit Losses on Financial Instruments The FASB issued an accounting update on the measurement of credit losses for certain financial assets measured at amortized cost 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 expected credit losses, (2) allowing reversals of the previously recognized credit losses until the entity has the intent to sell or the entity 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. The Company adopted this update in the first quarter of 2020 and applied this update on a modified retrospective basis. Upon adoption of the new standard on January 1, 2020, the Company recorded a net decrease to its retained earnings of $3 million, net of tax. See Note 7 for additional information related to allowance for expected credit losses on accounts receivable and other financial assets and Note 5 for additional information related to investments in available-for-sale debt securities. SEC Amendments to Regulation S-K On November 19, 2020, the U.S. Securities and Exchange Commission issued final rules to amend Regulation S-K. These changes are effective for annual filings for the first fiscal year ending on or after August 9, 2021 and early adoption is permitted. The Company elected to adopt the amendments to Item 302 of Regulation S-K in their entirety, which eliminates the requirement to disclose, in these Consolidated Financial Statements, selected financial information for each quarter during the two most recent fiscal years, except in situations with certain retrospective changes. Other Recent Accounting Pronouncements Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity In August 2020, the FASB issued a new accounting update relating to convertible instruments and contracts in an entity’s own equity. For convertible instruments, the accounting update reduces the number of accounting models for convertible debt instruments and convertible preferred stock. Limiting the accounting models results in fewer embedded conversion features being separately recognized from the host contract as compared with current U.S. GAAP. The accounting update amends the guidance for the derivatives scope exception for contracts in an entity’s own equity to reduce form-over-substance-based accounting conclusions. The accounting update also simplifies the diluted earnings per share calculation in certain areas. For public business entities, the update is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2020 and interim periods within those fiscal years. Entities are allowed to apply this update on either a full or modified retrospective basis. The Company is currently evaluating the impact to its Consolidated Financial Statements of adopting this update. Simplifying the Accounting for Income Taxes The FASB issued a new accounting update relating to income taxes. This update provides an exception to the general methodology for calculating income taxes in an interim period when a year-to-date loss exceeds the anticipated loss for the year. This update also (1) requires an entity to recognize a franchise tax (or similar tax) that is partially based on income as an income-based tax and account for any incremental amount incurred as a non-income-based tax, (2) requires an entity to evaluate when a step-up in the tax basis of goodwill should be considered part of the business combination in which goodwill was originally recognized for accounting purposes and when it should be considered a separate transaction, and (3) requires that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	Dec. 31, 2020
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash and Cash Equivalents	The following table reconciles cash and cash equivalents and restricted cash and cash equivalents reported in the Consolidated Balance Sheets to the total amount shown in the Consolidated Statements of Cash Flows (in millions): December 31, 2020 2019 2018 As included in the Consolidated Balance Sheets: Cash and cash equivalents $ 10,562 $ 6,312 $ 2,624 Restricted cash and cash equivalents included in "Other current assets" 20 20 21 Total cash and cash equivalents and restricted cash and cash equivalents as $ 10,582 $ 6,332 $ 2,645

REVENUE (Tables)

REVENUE (Tables)	12 Months Ended
REVENUE (Tables)	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Summary of the Activity of Deferred Revenue	The following table summarizes the activity of deferred revenue for online travel reservation services for the years ended December 31, 2020 and 2019 (in millions): Year Ended December 31, 2020 2019 Balance, beginning of year $ 220 $ 149 Revenues recognized from the beginning balance (154) (134) Cancellations (66) (15) Payments received from travelers net of amounts estimated to be payable to travel 50 220 Balance, end of year $ 50 $ 220

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
STOCK-BASED COMPENSATION (Tables)	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Activity of restricted stock units	The following table summarizes the activity of restricted stock units for employees and non-employee directors during the year ended December 31, 2020: Restricted Stock Units Shares Weighted-average Grant-date Fair Value Unvested at December 31, 2019 256,745 $ 1,801 Granted 222,977 $ 1,659 Vested (130,684) $ 1,822 Forfeited (43,079) $ 1,737 Unvested at December 31, 2020 305,959 $ 1,697
Activity of performance share units	The following table summarizes the activity of performance share units for employees during the year ended December 31, 2020: Performance Share Units Shares Weighted-average Grant-date Fair Value Unvested at December 31, 2019 216,083 $ 1,835 Granted 9,040 $ 2,498 Vested (82,023) $ 1,741 Performance Shares Adjustment * (49,775) $ 1,944 Forfeited (8,847) $ 1,829 Unvested at December 31, 2020 84,478 $ 1,930 *Probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable, and the impact of modifications.
Estimated vesting of performance share units granted	The following table summarizes the estimated vesting, as of December 31, 2020, of performance share units granted in 2020, 2019 and 2018, net of forfeiture and vesting since the respective grant dates: Performance Share Units, by grant year 2020 2019 2018 Shares probable to be issued 9,040 40,843 34,595 Shares not subject to the achievement of minimum performance thresholds — 40,843 N/A* Shares that could be issued if maximum performance thresholds are met 18,080 108,522 N/A* * The performance period for the performance share units granted in 2018 ended on December 31, 2020.
Assumptions used to value option grants	The following table summarizes the assumptions used to value option grants granted during the year ended December 31, 2020 using the Black-Scholes options pricing model: Black-Scholes assumptions Risk-free interest rate 0.56 % Expected term in years 6.4 Expected stock price volatility 33.8 % Expected dividend yield 0 %
Activity of outstanding stock options	The following table summarizes the activity for stock options during the year ended December 31, 2020: Employee Stock Options Number of Shares Weighted-average Aggregate Weighted-average Remaining Contractual Term (in years) Balance, December 31, 2019 15,122 $ 484 $ 24 2.6 Granted 163,494 $ 1,411 Exercised (13,217) $ 466 Forfeited (12,653) $ 1,411 Balance, December 31, 2020 152,746 $ 1,401 $ 126 9.3 Exercisable at December 31, 2020 1,954 $ 660 $ 3 2.1

INVESTMENTS (Tables)

INVESTMENTS (Tables)	12 Months Ended
INVESTMENTS (Tables)	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	The following table summarizes, by major security type, the Company's investments at December 31, 2020 (in millions): Cost Gross Gross Carrying Value Short-term investments: Debt securities: Trip.com Group convertible debt securities $ 500 $ 1 $ — $ 501 Long-term investments: Investments in private companies: Debt securities $ 200 $ — $ — $ 200 Equity securities 552 3 (100) 455 Other long-term investments: Debt securities: Trip.com Group convertible debt securities 25 — (1) 24 Equity securities 463 2,617 — 3,080 Total $ 1,240 $ 2,620 $ (101) $ 3,759 The following table summarizes, by major security type, the Company's investments at December 31, 2019 (in millions): prv Cost Gross Gross Carrying Value Short-term investments: Debt securities: International government securities $ 109 $ — $ — $ 109 U.S. government securities 138 — — 138 Corporate debt securities 751 1 (1) 751 Total $ 998 $ 1 $ (1) $ 998 Long-term investments: Investments in private companies: Debt securities $ 250 $ — $ — $ 250 Equity securities 501 — — 501 Other long-term investments: Debt securities: International government securities 68 — — 68 U.S. government securities 136 — (1) 135 Corporate debt securities 963 2 (2) 963 Trip.com Group convertible debt securities 775 — (8) 767 Equity securities 1,117 684 (8) 1,793 Total $ 3,810 $ 686 $ (19) $ 4,477

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
FAIR VALUE MEASUREMENTS (Tables)	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Financial assets and liabilities carried at fair value and nonrecurring fair value measurements	Financial assets and liabilities carried at fair value at December 31, 2020 and nonrecurring fair value measurements are classified in the categories described in the tables below (in millions): Level 1 Level 2 Level 3 Total Recurring fair value measurements ASSETS: Cash equivalents and restricted cash equivalents: Money market fund investments $ 10,208 $ — $ — $ 10,208 Time deposits and certificates of deposit 32 — — 32 Short-term investments: Trip.com Group convertible debt securities — 501 — 501 Long-term investments: Investments in private companies: Debt securities — — 200 200 Other long-term investments: Trip.com Group convertible debt securities — 24 — 24 Equity securities 3,080 — — 3,080 Derivatives: Foreign currency exchange derivatives — 9 — 9 Total assets at fair value $ 13,320 $ 534 $ 200 $ 14,054 LIABILITIES Foreign currency exchange derivatives $ — $ 7 $ — $ 7 Nonrecurring fair value measurements Investments in equity securities of private companies (1) $ — $ — $ 404 $ 404 Goodwill of the OpenTable and KAYAK reporting unit (2) — — 1,000 1,000 Total nonrecurring fair value measurements $ — $ — $ 1,404 $ 1,404 (1) At March 31, 2020, the investment in Didi Chuxing was written down to its estimated fair value of $400 million, resulting in an impairment charge of $100 million (see Note 5). (2) At March 31, 2020, the goodwill of the OpenTable and KAYAK reporting unit was written down to its estimated fair value of $1.5 billion, resulting in an impairment charge of $489 million. At September 30, 2020, th e goodwill was further written down to its estimated fair value of $1.0 billion, resulting in an additional impairment charge of $573 million (see Note 11). Financial assets and liabilities carried at fair value at December 31, 2019 are classified in the categories described in the tables below (in millions): Level 1 Level 2 Level 3 Total Recurring fair value measurements ASSETS: Cash equivalents and restricted cash equivalents: Money market fund investments $ 5,734 $ — $ — $ 5,734 Corporate debt securities — 2 — 2 Time deposits and certificates of deposit 29 — — 29 Short-term investments: International government securities — 109 — 109 U.S. government securities — 138 — 138 Corporate debt securities — 751 — 751 Long-term investments: Investments in private companies: Debt securities — — 250 250 Other long-term investments: International government securities — 68 — 68 U.S. government securities — 135 — 135 Corporate debt securities — 963 — 963 Trip.com Group convertible debt securities — 767 — 767 Equity securities 1,793 — — 1,793 Derivatives: Foreign currency exchange derivatives — 12 — 12 Total assets at fair value $ 7,556 $ 2,945 $ 250 $ 10,751 LIABILITIES Foreign currency exchange derivatives $ — $ 5 $ — $ 5
Schedule of derivative instruments	The table below provides estimated fair values and notional amounts of foreign currency exchange derivatives outstanding at December 31, 2020 and 2019 (in millions). The notional amount of a foreign currency forward contract is the contracted amount of foreign currency to be exchanged and is not recorded in the balance sheet. December 31, 2020 December 31, 2019 Estimated fair value of derivative assets $ 9 $ 12 Estimated fair value of derivative liabilities 7 5 Notional amount: Foreign currency purchases 898 1,770 Foreign currency sales 839 901 The effect of foreign currency exchange derivatives recorded in "Other income (expense), net" in the Consolidated Statements of Operations for the years ended December 31, 2020, 2019, and 2018 is as follows (in millions): For the Year Ended December 31, 2020 2019 2018 Losses on foreign currency exchange derivatives $ 31 $ 19 $ 44

ACCOUNTS RECEIVABLE AND OTHER_2

ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS (Tables)	12 Months Ended
ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS (Tables)	Dec. 31, 2020
Receivables [Abstract]
Changes in allowance for expected credit losses for receivables from customers and marketing affiliates	The following table summarizes the activity of the allowance for expected credit losses on receivables (in millions): For the Year Ended December 31, 2020 2019 2018 Balance, beginning of year $ 49 $ 51 $ 35 Provision charged to earnings 216 69 79 Write-offs and adjustments (116) (70) (62) Foreign currency translation adjustments 17 (1) (1) Balance, end of year $ 166 $ 49 $ 51

NET INCOME PER SHARE (Tables)

NET INCOME PER SHARE (Tables)	12 Months Ended
NET INCOME PER SHARE (Tables)	Dec. 31, 2020
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 net income per share is as follows (in thousands): For the Year Ended December 31, 2020 2019 2018 Weighted-average number of basic common shares outstanding 40,974 43,082 47,446 Weighted-average dilutive stock options, restricted stock units and performance share units 158 203 236 Assumed conversion of convertible senior notes 28 224 335 Weighted-average number of diluted common and common equivalent shares outstanding 41,160 43,509 48,017

