BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business	Business—American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) is one of the largest global real estate investment trusts and a leading independent owner, operator and developer of multitenant communications real estate. The Company’s primary business is the leasing of space on communications sites to wireless service providers, radio and television broadcast companies, wireless data providers, government agencies and municipalities and tenants in a number of other industries. The Company refers to this business as its property operations. Additionally, the Company offers tower-related services in the United States, which the Company refers to as its services operations. These services include site acquisition, zoning and permitting (“AZP”) and structural analysis, which primarily support the Company’s site leasing business, including the addition of new tenants and equipment on its sites. The Company’s portfolio primarily consists of towers that it owns and towers that it operates pursuant to long-term lease arrangements, as well as distributed antenna system (“DAS”) networks, which provide seamless coverage solutions in certain in-building and certain outdoor wireless environments. In addition to the communications sites in its portfolio, the Company manages rooftop and tower sites for property owners under various contractual arrangements. The Company also holds other telecommunications infrastructure, fiber and property interests that it leases primarily to communications service providers and third-party tower operators. American Tower Corporation is a holding company that conducts its operations through its directly and indirectly owned subsidiaries and joint ventures. ATC’s principal domestic operating subsidiaries are American Towers LLC and SpectraSite Communications, LLC. ATC conducts its international operations primarily through its subsidiary, American Tower International, Inc., which in turn conducts operations through its various international holding and operating subsidiaries and joint ventures. The Company operates as a real estate investment trust for U.S. federal income tax purposes (“REIT”). Accordingly, the Company generally is not required to pay U.S. federal income taxes on income generated by its REIT operations, including the income derived from leasing space on its towers, as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on earnings from its domestic taxable REIT subsidiaries (“TRSs”). In addition, the Company’s international assets and operations, regardless of their classification for U.S. tax purposes, continue to be subject to taxation in the jurisdictions where those assets are held or those operations are conducted. The use of TRSs enables the Company to continue to engage in certain businesses while complying with REIT qualification requirements. The Company may, from time to time, change the election of previously designated TRSs to be included as part of the REIT. As of December 31, 2019, the Company’s REIT-qualified businesses included its U.S. tower leasing business and a majority of its U.S. indoor DAS networks business and services segment, as well as most of its operations in Mexico, Germany, Costa Rica, Nigeria and France.
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation—The accompanying consolidated financial statements include the accounts of the Company and those entities in which it has a controlling interest. Investments in entities that the Company does not control are accounted for using the equity method or as investments in equity securities, depending upon the Company’s ability to exercise significant influence over operating and financial policies. All intercompany accounts and transactions have been eliminated.
Change in Reportable Segments	Change in Reportable Segments— During the fourth quarter of 2019, the Company’s Europe, Middle East and Africa (“EMEA”) property segment was divided into the Africa property segment and the Europe property segment. As a result, the Company has six reportable segments: U.S. property, Asia property, Africa property, Europe property, Latin America property and services, which are discussed further in note 21. The change in reportable segments had no impact on the Company’s consolidated financial statements for any periods. Historical financial information included in this Annual Report on Form 10-K has been adjusted to reflect the change in reportable segments.
Significant Accounting Policies and Use of Estimates	Significant Accounting Policies and Use of Estimates—The preparation of financial statements in conformity with accounting principles generally accepted in the United States (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results may differ from those estimates, and such differences could be material to the accompanying consolidated financial statements. The significant estimates in the accompanying consolidated financial statements include impairment of long-lived assets (including goodwill), asset retirement obligations, revenue recognition, rent expense and lease accounting, income taxes and accounting for business combinations and acquisitions of assets. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued as additional evidence for certain estimates or to identify matters that require additional disclosure.
Accounts Receivable and Deferred Rent Asset	Accounts Receivable and Deferred Rent Asset—The Company derives the largest portion of its revenues and corresponding accounts receivable and the related deferred rent asset from a relatively small number of tenants in the telecommunications industry, and 54% of its current-year revenues are derived from four tenants. The Company’s deferred rent asset is associated with non-cancellable tenant leases that contain fixed escalation clauses over the terms of the applicable lease in which revenue is recognized on a straight-line basis over the lease term. The Company mitigates its concentrations of credit risk with respect to notes and trade receivables and the related deferred rent assets by actively monitoring the creditworthiness of its borrowers and tenants. In recognizing tenant revenue, the Company assesses the collectibility of both the amounts billed and the portion recognized in advance of billing on a straight-line basis. This assessment takes tenant credit risk and business and industry conditions into consideration to ultimately determine the collectibility of the amounts billed. To the extent the amounts, based on management’s estimates, may not be collectible, revenue recognition is deferred until such point as collectibility is determined to be reasonably assured. Any amounts that were previously recognized as revenue and subsequently determined to be uncollectible are charged to bad debt expense included in Selling, general, administrative and development expense in the accompanying consolidated statements of operations. Accounts receivable is reported net of allowances for doubtful accounts related to estimated losses resulting from a tenant’s inability to make required payments and allowances for amounts invoiced whose collectibility is not reasonably assured. These allowances are generally estimated based on payment patterns, days past due and collection history, and incorporate changes in economic conditions that may not be reflected in historical trends, such as tenants in bankruptcy, liquidation or reorganization. Receivables are written-off against the allowances when they are determined to be uncollectible. Such determination includes analysis and consideration of the particular conditions of the account.
Functional Currency	Functional Currency—The functional currency of each of the Company’s foreign operating subsidiaries is normally the respective local currency, except for Costa Rica and Argentina, where the functional currency is the U.S. Dollar. All foreign currency assets and liabilities held by the subsidiaries are translated into U.S. Dollars at the exchange rate in effect at the end of the applicable fiscal reporting period and all foreign currency revenues and expenses are translated at the average monthly exchange rates. Translation adjustments are reflected in equity as a component of Accumulated other comprehensive loss (“AOCL”) in the consolidated balance sheets and included as a component of Comprehensive income in the consolidated statements of comprehensive income. Gains and losses on foreign currency transactions are reflected in Other expense in the consolidated statements of operations. However, the effect from fluctuations in foreign currency exchange rates on intercompany debt for which repayment is not anticipated in the foreseeable future is reflected in AOCL in the consolidated balance sheets and included as a component of Comprehensive income.
Cash and Cash Equivalents	Cash and Cash Equivalents—Cash and cash equivalents include cash on hand, demand deposits and short-term investments with original maturities of three months or less. The Company maintains its deposits at high-quality financial institutions and monitors the credit ratings of those institutions.
Restricted Cash	Restricted Cash—Restricted cash includes cash pledged as collateral to secure obligations and all cash whose use is otherwise limited by contractual provisions.
Property and Equipment	Property and Equipment—Property and equipment is recorded at cost or, in the case of acquired properties, at estimated fair value on the date acquired. Cost for self-constructed towers includes direct materials and labor, capitalized interest and certain indirect costs associated with construction of the tower, such as transportation costs, employee benefits and payroll taxes. The Company begins the capitalization of costs during the pre-construction period, which is the period during which costs are incurred to evaluate the site, and continues to capitalize costs until the tower is substantially completed and ready for occupancy by a tenant. Labor and related costs capitalized for the years ended December 31, 2019, 2018 and 2017 were $48.3 million, $55.0 million and $50.9 million, respectively. Capitalized interest costs were not material for the years ended December 31, 2019, 2018 and 2017. Expenditures for repairs and maintenance are expensed as incurred. Augmentation and improvements that extend an asset’s useful life or enhance capacity are capitalized. Depreciation expense is recorded using the straight-line method over the assets’ estimated useful lives. Towers and related assets on leased land are depreciated over the shorter of the estimated useful life of the asset or the term of the corresponding ground lease, taking into consideration lease renewal options and residual value. Towers or assets acquired through finance leases are recorded net at the present value of future minimum lease payments or the fair value of the leased asset at the inception of the lease. Property and equipment and assets held under finance leases are amortized over the shorter of the applicable lease term or the estimated useful life of the respective assets for periods generally not exceeding twenty years. The Company reviews its tower portfolio for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company reviews other long-lived assets for impairment whenever events, changes in circumstances or other evidence indicate that the carrying amount of the Company’s assets may not be recoverable. The Company records impairment charges in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets—The Company reviews goodwill for impairment at least annually (as of December 31) or whenever events or circumstances indicate the carrying value of an asset may not be recoverable. Goodwill is recorded in the applicable segment and assessed for impairment at the reporting unit level. The Company utilizes the two-step impairment test and employs a discounted cash flow analysis when testing goodwill for impairment. The key assumptions utilized in the discounted cash flow analysis include current operating performance, terminal sales growth rate, management’s expectations of future operating results and cash requirements, the current weighted average cost of capital and an expected tax rate. Under the first step of the test, the Company compares the fair value of the reporting unit, as calculated under an income approach using future discounted cash flows, to the carrying amount of the applicable reporting unit. If the carrying amount exceeds the fair value, the Company conducts the second step of this test, in which the implied fair value of the applicable reporting unit’s goodwill is compared to the carrying amount of that goodwill. If the carrying amount of goodwill exceeds its implied fair value, an impairment loss would be recognized for the amount of the excess. During the years ended December 31, 2019, 2018 and 2017, no potential impairment was identified under the first step of the test, as the fair value of each of the reporting units was in excess of its carrying amount. Intangible assets that are separable from goodwill and are deemed to have a definite life are amortized over their useful lives, generally ranging from three to twenty years and are evaluated separately for impairment at least annually or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. The Company reviews its network location intangible assets for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company monitors its tenant-related intangible assets on a tenant by tenant basis for indicators of impairment, such as high levels of turnover or attrition, non-renewal of a significant number of contracts or the cancellation or termination of a relationship. The Company assesses recoverability by determining whether the carrying amount of the related assets will be recovered primarily through projected undiscounted future cash flows. If the Company determines that the carrying amount of an asset may not be recoverable, the Company measures any impairment loss based on the projected future discounted cash flows to be provided from the asset or available market information relative to the asset’s fair value, as compared to the asset’s carrying amount. The Company records impairment charges, which are discussed in note 17, in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment.
