American Tower (AMT) 10-Q 29 Apr 21 2021 Q1 Quarterly report Financial data

COVER

COVER - shares	3 Months Ended
	Mar. 31, 2021	Apr. 22, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-14195
Entity Registrant Name	AMERICAN TOWER CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	65-0723837
Entity Address, Address Line One	116 Huntington Avenue
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02116
City Area Code	617
Local Phone Number	375-7500
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		444,797,395
Entity Central Index Key	0001053507
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock, $0.01 par value
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	AMT
Security Exchange Name	NYSE
1.375% Senior Notes due 2025
Document Information [Line Items]
Title of 12(b) Security	1.375% Senior Notes due 2025
Trading Symbol	AMT 25A
Security Exchange Name	NYSE
1.950% Senior Notes due 2026
Document Information [Line Items]
Title of 12(b) Security	1.950% Senior Notes due 2026
Trading Symbol	AMT 26B
Security Exchange Name	NYSE
0.500% Notes
Document Information [Line Items]
Title of 12(b) Security	0.500% Senior Notes due 2028
Trading Symbol	AMT 28A
Security Exchange Name	NYSE
1.000% Notes
Document Information [Line Items]
Title of 12(b) Security	1.000% Senior Notes due 2032
Trading Symbol	AMT 32
Security Exchange Name	NYSE

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 1,913.6	$ 1,746.3
Restricted cash	79.7	115.1
Accounts receivable, net	537.7	511.6
Prepaid and other current assets	490.6	532.6
Total current assets	3,021.6	2,905.6
PROPERTY AND EQUIPMENT, net	12,712.5	12,808.7
GOODWILL	7,262.4	7,282.7
OTHER INTANGIBLE ASSETS, net	13,507.3	13,839.8
DEFERRED TAX ASSET	127.3	123.1
DEFERRED RENT ASSET	2,197.4	2,084.3
RIGHT-OF-USE ASSET	7,719.9	7,789.2
NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS	394.1	400.1
TOTAL	46,942.5	47,233.5
CURRENT LIABILITIES:
Accounts payable	130.1	139.1
Accrued expenses	944.8	1,043.7
Distributions payable	555.8	544.6
Accrued interest	167.1	207.8
Current portion of operating lease liability	555.8	539.9
Current portion of long-term obligations	1,336.5	789.8
Unearned revenue	506.5	390.6
Total current liabilities	4,196.6	3,655.5
LONG-TERM OBLIGATIONS	27,990.3	28,497.7
OPERATING LEASE LIABILITY	6,812.9	6,884.4
ASSET RETIREMENT OBLIGATIONS	1,574.6	1,571.3
DEFERRED TAX LIABILITY	854.7	859.5
OTHER NON-CURRENT LIABILITIES	961.6	984.6
Total liabilities	42,390.7	42,453
COMMITMENTS AND CONTINGENCIES
REDEEMABLE NONCONTROLLING INTERESTS	212.9	212.1
EQUITY (shares in thousands):
Common stock: $.01 par value; 1,000,000 shares authorized; 455,708 and 455,245 shares issued; and 444,793 and 444,330 shares outstanding, respectively	4.6	4.6
Additional paid-in capital	10,474.6	10,473.7
Distributions in excess of earnings	(1,251.8)	(1,343)
Accumulated other comprehensive loss	(4,061.6)	(3,759.4)
Treasury stock (10,915 shares at cost)	(1,282.4)	(1,282.4)
Total American Tower Corporation equity	3,883.4	4,093.5
Noncontrolling interests	455.5	474.9
Total equity	4,338.9	4,568.4
TOTAL	$ 46,942.5	$ 47,233.5

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Common stock, par value (in usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	455,708,000	455,245,000
Common stock, shares outstanding (in shares)	444,793,000	444,330,000
Treasury stock, shares (in shares)	10,915,000	10,915,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
REVENUES:
Total operating revenues	$ 2,158.5	$ 1,993.1
Costs of operations (exclusive of items shown separately below):
Property	563.3	544.1
Depreciation, amortization and accretion	522.5	472.3
Selling, general, administrative and development expense	182.6	217.8
Other operating expenses	50.4	14.2
Total operating expenses	1,329.8	1,256.3
OPERATING INCOME	828.7	736.8
OTHER INCOME (EXPENSE):
Interest expense	(207)	(208.8)
Loss on retirement of long-term obligations	(25.7)	(34.6)
Other income (expense) (including foreign currency gains (losses) of $94.7 and $(65.5), respectively)	95.2	(63.8)
Total other expense	(126.1)	(297.1)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	702.6	439.7
Income tax provision	(50.3)	(21.1)
NET INCOME	652.3	418.6
Net income attributable to noncontrolling interests	(7.3)	(3.6)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 645	$ 415
NET INCOME PER COMMON SHARE AMOUNTS:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.45	$ 0.94
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.45	$ 0.93
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING (in thousands):
BASIC (in shares)	444,486	443,055
DILUTED (in shares)	446,294	445,832
Interest income	$ 11.4	$ 10.1
Property
REVENUES:
Total operating revenues	2,129.7	1,973.2
Services
REVENUES:
Total operating revenues	28.8	19.9
Costs of operations (exclusive of items shown separately below):
Services	$ 11	$ 7.9