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	12 Months Ended
PROPERTY AND EQUIPMENT, NET (Tables)	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property and equipment, net	Property and equipment, net at December 31, 2020 and 2019 consist of the following (in millions): 2020 2019 Estimated Computer equipment $ 746 $ 736 2 to 6 years Capitalized software 565 442 2 to 5 years Leasehold improvements 278 265 1 to 15 years Office equipment, furniture and fixtures 63 61 2 to 8 years Building construction-in-progress 257 161 Total 1,909 1,665 Less: Accumulated depreciation (1,153) (927) Property and equipment, net $ 756 $ 738

LEASES (Tables)

LEASES (Tables)	12 Months Ended
LEASES (Tables)	Dec. 31, 2020
Leases [Abstract]
Operating leases	The Company recognized the following related to operating leases in its Consolidated Balance Sheets at December 31, 2020 and 2019 (in millions): December 31, Classification in Consolidated Balance Sheet 2020 2019 Operating lease assets Operating lease assets $ 529 $ 620 Lease Liabilities: Current operating lease liabilities Accrued expenses and other current liabilities $ 159 $ 161 Non-current operating lease liabilities Operating lease liabilities 366 462 Total operating lease liabilities $ 525 $ 623
Operating lease cost	The Company recognized the following related to operating leases in its Consolidated Statements of Operations (in millions): Year Ended December 31, Classification in Consolidated Statement of Operations 2020 2019 Lease expense General and administrative and Information technology $ 194 $ 183 Variable lease expense General and administrative and Information technology 46 56 Less: Sublease income General and administrative (2) (2) Total lease expense, net of sublease income $ 238 $ 237
Operating lease liability maturity	As of December 31, 2020, the operating lease liabilities will mature over the following periods (in millions): 2021 $ 168 2022 122 2023 74 2024 50 2025 35 Thereafter 136 Total remaining lease payments $ 585 Less: Imputed interest (60) Total operating lease liabilities $ 525
Operating lease supplemental cash flow	Supplemental cash flow information related to operating leases is as follows (in millions): Year Ended December 31, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities $ 200 $ 189 Operating lease assets obtained in exchange for lease liabilities 67 155 "Operating lease amortization" presented in the operating activities section of the Consolidated Statements of Cash Flows reflects the portion of the operating lease expense from the amortization of the operating lease assets.

GOODWILL, INTANGIBLE ASSETS A_2

GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	The changes in the balance of goodwill for the years ended December 31, 2020 and 2019 consist of the following (in millions): 2020 2019 Balance, beginning of year $ 2,913 $ 2,910 Acquisitions — 7 Impairments (1,062) — Foreign currency translation adjustments 44 (4) Balance, end of year (1) $ 1,895 $ 2,913 (1) The balance of goodwill as of December 31, 2020 and 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively.
Intangible assets	The Company's intangible assets at December 31, 2020 and 2019 consist of the following (in millions): December 31, 2020 December 31, 2019 Gross Carrying Accumulated Net Carrying Gross Carrying Accumulated Net Carrying Amortization Supply and distribution $ 1,136 $ (552) $ 584 $ 1,100 $ (472) $ 628 3 - 20 years Technology 174 (144) 30 170 (129) 41 2 - 7 years Internet domain names 44 (37) 7 40 (32) 8 5 - 20 years Trade names 1,824 (633) 1,191 1,811 (534) 1,277 4 -20 years Other intangible assets 2 (2) — 2 (2) — Up to 15 years Total intangible assets $ 3,180 $ (1,368) $ 1,812 $ 3,123 $ (1,169) $ 1,954
Annual estimated amortization expense for intangible assets for the next five years and thereafter	The estimate d annual amortization expense for intangible assets for the next five years and thereafter is expected to be as follows (in millions): 2021 $ 163 2022 160 2023 158 2024 157 2025 152 Thereafter 1,022 $ 1,812 The Company reviews long-lived assets, including intangible assets and operating lease assets, whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The assessment of possible impairment is based upon the ability to recover the carrying value of the assets from the estimated undiscounted future net cash flows, before interest and taxes, of the related asset group. Due to the significant and negative financial impact of the COVID-19 pandemic (see Note 2), at March 31, 2020, the Company performed the recoverability test of its long-lived assets and concluded that there was no impairment. At September 30, 2020, for OpenTable and KAYAK, the Company performed the recoverability test of its long-lived assets due to additional impairment indicators and concluded that there was no impairment. At December 31, 2020, no additional impairment indicators were identified for the Company's long-lived assets.

DEBT (Tables)

DEBT (Tables)	12 Months Ended
DEBT (Tables)	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of outstanding debt	Outstanding debt at December 31, 2020 consists of the following (in millions): December 31, 2020 Outstanding Unamortized Debt Carrying Current Liabilities: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (15) $ 985 Long-term debt: 0.8% (€1 Billion) Senior Notes due March 2022 $ 1,223 $ (1) $ 1,222 2.15% (€750 Million) Senior Notes due November 2022 919 (4) 915 2.75% Senior Notes due March 2023 500 (1) 499 2.375% (€1 Billion) Senior Notes due September 2024 1,223 (7) 1,216 3.65% Senior Notes due March 2025 500 (2) 498 4.1% Senior Notes due April 2025 1,000 (5) 995 0.75% Convertible Senior Notes due May 2025 863 (128) 735 3.6% Senior Notes due June 2026 1,000 (4) 996 1.8% (€1 Billion) Senior Notes due March 2027 1,223 (2) 1,221 4.5% Senior Notes due April 2027 750 (5) 745 3.55% Senior Notes due March 2028 500 (2) 498 4.625% Senior Notes due April 2030 1,500 (11) 1,489 Total long-term debt $ 11,201 $ (172) $ 11,029 Outstanding debt at December 31, 2019 consists of the following (in millions): December 31, 2019 Outstanding Unamortized Debt Carrying Current Liabilities: 0.35% Convertible Senior Notes due June 2020 $ 1,000 $ (12) $ 988 Long-term debt: 0.9% Convertible Senior Notes due September 2021 $ 1,000 $ (39) $ 961 0.8% (€1 Billion) Senior Notes due March 2022 1,123 (3) 1,120 2.15% (€750 Million) Senior Notes due November 2022 842 (3) 839 2.75% Senior Notes due March 2023 500 (2) 498 2.375% (€1 Billion) Senior Notes due September 2024 1,123 (9) 1,114 3.65% Senior Notes due March 2025 500 (2) 498 3.6% Senior Notes due June 2026 1,000 (5) 995 1.8% (€1 Billion) Senior Notes due March 2027 1,123 (5) 1,118 3.55% Senior Notes due March 2028 500 (3) 497 Total long-term debt $ 7,711 $ (71) $ 7,640
Summary of interest expenses and weighted-average effective interest rates	The following table summarizes the interest expenses and weighted-average effective interest rates related to the convertible senior notes (in millions, except for interest rates). The remaining period for amortization of debt discount and debt issuance costs is the period until the stated maturity date for the respective debt. For the Year Ended December 31, 2020 2019 2018 Coupon interest expense $ 15 $ 12 14 Amortization of debt discount and debt issuance costs 54 50 52 Total interest expenses $ 69 $ 62 $ 66 Weighted-average effective interest rate 3.5 % 3.2 % 3.2 % The following table summarizes the interest expenses related to other long-term debt (in millions): For the Year Ended December 31, 2020 2019 2018 Coupon interest expense $ 264 $ 160 $ 163 Amortization of debt discount and debt issuance costs 9 6 7 Total interest expenses $ 273 $ 166 $ 170
Summary of interest expenses	The following table summarizes the information related to other long-term debt outstanding at December 31, 2020: Other Long-term Debt Date of Issuance Effective Interest Rate (1) Timing of Interest Payments 0.8% Senior Notes due March 2022 March 2017 0.94 % Annually in March 2.15% Senior Notes due November 2022 November 2015 2.27 % Annually in November 2.75% Senior Notes due March 2023 August 2017 2.88 % Semi-annually in March and September 2.375% Senior Notes due September 2024 September 2014 2.54 % Annually in September 3.65% Senior Notes due March 2025 March 2015 3.76 % Semi-annually in March and September 4.1% Senior Notes due April 2025 April 2020 4.22 % Semi-annually in April and October 3.6% Senior Notes due June 2026 May 2016 3.70 % Semi-annually in June and December 1.8% Senior Notes due March 2027 March 2015 1.86 % Annually in March 4.5% Senior Notes due April 2027 April 2020 4.63 % Semi-annually in April and October 3.55% Senior Notes due March 2028 August 2017 3.63 % Semi-annually in March and September 4.625% Senior Notes due April 2030 April 2020 4.72 % Semi-annually in April and October

TREASURY STOCK (Tables)

TREASURY STOCK (Tables)	12 Months Ended
TREASURY STOCK (Tables)	Dec. 31, 2020
Equity [Abstract]
Summary of stock repurchase activities	The following table summarizes the Company's stock repurchase activities during the years ended December 31, 2020, 2019 and 2018 (in millions, except for shares, which are reflected in thousands): 2020 2019 2018 Shares Amount Shares Amount Shares Amount Authorized stock repurchase programs 601 $ 1,122 4,358 $ 8,002 3,020 $ 5,850 General authorization for shares withheld on stock award vesting 84 142 87 151 80 162 Total 685 $ 1,264 4,445 $ 8,153 3,100 $ 6,012 Shares repurchased in December and settled in following January — $ — 19 $ 40 43 $ 74

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT (Tables)	12 Months Ended
	Dec. 31, 2020
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Balances of accumulated other comprehensive income (loss) by component	The table below presents the changes in the balances of accumulated other comprehensive income (loss) ("AOCI") by component for the years ended December 31, 2018, 2019 and 2020 (in millions): Foreign currency translation adjustments, net of tax Net unrealized gains (losses) on available-for-sale securities, net of tax (1) Total AOCI, net of tax Foreign currency translation Net investment hedges (2) Total, net of tax Before tax Tax (expense) benefit Total, net of tax Before tax Tax benefit (expense) (3) Before tax Tax benefit (expense) Balance, December 31, 2017 $ 210 $ — $ (290) $ 65 $ (15) $ 343 $ (90) $ 253 $ 238 Other Comprehensive Income (Loss) ("OCI") before (319) 41 217 (53) (114) (201) 2 (199) (313) OCI for the period (319) 41 217 (53) (114) (201) 2 (199) (313) Amounts reclassified to retained earnings (1) — — — — — (299) 58 (241) (241) Balance, December 31, 2018 $ (109) $ 41 $ (73) $ 12 $ (129) $ (157) $ (30) $ (187) $ (316) OCI before reclassifications (77) 13 71 (17) (10) 161 (37) 124 114 Amounts reclassified to net income (4) — — — — — (11) 22 11 11 OCI for the period (77) 13 71 (17) (10) 150 (15) 135 125 Balance, December 31, 2019 $ (186) $ 54 $ (2) $ (5) $ (139) $ (7) $ (45) $ (52) $ (191) OCI before reclassifications 197 (7) (182) 42 50 6 (1) 5 55 Amounts reclassified to net income (4) — — — — — 4 14 18 18 OCI for the period 197 (7) (182) 42 50 10 13 23 73 Balance, December 31, 2020 $ 11 $ 47 $ (184) $ 37 $ (89) $ 3 $ (32) $ (29) $ (118) (1) Upon the adoption of the accounting update on financial instruments on January 1, 2018, the Company reclassified net unrealized gains, net of tax, of $241 million ($299 million before tax) related to marketable equity securities from AOCI to retained earnings. Changes in fair value of marketable equity securities subsequent to January 1, 2018 are recognized in net income rather than "Accumulated other comprehensive loss" in the Consolidated Balance Sheets (see Note 2). (2) Net investment hedges balance, net of tax, at December 31, 2020 and earlier dates presented above, includes accumulated net losses from fair value adjustments of $35 million ($53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. The remaining balances relate to foreign currency transaction gains (losses) and related tax benefits (expenses) associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (see Notes 2 and 12). (3) The tax benefits relate to foreign currency translation adjustments to the Company's one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the enactment of the Tax Act. (4) The reclassified net gains (losses) on available-for-sale securities, before tax, are included in "Other income (expense), net" and the reclassified tax (expenses) benefits are included in "Income tax expense" in the Consolidated Statements of Operations. For the year ended December 31, 2020, the reclassified tax expenses include a tax expense of $15 million related to the maturity in May 2020 of the Company's investment of $250 million in Trip.com Group convertible senior notes (see Note 5). For the year ended December 31, 2019, the reclassified tax expenses include a tax expense of $21 million related to the maturity in August 2019 of the Company's investment of $500 million in Trip.com Group convertible senior notes.