Derivatives Financial Instruments	Derivative Financial Instruments—Derivatives are recorded on the consolidated balance sheet at fair value. If a derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in AOCL, as well as a component of comprehensive income, and are recognized in the results of operations when the hedged item affects earnings. Changes in fair value of the ineffective portions of cash flow hedges are recognized in the results of operations. For derivative instruments that are designated and qualify as fair value hedges, changes in value of the derivatives are recorded in Other expense in the consolidated statements of operations in the current period, along with the offsetting gain or loss on the hedged item attributable to the hedged risk. For derivative instruments not designated as hedging instruments, changes in fair value are recognized in the results of operations in the period that the change occurs. The primary risks managed through the use of derivative instruments is interest rate risk, exposure to changes in the fair value of debt attributable to interest rate risk and currency risk. From time to time, the Company enters into interest rate swap agreements or foreign currency contracts to manage exposure to these risks. Under these agreements, the Company is exposed to counterparty credit risk to the extent that a counterparty fails to meet the terms of a contract. The Company’s exposure is limited to the current value of the contract at the time the counterparty fails to perform. The Company assesses, both at the inception of the hedge and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in cash flows or fair values of hedged items. The Company does not hold derivatives for trading purposes.
Fair Value Measurements	Fair Value Measurements—The Company determines the fair value of its financial instruments based on the fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value.
Asset Retirement Obligations	Asset Retirement Obligations—When required, the Company recognizes the fair value of obligations to remove its tower assets and remediate the leased land upon which certain of its tower assets are located. Generally, the associated retirement costs are capitalized as part of the carrying amount of the related tower assets and depreciated over their estimated useful lives and the liability is accreted through the obligation’s estimated settlement date. Fair value estimates of asset retirement obligations generally involve discounting of estimated future cash flows associated with takedown costs. Periodic accretion of such liabilities due to the passage of time is included in Depreciation, amortization and accretion expense in the consolidated statements of operations. Adjustments are also made to the asset retirement obligation liability to reflect changes in the estimates of timing and amount of expected cash flows, with an offsetting adjustment made to the related long-lived tangible asset. The significant assumptions used in estimating the Company’s aggregate asset retirement obligation are: timing of tower removals; cost of tower removals; timing and number of land lease renewals; expected inflation rates; and credit-adjusted, risk-free interest rates that approximate the Company’s incremental borrowing rate.
Income Taxes	Income Taxes—As a REIT, the Company generally is not subject to U.S. federal income taxes on income generated by its REIT operations as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on certain earnings and continues to be subject to taxation in its foreign jurisdictions. Accordingly, the consolidated financial statements reflect provisions for federal, state, local and foreign income taxes. The Company recognizes deferred tax assets and liabilities for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, as well as operating loss and tax credit carryforwards. The Company measures deferred tax assets and liabilities using enacted tax rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities as a result of a change in tax rates is recognized in income in the period that includes the enactment date. The Company periodically reviews its deferred tax assets, and provides valuation allowances if, based on the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Valuation allowances would be reversed as a reduction to the provision for income taxes if related deferred tax assets are deemed realizable based on changes in facts and circumstances relevant to the assets’ recoverability. The Company classifies uncertain tax positions as income tax liabilities in Other non-current liabilities in the consolidated balance sheet, unless expected to be paid within one year. The Company reports penalties and tax-related interest expense as a component of the income tax provision and interest income from tax refunds as a component of Interest income in the consolidated statements of operations.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss)—Other comprehensive income (loss) refers to items excluded from net income that are recorded as an adjustment to equity, net of tax. The Company’s other comprehensive income (loss) primarily consisted of changes in fair value of effective derivative cash flow hedges, foreign currency translation adjustments and reclassification of unrealized losses on effective derivative cash flow hedges.
Distributions	Distributions—As a REIT, the Company must annually distribute to its stockholders an amount equal to at least 90% of its REIT taxable income (determined before the deduction for distributed earnings and excluding any net capital gain). Generally, the Company has distributed, and expects to continue to distribute, all or substantially all of its REIT taxable income after taking into consideration its utilization of net operating losses (“NOLs”). The amount, timing and frequency of future distributions will be at the sole discretion of the Board of Directors and will depend upon various factors, a number of which may be beyond the Company’s control, including the Company’s financial condition and operating cash flows, the amount required to maintain its qualification for taxation as a REIT and reduce any income and excise taxes that the Company otherwise would be required to pay, limitations on distributions in the Company’s existing and future debt and preferred equity instruments, the Company’s ability to utilize NOLs to offset the Company’s distribution requirements, limitations on its ability to fund distributions using cash generated through its TRSs and other factors that the Board of Directors may deem relevant.
Acquisitions	Acquisitions—For acquisitions that meet the definition of a business combination, the Company applies the acquisition method of accounting where assets acquired and liabilities assumed are recorded at fair value at the date of each acquisition, and the results of operations are included with those of the Company from the dates of the respective acquisitions. Any excess of the purchase price paid by the Company over the amounts recognized for assets acquired and liabilities assumed is recorded as goodwill. The Company continues to evaluate acquisitions for a period not to exceed one year after the applicable acquisition date of each transaction to determine whether any additional adjustments are needed to the allocation of the purchase price paid for the assets acquired and liabilities assumed. All other acquisitions are accounted for as asset acquisitions and the purchase price is allocated to the net assets acquired with no recognition of goodwill. The purchase price is not subsequently adjusted. The fair value of the assets acquired and liabilities assumed is typically determined by using either estimates of replacement costs or discounted cash flow valuation methods. When determining the fair value of tangible assets acquired, the Company must estimate the cost to replace the asset with a new asset taking into consideration such factors as age, condition and the economic useful life of the asset. When determining the fair value of intangible assets acquired and liabilities assumed, the Company must estimate the applicable discount rate and the timing and amount of future cash flows, including rate and terms of renewal and attrition.
Lessor, Leases	Lease—The new lease standard requires leases to be accounted for using a right-of-use model, which recognizes that, at the date of commencement, a lessee has a financial obligation to make lease payments to the lessor for the right to use the underlying asset during the lease term. The lessee recognizes a corresponding right-of-use asset related to this right. On January 1, 2019, the Company elected to adopt the new lease standard using the modified retrospective method applied to lease arrangements that were in place on the transition date. Results for reporting periods beginning January 1, 2019 are presented under the new standard, while prior-period amounts are not adjusted and continue to be reported in accordance with accounting under the previously applicable guidance. The Company elected certain available practical expedients which permit the adopter to not reassess certain items upon adoption, including: (i) whether any existing contracts are or contain leases, (ii) the classification of existing leases and (iii) initial direct costs for existing leases. The Company also elected the practical expedient related to easements, which permits carryforward accounting treatment for land easements on existing agreements. The Company recorded a net increase to opening Distributions in excess of earnings in its consolidated balance sheet of $24.7 million as of January 1, 2019 due to the cumulative impact of adopting the new lease standard. This adjustment related to right-of-use asset impairments. The Company also recorded a lease liability of $6.9 billion and a corresponding right-of-use asset of $7.1 billion upon adoption of the new lease standard. Those rights and obligations are primarily related to operating leases for ground space underneath the Company’s communications sites. The right-of-use assets recorded include, among other items, amounts previously classified as prepaid rent, deferred lease acquisition costs, fair value adjustments on acquired leases and long-term deferred rent obligations. Finance leases, which primarily relate to towers, equipment and vehicles, were largely unchanged. There was no significant change to the Company’s consolidated statements of operations resulting from the adoption of this standard. The Company did not elect the practical expedient for short-term leases, which permits an adopter to not apply the lease standard to leases with a remaining maturity of one year or less, and applied the new lease accounting standard to all leases, including short-term leases. In conjunction with the adoption of the new lease accounting guidance, the Company applied the lessor and lessee practical expedient and no longer separates lease and non-lease components within a lease agreement when the timing and pattern of revenue recognition for the components are the same and the combined single lease component is classified as an operating lease. Certain amounts, such as power and fuel and common area maintenance, which were previously reported as non-lease revenue, are now accounted for as lease revenue. Accordingly, the Company has reclassified certain prior-period amounts within its disclosures.