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Foreign currency (losses) gains	$ 94.7	$ (65.5)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 652.3	$ 418.6
Other comprehensive income (loss):
Changes in fair value of cash flow hedges, each net of tax expense of $0	0	0
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	0	0
Foreign currency translation adjustments, each net of tax benefit of $(0.0)	(323.7)	(1,343.5)
Other comprehensive loss	(323.7)	(1,343.5)
Comprehensive income (loss)	328.6	(924.9)
Allocation of accumulated other comprehensive income (loss) resulting from purchases of redeemable noncontrolling interests	0.1	(142.2)
Comprehensive loss attributable to noncontrolling interests	14.1	34
Comprehensive income (loss) attributable to American Tower Corporation stockholders	$ 342.8	$ (1,033.1)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Changes in fair value of cash flow hedges, tax	$ 0	$ 0
Reclassification of unrealized gains on cash flow hedges to net income, tax	0	0
Foreign currency translation adjustments, tax expense (benefit)	$ 0	$ 0

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 652.3	$ 418.6
Adjustments to reconcile net income to cash provided by operating activities
Depreciation, amortization and accretion	522.5	472.3
Stock-based compensation expense	38	47.7
Loss on early retirement of long-term obligations	25.7	34.6
Other non-cash items reflected in statements of operations	(87.5)	81.6
Increase in net deferred rent balances	(119.9)	(56.2)
Right-of-use asset and Operating lease liability, net	4.1	1
Decrease (increase) in assets	18.1	(210.8)
Increase in liabilities	39.4	11.2
Cash provided by operating activities	1,092.7	800
Payments to acquire towers	324.8	214.4
CASH FLOWS FROM INVESTING ACTIVITIES
Payments for acquisitions, net of cash acquired	(114.8)	(49.3)
Proceeds from sale of short-term investments and other non-current assets	4.4	5.8
Deposits and other	(3.5)	4.5
Cash used for investing activities	(438.7)	(253.4)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings under credit facilities	1,870	2,642.3
Proceeds from issuance of senior notes, net	1,398.1	1,496
Proceeds from term loan	0	750
Repayments of notes payable, credit facilities, senior notes, secured debt, term loan and finance leases	(3,071.3)	(4,351.2)
Distributions to noncontrolling interest holders, net	(8.1)	(13.5)
Purchases of common stock	0	(39.7)
Proceeds from stock options	1.9	11.1
Distributions paid on common stock	(544.9)	(454.9)
Payment for early retirement of long-term obligations	(61.9)	(33.5)
Deferred financing costs and other financing activities	(61.3)	(88.2)
Purchase of redeemable noncontrolling interest	(2.5)	(524.4)
Cash used for financing activities	(480)	(606)
Net effect of changes in foreign currency exchange rates on cash and cash equivalents, and restricted cash	(42.1)	(118.3)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH	131.9	(177.7)
CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH, BEGINNING OF PERIOD	1,861.4	1,578
CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH, END OF PERIOD	1,993.3	1,400.3
CASH PAID FOR INCOME TAXES (NET OF REFUNDS OF $24.8 AND $0.1, RESPECTIVELY)	5.8	35.1
CASH PAID FOR INTEREST	239.1	262
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment under finance leases and perpetual easements	10.5	13.1
Decrease in accounts payable and accrued expenses for purchases of property and equipment and construction activities	(34.4)	(15)
Settlement of third-party debt	$ 0	$ (5)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Cash Flows [Abstract]
Income tax refunds	$ 24.8	$ 0.1