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
INCOME TAXES (Tables)	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	The income tax expense (benefit) for the year ended December 31, 2020 is as follows (in millions): Current Deferred Total International $ 320 $ (62) $ 258 U.S. Federal (9) 296 287 U.S. State (16) (21) (37) Total $ 295 $ 213 $ 508 The income tax expense (benefit) for the year ended December 31, 2019 is as follows (in millions): Current Deferred Total International $ 915 $ (12) $ 903 U.S. Federal 22 166 188 U.S. State 34 (32) 2 Total $ 971 $ 122 $ 1,093 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
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, 2020 and 2019 are as follows (in millions): 2020 2019 Deferred tax assets/(liabilities): Net operating loss carryforward — U.S. $ 67 $ 37 Net operating loss carryforward — International 81 15 Accrued expenses 47 35 Stock-based compensation and other stock based payments 40 49 Foreign currency translation adjustment 29 36 Tax credits 9 14 Euro-denominated debt 77 — Operating lease liabilities 43 38 Property and equipment 11 31 Subtotal - deferred tax assets 404 255 Discount on convertible notes (29) (10) Intangible assets and other (119) (133) Euro-denominated debt — (14) State income tax on accumulated unremitted international earnings (5) (8) Unrealized gains on investments (550) (191) Operating lease assets (38) (35) Installment sale liability (263) (284) Other (14) (11) Subtotal - deferred tax liabilities (1,018) (686) Valuation allowance on deferred tax assets (58) (45) Net deferred tax liabilities (1) $ (672) $ (476) (1) Includes deferred tax assets of $455 million and $400 million at December 31, 2020 and 2019, respectively, reported in "Other assets, net" 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% for the years ended December 31, 2020, 2019 and 2018 as a result of the following items (in millions): 2020 2019 2018 Income tax expense at U.S. federal statutory rate $ 119 $ 1,251 $ 1,015 Adjustment due to: Foreign rate differential 55 210 210 Innovation Box Tax benefit (79) (443) (435) Goodwill impairment 228 — — Stock-based compensation 32 23 12 Federal GILTI 73 36 35 State income tax (benefit) expense (31) 9 1 Valuation allowance 36 1 (3) Uncertain tax positions 64 11 (4) Tax Act - Remeasurement of deferred tax balances — — (2) Tax Act - U.S. transition tax benefit and other transition impacts (8) (17) (46) Other 19 12 54 Income tax expense $ 508 $ 1,093 $ 837
Reconciliation of unrecognized tax benefits	The following is a reconciliation of the total beginning and ending amount of unrecognized tax benefits (in millions): 2020 2019 2018 Unrecognized tax benefit — January 1 $ 56 $ 45 $ 32 Gross increases — tax positions in current period 2 3 1 Gross increases — tax positions in prior periods 48 11 19 Gross decreases — tax positions in prior periods (11) (3) (3) Reduction due to lapse in statute of limitations — — (2) Reduction due to settlements during the current period (11) — (2) Unrecognized tax benefit — December 31 $ 84 $ 56 $ 45

GEOGRAPHIC INFORMATION (Tables)

GEOGRAPHIC INFORMATION (Tables)	12 Months Ended
GEOGRAPHIC INFORMATION (Tables)	Dec. 31, 2020
Segment Reporting [Abstract]
Geographic information on revenues	The Company's geographic information on revenues is as follows (in millions): United States International Total For the year ended: The Netherlands Other December 31, 2020 $ 783 $ 5,264 $ 749 $ 6,796 December 31, 2019 1,537 11,686 1,843 15,066 December 31, 2018 1,536 11,348 1,643 14,527
Property and equipment, excluding capitalized software, and operating lease assets by geographic area	The following table presents information on the Company's property and equipment (excluding capitalized software) and operating lease assets based on location of the assets at December 31, 2020 and 2019 (in millions): United States International Total The Netherlands United Kingdom Other December 31, 2020 $ 186 $ 499 $ 85 $ 278 $ 1,048 December 31, 2019 216 484 137 327 1,164

OTHER INCOME (EXPENSE), NET (Ta

OTHER INCOME (EXPENSE), NET (Tables)	12 Months Ended
OTHER INCOME (EXPENSE), NET (Tables)	Dec. 31, 2020
Other Income and Expenses [Abstract]
Components of other income (expense), net	The components of other income (expense), net included the following (in millions): Year Ended December 31, 2020 2019 2018 Interest and dividend income $ 54 $ 152 $ 187 Net gains (losses) on marketable equity securities (1) 1,811 745 (367) Impairment of investment (1) (100) — — Foreign currency transaction losses (207) (31) (53) Other (4) 13 (4) Other income (expense), net $ 1,554 $ 879 $ (237)

BUSINESS DESCRIPTION (Details)

BUSINESS DESCRIPTION (Details)	Dec. 31, 2020brand
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of consumer-facing brands	6

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reconciliation of Cash and Cash Equivalents and Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 10,562	$ 6,312	$ 2,624
Restricted cash and cash equivalents included in "Other current assets"	20	20	21
Total cash and cash equivalents and restricted cash and cash equivalents as shown in the Consolidated Statements of Cash Flows	$ 10,582	$ 6,332	$ 2,645	$ 2,563

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2020USD ($)	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)segment	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)
Accounting Policies [Line Items]
Proceeds from the issuance of long-term debt	$ 4,100	$ 4,108	$ 0	$ 0
Equity		4,893	5,933	$ 8,785	$ 11,261
Accrued performance advertising liabilities		156	333
Accrued compensation liabilities		$ 333	$ 344
Number of operating segments \| segment		4	4	6
Number of reportable segments \| segment		1
Cumulative effect of adoption of accounting standards updates
Accounting Policies [Line Items]
Equity			$ (3)		189
Retained Earnings
Accounting Policies [Line Items]
Equity		$ 23,288	23,232	$ 18,367	13,939
Retained Earnings \| Cumulative effect of adoption of accounting standards updates
Accounting Policies [Line Items]
Equity			$ (3)		430
Retained Earnings \| Cumulative effect of adoption of accounting standards updates \| Accounting Standards Update 2014-09
Accounting Policies [Line Items]
Equity					$ 189
Maximum
Accounting Policies [Line Items]
Term of available-for-sale debt securities		5 years
Renewal terms		9 years

REVENUE - Disaggregation of Rev

REVENUE - Disaggregation of Revenue (Details) - Product Concentration Risk - Revenue Benchmark	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Online accommodation reservation services
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	88.00%	87.00%	87.00%
Other sources of online travel reservation services and advertising and other revenues \| Maximum
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	10.00%	10.00%	10.00%

REVENUE - Summary of the Activi

REVENUE - Summary of the Activity of Deferred Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Time period from the reservation date that performance obligations are expected to be completed	one year
Online Travel Reservation Services
Movement in Deferred Revenue [Roll Forward]
Revenues recognized from the beginning balance	$ (154)	$ (134)
Cancellations	(66)	(15)
Payments received from travelers net of amounts estimated to be payable to travel service providers and other changes	50	220
Online Travel Reservation Services \| Deferred Merchant Bookings
Movement in Deferred Revenue [Roll Forward]
Balance, beginning of year	220	149
Balance, end of year	$ 50	$ 220

REVENUE - Loyalty and Other Inc

REVENUE - Loyalty and Other Incentive Programs (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues		$ (6,796)	$ (15,066)	$ (14,527)
Loyalty Incentive Programs \| OpenTable
Disaggregation of Revenue [Line Items]
Reward expiration period	3 years	3 years
Decrease in liability balance with a corresponding increase to revenue	$ (27)	$ (28)
Loyalty Incentive Programs \| Accrued expenses and other current liabilities
Disaggregation of Revenue [Line Items]
Liabilities for loyalty program incentives		21	80
Other Incentive Programs \| Accrued expenses and other current liabilities
Disaggregation of Revenue [Line Items]
Liabilities for loyalty program incentives		60	$ 22
Other Incentive Programs - Additional Rebates \| Booking.com
Disaggregation of Revenue [Line Items]
Liabilities for loyalty program incentives		25
Revenues		$ 100

REVENUE - Impact of COVID-19 (D

REVENUE - Impact of COVID-19 (Details) $ in Millions	12 Months Ended
REVENUE - Impact of COVID-19 (Details) $ in Millions	Dec. 31, 2020USD ($)
Revenue from Contract with Customer [Abstract]
Reduction in revenue for refunds paid or estimated to be payable	$ 44

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Jan. 31, 2021	May 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit for stock-based compensation			$ 30	$ 38	$ 36
Restricted stock units and performance share units aggregate grant-date fair value			392	380	337
Aggregate fair value of performance share units and restricted stock units vested during the period			358	373	415
Options aggregate grant-date fair value			$ 79
Weighted-average grant-date fair value per option (in dollars per share)			$ 485
Aggregate intrinsic value of stock options exercised			$ 15	20	5
Executive Officers
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options granted		0
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction in stock-based compensation expense due to significant decline in estimated performance due to the impact of COVID-19 pandemic			$ 73
Vesting period			3 years
Performance Share Units \| Adjustment for change in estimated probable outcome at the end of the performance period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			$ (71)	(4)	48
Performance Share Units \| 2018 Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional stock-based compensation expense to be recognized over the remaining requisite service period			11
Performance Share Units \| 2018 and 2019 Grants \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional stock-based compensation expense to be recognized over the remaining requisite service period	$ 40
Restricted Stock Units and Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total future compensation cost related to unvested share-based awards			$ 384
Total future compensation cost related to unvested share-based awards, expected period of recognition			1 year 10 months 24 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total future compensation cost related to unvested share-based awards			$ 57
Total future compensation cost related to unvested share-based awards, expected period of recognition			2 years 2 months 12 days
Number of stock options granted			163,494
Grant term (in years)			10 years
Personnel Expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			$ 233	$ 308	$ 317
1999 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available to be issued under the plan (in shares)			1,614,570
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)			52,192

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of the Activity of Restricted Stock Units for Employees and Non-Employee Directors (Details) - Restricted Stock Units	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares
Unvested, beginning of period (in shares) \| shares	256,745
Granted (in shares) \| shares	222,977
Vested (in shares) \| shares	(130,684)
Forfeited (in shares) \| shares	(43,079)
Unvested, end of period (in shares) \| shares	305,959
Weighted-average Grant-date Fair Value
Unvested, beginning of period (in dollars per share) \| $ / shares	$ 1,801
Granted (in dollars per share) \| $ / shares	1,659
Vested (in dollars per share) \| $ / shares	1,822
Forfeited (in dollars per share) \| $ / shares	1,737
Unvested, end of period (in dollars per share) \| $ / shares	$ 1,697
Minimum
Weighted-average Grant-date Fair Value
Vesting period	1 year
Maximum
Weighted-average Grant-date Fair Value
Vesting period	3 years

STOCK-BASED COMPENSATION - Su_2

STOCK-BASED COMPENSATION - Summary of the Activity of Performance Share Units for Employees (Details) - Performance Share Units	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares
Unvested, beginning of period (in shares) \| shares	216,083
Granted (in shares) \| shares	9,040
Vested (in shares) \| shares	(82,023)
Performance Shares Adjustment (in shares) \| shares	(49,775)	[1]
Forfeited (in shares) \| shares	(8,847)
Unvested, end of period (in shares) \| shares	84,478
Weighted-average Grant-date Fair Value
Unvested, beginning of period (in dollars per share) \| $ / shares	$ 1,835
Granted (in dollars per share) \| $ / shares	2,498
Vested (in dollars per share) \| $ / shares	1,741
Performance Share Adjustment (in dollars per share) \| $ / shares	1,944	[1]
Forfeited (in dollars per share) \| $ / shares	1,829
Unvested, end of period (in dollars per share) \| $ / shares	$ 1,930

[1]	Probable outcome for these performance-based awards is updated based upon changes in actual and forecasted operating results or expected achievement of performance goals, as applicable, and the impact of modifications.

