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, income taxes, stock-based compensation, the allowance for doubtful accounts, customer chargeback provisions and the accrual of obligations for loyalty and other incentive programs.

The Company's financial instruments, including cash, restricted cash, accounts receivable, accounts payable, accrued expenses and deferred merchant bookings, are carried at cost which approximates their fair value because of the short-term nature of these financial instruments. See Notes 5, 6 and 12 for information related to fair value for investments, derivatives, and the Company's outstanding senior notes.

Restricted cash and cash equivalents are restricted through legal contracts or regulations. Restricted cash and cash equivalents at December 31, 2019, 2018 and 2017 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):

Investments held by the Company include debt securities and equity securities. Preferred stock that is either mandatorily redeemable or redeemable at the option of the investor is considered a debt security for accounting purposes. 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.

The Company has classified its investments in debt securities as available-for-sale securities. These securities are reported at estimated fair value with the aggregate unrealized gains and losses, net of tax, reflected in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. Investments in debt securities are considered to be impaired when a decline in fair value is judged to be other than temporary because the Company either intends to sell or it is more-likely-than not that it will be required to sell the impaired security before recovery. Once a decline in fair value is determined to be other than temporary, an impairment charge is recorded and a new cost basis in the investment is established. If the Company does not intend to sell the debt security, but it is probable that the Company will not collect all amounts due, then only the impairment due to the credit risk would be recognized in net income and the remaining amount of the impairment would be recognized in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. See "Other Recent Accounting Pronouncements" later in this Note for the accounting change to the other-than-temporary impairment model, effective January 1, 2020. 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 reported as "Short-term investments in marketable securities" or "Long-term investments" in the Consolidated Balance Sheets based on the maturity dates of the debt securities and the Company's expectations regarding the timing of sales and redemptions. Investments of a strategic nature that have been made for the purpose of affiliation or potential business advantage or in connection with a commercial relationship are included in "Long-term investments" in the Consolidated Balance Sheets. The cost of marketable debt securities sold is determined using a first-in and first-out method.

For periods beginning after December 31, 2017, marketable equity securities are reported at estimated fair value with changes in fair value recognized in "Net unrealized gains (losses) on marketable equity securities" in the Consolidated Statements of Operations rather than "Accumulated other comprehensive loss" in the Consolidated Balance Sheets, pursuant to the adoption of the accounting update on financial instruments in 2018.

The Company holds investments in equity securities of private companies, over which the Company does not have the ability to exercise significant influence or control. Pursuant to the adoption of the accounting update on financial instruments in 2018, for periods beginning after December 31, 2017, the Company elected to measure these investments at cost less impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Previously, these investments were carried at cost and adjusted to fair value only for other-than-temporary declines in fair value.

Receivables from customers are recorded at the original invoiced amounts net of an allowance for doubtful accounts. The allowance for doubtful accounts is estimated based on historical experience, aging of the receivable, credit quality of the customers, current economic trends and other factors that may affect the Company's ability to collect from customers. See Note 7 for additional information. See "Other Recent Accounting Pronouncements" later in this Note for the accounting change to the measurement of credit losses for accounts receivable, effective January 1, 2020.

Certain direct development costs associated with website and internal-use software are capitalized and include external direct costs of services and payroll costs for employees devoting time to the software projects principally related to platform development, including support systems, software coding, designing system interfaces and installation and testing of the software. These costs are recorded as property and equipment and are generally amortized over a period of two to five years beginning when the asset is substantially ready for use. Costs incurred for enhancements that are expected to result in additional features or functionalities are capitalized and amortized over the estimated useful life of the enhancements. Costs incurred during the preliminary project stage, as well as maintenance and training costs, are expensed as incurred. Additions to capitalized costs during the years ended December 31, 2019, 2018 and 2017 were $106 million, $97 million and $80 million, respectively.

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 (see "Recent Accounting Pronouncements Adopted" later in this Note). The capitalized implementation costs are reported as "Prepaid expenses and other current assets" or "Other assets" 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.