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Distributions in Excess of Earnings	Noncontrolling Interests
BEGINNING BALANCE (shares) at Dec. 31, 2019		453,541	10,651
BEGINNING BALANCE at Dec. 31, 2019	$ 5,490.4	$ 4.5	$ (1,226.4)	$ 10,117.7	$ (2,823.6)	$ (1,016.8)	$ 435
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation related activity (shares)		655
Stock-based compensation related activity	(4.3)	$ 0		(4.3)
Treasury stock activity (shares)			(213)
Treasury stock activity	(45.1)		$ (45.1)
Changes in fair value of cash flow hedges, net of tax	0				0
Reclassification of unrealized losses on cash flow hedges to net income, net of tax	0				0
Foreign currency translation adjustment, net of tax	(1,311.4)				(1,305.9)		(5.5)
Distributions to noncontrolling interest	(1.5)						(1.5)
Common stock distributions declared	(480.7)					(480.7)
Net income	417.2					415	2.2
ENDING BALANCE (shares) at Mar. 31, 2020		454,196	10,864
ENDING BALANCE at Mar. 31, 2020	4,064.6	$ 4.5	$ (1,271.5)	10,255.6	(4,271.7)	(1,082.5)	430.2
BEGINNING BALANCE (shares) at Dec. 31, 2020		455,245	10,915
BEGINNING BALANCE at Dec. 31, 2020	4,568.4	$ 4.6	$ (1,282.4)	10,473.7	(3,759.4)	(1,343)	474.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation related activity (shares)		437
Stock-based compensation related activity	(0.7)	$ 0		(0.7)
Changes in fair value of cash flow hedges, net of tax	0				0
Reclassification of unrealized losses on cash flow hedges to net income, net of tax	0				0
Foreign currency translation adjustment, net of tax	(323.5)				(302.3)		(21.2)
Distributions to noncontrolling interest	(0.3)						(0.3)
Redemption of noncontrolling interest (shares)		26
Redemption of noncontrolling interest		$ 0		1.7			(1.7)
Purchase of redeemable noncontrolling interest	0			(0.1)	0.1
Common stock distributions declared	(553.8)					(553.8)
Net income	648.8					645	3.8
ENDING BALANCE (shares) at Mar. 31, 2021		455,708	10,915
ENDING BALANCE at Mar. 31, 2021	$ 4,338.9	$ 4.6	$ (1,282.4)	$ 10,474.6	$ (4,061.6)	$ (1,251.8)	$ 455.5

BASIS OF PRESENTATION AND SIGNI

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES	BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES The accompanying consolidated and condensed consolidated financial statements have been prepared by American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The financial information included herein is unaudited. However, the Company believes that all adjustments, which are of a normal and recurring nature, considered necessary for a fair presentation of its financial position and results of operations for such periods have been included herein. The consolidated and condensed consolidated financial statements and related notes should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 (the “2020 Form 10-K”). The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results that may be expected for the entire year. Principles of Consolidation and Basis of Presentation —The accompanying consolidated and condensed 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. As of March 31, 2021, the Company holds (i) a 51% controlling interest in ATC Europe B.V. (“ATC Europe”), a joint venture that primarily consists of the Company’s operations in France, Germany and Poland (PGGM holds a 49% noncontrolling interest) and (ii) a 92% controlling interest in ATC Telecom Infrastructure Private Limited (“ATC TIPL”), formerly Viom Networks Limited (“Viom”), in India. Reportable Segments — During the fourth quarter of 2020, as a result of the Company’s acquisition of InSite Wireless Group, LLC (“InSite,” and the acquisition, the “InSite Acquisition”), the Company updated its reportable segments to rename U.S. property and Asia property to U.S. & Canada property and Asia-Pacific property, respectively. The Company continues to report its results in six segments – U.S. & Canada property, Asia-Pacific property, Africa property, Europe property, Latin America property and services, which are discussed further in note 15. The change in reportable segment names is solely reflective of the inclusion of Canada and Australia in the Company’s business operations, as a result of the InSite Acquisition, and had no impact on the Company’s consolidated financial statements or historical segment financial information for any prior periods. Significant Accounting Policies —The Company’s significant accounting policies are described in note 1 to the Company’s consolidated financial statements included in the 2020 Form 10-K. There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2021. Cash and Cash Equivalents and Restricted Cash —The reconciliation of cash and cash equivalents and restricted cash reported within the applicable balance sheet that sum to the total of the same such amounts shown in the statement of cash flows is as follows: Three Months Ended March 31, 2021 2020 Cash and cash equivalents $ 1,913.6 $ 1,326.0 Restricted cash 79.7 74.3 Total cash, cash equivalents and restricted cash $ 1,993.3 $ 1,400.3 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 distributed antenna system (“DAS”) networks and fiber and other related assets results from agreements with tenants that are not leases. 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. There were no material changes in the receivables, contract assets and contract liabilities from contracts with tenants for the three months ended March 31, 2021. Services revenue —The Company offers tower-related services in the United States. These services include site application, zoning and permitting (“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. A summary of revenue disaggregated by source and geography is as follows: Three Months Ended March 31, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 71.6 $ 2.5 $ 4.9 $ 2.2 $ 31.9 $ 113.1 Services revenue 28.8 — — — — 28.8 Total non-lease revenue $ 100.4 $ 2.5 $ 4.9 $ 2.2 $ 31.9 $ 141.9 Property lease revenue 1,159.7 278.9 230.8 42.4 304.8 2,016.6 Total revenue $ 1,260.1 $ 281.4 $ 235.7 $ 44.6 $ 336.7 $ 2,158.5 Three Months Ended March 31, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 58.6 $ 2.2 $ 2.9 $ 1.5 $ 32.9 $ 98.1 Services revenue 19.9 — — — — 19.9 Total non-lease revenue $ 78.5 $ 2.2 $ 2.9 $ 1.5 $ 32.9 $ 118.0 Property lease revenue 1,031.3 284.4 222.6 33.0 303.8 1,875.1 Total revenue $ 1,109.8 $ 286.6 $ 225.5 $ 34.5 $ 336.7 $ 1,993.1 Accounting Standards Updates In March 2020, the Financial Accounting Standards Board (the “FASB”) issued guidance to provide optional expedients and exceptions for applying accounting principles generally accepted in the United States to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The guidance applies only to contracts, hedging relationships and other transactions that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. The expedients and exceptions provided by the guidance do not apply to contract modifications made and hedging relationships entered into or evaluated after December 31, 2022, except for hedging relationships existing as of December 31, 2022 for which an entity has elected certain optional expedients that are retained through the end of the hedging relationship. In January 2021, the FASB issued additional guidance that clarifies that certain practical expedients and exceptions for contract modifications and hedge accounting apply to derivatives that are affected by reference rate reform. As of March 31, 2021, the Company has not modified any contracts as a result of reference rate reform and is evaluating the impact this standard may have on its financial statements.