STOCK-BASED COMPENSATION - Su_3

STOCK-BASED COMPENSATION - Summary of Estimated Vesting of Performance Share Units (Details) - Performance Share Units - shares	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	84,478	216,083
2020 \| Shares probable to be issued
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	9,040
2020 \| Shares not subject to the achievement of minimum performance thresholds
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	0
2020 \| Shares that could be issued if maximum performance thresholds are met
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	18,080
2019 \| Shares probable to be issued
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	40,843
2019 \| Shares not subject to the achievement of minimum performance thresholds
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	40,843
2019 \| Shares that could be issued if maximum performance thresholds are met
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	108,522
2018 \| Shares probable to be issued
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units (in shares)	34,595

STOCK-BASED COMPENSATION - Weig

STOCK-BASED COMPENSATION - Weighted-Average Assumptions Used to Value Options Granted (Details) - Stock Options	12 Months Ended
	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.56%
Expected term in years	6 years 4 months 24 days
Expected stock price volatility	33.80%
Expected dividend yield	0.00%

STOCK-BASED COMPENSATION - Su_4

STOCK-BASED COMPENSATION - Summary of Activity for Stock Options (Details) - Employee Stock Option - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Balance, beginning of period (in shares)	15,122
Granted (in shares)	163,494
Exercised (in shares)	(13,217)
Forefeited, (in shares)	(12,653)
Balance, end of period (in shares)	152,746	15,122
Exercisable, (in shares)	1,954
Weighted-average Exercise Price
Balance, beginning of period (in dollars per share)	$ 484
Granted (in dollars per share)	1,411
Exercised (in dollars per share)	466
Forfeited (in dollars per share)	1,411
Balance, end of period (in dollars per share)	1,401	$ 484
Exercisable (in dollars per share)	$ 660
Aggregate Intrinsic Value (in millions)
Balance	$ 126	$ 24
Exercisable	$ 3
Weighted-average Remaining Contractual Term (in years)
Balance	9 years 3 months 18 days	2 years 7 months 6 days
Exercisable	2 years 1 month 6 days

INVESTMENTS - Summary of Invest

INVESTMENTS - Summary of Investments by Major Security Type (Details) - USD ($) $ in Millions	Dec. 31, 2020	May 31, 2020	Dec. 31, 2019	Aug. 31, 2019
Total
Carrying Value	$ 3,759		$ 4,477
Convertible debt securities \| Trip.com Group
Debt securities
Cost	525	$ 250		$ 500
Short-term Investments
Debt securities
Cost			998
Gross Unrealized Gains /Upward Adjustments			1
Gross Unrealized Losses /Downward Adjustments			(1)
Carrying Value			998
Short-term Investments \| Convertible debt securities \| Trip.com Group
Debt securities
Cost	500
Gross Unrealized Gains /Upward Adjustments	1
Gross Unrealized Losses /Downward Adjustments	0
Carrying Value	501
Short-term Investments \| International government securities
Debt securities
Cost			109
Gross Unrealized Gains /Upward Adjustments			0
Gross Unrealized Losses /Downward Adjustments			0
Carrying Value			109
Short-term Investments \| U.S. government securities
Debt securities
Cost			138
Gross Unrealized Gains /Upward Adjustments			0
Gross Unrealized Losses /Downward Adjustments			0
Carrying Value			138
Short-term Investments \| Corporate debt securities
Debt securities
Cost			751
Gross Unrealized Gains /Upward Adjustments			1
Gross Unrealized Losses /Downward Adjustments			(1)
Carrying Value			751
Long-term Investments
Total
Cost	1,240		3,810
Gross Unrealized Gains /Upward Adjustments	2,620		686
Gross Unrealized Losses /Downward Adjustments	(101)		(19)
Carrying Value	3,759		4,477
Long-term Investments \| Trip.com Group
Equity securities - other investments
Cost			655
Carrying Value			726
Long-term Investments \| Convertible debt securities \| Trip.com Group
Debt securities
Cost	25		775
Gross Unrealized Gains /Upward Adjustments	0		0
Gross Unrealized Losses /Downward Adjustments	(1)		(8)
Carrying Value	24		767
Long-term Investments \| International government securities
Debt securities
Cost			68
Gross Unrealized Gains /Upward Adjustments			0
Gross Unrealized Losses /Downward Adjustments			0
Carrying Value			68
Long-term Investments \| U.S. government securities
Debt securities
Cost			136
Gross Unrealized Gains /Upward Adjustments			0
Gross Unrealized Losses /Downward Adjustments			(1)
Carrying Value			135
Long-term Investments \| Corporate debt securities
Debt securities
Cost			963
Gross Unrealized Gains /Upward Adjustments			2
Gross Unrealized Losses /Downward Adjustments			(2)
Carrying Value			963
Long-term Investments \| Investments in private companies, debt securities
Debt securities
Cost	200		250
Gross Unrealized Gains /Upward Adjustments	0		0
Gross Unrealized Losses /Downward Adjustments	0		0
Carrying Value	200		250
Long-term Investments \| Investments in private companies, equity securities
Equity securities - investments in private companies
Cost	552		501
Gross Unrealized Gains /Upward Adjustments	3		0
Gross Unrealized Losses /Downward Adjustments	(100)		0
Carrying Value	455		501
Long-term Investments \| Equity securities
Equity securities - other investments
Cost	463		1,117
Gross Unrealized Gains /Upward Adjustments	2,617		684
Gross Unrealized Losses /Downward Adjustments	0		(8)
Carrying Value	$ 3,080		$ 1,793

INVESTMENTS - Narrative (Detail

INVESTMENTS - Narrative (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
INVESTMENTS - Narrative (Details) - USD ($) $ in Millions		May 31, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 31, 2019
Schedule of Investments [Line Items]
Net gains (losses) on marketable equity securities	[1]			$ 1,811	$ 745	$ (367)
Impairment of investment	[1]			100	0	0
Short-term Investments
Schedule of Investments [Line Items]
Investment in debt securities					998
Investments in private companies accounted for as debt securities					998
Trip.com Group
Schedule of Investments [Line Items]
Proceeds from sale and maturity of marketable securities				525
Equity securities, net realized loss				201
Equity securities, net unrealized gains					141
Equity securities, net unrealized loss						368
Trip.com Group \| Long-term Investments
Schedule of Investments [Line Items]
Investment in equity securities					655
Fair value of investment in equity securities					726
Meituan
Schedule of Investments [Line Items]
Equity securities, net unrealized gains				2,000	602	$ 1
Payments to Acquire Other Investments							$ 450
Meituan \| Long-term Investments
Schedule of Investments [Line Items]
Fair value of investment in equity securities				3,100	1,100
Government and corporate debt securities
Schedule of Investments [Line Items]
Cash realized from the sales and maturities of investments in debt securities				2,200
Convertible debt securities \| Trip.com Group
Schedule of Investments [Line Items]
Investment in debt securities		$ 250		525				$ 500
Proceeds from maturities of debt securities		$ 250
Convertible debt securities \| Trip.com Group \| Long-term Investments
Schedule of Investments [Line Items]
Investment in debt securities				25	775
Investments in private companies accounted for as debt securities				24	767
Convertible debt securities \| Trip.com Group \| Short-term Investments
Schedule of Investments [Line Items]
Investment in debt securities				500
Investments in private companies accounted for as debt securities				501
Investments in private companies, equity securities \| Long-term Investments
Schedule of Investments [Line Items]
Investment in equity securities of private companies				552	501
Fair value of investment in equity securities of private companies				455	501
Investments in private companies, equity securities \| Didi Chuxing \| Long-term Investments
Schedule of Investments [Line Items]
Investment in equity securities of private companies					500
Fair value of investment in equity securities of private companies			$ 400	400
Impairment of investment			$ 100
Investments in private companies, equity securities \| Investment in a private company \| Long-term Investments
Schedule of Investments [Line Items]
Fair value of investment in equity securities of private companies				51
Redeemable convertible preferred stock \| Long-term Investments
Schedule of Investments [Line Items]
Investment in debt securities				200	250
Investments in private companies accounted for as debt securities				$ 200	$ 250

[1]	See Note 5 for additional information related to the net gains (losses) on marketable equity securities and impairment of investment.

FAIR VALUE MEASUREMENTS - Finan

FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
LIABILITIES:
Impairment of investment	[1]			$ 100		$ 0		$ 0
Impairment of goodwill				1,062		0		0
Goodwill				1,895	[2]	2,913	[2]	$ 2,910
OpenTable and KAYAK
LIABILITIES:
Impairment of goodwill		$ 573	$ 489	1,062		0
Goodwill		$ 1,000	1,500
Investments in private companies, equity securities \| Long-term investments
LIABILITIES:
Carrying Value				455		501
Investments in private companies, equity securities \| Long-term investments \| Didi Chuxing
LIABILITIES:
Impairment of investment			100
Carrying Value			400	400
Investments in private companies, equity securities \| Long-term investments \| Investment in a private company
LIABILITIES:
Carrying Value				51
Recurring fair value measurements
ASSETS:
Total assets at fair value				14,054		10,751
Recurring fair value measurements \| Foreign currency exchange derivatives \| Not designated as hedging instrument
ASSETS:
Total assets at fair value				9		12
LIABILITIES:
Total liabilities at fair value				7		5
Recurring fair value measurements \| Money market fund investments \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				10,208		5,734
Recurring fair value measurements \| Time deposits and certificates of deposit \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				32		29
Recurring fair value measurements \| International government securities \| Short-term Investments
ASSETS:
Total assets at fair value						109
Recurring fair value measurements \| International government securities \| Long-term investments
ASSETS:
Total assets at fair value						68
Recurring fair value measurements \| U.S. government securities \| Short-term Investments
ASSETS:
Total assets at fair value						138
Recurring fair value measurements \| U.S. government securities \| Long-term investments
ASSETS:
Total assets at fair value						135
Recurring fair value measurements \| Corporate debt securities \| Short-term Investments
ASSETS:
Total assets at fair value						751
Recurring fair value measurements \| Corporate debt securities \| Long-term investments
ASSETS:
Total assets at fair value						963
Recurring fair value measurements \| Corporate debt securities \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value						2
Recurring fair value measurements \| Convertible debt securities \| Short-term Investments \| Trip.com Group
ASSETS:
Total assets at fair value				501
Recurring fair value measurements \| Convertible debt securities \| Long-term investments \| Trip.com Group
ASSETS:
Total assets at fair value				24		767
Recurring fair value measurements \| Investments in private companies, debt securities \| Long-term investments
ASSETS:
Total assets at fair value				200		250
Recurring fair value measurements \| Equity securities \| Long-term investments
ASSETS:
Total assets at fair value				3,080		1,793
Recurring fair value measurements \| Level 1
ASSETS:
Total assets at fair value				13,320		7,556
Recurring fair value measurements \| Level 1 \| Foreign currency exchange derivatives \| Not designated as hedging instrument
ASSETS:
Total assets at fair value				0		0
LIABILITIES:
Total liabilities at fair value				0		0
Recurring fair value measurements \| Level 1 \| Money market fund investments \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				10,208		5,734
Recurring fair value measurements \| Level 1 \| Time deposits and certificates of deposit \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				32		29
Recurring fair value measurements \| Level 1 \| International government securities \| Short-term Investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| International government securities \| Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| U.S. government securities \| Short-term Investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| U.S. government securities \| Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| Corporate debt securities \| Short-term Investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| Corporate debt securities \| Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| Corporate debt securities \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 1 \| Convertible debt securities \| Short-term Investments \| Trip.com Group
ASSETS:
Total assets at fair value				0
Recurring fair value measurements \| Level 1 \| Convertible debt securities \| Long-term investments \| Trip.com Group
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 1 \| Investments in private companies, debt securities \| Long-term investments
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 1 \| Equity securities \| Long-term investments
ASSETS:
Total assets at fair value				3,080		1,793
Recurring fair value measurements \| Level 2
ASSETS:
Total assets at fair value				534		2,945
Recurring fair value measurements \| Level 2 \| Foreign currency exchange derivatives \| Not designated as hedging instrument
ASSETS:
Total assets at fair value				9		12
LIABILITIES:
Total liabilities at fair value				7		5
Recurring fair value measurements \| Level 2 \| Money market fund investments \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 2 \| Time deposits and certificates of deposit \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 2 \| International government securities \| Short-term Investments
ASSETS:
Total assets at fair value						109
Recurring fair value measurements \| Level 2 \| International government securities \| Long-term investments
ASSETS:
Total assets at fair value						68
Recurring fair value measurements \| Level 2 \| U.S. government securities \| Short-term Investments
ASSETS:
Total assets at fair value						138
Recurring fair value measurements \| Level 2 \| U.S. government securities \| Long-term investments
ASSETS:
Total assets at fair value						135
Recurring fair value measurements \| Level 2 \| Corporate debt securities \| Short-term Investments
ASSETS:
Total assets at fair value						751
Recurring fair value measurements \| Level 2 \| Corporate debt securities \| Long-term investments
ASSETS:
Total assets at fair value						963
Recurring fair value measurements \| Level 2 \| Corporate debt securities \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value						2
Recurring fair value measurements \| Level 2 \| Convertible debt securities \| Short-term Investments \| Trip.com Group
ASSETS:
Total assets at fair value				501
Recurring fair value measurements \| Level 2 \| Convertible debt securities \| Long-term investments \| Trip.com Group
ASSETS:
Total assets at fair value				24		767
Recurring fair value measurements \| Level 2 \| Investments in private companies, debt securities \| Long-term investments
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 2 \| Equity securities \| Long-term investments
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 3
ASSETS:
Total assets at fair value				200		250
Recurring fair value measurements \| Level 3 \| Foreign currency exchange derivatives \| Not designated as hedging instrument
ASSETS:
Total assets at fair value				0		0
LIABILITIES:
Total liabilities at fair value				0		0
Recurring fair value measurements \| Level 3 \| Money market fund investments \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 3 \| Time deposits and certificates of deposit \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 3 \| International government securities \| Short-term Investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| International government securities \| Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| U.S. government securities \| Short-term Investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| U.S. government securities \| Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| Corporate debt securities \| Short-term Investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| Corporate debt securities \| Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| Corporate debt securities \| Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value						0
Recurring fair value measurements \| Level 3 \| Convertible debt securities \| Short-term Investments \| Trip.com Group
ASSETS:
Total assets at fair value				0
Recurring fair value measurements \| Level 3 \| Convertible debt securities \| Long-term investments \| Trip.com Group
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements \| Level 3 \| Investments in private companies, debt securities \| Long-term investments
ASSETS:
Total assets at fair value				200		250
Recurring fair value measurements \| Level 3 \| Equity securities \| Long-term investments
ASSETS:
Total assets at fair value				0		$ 0
Nonrecurring fair value measurements
ASSETS:
Total assets at fair value				1,404
Nonrecurring fair value measurements \| Investments in private companies, equity securities \| Long-term investments
ASSETS:
Total assets at fair value	[3]			404
Nonrecurring fair value measurements \| Investments in private companies, equity securities \| Long-term investments \| Didi Chuxing
ASSETS:
Total assets at fair value			$ 400
Nonrecurring fair value measurements \| Goodwill \| OpenTable and KAYAK
ASSETS:
Total assets at fair value	[4]			1,000
Nonrecurring fair value measurements \| Level 1
ASSETS:
Total assets at fair value				0
Nonrecurring fair value measurements \| Level 1 \| Investments in private companies, equity securities \| Long-term investments
ASSETS:
Total assets at fair value	[3]			0
Nonrecurring fair value measurements \| Level 1 \| Goodwill \| OpenTable and KAYAK
ASSETS:
Total assets at fair value	[4]			0
Nonrecurring fair value measurements \| Level 2
ASSETS:
Total assets at fair value				0
Nonrecurring fair value measurements \| Level 2 \| Investments in private companies, equity securities \| Long-term investments
ASSETS:
Total assets at fair value	[3]			0
Nonrecurring fair value measurements \| Level 2 \| Goodwill \| OpenTable and KAYAK
ASSETS:
Total assets at fair value	[4]			0
Nonrecurring fair value measurements \| Level 3
ASSETS:
Total assets at fair value				1,404
Nonrecurring fair value measurements \| Level 3 \| Investments in private companies, equity securities \| Long-term investments
ASSETS:
Total assets at fair value	[3]			404
Nonrecurring fair value measurements \| Level 3 \| Goodwill \| OpenTable and KAYAK
ASSETS:
Total assets at fair value	[4]			$ 1,000