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"). See "Recent Accounting Pronouncements Adopted" later in this Note for further information related to the impact of the adoption of this accounting 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 rates approximate the rate the Company would pay to borrow in the currency of the lease payments on a collateralized basis for the weighted-average life of the lease. 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 initially extend the lease term for various periods up to 9 years. The exercise of renewal options for office space and data centers is at the Company’s discretion and are included if they are reasonably certain to be exercised. The land lease for Booking.com's 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.

At December 31, 2018, the Company had $47 million 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 were included in "Other assets" in the Consolidated Balance Sheets, for periods prior to January 1, 2019, and reclassified from "Other assets" to "Operating lease assets" on January 1, 2019 as part of the adoption of ASC 842, Leases (see "Recent Accounting Pronouncements Adopted" later in this Note). 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 Note 10 and 16 for further information.

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 at least annually for impairment, or earlier if an event occurs or circumstances change and there is an indication of impairment. The Company tests goodwill at a reporting unit level. The fair value of the reporting unit is compared to its carrying value, including goodwill. Fair values are determined using a combination of standard valuation techniques, including an income approach (discounted cash flows) and market approaches (EBITDA multiples of comparable publicly-traded companies and precedent transactions) and based on market participant assumptions. An impairment is recorded to the extent that the implied fair value of goodwill is less than the carrying value of goodwill. See Note 11 for further information. See "Other Recent Accounting Pronouncements" later in this Note for the new accounting standard that the Company adopted in the first quarter of 2020.

The Company reviews long-lived 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.

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 "Foreign currency transactions and other" in the Company's Consolidated Statements of Operations.

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. The Company's primary foreign currency exposures are in Euros and British Pounds Sterling, in which it conducts a significant portion of its business activities. As a result, the Company faces exposure to adverse movements in 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 "Prepaid expenses and 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 "Foreign currency transactions and other" 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.

Historically, the aggregate principal value of the Euro-denominated Senior Notes maturing in March 2022, November 2022, September 2024 and March 2027 (collectively "Euro-denominated debt") and accrued interest 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 aggregate principal value of the Euro-denominated debt as a hedge. The foreign currency transaction gains or losses on these Euro-denominated liabilities are measured based upon changes in spot rates. The foreign currency transaction gains or losses on the Euro-denominated debt that is designated as a hedging instrument for accounting purposes are recorded in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. The net assets of this Euro functional currency subsidiary are translated into U.S. Dollars at each balance sheet date, with the effects of foreign currency changes also reported in "Accumulated other comprehensive loss" in the Consolidated Balance Sheets. The foreign currency transaction gains or losses on the Euro-denominated debt that is not designated as a hedging instrument are recognized in "Foreign currency transactions and other" in the Consolidated Statement of Operations. See Notes 12 and 14 for further information related to the net investment hedge.

On January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers, using a modified retrospective method applied to all contracts as of January 1, 2018. Therefore, for reporting periods beginning after December 31, 2017, the financial statements are prepared in accordance with the current revenue recognition standard and the financial statements for all periods prior to January 1, 2018 are presented under the previous revenue recognition accounting standard. 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 travel reservation services.

For periods beginning after December 31, 2017, the Company recognizes revenue for travel reservation services when the travel begins rather than when the travel is completed. Substantially all of the Company's revenues are generated by providing online travel reservation services, which principally allows travelers to book travel reservations with travel service providers through the Company’s platforms. While the Company generally refers to a consumer that books travel reservation services on the Company's platforms as its customer, for accounting purposes, the Company's customers are the travel service providers and, in certain merchant transactions, the travelers. The Company's contracts with travel service providers give them the ability to market their reservation availability without transferring responsibility to deliver the travel service to the Company. Therefore, the Company's revenues are presented on a net basis in the Consolidated Statements of Operations. These contracts include payment terms and establish the consideration to which the Company is entitled, which includes either a commission or a margin on the travel transaction. Revenue is measured based on the expected consideration specified in the contract with the travel service provider, considering the effects of sales incentives, "no show" cancellations (where the traveler has not cancelled the reservation but does not arrive on the scheduled reservation date) and "late" cancellations (where the travel service provider accepts a cancellation after its cancellation cut-off date). Estimates for cancellations and sales incentives are based on historical experience and current trends. Coupons are recorded as a reduction of the transaction price at the time they are redeemed. 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.