PREPAID AND OTHER CURRENT ASSET

PREPAID AND OTHER CURRENT ASSETS	3 Months Ended
	Mar. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID AND OTHER CURRENT ASSETS	PREPAID AND OTHER CURRENT ASSETS Prepaid and other current assets consisted of the following: As of March 31, 2021 December 31, 2020 Prepaid assets $ 76.2 $ 66.1 Prepaid income tax 100.3 143.7 Unbilled receivables 160.8 176.9 Value added tax and other consumption tax receivables 58.1 66.3 Other miscellaneous current assets 95.2 79.6 Prepaid and other current assets $ 490.6 $ 532.6

LEASES

LEASES	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
LEASES	LEASES The Company determines if an arrangement is a lease at the inception of the agreement. The Company considers an arrangement to be a lease if it conveys the right to control the use of the communications site or ground space underneath a communications site for a period of time in exchange for consideration. The Company is both a lessor and a lessee. During the three months ended March 31, 2021, the Company made no changes to the methods described in note 4 to its consolidated financial statements included in the 2020 Form 10-K. As of March 31, 2021, the Company does not have any material related party leases as either a lessor or a lessee. To the extent there are any intercompany leases, these are eliminated in consolidation. Lessor — Historically, the Company has been able to successfully renew its ground leases as needed to ensure continuation of its tower revenue. Accordingly, the Company assumes that it will have access to the land underneath its tower sites when calculating future minimum rental receipts. Future minimum rental receipts expected under non-cancellable operating lease agreements as of March 31, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 4,632.2 2022 5,976.8 2023 5,866.5 2024 5,755.9 2025 5,330.3 Thereafter 32,576.0 Total $ 60,137.7 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods. Lessee —The Company assesses its right-of-use asset and other lease-related assets for impairment, as described in note 1 to the Company’s consolidated financial statements included in the 2020 Form 10-K. There were no material impairments recorded related to these assets during the three months ended March 31, 2021 and 2020. The Company leases certain land and office space under operating leases and land and improvements, towers and vehicles under finance leases. As of March 31, 2021, operating lease assets were included in Right-of-use asset and finance lease assets were included in Property and equipment, net in the consolidated balance sheet. During the three months ended March 31, 2021, there were no material changes in the terms and provisions of the Company’s operating leases in which the Company is a lessee. There were no material changes in finance lease assets and liabilities during the three months ended March 31, 2021. Information about other lease-related balances is as follows: As of March 31, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 7,719.9 $ 7,789.2 Current portion of lease liability $ 555.8 $ 539.9 Lease liability 6,812.9 6,884.4 Total operating lease liability $ 7,368.7 $ 7,424.3 The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of March 31, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.6 13.7 Weighted-average incremental borrowing rate 5.6 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended March 31, 2021 2020 Operating lease cost $ 251.3 $ 250.7 Variable lease costs not included in lease liability (1) 69.3 61.4 _______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (244.9) $ (252.0) Non-cash items: New operating leases (1) $ 89.2 $ 50.1 Operating lease modifications and reassessments $ 85.7 $ 96.9 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions. As of March 31, 2021, the Company does not have material operating or financing leases that have not yet commenced. Maturities of operating lease liabilities as of March 31, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 678.3 2022 874.6 2023 842.7 2024 805.2 2025 759.8 Thereafter 6,497.9 Total lease payments 10,458.5 Less amounts representing interest (3,089.8) Total lease liability 7,368.7 Less current portion of lease liability 555.8 Non-current lease liability $ 6,812.9 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods.
LEASES	LEASES The Company determines if an arrangement is a lease at the inception of the agreement. The Company considers an arrangement to be a lease if it conveys the right to control the use of the communications site or ground space underneath a communications site for a period of time in exchange for consideration. The Company is both a lessor and a lessee. During the three months ended March 31, 2021, the Company made no changes to the methods described in note 4 to its consolidated financial statements included in the 2020 Form 10-K. As of March 31, 2021, the Company does not have any material related party leases as either a lessor or a lessee. To the extent there are any intercompany leases, these are eliminated in consolidation. Lessor — Historically, the Company has been able to successfully renew its ground leases as needed to ensure continuation of its tower revenue. Accordingly, the Company assumes that it will have access to the land underneath its tower sites when calculating future minimum rental receipts. Future minimum rental receipts expected under non-cancellable operating lease agreements as of March 31, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 4,632.2 2022 5,976.8 2023 5,866.5 2024 5,755.9 2025 5,330.3 Thereafter 32,576.0 Total $ 60,137.7 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods. Lessee —The Company assesses its right-of-use asset and other lease-related assets for impairment, as described in note 1 to the Company’s consolidated financial statements included in the 2020 Form 10-K. There