[1]	See Note 5 for additional information related to the net gains (losses) on marketable equity securities and impairment of investment.
[2]	The balance of goodwill as of December 31, 2020 and 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively.
[3]	At March 31, 2020, the investment in Didi Chuxing was written down to its estimated fair value of $400 million, resulting in an impairment charge of $100 million (see Note 5).
[4]	At March 31, 2020, the goodwill of the OpenTable and KAYAK reporting unit was written down to its estimated fair value of $1.5 billion, resulting in an impairment charge of $489 million. At September 30, 2020, th e goodwill was further written down to its estimated fair value of $1.0 billion, resulting in an additional impairment charge of $573 million (see

FAIR VALUE MEASUREMENTS - Inves

FAIR VALUE MEASUREMENTS - Investments (Details) $ in Millions	Dec. 31, 2020USD ($)	Mar. 31, 2020USD ($)Years	Dec. 31, 2019USD ($)
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of derivative assets	$ 14,054		$ 10,751
Level 3 \| Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of derivative assets	200		250
Investments in private companies, equity securities \| Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investment in equity securities of private companies	455		501
Investments in private companies, debt securities \| Long-term Investments \| Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of derivative assets	200		250
Investments in private companies, debt securities \| Long-term Investments \| Level 3 \| Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of derivative assets	200		250
Didi Chuxing \| Discount Rate \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		12.00%
Didi Chuxing \| Discount Rate \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		14.00%
Didi Chuxing \| EBITDA Multiple \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (number)		13
Didi Chuxing \| EBITDA Multiple \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (number)		15
Didi Chuxing \| Price Volatility \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		60.00%
Didi Chuxing \| Price Volatility \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		70.00%
Didi Chuxing \| Expected Term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (number) \| Years		4
Didi Chuxing \| Investments in private companies, equity securities \| Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investment in equity securities of private companies	400	$ 400
Grab \| Redeemable convertible preferred stock \| Long-term Investments \| Level 3 \| Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of derivative assets	$ 200		$ 200

FAIR VALUE MEASUREMENTS - Estim

FAIR VALUE MEASUREMENTS - Estimated Fair Values and Notional Amounts of Derivatives (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Losses on foreign currency exchange derivatives	$ 31	$ 19	$ 44
Recurring Basis
Derivative [Line Items]
Estimated fair value of derivative assets	14,054	10,751
Not Designated as Hedging Instrument \| Recurring Basis \| Foreign currency exchange derivatives
Derivative [Line Items]
Estimated fair value of derivative assets	9	12
Estimated fair value of derivative liabilities	7	5
Level 2 \| Recurring Basis
Derivative [Line Items]
Estimated fair value of derivative assets	534	2,945
Level 2 \| Not Designated as Hedging Instrument \| Recurring Basis \| Foreign currency exchange derivatives
Derivative [Line Items]
Estimated fair value of derivative assets	9	12
Estimated fair value of derivative liabilities	7	5
Foreign currency purchases \| Not Designated as Hedging Instrument \| Foreign currency exchange derivatives
Derivative [Line Items]
Notional amount:	898	1,770
Foreign currency sales \| Not Designated as Hedging Instrument \| Foreign currency exchange derivatives
Derivative [Line Items]
Notional amount:	$ 839	$ 901

FAIR VALUE MEASUREMENTS - Other

FAIR VALUE MEASUREMENTS - Other Financial Assets and Liabilities (Details) - Trip.com Group - Convertible debt securities - USD ($) $ in Millions	Dec. 31, 2020	May 31, 2020	Dec. 31, 2019	Aug. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in debt securities	$ 525	$ 250		$ 500
Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in debt securities	$ 25		$ 775

ACCOUNTS RECEIVABLE AND OTHER_3

ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables from customers, gross, current	$ 510	$ 1,200
Receivables from marketing affiliates, gross, current	32	110
Accounts receivable, credit loss expense	216	69	$ 79
Prepaid expenses, allowance for credit loss	55	6
Prepaid expenses, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Prepayments to certain customers	107	232
Other assets, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Prepayments to certain customers	45
Sales and other expenses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for other credit losses	230	$ 69
Sales and other expenses \| Prepayments to customers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for other credit losses	51
Merchant revenue
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, credit loss expense	$ 37

ACCOUNTS RECEIVABLE AND OTHER_4

ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS - Summary of the Activity of the Allowance for Expected Credit Losses on Receivables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	$ 49	$ 51	$ 35
Provision charged to earnings	216	69	79
Write-offs and adjustments	(116)	(70)	(62)
Foreign currency translation adjustments	17	(1)	(1)
Balance, end of year	$ 166	$ 49	$ 51

NET INCOME PER SHARE (Details)

NET INCOME PER SHARE (Details) - shares	12 Months Ended
NET INCOME PER SHARE (Details) - shares	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Weighted-average number of basic common shares outstanding	40,974,000	43,082,000	47,446,000
Weighted-average dilutive stock options, restricted stock units and performance share units	158,000	203,000	236,000
Assumed conversion of convertible senior notes	28,000	224,000	335,000
Weighted-average number of diluted common and common equivalent shares outstanding	41,160,000	43,509,000	48,017,000
Antidilutive securities excluded from computation of earnings per share, amount	125,000

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,909	$ 1,665
Less: Accumulated depreciation	(1,153)	(927)
Property and equipment, net	756	738
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 746	736
Computer equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	2 years
Computer equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	6 years
Capitalized software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 565	442
Capitalized software \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (years)	2 years
Capitalized 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	$ 278	265
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)	15 years
Office equipment, furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 63	61
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)	8 years
Building construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 257	$ 161

PROPERTY AND EQUIPMENT, NET - N

PROPERTY AND EQUIPMENT, NET - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 291	$ 294	$ 248
Capitalized software
Property, Plant and Equipment [Line Items]
Additions to capitalized website development	$ 144	$ 109	$ 103

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
LEASES - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Weighted-average discount rate		2.20%	2.00%
Weighted average remaining lease term		8 years 1 month 6 days	7 years 9 months 18 days
Lease expense under ASC 840	$ 149
Minimum lease payments related to operating lease which have not yet commenced		$ 7
Maximum
Lessee, Lease, Description [Line Items]
Lease term of operating leases which have not yet commenced		7 years 6 months

LEASES - Operating Leases Recog

LEASES - Operating Leases Recognized in the Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease assets	$ 529	$ 620
Lease Liabilities:
Current operating lease liabilities	159	161
Non-current operating lease liabilities	366	462
Total operating lease liabilities	$ 525	$ 623
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent

LEASES - Operating Leases Rec_2

LEASES - Operating Leases Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Lease expense	$ 194	$ 183
Variable lease expense	46	56
Less: Sublease income	(2)	(2)
Total lease expense, net of sublease income	$ 238	$ 237

LEASES - Maturities of Operatin

LEASES - Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 168
2022	122
2023	74
2024	50
2025	35
Thereafter	136
Total remaining lease payments	585
Less: Imputed interest	(60)
Total operating lease liabilities	$ 525	$ 623

LEASES - Supplemental Cash Flow

LEASES - Supplemental Cash Flow Information Related To Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 200	$ 189
Operating lease assets obtained in exchange for lease liabilities	$ 67	$ 155

GOODWILL, INTANGIBLE ASSETS A_3

GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS - Changes in the Balance of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Goodwill [Roll Forward]
Balance, beginning of year	$ 2,913	[1]	$ 2,910
Acquisitions	0		7
Impairments	(1,062)		0		$ 0
Foreign currency translation adjustments	44		(4)
Balance, end of year	1,895	[1]	2,913	[1]	$ 2,910
Cumulative impairment charges	$ 2,000		$ 941

[1]	The balance of goodwill as of December 31, 2020 and 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively.

GOODWILL, INTANGIBLE ASSETS A_4

GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Goodwill [Line Items]
Impairment of goodwill			$ 1,062		$ 0		$ 0
Goodwill			1,895	[1]	2,913	[1]	2,910
Intangible assets amortization expense			167		175		$ 178
OpenTable and KAYAK
Goodwill [Line Items]
Impairment of goodwill	$ 573	$ 489	$ 1,062		$ 0
Goodwill	1,000	$ 1,500
Potential increase in fair value from 1% point increase in profitability growth rate	100
Potential decrease in fair value from 1% point decrease in profitability growth rate	100
Potential decrease in fair value due to 0.5% increase in discount rate	65
Potential increase in fair value due to 0.5% decrease in discount rate	$ 70
Sensitivity Analysis, Reporting Unit, Change in Growth Rate	1.00%
Sensitivity Analysis, Reporting Unit, Change in Discount Rate	0.50%

[1]	The balance of goodwill as of December 31, 2020 and 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively.