Revenue Recognition	Revenue—The Company’s revenue is derived from leasing the right to use its communications sites and the land on which the sites are located (the “lease component”) and from the reimbursement of costs incurred by the Company in operating the communications sites and supporting the tenants’ equipment as well as other services and contractual rights (the “non-lease component”). Most of the Company’s revenue is derived from leasing arrangements and is accounted for as lease revenue unless the timing and pattern of revenue recognition of the non-lease component differs from the lease component. If the timing and pattern of the non-lease component revenue recognition differs from that of the lease component, the Company separately determines the stand-alone selling prices and pattern of revenue recognition for each performance obligation. Revenue related to DAS networks and fiber and other related assets results from agreements with tenants that are not leases. The Company’s revenue from leasing arrangements, including fixed escalation clauses present in non-cancellable lease arrangements, is reported on a straight-line basis over the term of the respective leases when collectibility is probable. Escalation clauses tied to a consumer price index (“CPI”), or other inflation-based indices, and other incentives present in lease agreements with the Company’s tenants are excluded from the straight-line calculation. Total property straight-line revenues for the years ended December 31, 2019, 2018 and 2017 were $183.5 million, $87.6 million and $194.4 million, respectively. Non-lease revenue—Non-lease revenue consists primarily of revenue generated from DAS networks, fiber and other property related revenue. DAS networks and fiber arrangements require that the Company provide the tenant the right to use the applicable communications infrastructure. Performance obligations are satisfied over time for the duration of the arrangements. Other property related revenue streams, which include site inspections, are not material on either an individual or consolidated basis. Services revenue—The Company offers tower-related services in the United States. These services include AZP and structural analysis. There is a single performance obligation related to AZP and revenue is recognized over time based on milestones achieved, which are determined based on costs expected to be incurred. Structural analysis services may have more than one performance obligation, contingent upon the number of contracted services. Revenue is recognized at the point in time the services are completed. Some of the Company’s contracts with tenants contain multiple performance obligations. For these arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price, which is typically based on the price charged to tenants. Since most of the Company’s contracts are leases, costs to enter into lease arrangements are capitalized under the applicable lease accounting guidance. Costs incurred to obtain non-lease contracts that are capitalized primarily relate to DAS networks and are not material to the consolidated financial statements. The Company has excluded sales tax, value-added tax and similar taxes from non-lease revenue. The Company records unearned revenue when payments are received from tenants in advance of the completion of the Company’s performance obligations. Long-term unearned revenue is included in Other non-current liabilities. During the year ended December 31, 2019, the Company recognized $62.2 million of revenue that was included in the Unearned revenue balance as of December 31, 2018. During the year ended December 31, 2018, the Company recognized $44.4 million of revenue that was included in the Unearned revenue balance as of January 1, 2018. The Company also recognized revenues of $59.2 million and $55.4 million during the years ended December 31, 2019 and December 31, 2018, respectively, for capital contributions related to DAS networks. There was $0.4 million of revenue recognized from Other non-current liabilities during each of the years ended December 31, 2019 and 2018. The Company records unbilled receivables, which are included in Prepaids and other current assets, when it has completed a performance obligation prior to its ability to bill under the customer arrangement. Other contract assets are included in Notes receivable and other non-current assets. The Company did not record any change in unbilled receivables attributable to non-lease property revenue recognized during each of the years ended December 31, 2019 and 2018. The change in contract assets attributable to revenue recognized during the years ended December 31, 2019 and 2018 was $3.1 million and $1.5 million, respectively. The Company does not disclose the value of unsatisfied performance obligations for agreements (i) with an original expected length of one year or less or (ii) for which it recognizes revenue at the amount to which it has the right to invoice for services performed.
Rent Expense and Lease Accounting	Rent Expense and Lease Accounting—Many of the leases underlying the Company’s tower sites have fixed rent escalations, which provide for periodic increases in the amount of ground rent payable by the Company over time. In addition, certain of the Company’s tenant leases require the Company to exercise available renewal options pursuant to the underlying ground lease if the tenant exercises its renewal option. The Company calculates straight-line ground rent expense for these leases based on the fixed non-cancellable term of the underlying ground lease plus all periods, if any, for which failure to renew the lease imposes an economic penalty to the Company such that renewal appears to be reasonably assured. Effective January 1, 2019, the Company adopted the new lease standard using the modified retrospective method applied to lease arrangements that were in place on the transition date. The new lease accounting guidance required the Company to recognize a right-of-use lease asset and lease liability for operating and finance leases. The right-of-use asset is measured as the sum of the lease liability, prepaid or accrued lease payments, any initial direct costs incurred and any other applicable amounts. The calculation of the lease liability requires the Company to make certain assumptions for each lease, including lease term and discount rate implicit in each lease, which could significantly impact the gross lease obligation, the duration and the present value of the lease liability. When calculating the lease term, the Company considers the renewal, cancellation and termination rights available to the Company and the lessor. The Company determines the discount rate by calculating the incremental borrowing rate on a collateralized basis at the commencement of a lease or upon a change in the lease term.
Selling, General, Administrative and Development Expense	Selling, General, Administrative and Development Expense—Selling, general and administrative expense consists of overhead expenses related to the Company’s property and services operations and corporate overhead costs not specifically allocable to any of the Company’s individual business operations. Development expense consists of costs related to the Company’s acquisition efforts, costs associated with new business initiatives and project cancellation costs.
Stock-Based Compensation	Stock-Based Compensation—Stock-based compensation expense is measured at the accounting measurement date based on the fair value of the award and is generally recognized as an expense over the service period, which typically represents the vesting period. The Company provides for accelerated vesting and extended exercise periods of stock options and restricted stock units upon an employee’s death or permanent disability, or upon an employee’s qualified retirement, provided certain eligibility criteria are met. Accordingly, the Company recognizes compensation expense for stock options and time-based restricted stock units (“RSUs”) over the shorter of (i) the four-year vesting period or (ii) the period from the date of grant to the date the employee becomes eligible for such benefits due to death, disability or qualified retirement, which may occur upon grant. The expense recognized includes the impact of forfeitures as they occur. The Company grants performance-based restricted stock units (“PSUs”) to its executive officers. Threshold, target and maximum parameters are established for a three-year performance period at the time of grant. The metrics are used to calculate the number of shares that will be issuable when the awards vest, which may range from zero to 200% of the target amounts. The Company recognizes compensation expense for PSUs over the three-year vesting period, subject to adjustment based on the date the employee becomes eligible for retirement benefits as well as performance relative to grant parameters. The fair value of stock options is determined using the Black-Scholes option-pricing model and the fair value of RSUs and PSUs is based on the fair value of the Company’s common stock on the date of grant. The Company recognizes all stock-based compensation expense in either Selling, general, administrative and development expense, costs of operations or as part of the costs associated with the construction of the tower assets. In connection with the vesting of restricted stock units, the Company withholds from issuance a number of shares of common stock to satisfy certain employee tax withholding obligations arising from such vesting. The shares withheld are considered constructively retired. The Company recognizes the fair value of the shares withheld in Additional paid-in capital on the consolidated balance sheets.
Litigation Costs	Litigation Costs—The Company periodically becomes involved in various claims and lawsuits that are incidental to its business. The Company regularly monitors the status of pending legal actions to evaluate both the magnitude and likelihood of any potential loss. The Company accrues for these potential losses when it is probable that a liability has been incurred and the amount of loss, or possible range of loss, can be reasonably estimated. Should the ultimate losses on contingencies or litigation vary from estimates, adjustments to those liabilities may be required. The Company also incurs legal costs in connection with these matters and records estimates of these expenses, which are reflected in Selling, general, administrative and development expense in the accompanying consolidated statements of operations.
Earnings Per Common Share-Basic and Diluted	Earnings Per Common Share—Basic and Diluted—Basic net income per common share represents net income attributable to American Tower Corporation common stockholders divided by the weighted average number of common shares outstanding during the period. Diluted net income per common share represents net income attributable to American Tower Corporation common stockholders divided by the weighted average number of common shares outstanding during the period and any dilutive common share equivalents, including (A) shares issuable upon (i) the vesting of RSUs, (ii) exercise of stock options, and (iii) conversion of the Company’s mandatory convertible preferred stock and (B) shares expected to be earned upon the achievement of the parameters established for PSUs, each to the extent not anti-dilutive. Dilutive common share equivalents also include the dilutive impact of the shares issuable in the ALLTEL transaction, which is described in note 19, through August 30, 2019. The Company uses the treasury stock method to calculate the effect of its outstanding RSUs, PSUs and stock options and used the if-converted method to calculate the effect of its outstanding mandatory convertible preferred stock.
Retirement Plan	Retirement Plan—The Company has a 401(k) plan covering substantially all employees who meet certain age and employment requirements.
Accounting Standards Updates	Accounting Standards Updates In June 2016, the Financial Accounting Standards Board (the “FASB”) issued guidance that modifies how entities measure credit losses on most financial instruments. The new guidance replaces the current "incurred loss" model with an "expected credit loss" model that requires consideration of a broader range of information to estimate expected credit losses over the lifetime of the asset. The new guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, and will be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the effective date. Operating lease receivables are not within the scope of this guidance. The Company is finalizing its analysis of the impact of this guidance on its financial statements and does not expect the adoption of this guidance to have a material impact on the Company’s financial statements. In January 2017, the FASB issued guidance on accounting for goodwill impairments. The guidance eliminates Step 2 from the goodwill impairment test and requires, among other things, recognition of an impairment loss when the carrying value of a reporting unit exceeds its fair value. The loss recognized is limited to the total amount of goodwill allocated to that reporting unit. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a material impact on the Company’s financial statements. In August 2018, the FASB issued guidance on the accounting for implementation costs incurred in a cloud computing arrangement that is a service contract. This guidance aligns the accounting for costs incurred to implement a cloud computing arrangement that is a service arrangement with the guidance on capitalizing costs associated with developing or obtaining internal-use software. The Company adopted this guidance prospectively on July 1, 2019. The adoption of this guidance did not have a material impact on the Company’s financial statements.