Under the previous revenue recognition standard, revenues from priceline's Name Your Own Price® transactions were presented on a gross basis with the amount remitted to the travel service providers reported as cost of revenues. Under the current revenue recognition standard, Name Your Own Price® revenues are reported on a net basis with the amount remitted to the travel service providers recorded as an offset in merchant revenues. Therefore, for periods beginning after December 31, 2017, the Company no longer presents "Cost of revenues" or "Gross profit" in its Consolidated Statements of Operations. Total revenues reported in 2019 and 2018 are comparable to gross profit reported in previous years.

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.

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.

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.

Sales and other expenses are generally variable in nature and consist primarily of: (1) credit cards and other payment processing fees associated with merchant transactions; (2) fees paid to third parties that provide call center, website content translations and other services; (3) customer chargeback provisions and fraud prevention expenses associated with merchant transactions; (4) customer relations costs; (5) provisions for bad debt, primarily related to agency accommodation commission receivables; and (6) insurance claim costs for the Company's travel-related insurance business.

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. 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. The fair value of employee stock options assumed in acquisitions was

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. See Note 4 for further information related to stock-based awards.

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.

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.

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 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.

In August 2018, the Financial Accounting Standards Board ("FASB") issued a new accounting standard to address a customer's accounting for implementation costs incurred in a cloud computing arrangement that is a service contract and also added certain disclosure requirements related to implementation costs incurred for internal-use software and cloud computing arrangements. The amendment aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The Company adopted this standard on January 1, 2019 and applied it on a prospective basis. The adoption did not have a material impact to the Consolidated Financial Statements.

In February 2016, the FASB issued a new accounting standard that requires lessees to recognize an asset and a liability in the balance sheet for the rights and obligations created by entering into lease transactions. The new standard retains the dual-model concept by requiring entities to determine if a lease is an operating or finance lease. The new standard also expands qualitative and quantitative disclosures for lessees.

The Company adopted this new standard on January 1, 2019 on a modified retrospective basis and has elected not to restate comparative periods. The Company elected other options, which allow the Company to use its previous evaluations regarding if an arrangement contains a lease, if a lease is an operating or finance lease and what costs are capitalized as initial direct costs prior to adoption. The Company also elected to combine lease and non-lease components.

Upon the adoption of the new lease standard, on January 1, 2019, the Company recognized operating lease assets of $646 million and total operating lease liabilities of $646 million (including a current liability of $152 million) in the consolidated balance sheet and reclassified certain balances related to existing leases. There was no impact to retained earnings at adoption. See Note 10 for more information related to leases.

In December 2019, 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.

For public business entities, this update is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. Early adoption is permitted. The amendment related to franchise taxes that are partially based on income should be applied on either a retrospective basis for all periods presented or a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. All other amendments should be applied on a prospective basis. The Company is currently evaluating the impact to its Consolidated Financial Statements of adopting this update and does not expect it to have a material impact.

In January 2017, the FASB issued a new 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 will apply it on a prospective basis.

In June 2016, the FASB issued a new 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 credit losses, (2) allowing reversals of the previously recognized credit losses until the entity has the intent to sell, is more-likely-than-not required to sell the securities or the maturity of the securities, (3) limiting impairment to the difference between the amortized cost basis and fair value and (4) not allowing entities to consider the length of time that fair value has been less than amortized cost as a factor in evaluating whether a credit loss exists. The Company adopted this update in the first quarter of 2020 and applied this update on a modified retrospective basis. The adoption did not have a material impact to the Company's Consolidated Financial Statements.