GOODWILL, INTANGIBLE ASSETS A_5

GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS - Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finite-lived intangible assets
Gross Carrying Amount	$ 3,180	$ 3,123
Accumulated Amortization	(1,368)	(1,169)
Net Carrying Amount	1,812	1,954
Supply and distribution agreements
Finite-lived intangible assets
Gross Carrying Amount	1,136	1,100
Accumulated Amortization	(552)	(472)
Net Carrying Amount	$ 584	628
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	$ 174	170
Accumulated Amortization	(144)	(129)
Net Carrying Amount	$ 30	41
Technology \| Minimum
Finite-lived intangible assets
Amortization Period	2 years
Technology \| Maximum
Finite-lived intangible assets
Amortization Period	7 years
Internet domain names
Finite-lived intangible assets
Gross Carrying Amount	$ 44	40
Accumulated Amortization	(37)	(32)
Net Carrying Amount	$ 7	8
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	$ 1,824	1,811
Accumulated Amortization	(633)	(534)
Net Carrying Amount	$ 1,191	1,277
Trade names \| Minimum
Finite-lived intangible assets
Amortization Period	4 years
Trade names \| Maximum
Finite-lived intangible assets
Amortization Period	20 years
Other intangible assets
Finite-lived intangible assets
Gross Carrying Amount	$ 2	2
Accumulated Amortization	(2)	(2)
Net Carrying Amount	$ 0	$ 0
Other intangible assets \| Maximum
Finite-lived intangible assets
Amortization Period	15 years

GOODWILL, INTANGIBLE ASSETS A_6

GOODWILL, INTANGIBLE ASSETS AND OTHER LONG-LIVED ASSETS - Annual Estimated Amortization Expense for Intangible Assets (Details) $ in Millions	Dec. 31, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2021	$ 163
2022	160
2023	158
2024	157
2025	152
Thereafter	1,022
Total	$ 1,812

DEBT - Revolving Credit Facilit

DEBT - Revolving Credit Facility (Details) - USD ($)	1 Months Ended		6 Months Ended
DEBT - Revolving Credit Facility (Details) - USD ($)	Aug. 31, 2019	Jun. 30, 2015	Jun. 30, 2019	Dec. 31, 2020	Oct. 31, 2020	Apr. 30, 2020	Dec. 31, 2019
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	$ 2,000,000,000	$ 2,000,000,000
Term of revolving credit facility	5 years	5 years
Line of credit, outstanding				$ 0			$ 0
Proceeds from borrowings under credit facility			$ 400,000,000
Repayments of borrowings under credit facility			$ 400,000,000
Weighted-average interest rate			3.50%
Debt instrument, minimum liquidity covenant, amount						$ 4,500,000,000
Debt instrument, covenant, required minimum liquidity on a pro forma basis required for cash distribution and share repurchases					$ 6,000,000,000
Revolving Credit Facility \| Minimum
Debt Instrument [Line Items]
Revolving credit facility commitment fee percentage on undrawn balances	0.07%
Revolving Credit Facility \| Maximum
Debt Instrument [Line Items]
Revolving credit facility commitment fee percentage on undrawn balances	0.20%
Revolving Credit Facility \| Rate 1 \| London Interbank Offered Rate (LIBOR) \| Minimum
Debt Instrument [Line Items]
Reference rate	0.00%
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 \| U. S. Federal Funds Rate
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%
Revolving Credit Facility \| Rate 2C \| One Month LIBOR \| Minimum
Debt Instrument [Line Items]
Reference rate	0.00%
Letter of Credit
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	$ 80,000,000
Letters of credit outstanding				$ 4,000,000			$ 5,000,000
Swingline Loans
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	$ 100,000,000

DEBT - Schedule of Outstanding

DEBT - Schedule of Outstanding Debt (Details) € in Millions, $ in Millions	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Apr. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2019EUR (€)	Aug. 31, 2017	Mar. 31, 2017	May 31, 2016	Nov. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Aug. 31, 2014USD ($)	May 31, 2013USD ($)
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (172)			$ (71)
Long-term debt:
Outstanding Principal Amount	11,201			7,711
Long-term debt	11,029			7,640
0.35% Convertible Senior Notes due June 2020 \| Convertible Senior Notes
Long-term debt:
Face amount of debt													$ 1,000
Stated interest rate													0.35%
0.35% Convertible Senior Notes due June 2020 \| Convertible Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost				(12)
Carrying Value				988
Long-term debt:
Outstanding Principal Amount				$ 1,000
Stated interest rate				0.35%	0.35%
0.9% Convertible Senior Notes due September 2021 \| Convertible Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost				$ (39)
Long-term debt:
Outstanding Principal Amount				1,000
Long-term debt				$ 961
Face amount of debt												$ 1,000
Stated interest rate				0.90%	0.90%							0.90%
0.9% Convertible Senior Notes due September 2021 \| Convertible Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	(15)
Carrying Value	985
Long-term debt:
Outstanding Principal Amount	$ 1,000
Stated interest rate	0.90%	0.90%
0.8% (€1 Billion) Senior Notes due March 2022 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (1)			$ (3)
Long-term debt:
Outstanding Principal Amount	1,223			1,123
Long-term debt	$ 1,222			$ 1,120
Face amount of debt \| €		€ 1,000			€ 1,000
Stated interest rate	0.80%	0.80%		0.80%	0.80%		0.80%
2.15% (€750 Million) Senior Notes due November 2022 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (4)			$ (3)
Long-term debt:
Outstanding Principal Amount	919			842
Long-term debt	$ 915			$ 839
Face amount of debt \| €		€ 750			€ 750
Stated interest rate	2.15%	2.15%		2.15%	2.15%				2.15%
2.75% Senior Notes due March 2023 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (1)			$ (2)
Long-term debt:
Outstanding Principal Amount	500			500
Long-term debt	$ 499			$ 498
Stated interest rate	2.75%	2.75%		2.75%	2.75%	2.75%
2.375% (€1 Billion) Senior Notes due September 2024 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (7)			$ (9)
Long-term debt:
Outstanding Principal Amount	1,223			1,123
Long-term debt	$ 1,216			$ 1,114
Face amount of debt \| €		€ 1,000			€ 1,000
Stated interest rate	2.375%	2.375%		2.375%	2.375%						2.375%
3.65% Senior Notes due March 2025 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (2)			$ (2)
Long-term debt:
Outstanding Principal Amount	500			500
Long-term debt	$ 498			$ 498
Stated interest rate	3.65%	3.65%		3.65%	3.65%					3.65%
4.1% Senior Notes due April 2025 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (5)
Long-term debt:
Outstanding Principal Amount	1,000		$ 1,000
Long-term debt	$ 995
Stated interest rate	4.10%	4.10%	4.10%
0.75% Convertible Senior Notes due May 2025 \| Convertible Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (128)
Long-term debt:
Outstanding Principal Amount	863
Long-term debt	$ 735
Face amount of debt			$ 863
Stated interest rate	0.75%	0.75%	0.75%
3.6% Senior Notes due June 2026 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (4)			$ (5)
Long-term debt:
Outstanding Principal Amount	1,000			1,000
Long-term debt	$ 996			$ 995
Stated interest rate	3.60%	3.60%		3.60%	3.60%			3.60%
1.8% (€1 Billion) Senior Notes due March 2027 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (2)			$ (5)
Long-term debt:
Outstanding Principal Amount	1,223			1,123
Long-term debt	$ 1,221			$ 1,118
Face amount of debt \| €		€ 1,000			€ 1,000
Stated interest rate	1.80%	1.80%		1.80%	1.80%					1.80%
4.5% Senior Notes due April 2027 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (5)
Long-term debt:
Outstanding Principal Amount	750		$ 750
Long-term debt	$ 745
Stated interest rate	4.50%	4.50%	4.50%
3.55% Senior Notes due March 2028 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (2)			$ (3)
Long-term debt:
Outstanding Principal Amount	500			500
Long-term debt	$ 498			$ 497
Stated interest rate	3.55%	3.55%		3.55%	3.55%	3.55%
4.625% Senior Notes due April 2030 \| Senior Notes
Current Liabilities:
Unamortized Debt Discount and Debt Issuance Cost	$ (11)
Long-term debt:
Outstanding Principal Amount	1,500		$ 1,500
Long-term debt	$ 1,489
Stated interest rate	4.625%	4.625%	4.625%

DEBT - Fair Value of Debt (Deta

DEBT - Fair Value of Debt (Details) - USD ($) $ in Billions	Dec. 31, 2020	Dec. 31, 2019
Level 2
Debt Instrument [Line Items]
Estimated market value of outstanding senior notes	$ 14	$ 9.8

DEBT - Convertible Senior Notes

DEBT - Convertible Senior Notes (Details) - Convertible Senior Notes $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Jun. 30, 2020USD ($)	Apr. 30, 2020USD ($)day$ / shares	Mar. 31, 2018USD ($)	Aug. 31, 2014USD ($)day$ / shares	Dec. 31, 2020USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2019	May 31, 2013USD ($)	Mar. 31, 2012USD ($)
0.35% Convertible Senior Notes due June 2020
Debt Instrument [Line Items]
Face amount of debt								$ 1,000
Stated interest rate								0.35%
Payments related to principal amount	$ 1,000
Cash payment of the conversion value in excess of the principal amount	$ 245
Effective interest rate								3.13%
Debt discount related to convertible notes, net of tax								$ 92
Debt discount related to convertible notes, before tax								$ 154
0.9% Convertible Senior Notes due September 2021
Debt Instrument [Line Items]
Face amount of debt				$ 1,000
Stated interest rate				0.90%			0.90%
Payments of debt issuance costs						$ 11
Conversion price (in dollars per share) \| $ / shares				$ 2,055.50
Ratio of closing share price to conversion price as a condition for conversion of the convertible notes				150.00%
If-converted value over the aggregate principal amount					$ 17
Effective interest rate				3.18%
Debt discount related to convertible notes, net of tax				$ 83
Debt discount related to convertible notes, before tax				$ 143
0.9% Convertible Senior Notes due September 2021 \| Minimum
Debt Instrument [Line Items]
Consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) \| day				20
Additional payment to debt holder, settled in shares, aggregate value of shares				$ 0
0.9% Convertible Senior Notes due September 2021 \| Maximum
Debt Instrument [Line Items]
Consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) \| day				30
Additional payment to debt holder, settled in shares, aggregate value of shares				$ 375
0.75% Convertible Senior Notes due May 2025
Debt Instrument [Line Items]
Face amount of debt		$ 863
Stated interest rate		0.75%			0.75%
Payments of debt issuance costs					$ 19
Conversion price (in dollars per share) \| $ / shares		$ 1,886.44
Ratio of closing share price to conversion price as a condition for conversion of the convertible notes		130.00%
If-converted value over the aggregate principal amount					$ 97
Effective interest rate		4.10%
Debt discount related to convertible notes, net of tax		$ 100
Debt discount related to convertible notes, before tax		$ 130
0.75% Convertible Senior Notes due May 2025 \| Minimum
Debt Instrument [Line Items]
Consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) \| day		20
Additional payment to debt holder, settled in shares, aggregate value of shares		$ 0
0.75% Convertible Senior Notes due May 2025 \| Maximum
Debt Instrument [Line Items]
Consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days) \| day		30
Additional payment to debt holder, settled in shares, aggregate value of shares		$ 235
1.00% Convertible Debt due March 2018
Debt Instrument [Line Items]
Face amount of debt									$ 1,000
Stated interest rate									1.00%
Payments related to principal amount			$ 714
Cash payment of the conversion value in excess of the principal amount			$ 773

DEBT - Summary of Interest Expe

DEBT - Summary of Interest Expenses and Weighted-Average Effective Interest Rates Related To Convertible Senior Notes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Amortization of debt discount and debt issuance costs	$ 64	$ 58	$ 59
Total interest expenses	356	266	269
Convertible Senior Notes
Debt Instrument [Line Items]
Coupon interest expense	15	12	14
Amortization of debt discount and debt issuance costs	54	50	52
Total interest expenses	$ 69	$ 62	$ 66
Weighted-average effective interest rate	3.50%	3.20%	3.20%