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Business—American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) is one of the largest global real estate investment trusts and a leading independent owner, operator and developer of multitenant communications real estate. The Company’s primary business is the leasing of space on communications sites to wireless service providers, radio and television broadcast companies, wireless data providers, government agencies and municipalities and tenants in a number of other industries. The Company refers to this business as its property operations. Additionally, the Company offers tower-related services in the United States, which the Company refers to as its services operations. These services include site acquisition, zoning and permitting (“AZP”) and structural analysis, which primarily support the Company’s site leasing business, including the addition of new tenants and equipment on its sites.

The Company’s portfolio primarily consists of towers that it owns and towers that it operates pursuant to long-term lease arrangements, as well as distributed antenna system (“DAS”) networks, which provide seamless coverage solutions in certain in-building and certain outdoor wireless environments. In addition to the communications sites in its portfolio, the Company manages rooftop and tower sites for property owners under various contractual arrangements. The Company also holds other telecommunications infrastructure, fiber and property interests that it leases primarily to communications service providers and third-party tower operators.

American Tower Corporation is a holding company that conducts its operations through its directly and indirectly owned subsidiaries and joint ventures. ATC’s principal domestic operating subsidiaries are American Towers LLC and SpectraSite Communications, LLC. ATC conducts its international operations primarily through its subsidiary, American Tower International, Inc., which in turn conducts operations through its various international holding and operating subsidiaries and joint ventures.