were no material impairments recorded related to these assets during the three months ended March 31, 2021 and 2020. The Company leases certain land and office space under operating leases and land and improvements, towers and vehicles under finance leases. As of March 31, 2021, operating lease assets were included in Right-of-use asset and finance lease assets were included in Property and equipment, net in the consolidated balance sheet. During the three months ended March 31, 2021, there were no material changes in the terms and provisions of the Company’s operating leases in which the Company is a lessee. There were no material changes in finance lease assets and liabilities during the three months ended March 31, 2021. Information about other lease-related balances is as follows: As of March 31, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 7,719.9 $ 7,789.2 Current portion of lease liability $ 555.8 $ 539.9 Lease liability 6,812.9 6,884.4 Total operating lease liability $ 7,368.7 $ 7,424.3 The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of March 31, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.6 13.7 Weighted-average incremental borrowing rate 5.6 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended March 31, 2021 2020 Operating lease cost $ 251.3 $ 250.7 Variable lease costs not included in lease liability (1) 69.3 61.4 _______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (244.9) $ (252.0) Non-cash items: New operating leases (1) $ 89.2 $ 50.1 Operating lease modifications and reassessments $ 85.7 $ 96.9 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions. As of March 31, 2021, the Company does not have material operating or financing leases that have not yet commenced. Maturities of operating lease liabilities as of March 31, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 678.3 2022 874.6 2023 842.7 2024 805.2 2025 759.8 Thereafter 6,497.9 Total lease payments 10,458.5 Less amounts representing interest (3,089.8) Total lease liability 7,368.7 Less current portion of lease liability 555.8 Non-current lease liability $ 6,812.9 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods.
LEASES	LEASES The Company determines if an arrangement is a lease at the inception of the agreement. The Company considers an arrangement to be a lease if it conveys the right to control the use of the communications site or ground space underneath a communications site for a period of time in exchange for consideration. The Company is both a lessor and a lessee. During the three months ended March 31, 2021, the Company made no changes to the methods described in note 4 to its consolidated financial statements included in the 2020 Form 10-K. As of March 31, 2021, the Company does not have any material related party leases as either a lessor or a lessee. To the extent there are any intercompany leases, these are eliminated in consolidation. Lessor — Historically, the Company has been able to successfully renew its ground leases as needed to ensure continuation of its tower revenue. Accordingly, the Company assumes that it will have access to the land underneath its tower sites when calculating future minimum rental receipts. Future minimum rental receipts expected under non-cancellable operating lease agreements as of March 31, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 4,632.2 2022 5,976.8 2023 5,866.5 2024 5,755.9 2025 5,330.3 Thereafter 32,576.0 Total $ 60,137.7 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods. Lessee —The Company assesses its right-of-use asset and other lease-related assets for impairment, as described in note 1 to the Company’s consolidated financial statements included in the 2020 Form 10-K. There were no material impairments recorded related to these assets during the three months ended March 31, 2021 and 2020. The Company leases certain land and office space under operating leases and land and improvements, towers and vehicles under finance leases. As of March 31, 2021, operating lease assets were included in Right-of-use asset and finance lease assets were included in Property and equipment, net in the consolidated balance sheet. During the three months ended March 31, 2021, there were no material changes in the terms and provisions of the Company’s operating leases in which the Company is a lessee. There were no material changes in finance lease assets and liabilities during the three months ended March 31, 2021. Information about other lease-related balances is as follows: As of March 31, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 7,719.9 $ 7,789.2 Current portion of lease liability $ 555.8 $ 539.9 Lease liability 6,812.9 6,884.4 Total operating lease liability $ 7,368.7 $ 7,424.3 The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of March 31, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.6 13.7 Weighted-average incremental borrowing rate 5.6 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended March 31, 2021 2020 Operating lease cost $ 251.3 $ 250.7 Variable lease costs not included in lease liability (1) 69.3 61.4 _______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (244.9) $ (252.0) Non-cash items: New operating leases (1) $ 89.2 $ 50.1 Operating lease modifications and reassessments $ 85.7 $ 96.9 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions. As of March 31, 2021, the Company does not have material operating or financing leases that have not yet commenced. Maturities of operating lease liabilities as of March 31, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 678.3 2022 874.6 2023 842.7 2024 805.2 2025 759.8 Thereafter 6,497.9 Total lease payments 10,458.5 Less amounts representing interest (3,089.8) Total lease liability 7,368.7 Less current portion of lease liability 555.8 Non-current lease liability $ 6,812.9 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods.