DEBT - Other Long-term Debt (De

DEBT - Other Long-term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Apr. 30, 2020
Debt Instrument [Line Items]
Aggregate principal amount	$ 11,201	$ 7,711
Euro-Denominated Debt \| Designated as Hedging Instrument \| Minimum
Debt Instrument [Line Items]
Carrying value of the portions of Euro-denominated debt, including accrued interest, designated as a net investment hedge	1,800	2,400
Euro-Denominated Debt \| Designated as Hedging Instrument \| Maximum
Debt Instrument [Line Items]
Carrying value of the portions of Euro-denominated debt, including accrued interest, designated as a net investment hedge	3,200	4,300
Senior Notes
Debt Instrument [Line Items]
Payments of debt issuance costs	19
Carrying value of long-term debt	$ 10,300	$ 6,700
Senior Notes \| 4.1% Senior Notes due April 2025
Debt Instrument [Line Items]
Stated interest rate	4.10%		4.10%
Aggregate principal amount	$ 1,000		$ 1,000
Senior Notes \| 4.5% Senior Notes due April 2027
Debt Instrument [Line Items]
Stated interest rate	4.50%		4.50%
Aggregate principal amount	$ 750		$ 750
Senior Notes \| 4.625% Senior Notes due April 2030
Debt Instrument [Line Items]
Stated interest rate	4.625%		4.625%
Aggregate principal amount	$ 1,500		$ 1,500

DEBT - Summary of Interest Ex_2

DEBT - Summary of Interest Expenses Related to Other Long-Term Debt (Details) - Senior Notes		Dec. 31, 2020	Apr. 30, 2020	Dec. 31, 2019	Aug. 31, 2017	Mar. 31, 2017	May 31, 2016	Nov. 30, 2015	Mar. 31, 2015	Sep. 30, 2014
0.8% (€1 Billion) Senior Notes due March 2022
Debt Instrument [Line Items]
Stated interest rate		0.80%		0.80%		0.80%
Effective interest rate at debt origination	[1]					0.94%
2.15% (€750 Million) Senior Notes due November 2022
Debt Instrument [Line Items]
Stated interest rate		2.15%		2.15%				2.15%
Effective interest rate at debt origination	[1]							2.27%
2.75% Senior Notes due March 2023
Debt Instrument [Line Items]
Stated interest rate		2.75%		2.75%	2.75%
Effective interest rate at debt origination	[1]				2.88%
2.375% (€1 Billion) Senior Notes due September 2024
Debt Instrument [Line Items]
Stated interest rate		2.375%		2.375%						2.375%
Effective interest rate at debt origination	[1]									2.54%
3.65% Senior Notes due March 2025
Debt Instrument [Line Items]
Stated interest rate		3.65%		3.65%					3.65%
Effective interest rate at debt origination	[1]								3.76%
4.1% Senior Notes due April 2025
Debt Instrument [Line Items]
Stated interest rate		4.10%	4.10%
Effective interest rate at debt origination	[1]		4.22%
3.6% Senior Notes due June 2026
Debt Instrument [Line Items]
Stated interest rate		3.60%		3.60%			3.60%
Effective interest rate at debt origination	[1]						3.70%
1.8% (€1 Billion) Senior Notes due March 2027
Debt Instrument [Line Items]
Stated interest rate		1.80%		1.80%					1.80%
Effective interest rate at debt origination	[1]								1.86%
4.5% Senior Notes due April 2027
Debt Instrument [Line Items]
Stated interest rate		4.50%	4.50%
Effective interest rate at debt origination	[1]		4.63%
3.55% Senior Notes due March 2028
Debt Instrument [Line Items]
Stated interest rate		3.55%		3.55%	3.55%
Effective interest rate at debt origination	[1]				3.63%
4.625% Senior Notes due April 2030
Debt Instrument [Line Items]
Stated interest rate		4.625%	4.625%
Effective interest rate at debt origination	[1]		4.72%

[1]	Represents the coupon interest rate adjusted for deferred debt issuance costs, premiums or discounts existing at the origination of the debt.

DEBT - Summary of Interest Ex_3

DEBT - Summary of Interest Expenses Related to Other Long-term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Amortization of debt discount and debt issuance costs	$ 64	$ 58	$ 59
Senior Notes
Debt Instrument [Line Items]
Coupon interest expense	264	160	163
Amortization of debt discount and debt issuance costs	9	6	7
Total interest expenses	$ 273	$ 166	$ 170

TREASURY STOCK - Narrative (Det

TREASURY STOCK - Narrative (Details) - USD ($)	9 Months Ended	12 Months Ended
TREASURY STOCK - Narrative (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Remittances of employee withholding taxes		$ 141,000,000	$ 151,000,000	$ 163,000,000
Treasury stock, shares (in shares)	22,446,897	22,446,897	21,762,070
2019 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Remaining authorization to repurchase common stock	$ 10,400,000,000	$ 10,400,000,000	$ 11,500,000,000
Amount of common stock repurchases authorized			$ 15,000,000,000
Shares repurchased (in shares)	0

TREASURY STOCK - Summary of Sto

TREASURY STOCK - Summary of Stock Repurchase Activities (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Repurchases (in shares)	685	4,445	3,100
Repurchases	$ 1,264	$ 8,153	$ 6,012
General authorization for shares withheld on stock award vesting (in shares)	84	87	80
General authorization for shares withheld on stock award vesting	$ 142	$ 151	$ 162
Shares repurchased in December and settled in following January (in shares)	0	19	43
Shares repurchased in December and settled in following January	$ 0	$ 40	$ 74
Authorized stock repurchase programs
Equity, Class of Treasury Stock [Line Items]
Repurchases (in shares)	601	4,358	3,020
Repurchases	$ 1,122	$ 8,002	$ 5,850

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) BY COMPONENT (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2020	Aug. 31, 2019
Total, net of tax
Balance, beginning of period		$ 5,933	$ 8,785	$ 11,261
OCI before reclassifications		55	114	(313)
Amounts reclassified to net income	[1]	18	11
Total other comprehensive income (loss), net of tax		73	125	(313)
Balance, end of period		4,893	5,933	8,785
Convertible debt securities \| Trip.com Group
Total, net of tax
Investment in convertible notes		525			$ 250	$ 500
Cumulative effect of adoption of accounting standards updates
Total, net of tax
Balance, beginning of period		(3)		189
Balance, end of period			(3)
Foreign currency translation adjustments, net of tax
Total, net of tax
Balance, beginning of period		(139)	(129)	(15)
OCI before reclassifications		50	(10)	(114)
Amounts reclassified to net income	[1]	0	0
Total other comprehensive income (loss), net of tax		50	(10)	(114)
Balance, end of period		(89)	(139)	(129)
Foreign currency translation adjustments, net of tax \| Foreign Exchange Forward \| Net Investment Hedging
Before tax
Balance, beginning of period		(53)	(53)	(53)
Balance, end of period		(53)	(53)	(53)
Total, net of tax
Balance, beginning of period		(35)	(35)	(35)
Balance, end of period		(35)	(35)	(35)
Foreign currency translation adjustments, net of tax \| Cumulative effect of adoption of accounting standards updates \| ASU 2016-01
Total, net of tax
Balance, beginning of period	[2]			0
Foreign Currency Translation Adjustments - Foreign Currency Translation
Before tax
Balance, beginning of period		(186)	(109)	210
OCI before reclassifications		197	(77)	(319)
Amounts reclassified to net income	[1]	0	0
OCI for the period		197	(77)	(319)
Balance, end of period		11	(186)	(109)
Tax benefit (expense)
AOCI Tax, Attributable to Parent	[3]	54	41	0
OCI before reclassifications	[3]	(7)	13	41
Amounts reclassified to net income	[1],[3]	0	0
OCI for the period	[3]	(7)	13	41
AOCI Tax, Attributable to Parent	[3]	47	54	41
Foreign Currency Translation Adjustments - Foreign Currency Translation \| Cumulative effect of adoption of accounting standards updates \| ASU 2016-01
Before tax
Balance, beginning of period	[2]			0
Tax benefit (expense)
AOCI Tax, Attributable to Parent	[2],[3]			0
Foreign Currency Translation Adjustments - Net Investment Hedges
Before tax
Balance, beginning of period	[4]	(2)	(73)	(290)
OCI before reclassifications	[4]	(182)	71	217
Amounts reclassified to net income	[1],[4]	0	0
OCI for the period	[4]	(182)	71	217
Balance, end of period	[4]	(184)	(2)	(73)
Tax benefit (expense)
AOCI Tax, Attributable to Parent	[4]	(5)	12	65
OCI before reclassifications	[4]	42	(17)	(53)
Amounts reclassified to net income	[1],[4]	0	0
OCI for the period	[4]	42	(17)	(53)
AOCI Tax, Attributable to Parent	[4]	37	(5)	12
Foreign Currency Translation Adjustments - Net Investment Hedges \| Cumulative effect of adoption of accounting standards updates \| ASU 2016-01
Before tax
Balance, beginning of period	[2],[4]			0
Tax benefit (expense)
AOCI Tax, Attributable to Parent	[2],[4]			0
Net Unrealized Gains (Losses) on Available-For-Sale Securities
Before tax
Balance, beginning of period	[2]	(7)	(157)	343
OCI before reclassifications	[2]	6	161	(201)
Amounts reclassified to net income	[1],[2]	4	(11)
OCI for the period	[2]	10	150	(201)
Balance, end of period	[2]	3	(7)	(157)
Tax benefit (expense)
AOCI Tax, Attributable to Parent	[2]	(45)	(30)	(90)
OCI before reclassifications	[2]	(1)	(37)	2
Amounts reclassified to net income	[1],[2]	14	22
OCI for the period	[2]	13	(15)	2
AOCI Tax, Attributable to Parent	[2]	(32)	(45)	(30)
Total, net of tax
Balance, beginning of period	[2]	(52)	(187)	253
OCI before reclassifications	[2]	5	124	(199)
Amounts reclassified to net income	[1],[2]	18	11
Total other comprehensive income (loss), net of tax	[2]	23	135	(199)
Balance, end of period	[2]	(29)	(52)	(187)
Net Unrealized Gains (Losses) on Available-For-Sale Securities \| Convertible debt securities \| Trip.com Group
Tax benefit (expense)
Amounts reclassified to net income		15	21
Net Unrealized Gains (Losses) on Available-For-Sale Securities \| Cumulative effect of adoption of accounting standards updates \| ASU 2016-01
Before tax
Balance, beginning of period	[2]			(299)
Tax benefit (expense)
AOCI Tax, Attributable to Parent	[2]			58
Total, net of tax
Balance, beginning of period	[2]			(241)
Total AOCI, net of tax
Total, net of tax
Balance, beginning of period		(191)	(316)	238
Balance, end of period		$ (118)	$ (191)	(316)
Total AOCI, net of tax \| Cumulative effect of adoption of accounting standards updates
Total, net of tax
Balance, beginning of period				(241)
Total AOCI, net of tax \| Cumulative effect of adoption of accounting standards updates \| ASU 2016-01
Total, net of tax
Balance, beginning of period				$ (241)

[1]	The reclassified net gains (losses) on available-for-sale securities, before tax, are included in "Other income (expense), net" and the reclassified tax (expenses) benefits are included in "Income tax expense" in the Consolidated Statements of Operations. For the year ended December 31, 2020, the reclassified tax expenses include a tax expense of $15 million related to the maturity in May 2020 of the Company's investment of $250 million in Trip.com Group convertible senior notes (see Note 5). For the year ended December 31, 2019, the reclassified tax expenses include a tax expense of $21 million related to the maturity in August 2019 of the Company's investment of $500 million in Trip.com Group convertible senior notes.
[2]	Upon the adoption of the accounting update on financial instruments on January 1, 2018, the Company reclassified net unrealized gains, net of tax, of $241 million ($299 million before tax) related to marketable equity securities from AOCI to retained earnings. Changes in fair value of marketable equity securities subsequent to January 1, 2018 are recognized in net income rather than "Accumulated other comprehensive loss" in the Consolidated Balance Sheets (see Note 2).
[3]	The tax benefits relate to foreign currency translation adjustments to the Company's one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the enactment of the Tax Act.
[4]	Net investment hedges balance, net of tax, at December 31, 2020 and earlier dates presented above, includes accumulated net losses from fair value adjustments of $35 million ($53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. The remaining balances relate to foreign currency transaction gains (losses) and related tax benefits (expenses) associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (see Notes 2 and 12).