The Company operates as a real estate investment trust for U.S. federal income tax purposes (“REIT”). Accordingly, the Company generally is not required to pay U.S. federal income taxes on income generated by its REIT operations, including the income derived from leasing space on its towers, as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on earnings from its domestic taxable REIT subsidiaries (“TRSs”). In addition, the Company’s international assets and operations, regardless of their classification for U.S. tax purposes, continue to be subject to taxation in the jurisdictions where those assets are held or those operations are conducted.

The use of TRSs enables the Company to continue to engage in certain businesses while complying with REIT qualification requirements. The Company may, from time to time, change the election of previously designated TRSs to be included as part of the REIT. As of December 31, 2019, the Company’s REIT-qualified businesses included its U.S. tower leasing business and a majority of its U.S. indoor DAS networks business and services segment, as well as most of its operations in Mexico, Germany, Costa Rica, Nigeria and France.

Principles of Consolidation and Basis of Presentation

Principles of Consolidation and Basis of Presentation—The accompanying consolidated financial statements include the accounts of the Company and those entities in which it has a controlling interest. Investments in entities that the Company does not control are accounted for using the equity method or as investments in equity securities, depending upon the Company’s ability to exercise significant influence over operating and financial policies. All intercompany accounts and transactions have been eliminated.

Change in Reportable Segments

Change in Reportable Segments— During the fourth quarter of 2019, the Company’s Europe, Middle East and Africa (“EMEA”) property segment was divided into the Africa property segment and the Europe property segment. As a result, the Company has six reportable segments: U.S. property, Asia property, Africa property, Europe property, Latin America property and services, which are discussed further in note 21. The change in reportable segments had no impact on the Company’s consolidated financial statements for any periods. Historical financial information included in this Annual Report on Form 10-K has been adjusted to reflect the change in reportable segments.

Significant Accounting Policies and Use of Estimates

Significant Accounting Policies and Use of Estimates—The preparation of financial statements in conformity with accounting principles generally accepted in the United States (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results may differ from those estimates, and such differences could be material to the accompanying consolidated financial statements. The significant estimates in the accompanying consolidated financial statements include impairment of long-lived assets (including goodwill), asset retirement obligations, revenue recognition, rent expense and lease accounting, income taxes and accounting for business combinations and acquisitions of assets. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued as additional evidence for certain estimates or to identify matters that require additional disclosure.

Accounts Receivable and Deferred Rent Asset

Accounts Receivable and Deferred Rent Asset—The Company derives the largest portion of its revenues and corresponding accounts receivable and the related deferred rent asset from a relatively small number of tenants in the telecommunications industry, and 54% of its current-year revenues are derived from four tenants.

The Company’s deferred rent asset is associated with non-cancellable tenant leases that contain fixed escalation clauses over the terms of the applicable lease in which revenue is recognized on a straight-line basis over the lease term.

The Company mitigates its concentrations of credit risk with respect to notes and trade receivables and the related deferred rent assets by actively monitoring the creditworthiness of its borrowers and tenants. In recognizing tenant revenue, the Company assesses the collectibility of both the amounts billed and the portion recognized in advance of billing on a straight-line basis. This assessment takes tenant credit risk and business and industry conditions into consideration to ultimately determine the collectibility of the amounts billed. To the extent the amounts, based on management’s estimates, may not be collectible, revenue recognition is deferred until such point as collectibility is determined to be reasonably assured. Any amounts that were previously recognized as revenue and subsequently determined to be uncollectible are charged to bad debt expense included in Selling, general, administrative and development expense in the accompanying consolidated statements of operations.

Accounts receivable is reported net of allowances for doubtful accounts related to estimated losses resulting from a tenant’s inability to make required payments and allowances for amounts invoiced whose collectibility is not reasonably assured. These allowances are generally estimated based on payment patterns, days past due and collection history, and incorporate changes in economic conditions that may not be reflected in historical trends, such as tenants in bankruptcy, liquidation or reorganization. Receivables are written-off against the allowances when they are determined to be uncollectible. Such determination includes analysis and consideration of the particular conditions of the account.

Functional Currency

Functional Currency—The functional currency of each of the Company’s foreign operating subsidiaries is normally the respective local currency, except for Costa Rica and Argentina, where the functional currency is the U.S. Dollar. All foreign currency assets and liabilities held by the subsidiaries are translated into U.S. Dollars at the exchange rate in effect at the end of the applicable fiscal reporting period and all foreign currency revenues and expenses are translated at the average monthly exchange rates. Translation adjustments are reflected in equity as a component of Accumulated other comprehensive loss

(“AOCL”) in the consolidated balance sheets and included as a component of Comprehensive income in the consolidated statements of comprehensive income.

Gains and losses on foreign currency transactions are reflected in Other expense in the consolidated statements of operations. However, the effect from fluctuations in foreign currency exchange rates on intercompany debt for which repayment is not anticipated in the foreseeable future is reflected in AOCL in the consolidated balance sheets and included as a component of Comprehensive income.

Cash and Cash Equivalents

Cash and Cash Equivalents—Cash and cash equivalents include cash on hand, demand deposits and short-term investments with original maturities of three months or less. The Company maintains its deposits at high-quality financial institutions and monitors the credit ratings of those institutions.

Restricted Cash

Restricted Cash—Restricted cash includes cash pledged as collateral to secure obligations and all cash whose use is otherwise limited by contractual provisions.

Property and Equipment

Property and Equipment—Property and equipment is recorded at cost or, in the case of acquired properties, at estimated fair value on the date acquired. Cost for self-constructed towers includes direct materials and labor, capitalized interest and certain indirect costs associated with construction of the tower, such as transportation costs, employee benefits and payroll taxes. The Company begins the capitalization of costs during the pre-construction period, which is the period during which costs are incurred to evaluate the site, and continues to capitalize costs until the tower is substantially completed and ready for occupancy by a tenant. Labor and related costs capitalized for the years ended December 31, 2019, 2018 and 2017 were $48.3 million, $55.0 million and $50.9 million, respectively. Capitalized interest costs were not material for the years ended December 31, 2019, 2018 and 2017.