GOODWILL AND OTHER INTANGIBLE A

GOODWILL AND OTHER INTANGIBLE ASSETS	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND OTHER INTANGIBLE ASSETS	GOODWILL AND OTHER INTANGIBLE ASSETS The changes in the carrying value of goodwill for each of the Company’s business segments were as follows: Property Services Total U.S. & Canada Asia-Pacific Africa Europe Latin America Balance as of January 1, 2021 $ 4,750.8 $ 1,016.9 $ 625.6 $ 279.1 $ 608.3 $ 2.0 $ 7,282.7 Additions and adjustments (1) 21.3 (0.0) — — — — 21.3 Effect of foreign currency translation 4.2 (0.5) (3.4) (11.1) (30.8) — (41.6) Balance as of March 31, 2021 $ 4,776.3 $ 1,016.4 $ 622.2 $ 268.0 $ 577.5 $ 2.0 $ 7,262.4 _______________ (1) Consists of an aggregate of $21.3 million of measurement period adjustments related to the InSite Acquisition. The Company’s other intangible assets subject to amortization consisted of the following: As of March 31, 2021 As of December 31, 2020 Estimated Useful Gross Accumulated Net Book Gross Accumulated Net Book Acquired network location intangibles (1) Up to 20 $ 5,751.7 $ (2,171.1) $ 3,580.6 $ 5,784.0 $ (2,117.6) $ 3,666.4 Acquired tenant-related intangibles Up to 20 14,221.7 (4,379.6) 9,842.1 14,322.5 (4,237.5) 10,085.0 Acquired licenses and other intangibles 3-20 94.6 (10.0) 84.6 97.8 (9.4) 88.4 Total other intangible assets $ 20,068.0 $ (6,560.7) $ 13,507.3 $ 20,204.3 $ (6,364.5) $ 13,839.8 _______________ (1) Acquired network location intangibles are amortized over the shorter of the term of the corresponding ground lease, taking into consideration lease renewal options and residual value, generally up to 20 years, as the Company considers these intangibles to be directly related to the tower assets. The acquired network location intangibles represent the value to the Company of the incremental revenue growth that could potentially be obtained from leasing the excess capacity on acquired communications sites. The acquired tenant- related intangibles typically represent the value to the Company of tenant contracts and relationships in place at the time of an acquisition or similar transaction, including assumptions regarding estimated renewals. The Company amortizes its acquired network location intangibles and tenant-related intangibles on a straight-line basis over their estimated useful lives. As of March 31, 2021, the remaining weighted average amortization period of the Company’s intangible assets was 15 years. Amortization of intangible assets for the three months ended March 31, 2021 and 2020 was $253.4 million and $217.5 million, respectively. Based on current exchange rates, the Company expects to record amortization expense as follows over the remaining current year and the five subsequent years: Fiscal Year Amount Remainder of 2021 $ 735.9 2022 975.8 2023 954.5 2024 944.9 2025 914.5 2026 873.2