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017	Mar. 31, 2020USD ($)	Mar. 31, 2020EUR (€)
Income Tax Contingency [Line Items]
International pre-tax income	$ 2,600	$ 5,700	$ 4,800
Domestic pre-tax (loss) income	(2,000)	213	47
Income tax benefit recorded to adjust the remeasurement of deferred tax balances due to the reduction of the U.S. federal statutory tax rate			2
Income tax benefit recorded to adjust the provisional income tax expense relating to the federal one-time deemed repatriation liability	8	17	$ 46
Tax credit carryforward, used in period	115
Other deferred tax liabilities	263	284
Valuation allowance on deferred tax assets	58	45
Statutory rate (as a percent)			21.00%	35.00%
Gross interest and penalties accrued	$ 31	10
The Netherlands
Income Tax Contingency [Line Items]
Prepaid Taxes					$ 717	€ 660
Innovation Box Tax rate	7.00%
Statutory rate (as a percent)	25.00%
Domestic Tax Authority
Income Tax Contingency [Line Items]
Deferred tax assets, operating loss carryforwards, used in period	$ 108
NOLs utilized in period	309
Operating loss carryforwards	179
Domestic Tax Authority \| Research credit, capital loss carryforward and state net operating losses
Income Tax Contingency [Line Items]
Valuation allowance on deferred tax assets	40	15
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Operating loss carryforwards	457
Foreign Tax Authority
Income Tax Contingency [Line Items]
Operating loss carryforwards	488
Valuation allowance on deferred tax assets	18	30
Research Tax Credit Carryforward \| Domestic Tax Authority
Income Tax Contingency [Line Items]
Tax credit carryforward	14
Other assets, net
Income Tax Contingency [Line Items]
Other deferred tax assets	335
Deferred tax assets	455	400
Other liabilities, noncurrent
Income Tax Contingency [Line Items]
Other deferred tax liabilities	325
Accrued expenses and other current liabilities
Income Tax Contingency [Line Items]
Income taxes liability	$ 174	$ 158

INCOME TAXES - Income Tax Expen

INCOME TAXES - Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current
International	$ 320	$ 915	$ 887
U.S. Federal	(9)	22	45
U.S. State	(16)	34	55
Total	295	971	987
Deferred
International	(62)	(12)	(3)
U.S. Federal	296	166	(107)
U.S. State	(21)	(32)	(40)
Total	213	122	(150)
Total
International	258	903	884
U.S. Federal	287	188	(62)
U.S. State	(37)	2	15
Income tax expense	$ 508	$ 1,093	$ 837

INCOME TAXES - Net Deferred Tax

INCOME TAXES - Net Deferred Tax Assets/(Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets/(liabilities):
Net operating loss carryforward — U.S.		$ 67	$ 37
Net operating loss carryforward — International		81	15
Accrued expenses		47	35
Stock-based compensation and other stock based payments		40	49
Foreign currency translation adjustment		29	36
Tax credits		9	14
Euro-denominated debt		77	0
Operating lease liabilities		43	38
Property and equipment		11	31
Subtotal - deferred tax assets		404	255
Discount on convertible notes		(29)	(10)
Intangible assets and other		(119)	(133)
Euro-denominated debt		0	(14)
State income tax on accumulated unremitted international earnings		(5)	(8)
Unrealized gains on investments		(550)	(191)
Operating lease assets		(38)	(35)
Installment sale liability		(263)	(284)
Other		(14)	(11)
Subtotal - deferred tax liabilities		(1,018)	(686)
Valuation allowance on deferred tax assets		(58)	(45)
Net deferred tax liabilities	[1]	$ (672)	$ (476)

[1]	Includes deferred tax assets of $455 million and $400 million at December 31, 2020 and 2019, respectively, reported in "Other assets, net" in the Consolidated Balance Sheets.

INCOME TAXES - Effective Income

INCOME TAXES - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of effective income tax rate and amount computed using expected U.S. statutory federal rate
Income tax expense at U.S. federal statutory rate	$ 119	$ 1,251	$ 1,015
Adjustment due to:
Foreign rate differential	55	210	210
Innovation Box Tax benefit	(79)	(443)	(435)
Goodwill impairment	228	0	0
Stock-based compensation	32	23	12
Federal GILTI	73	36	35
State income tax (benefit) expense	(31)	9	1
Valuation allowance	36	1	(3)
Uncertain tax positions	64	11	(4)
Tax Act - Remeasurement of deferred tax balances	0	0	(2)
Tax Act - U.S. transition tax benefit and other transition impacts	(8)	(17)	(46)
Other	19	12	54
Income tax expense	$ 508	$ 1,093	$ 837

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized tax benefits
Unrecognized tax benefit — January 1	$ 56	$ 45	$ 32
Gross increases — tax positions in current period	2	3	1
Gross increases — tax positions in prior periods	48	11	19
Gross decreases — tax positions in prior periods	(11)	(3)	(3)
Reduction due to lapse in statute of limitations	0	0	(2)
Reduction due to settlements during the current period	(11)	0	(2)
Unrecognized tax benefit — December 31	$ 84	$ 56	$ 45

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Competition and Consumer Protection Reviews (Details) $ in Millions	Dec. 31, 2020USD ($)
Potential Fine Under Contractual Parity Agreement
Commitments and Contingencies
Accruals for loss contingencies	$ 23

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Tax Matters (Details) ₺ in Millions, € in Millions, $ in Millions	1 Months Ended							12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2019EUR (€)	Jan. 31, 2019USD ($)	Jan. 31, 2019EUR (€)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2015EUR (€)	Dec. 31, 2020USD ($)	Dec. 31, 2020TRY (₺)	Dec. 31, 2019USD ($)	Dec. 31, 2020EUR (€)	Dec. 31, 2017USD ($)
Commitments and Contingencies
Unrecognized tax benefits	$ 56				$ 45			$ 84		$ 56		$ 32
French Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties	86	€ 70					€ 356
Payment required to appeal a litigation matter			$ 403	€ 356
Unrecognized tax benefits								61			€ 50
Potential loss related to loss contingencies in excess of the accrued amount								24			20
Transfer Tax Assessments
Commitments and Contingencies
Assessed taxes including interest and penalties	48	39
Italian Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties	71	58			$ 58	€ 48
Payment required to appeal a litigation matter	11	€ 10
Unrecognized tax benefits								5			€ 4
Turkish Tax Audit
Commitments and Contingencies
Assessed taxes including interest and penalties								103	₺ 766
Travel Transaction Related Taxes
Commitments and Contingencies
Accruals for loss contingencies	$ 67							59		67
Potential loss related to loss contingencies in excess of the accrued amount								$ 25
Wage-Related Taxes and Interest Owed for Prior Periods
Commitments and Contingencies
Payments for estimated probable taxes owed for prior tax years										$ 61

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Other Matters (Details) - Dec. 31, 2020 € in Millions, $ in Millions	EUR (€)	USD ($)
Pension-Related Litigation
Commitments and Contingencies
Potential loss related to loss contingencies in excess of the accrued amount		$ 290
E.U. General Data Protection Regulation Rulings \| Maximum
Commitments and Contingencies
Estimated possible fine per incident	€ 20	$ 24

COMMITMENTS AND CONTINGENCIES_4

COMMITMENTS AND CONTINGENCIES - Building Construction (Details) € in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Sep. 30, 2016USD ($)	Sep. 30, 2016EUR (€)	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Dec. 31, 2020EUR (€)	Sep. 30, 2016EUR (€)
Other Commitments [Line Items]
Remaining lease obligations			$ 585
Booking.com \| Headquarters
Other Commitments [Line Items]
Acquisition of land use rights	$ 48	€ 43
Contractual obligation	$ 331		68		€ 56	€ 270
Decrease in contractual obligation			11	€ 9
Booking.com \| Headquarters \| Vendors used to fit out and furnish office space
Other Commitments [Line Items]
Contractual obligation			35		29
Booking.com \| Headquarters \| Ground Lease
Other Commitments [Line Items]
Remaining lease obligations			$ 86		€ 70

COMMITMENTS AND CONTINGENCIES_5

COMMITMENTS AND CONTINGENCIES - Other Contractual Obligations (Details) ft² in Thousands, £ in Millions, $ in Millions	Dec. 31, 2020USD ($)	Dec. 31, 2020GBP (£)	Dec. 31, 2019USD ($)	Dec. 31, 2018ft²
Headquarters \| Manchester, England \| Rentalcars.com
Other Commitments [Line Items]
Area of property subject to lease (in square feet) \| ft²				222
Term of lease not yet commenced	13 years	13 years
Headquarters \| Manchester, England \| Rentalcars.com \| Operating lease obligations
Other Commitments [Line Items]
Contractual obligation	$ 88	£ 65
Standby Letters of Credit
Other Commitments [Line Items]
Letters of credit outstanding \| $	$ 134		$ 155

BENEFIT PLANS (Details)

BENEFIT PLANS (Details) - USD ($) $ in Millions	12 Months Ended
BENEFIT PLANS (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Matching contributions	$ 33	$ 26	$ 22

GEOGRAPHIC INFORMATION - Geogra

GEOGRAPHIC INFORMATION - Geographic Information on Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Geographic Information
Revenues	$ 6,796	$ 15,066	$ 14,527
United States
Geographic Information
Revenues	783	1,537	1,536
The Netherlands
Geographic Information
Revenues	5,264	11,686	11,348
Other
Geographic Information
Revenues	$ 749	$ 1,843	$ 1,643

GEOGRAPHIC INFORMATION - Proper

GEOGRAPHIC INFORMATION - Property and Equipment, Excluding Capitalized Software, and Operating Lease Assets by Geographic Area (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment (excluding capitalized software) and operating lease assets	$ 1,048	$ 1,164
United States
Property, Plant and Equipment [Line Items]
Property and equipment (excluding capitalized software) and operating lease assets	186	216
The Netherlands
Property, Plant and Equipment [Line Items]
Property and equipment (excluding capitalized software) and operating lease assets	499	484
United Kingdom
Property, Plant and Equipment [Line Items]
Property and equipment (excluding capitalized software) and operating lease assets	85	137
Other
Property, Plant and Equipment [Line Items]
Property and equipment (excluding capitalized software) and operating lease assets	$ 278	$ 327

ACQUISITIONS (Details)

ACQUISITIONS (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
ACQUISITIONS (Details) - USD ($) $ in Millions	Nov. 30, 2018	Apr. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Common stock issued in an acquisition				$ 110
Payments to settle contingent liabilities			$ 37
Additional Paid-in Capital
Business Acquisition [Line Items]
Common stock issued in an acquisition				$ 110
FareHarbor
Business Acquisition [Line Items]
Payments to acquire businesses, net of cash acquired		$ 139
Shares for purchase price consideration		59
FareHarbor \| Restricted Stock
Business Acquisition [Line Items]
Shares restricted for trading purposes		51
FareHarbor \| Additional Paid-in Capital
Business Acquisition [Line Items]
Common stock issued in an acquisition		$ 110
HotelsCombined
Business Acquisition [Line Items]
Payments to acquire businesses, net of cash acquired	$ 134

RESTRUCTURING AND OTHER EXIT _2

RESTRUCTURING AND OTHER EXIT COSTS (Details) $ in Millions	12 Months Ended
RESTRUCTURING AND OTHER EXIT COSTS (Details) $ in Millions	Dec. 31, 2020USD ($)country	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other exit costs	$ 149	$ 0	$ 0
Noncash restructuring and other exit costs	7
Estimated additional restructuring expenses	$ 40
Minimum
Restructuring Cost and Reserve [Line Items]
Number of countries in which restructuring actions have taken place \| country	60
Accrued expenses and other current liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring liabilities	$ 37

GOVERNMENT GRANTS AND OTHER A_2

GOVERNMENT GRANTS AND OTHER ASSISTANCE (Details) - COVID-19 $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Unusual or Infrequent Item, or Both [Line Items]
Government grants and other assistance benefits, recognized amount	$ 127
Government grants and other assistance, amount received	99
Other current assets
Unusual or Infrequent Item, or Both [Line Items]
Grants receivable	$ 28

OTHER INCOME (EXPENSE), NET (De

OTHER INCOME (EXPENSE), NET (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Income and Expenses [Abstract]
Interest and dividend income		$ 54	$ 152	$ 187
Net gains (losses) on marketable equity securities	[1]	1,811	745	(367)
Impairment of investment	[1]	(100)	0	0
Foreign currency transaction losses		(207)	(31)	(53)
Other		(4)	13	(4)
Other income (expense), net		$ 1,554	$ 879	$ (237)

[1]	See Note 5 for additional information related to the net gains (losses) on marketable equity securities and impairment of investment.