Expenditures for repairs and maintenance are expensed as incurred. Augmentation and improvements that extend an asset’s useful life or enhance capacity are capitalized.

Depreciation expense is recorded using the straight-line method over the assets’ estimated useful lives. Towers and related assets on leased land are depreciated over the shorter of the estimated useful life of the asset or the term of the corresponding ground lease, taking into consideration lease renewal options and residual value.

Towers or assets acquired through finance leases are recorded net at the present value of future minimum lease payments or the fair value of the leased asset at the inception of the lease. Property and equipment and assets held under finance leases are amortized over the shorter of the applicable lease term or the estimated useful life of the respective assets for periods generally not exceeding twenty years.

The Company reviews its tower portfolio for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company reviews other long-lived assets for impairment whenever events, changes in circumstances or other evidence indicate that the carrying amount

of the Company’s assets may not be recoverable. The Company records impairment charges in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment.

Goodwill and Other Intangible Assets

Goodwill and Other Intangible Assets—The Company reviews goodwill for impairment at least annually (as of December 31) or whenever events or circumstances indicate the carrying value of an asset may not be recoverable.

Goodwill is recorded in the applicable segment and assessed for impairment at the reporting unit level. The Company utilizes the two-step impairment test and employs a discounted cash flow analysis when testing goodwill for impairment. The key assumptions utilized in the discounted cash flow analysis include current operating performance, terminal sales growth rate, management’s expectations of future operating results and cash requirements, the current weighted average cost of capital and an expected tax rate. Under the first step of the test, the Company compares the fair value of the reporting unit, as calculated under an income approach using future discounted cash flows, to the carrying amount of the applicable reporting unit. If the carrying amount exceeds the fair value, the Company conducts the second step of this test, in which the implied fair value of the applicable reporting unit’s goodwill is compared to the carrying amount of that goodwill. If the carrying amount of goodwill exceeds its implied fair value, an impairment loss would be recognized for the amount of the excess.

During the years ended December 31, 2019, 2018 and 2017, no potential impairment was identified under the first step of the test, as the fair value of each of the reporting units was in excess of its carrying amount.

Intangible assets that are separable from goodwill and are deemed to have a definite life are amortized over their useful lives, generally ranging from three to twenty years and are evaluated separately for impairment at least annually or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable.

The Company reviews its network location intangible assets for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company monitors its tenant-related intangible assets on a tenant by tenant basis for indicators of impairment, such as high levels of turnover or attrition, non-renewal of a significant number of contracts or the cancellation or termination of a relationship. The Company assesses recoverability by determining whether the carrying amount of the related assets will be recovered primarily through projected undiscounted future cash flows. If the Company determines that the carrying amount of an asset may not be recoverable, the Company measures any impairment loss based on the projected future discounted cash flows to be provided from the asset or available market information relative to the asset’s fair value, as compared to the asset’s carrying amount. The Company records impairment charges, which are discussed in note 17, in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment.

Derivatives Financial Instruments

Derivative Financial Instruments—Derivatives are recorded on the consolidated balance sheet at fair value. If a derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in AOCL, as well as a component of comprehensive income, and are recognized in the results of operations when the hedged item affects earnings. Changes in fair value of the ineffective portions of cash flow hedges are recognized in the results of operations. For derivative instruments that are designated and qualify as fair value hedges, changes in value of the derivatives are recorded in Other expense in the consolidated statements of operations in the current period, along with the offsetting gain or loss on the hedged item attributable to the hedged risk. For derivative instruments not designated as hedging instruments, changes in fair value are recognized in the results of operations in the period that the change occurs.

The primary risks managed through the use of derivative instruments is interest rate risk, exposure to changes in the fair value of debt attributable to interest rate risk and currency risk. From time to time, the Company enters into interest rate swap agreements or foreign currency contracts to manage exposure to these risks. Under these agreements, the Company is exposed to counterparty credit risk to the extent that a counterparty fails to meet the terms of a contract. The Company’s exposure is limited to the current value of the contract at the time the counterparty fails to perform. The Company assesses, both at the inception of the hedge and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in cash flows or fair values of hedged items. The Company does not hold derivatives for trading purposes.

Fair Value Measurements

Fair Value Measurements—The Company determines the fair value of its financial instruments based on the fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value.

Asset Retirement Obligations

Asset Retirement Obligations—When required, the Company recognizes the fair value of obligations to remove its tower assets and remediate the leased land upon which certain of its tower assets are located. Generally, the associated retirement costs are capitalized as part of the carrying amount of the related tower assets and depreciated over their estimated useful lives and the

liability is accreted through the obligation’s estimated settlement date. Fair value estimates of asset retirement obligations generally involve discounting of estimated future cash flows associated with takedown costs. Periodic accretion of such liabilities due to the passage of time is included in Depreciation, amortization and accretion expense in the consolidated statements of operations. Adjustments are also made to the asset retirement obligation liability to reflect changes in the estimates of timing and amount of expected cash flows, with an offsetting adjustment made to the related long-lived tangible asset. The significant assumptions used in estimating the Company’s aggregate asset retirement obligation are: timing of tower removals; cost of tower removals; timing and number of land lease renewals; expected inflation rates; and credit-adjusted, risk-free interest rates that approximate the Company’s incremental borrowing rate.

Income Taxes

Income Taxes—As a REIT, the Company generally is not subject to U.S. federal income taxes on income generated by its REIT operations as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on certain earnings and continues to be subject to taxation in its foreign jurisdictions. Accordingly, the consolidated financial statements reflect provisions for federal, state, local and foreign income taxes. The Company recognizes deferred tax assets and liabilities for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, as well as operating loss and tax credit carryforwards. The Company measures deferred tax assets and liabilities using enacted tax rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities as a result of a change in tax rates is recognized in income in the period that includes the enactment date.

The Company periodically reviews its deferred tax assets, and provides valuation allowances if, based on the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Valuation allowances would be reversed as a reduction to the provision for income taxes if related deferred tax assets are deemed realizable based on changes in facts and circumstances relevant to the assets’ recoverability.

The Company classifies uncertain tax positions as income tax liabilities in Other non-current liabilities in the consolidated balance sheet, unless expected to be paid within one year. The Company reports penalties and tax-related interest expense as a component of the income tax provision and interest income from tax refunds as a component of Interest income in the consolidated statements of operations.

Other Comprehensive Income (Loss)

Other Comprehensive Income (Loss)—Other comprehensive income (loss) refers to items excluded from net income that are recorded as an adjustment to equity, net of tax. The Company’s other comprehensive income (loss) primarily consisted of changes in fair value of effective derivative cash flow hedges, foreign currency translation adjustments and reclassification of unrealized losses on effective derivative cash flow hedges.

Distributions

Distributions—As a REIT, the Company must annually distribute to its stockholders an amount equal to at least 90% of its REIT taxable income (determined before the deduction for distributed earnings and excluding any net capital gain). Generally, the Company has distributed, and expects to continue to distribute, all or substantially all of its REIT taxable income after taking into consideration its utilization of net operating losses (“NOLs”).