ACCRUED EXPENSES

ACCRUED EXPENSES	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consisted of the following: As of March 31, 2021 December 31, 2020 Accrued construction costs $ 37.8 $ 46.5 Accrued income tax payable 22.3 20.6 Accrued pass-through costs 78.3 67.1 Amounts payable for acquisitions 15.7 58.9 Amounts payable to tenants 63.5 66.4 Accrued property and real estate taxes 222.0 219.1 Accrued rent 81.0 82.6 Payroll and related withholdings 67.1 104.4 Other accrued expenses 357.1 378.1 Total accrued expenses $ 944.8 $ 1,043.7

LONG-TERM OBLIGATIONS

LONG-TERM OBLIGATIONS	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
LONG-TERM DEBT OBLIGATIONS	LONG-TERM OBLIGATIONS Outstanding amounts under the Company’s long-term obligations, reflecting discounts, premiums, debt issuance costs and fair value adjustments due to interest rate swaps consisted of the following: As of March 31, 2021 December 31, 2020 Maturity Date 2020 Term Loan (1) (2) $ — $ 749.4 N/A 2021 Multicurrency Credit Facility (1) 270.0 — June 28, 2024 2019 Term Loan (1) 995.8 996.1 January 31, 2025 2021 Credit Facility (1) 2,345.0 2,295.0 January 31, 2026 2.250% senior notes 604.0 605.1 January 15, 2022 4.70% senior notes 699.2 699.0 March 15, 2022 3.50% senior notes 996.5 996.1 January 31, 2023 3.000% senior notes 718.7 721.9 June 15, 2023 0.600% senior notes 497.1 496.8 January 15, 2024 5.00% senior notes 1,001.2 1,001.3 February 15, 2024 3.375% senior notes 646.0 645.7 May 15, 2024 2.950% senior notes 643.4 643.1 January 15, 2025 2.400% senior notes 745.3 745.0 March 15, 2025 1.375% senior notes (3) 580.2 604.1 April 4, 2025 4.000% senior notes 744.8 744.3 June 1, 2025 1.300% senior notes 495.6 495.4 September 15, 2025 4.400% senior notes 497.2 497.1 February 15, 2026 1.600% senior notes 694.4 — April 15, 2026 1.950% senior notes (3) 581.2 605.2 May 22, 2026 3.375% senior notes 989.9 989.5 October 15, 2026 3.125% senior notes 398.0 397.9 January 15, 2027 2.750% senior notes 744.5 744.3 January 15, 2027 3.55% senior notes 745.0 744.8 July 15, 2027 0.500% senior notes (3) 871.2 907.4 January 15, 2028 3.600% senior notes 693.6 693.4 January 15, 2028 1.500% senior notes 645.3 645.1 January 31, 2028 3.950% senior notes 590.8 590.6 March 15, 2029 3.800% senior notes 1,633.9 1,633.5 August 15, 2029 2.900% senior notes 741.9 741.7 January 15, 2030 2.100% senior notes 740.5 740.2 June 15, 2030 1.875% senior notes 790.8 790.5 October 15, 2030 2.700% senior notes 693.3 — April 15, 2031 1.000% senior notes (3) 754.5 786.1 January 15, 2032 3.700% senior notes 591.9 591.9 October 15, 2049 3.100% senior notes 1,037.8 1,037.7 June 15, 2050 2.950% senior notes 538.3 538.2 January 15, 2051 Total American Tower Corporation debt 26,956.8 26,113.4 Series 2013-2A securities (4) 1,297.0 1,296.6 March 15, 2023 Series 2018-1A securities (4) 494.8 494.6 March 15, 2028 Series 2015-2 notes (5) 522.2 522.1 June 16, 2025 InSite Debt (6) — 800.0 N/A Other subsidiary debt (7) 26.1 32.9 Various Total American Tower subsidiary debt 2,340.1 3,146.2 Finance lease obligations 29.9 27.9 Total 29,326.8 29,287.5 Less current portion of long-term obligations (1,336.5) (789.8) Long-term obligations $ 27,990.3 $ 28,497.7 _______________ (1) Accrues interest at a variable rate. (2) Repaid in full on February 5, 2021 using borrowings from the 2021 Multicurrency Credit Facility (as defined below) and cash on hand. (3) Notes are denominated in Euros (“EUR”). (4) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (5) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (6) Debt entered into by certain InSite subsidiaries acquired in connection with the InSite Acquisition (the “InSite Debt”). On January 15, 2021, all amounts outstanding under the InSite Debt were repaid. (7) Includes (a) the Colombian credit facility, which is denominated in Colombian Pesos (“COP”) and amortizes through April 24, 2021, (b) debt entered into by the Company’s Kenyan subsidiary in connection with an acquisition of sites in Kenya, which is denominated in U.S. Dollars (“USD”) and is payable either (i) in future installments subj ect to the satisfaction of specified conditions or (ii) three years from the note origination date, and (c) U.S. subsidiary debt related to a seller-financed acquisition. Current portion of long-term obligations— The Company’s current portion of long-term obligations primarily includes (i) $600.0 million aggregate principal amount of 