The amount, timing and frequency of future distributions will be at the sole discretion of the Board of Directors and will depend upon various factors, a number of which may be beyond the Company’s control, including the Company’s financial condition and operating cash flows, the amount required to maintain its qualification for taxation as a REIT and reduce any income and excise taxes that the Company otherwise would be required to pay, limitations on distributions in the Company’s existing and future debt and preferred equity instruments, the Company’s ability to utilize NOLs to offset the Company’s distribution requirements, limitations on its ability to fund distributions using cash generated through its TRSs and other factors that the Board of Directors may deem relevant.

Acquisitions

Acquisitions—For acquisitions that meet the definition of a business combination, the Company applies the acquisition method of accounting where assets acquired and liabilities assumed are recorded at fair value at the date of each acquisition, and the results of operations are included with those of the Company from the dates of the respective acquisitions. Any excess of the purchase price paid by the Company over the amounts recognized for assets acquired and liabilities assumed is recorded as goodwill. The Company continues to evaluate acquisitions for a period not to exceed one year after the applicable acquisition date of each transaction to determine whether any additional adjustments are needed to the allocation of the purchase price paid for the assets acquired and liabilities assumed. All other acquisitions are accounted for as asset acquisitions and the purchase price is allocated to the net assets acquired with no recognition of goodwill. The purchase price is not subsequently adjusted.

The fair value of the assets acquired and liabilities assumed is typically determined by using either estimates of replacement costs or discounted cash flow valuation methods. When determining the fair value of tangible assets acquired, the Company must estimate the cost to replace the asset with a new asset taking into consideration such factors as age, condition and the economic useful life of the asset. When determining the fair value of intangible assets acquired and liabilities assumed, the Company must estimate the applicable discount rate and the timing and amount of future cash flows, including rate and terms of renewal and attrition.

Lessor, Leases

Lease—The new lease standard requires leases to be accounted for using a right-of-use model, which recognizes that, at the date of commencement, a lessee has a financial obligation to make lease payments to the lessor for the right to use the underlying asset during the lease term. The lessee recognizes a corresponding right-of-use asset related to this right.

On January 1, 2019, the Company elected to adopt the new lease standard using the modified retrospective method applied to lease arrangements that were in place on the transition date. Results for reporting periods beginning January 1, 2019 are presented under the new standard, while prior-period amounts are not adjusted and continue to be reported in accordance with accounting under the previously applicable guidance.

The Company elected certain available practical expedients which permit the adopter to not reassess certain items upon adoption, including: (i) whether any existing contracts are or contain leases, (ii) the classification of existing leases and (iii) initial direct costs for existing leases. The Company also elected the practical expedient related to easements, which permits carryforward accounting treatment for land easements on existing agreements.

The Company recorded a net increase to opening Distributions in excess of earnings in its consolidated balance sheet of $24.7 million as of January 1, 2019 due to the cumulative impact of adopting the new lease standard. This adjustment related to right-of-use asset impairments. The Company also recorded a lease liability of $6.9 billion and a corresponding right-of-use asset of $7.1 billion upon adoption of the new lease standard. Those rights and obligations are primarily related to operating leases for ground space underneath the Company’s communications sites. The right-of-use assets recorded include, among other items, amounts previously classified as prepaid rent, deferred lease acquisition costs, fair value adjustments on acquired leases and long-term deferred rent obligations. Finance leases, which primarily relate to towers, equipment and vehicles, were largely unchanged. There was no significant change to the Company’s consolidated statements of operations resulting from the adoption of this standard.

The Company did not elect the practical expedient for short-term leases, which permits an adopter to not apply the lease standard to leases with a remaining maturity of one year or less, and applied the new lease accounting standard to all leases, including short-term leases.

In conjunction with the adoption of the new lease accounting guidance, the Company applied the lessor and lessee practical expedient and no longer separates lease and non-lease components within a lease agreement when the timing and pattern of revenue recognition for the components are the same and the combined single lease component is classified as an operating lease. Certain amounts, such as power and fuel and common area maintenance, which were previously reported as non-lease revenue, are now accounted for as lease revenue. Accordingly, the Company has reclassified certain prior-period amounts within its disclosures.

Revenue Recognition

Revenue—The Company’s revenue is derived from leasing the right to use its communications sites and the land on which the sites are located (the “lease component”) and from the reimbursement of costs incurred by the Company in operating the communications sites and supporting the tenants’ equipment as well as other services and contractual rights (the “non-lease component”). Most of the Company’s revenue is derived from leasing arrangements and is accounted for as lease revenue unless the timing and pattern of revenue recognition of the non-lease component differs from the lease component. If the timing and pattern of the non-lease component revenue recognition differs from that of the lease component, the Company separately determines the stand-alone selling prices and pattern of revenue recognition for each performance obligation. Revenue related to DAS networks and fiber and other related assets results from agreements with tenants that are not leases.

The Company’s revenue from leasing arrangements, including fixed escalation clauses present in non-cancellable lease arrangements, is reported on a straight-line basis over the term of the respective leases when collectibility is probable. Escalation clauses tied to a consumer price index (“CPI”), or other inflation-based indices, and other incentives present in lease agreements with the Company’s tenants are excluded from the straight-line calculation. Total property straight-line revenues for the years ended December 31, 2019, 2018 and 2017 were $183.5 million, $87.6 million and $194.4 million, respectively.

Non-lease revenue—Non-lease revenue consists primarily of revenue generated from DAS networks, fiber and other property related revenue. DAS networks and fiber arrangements require that the Company provide the tenant the right to use the

applicable communications infrastructure. Performance obligations are satisfied over time for the duration of the arrangements. Other property related revenue streams, which include site inspections, are not material on either an individual or consolidated basis.

Services revenue—The Company offers tower-related services in the United States. These services include AZP and structural analysis. There is a single performance obligation related to AZP and revenue is recognized over time based on milestones achieved, which are determined based on costs expected to be incurred. Structural analysis services may have more than one performance obligation, contingent upon the number of contracted services. Revenue is recognized at the point in time the services are completed.

Some of the Company’s contracts with tenants contain multiple performance obligations. For these arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price, which is typically based on the price charged to tenants.

Since most of the Company’s contracts are leases, costs to enter into lease arrangements are capitalized under the applicable lease accounting guidance. Costs incurred to obtain non-lease contracts that are capitalized primarily relate to DAS networks and are not material to the consolidated financial statements. The Company has excluded sales tax, value-added tax and similar taxes from non-lease revenue.

The Company records unearned revenue when payments are received from tenants in advance of the completion of the Company’s performance obligations. Long-term unearned revenue is included in Other non-current liabilities. During the year ended December 31, 2019, the Company recognized $62.2 million of revenue that was included in the Unearned revenue balance as of December 31, 2018. During the year ended December 31, 2018, the Company recognized $44.4 million of

revenue that was included in the Unearned revenue balance as of January 1, 2018. The Company also recognized revenues of $59.2 million and $55.4 million during the years ended December 31, 2019 and December 31, 2018, respectively, for capital contributions related to DAS networks. There was $0.4 million of revenue recognized from Other non-current liabilities during each of the years ended December 31, 2019 and 2018.

The Company records unbilled receivables, which are included in Prepaids and other current assets, when it has completed a performance obligation prior to its ability to bill under the customer arrangement. Other contract assets are included in Notes receivable and other non-current assets. The Company did not record any change in unbilled receivables attributable to non-lease property revenue recognized during each of the years ended December 31, 2019 and 2018. The change in contract assets attributable to revenue recognized during the years ended December 31, 2019 and 2018 was $3.1 million and $1.5 million, respectively.

The Company does not disclose the value of unsatisfied performance obligations for agreements (i) with an original expected length of one year or less or (ii) for which it recognizes revenue at the amount to which it has the right to invoice for services performed.

Rent Expense and Lease Accounting

Rent Expense and Lease Accounting—Many of the leases underlying the Company’s tower sites have fixed rent escalations, which provide for periodic increases in the amount of ground rent payable by the Company over time. In addition, certain of the Company’s tenant leases require the Company to exercise available renewal options pursuant to the underlying ground lease if the tenant exercises its renewal option. The Company calculates straight-line ground rent expense for these leases based on the fixed non-cancellable term of the underlying ground lease plus all periods, if any, for which failure to renew the lease imposes an economic penalty to the Company such that renewal appears to be reasonably assured.

Effective January 1, 2019, the Company adopted the new lease standard using the modified retrospective method applied to lease arrangements that were in place on the transition date. The new lease accounting guidance required the Company to recognize a right-of-use lease asset and lease liability for operating and finance leases. The right-of-use asset is measured as the sum of the lease liability, prepaid or accrued lease payments, any initial direct costs incurred and any other applicable amounts.

The calculation of the lease liability requires the Company to make certain assumptions for each lease, including lease term and discount rate implicit in each lease, which could significantly impact the gross lease obligation, the duration and the present value of the lease liability. When calculating the lease term, the Company considers the renewal, cancellation and termination rights available to the Company and the lessor. The Company determines the discount rate by calculating the incremental borrowing rate on a collateralized basis at the commencement of a lease or upon a change in the lease term.

Selling, General, Administrative and Development Expense

Selling, General, Administrative and Development Expense—Selling, general and administrative expense consists of overhead expenses related to the Company’s property and services operations and corporate overhead costs not specifically allocable to any of the Company’s individual business operations. Development expense consists of costs related to the Company’s acquisition efforts, costs associated with new business initiatives and project cancellation costs.

Stock-Based Compensation

Stock-Based Compensation—Stock-based compensation expense is measured at the accounting measurement date based on the fair value of the award and is generally recognized as an expense over the service period, which typically represents the vesting period. The Company provides for accelerated vesting and extended exercise periods of stock options and restricted stock units upon an employee’s death or permanent disability, or upon an employee’s qualified retirement, provided certain eligibility criteria are met. Accordingly, the Company recognizes compensation expense for stock options and time-based restricted stock units (“RSUs”) over the shorter of (i) the four-year vesting period or (ii) the period from the date of grant to the date the employee becomes eligible for such benefits due to death, disability or qualified retirement, which may occur upon grant. The expense recognized includes the impact of forfeitures as they occur.

The Company grants performance-based restricted stock units (“PSUs”) to its executive officers. Threshold, target and maximum parameters are established for a three-year performance period at the time of grant. The metrics are used to calculate the number of shares that will be issuable when the awards vest, which may range from zero to 200% of the target amounts. The Company recognizes compensation expense for PSUs over the three-year vesting period, subject to adjustment based on the date the employee becomes eligible for retirement benefits as well as performance relative to grant parameters.

The fair value of stock options is determined using the Black-Scholes option-pricing model and the fair value of RSUs and PSUs is based on the fair value of the Company’s common stock on the date of grant. The Company recognizes all stock-based

compensation expense in either Selling, general, administrative and development expense, costs of operations or as part of the costs associated with the construction of the tower assets.

In connection with the vesting of restricted stock units, the Company withholds from issuance a number of shares of common stock to satisfy certain employee tax withholding obligations arising from such vesting. The shares withheld are considered constructively retired. The Company recognizes the fair value of the shares withheld in Additional paid-in capital on the consolidated balance sheets.

Litigation Costs

Litigation Costs—The Company periodically becomes involved in various claims and lawsuits that are incidental to its business. The Company regularly monitors the status of pending legal actions to evaluate both the magnitude and likelihood of any potential loss. The Company accrues for these potential losses when it is probable that a liability has been incurred and the amount of loss, or possible range of loss, can be reasonably estimated. Should the ultimate losses on contingencies or litigation vary from estimates, adjustments to those liabilities may be required. The Company also incurs legal costs in connection with these matters and records estimates of these expenses, which are reflected in Selling, general, administrative and development expense in the accompanying consolidated statements of operations.

Earnings Per Common Share-Basic and Diluted

Earnings Per Common Share—Basic and Diluted—Basic net income per common share represents net income attributable to American Tower Corporation common stockholders divided by the weighted average number of common shares outstanding during the period. Diluted net income per common share represents net income attributable to American Tower Corporation common stockholders divided by the weighted average number of common shares outstanding during the period and any dilutive common share equivalents, including (A) shares issuable upon (i) the vesting of RSUs, (ii) exercise of stock options, and (iii) conversion of the Company’s mandatory convertible preferred stock and (B) shares expected to be earned upon the achievement of the parameters established for PSUs, each to the extent not anti-dilutive. Dilutive common share equivalents also include the dilutive impact of the shares issuable in the ALLTEL transaction, which is described in note 19, through August 30, 2019. The Company uses the treasury stock method to calculate the effect of its outstanding RSUs, PSUs and stock options and used the if-converted method to calculate the effect of its outstanding mandatory convertible preferred stock.

Retirement Plan

Retirement Plan—The Company has a 401(k) plan covering substantially all employees who meet certain age and employment requirements.

Accounting Standards Updates

In June 2016, the Financial Accounting Standards Board (the “FASB”) issued guidance that modifies how entities measure credit losses on most financial instruments. The new guidance replaces the current "incurred loss" model with an "expected credit loss" model that requires consideration of a broader range of information to estimate expected credit losses over the lifetime of the asset. The new guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, and will be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the effective date. Operating lease receivables are not within the scope of this guidance. The Company is finalizing its analysis of the impact of this guidance on its financial statements and does not expect the adoption of this guidance to have a material impact on the Company’s financial statements.

In January 2017, the FASB issued guidance on accounting for goodwill impairments. The guidance eliminates Step 2 from the goodwill impairment test and requires, among other things, recognition of an impairment loss when the carrying value of a reporting unit exceeds its fair value. The loss recognized is limited to the total amount of goodwill allocated to that reporting unit. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a material impact on the Company’s financial statements.

In August 2018, the FASB issued guidance on the accounting for implementation costs incurred in a cloud computing arrangement that is a service contract. This guidance aligns the accounting for costs incurred to implement a cloud computing arrangement that is a service arrangement with the guidance on capitalizing costs associated with developing or obtaining internal-use software. The Company adopted this guidance prospectively on July 1, 2019. The adoption of this guidance did not have a material impact on the Company’s financial statements.