2.250% senior unsecured notes due January 15, 2022 and (ii) $700.0 million aggregate principal amount of 4.70% senior unsecured notes due March 15, 2022. Securitized Debt— Cash flows generated by the sites that secure the securitized debt of the Company are only available for payment of such debt and are not available to pay the Company’s other obligations or the claims of its creditors. However, subject to certain restrictions, the Company holds the right to receive the excess cash flows not needed to service the securitized debt and other obligations arising out of the securitizations. The securitized debt is the obligation of the issuers thereof or borrowers thereunder, as applicable, and their subsidiaries, and not of the Company or its other subsidiaries. Repayment of InSite Debt— The InSite Debt included securitizations entered into by certain InSite subsidiaries. The Company acquired this debt in connection with the InSite Acquisition. The InSite Debt was recorded at fair value upon acquisition. On January 15, 2021, the Company repaid the entire amount outstanding under the InSite Debt, plus accrued and unpaid interest up to, but excluding, January 15, 2021, for an aggregate redemption price of $826.4 million, including $2.3 million in accrued and unpaid interest. The Company recorded a loss on retirement of long-term obligations of approximately $25.7 million, which includes prepayment consideration partially offset by the unamortized fair value adjustment recorded upon acquisition. The repayment of the InSite Debt was funded with borrowings under the 2021 Multicurrency Credit Facility and the 2021 Credit Facility (as defined below) and cash on hand. Offerings of Senior Notes 1.600% Senior Notes and 2.700% Senior Notes Offering— On March 29, 2021, the Company completed a registered public offering of $700.0 million aggregate principal amount of 1.600% senior unsecured notes due 2026 (the “1.600% Notes”) and $700.0 million aggregate principal amount of 2.700% senior unsecured notes due 2031 (the “2.700% Notes” and, together with the 1.600% Notes, the “Notes”). The net proceeds from this offering were approximately $1,386.3 million , after deducting commissions and estimated expenses. The Company used all of the net proceeds to repay existing indebtedness under the 2021 Multicurrency Credit Facility. The key terms of the Notes are as follows: Senior Notes Aggregate Principal Amount (in millions) Issue Date and Interest Accrual Date Maturity Date Contractual Interest Rate First Interest Payment Interest Payments Due (1) Par Call Date (2) 1.600% Notes $ 700.0 March 29, 2021 April 15, 2026 1.600 % October 15, 2021 April 15 and October 15 March 15, 2026 2.700% Notes $ 700.0 March 29, 2021 April 15, 2031 2.700 % October 15, 2021 April 15 and October 15 January 15, 2031 ___________ (1) Accrued and unpaid interest is payable in USD semi-annually in arrears and will be computed from the issue date on the basis of a 360-day year comprised of twelve 30-day months. (2) The Company may redeem the Notes at any time, in whole or in part, at a redemption price equal to 100% of the principal amount of the Notes plus a make-whole premium, together with accrued interest to the redemption date. If the Company redeems the Notes on or after the par call date, the Company will not be required to pay a make-whole premium. If the Company undergoes a change of control and corresponding ratings decline, each as defined in the supplemental indenture for the Notes, the Company may be required to repurchase all of the Notes at a purchase price equal to 101% of the principal amount of such Notes, plus accrued and unpaid interest (including additional interest, if any), up to but not including the repurchase date. The Notes rank equally with all of the Company’s other senior unsecured debt and are structurally subordinated to all existing and future indebtedness and other obligations of its subsidiaries. The supplemental indenture contains certain covenants that restrict the Company’s ability to merge, consolidate or sell assets and its (together with its subsidiaries’) ability to incur liens. These covenants are subject to a number of exceptions, including that the Company and its subsidiaries may incur certain liens on assets, mortgages or other liens securing indebtedness if the aggregate amount of indebtedness secured by such liens does not exceed 3.5x Adjusted EBITDA, as defined in the applicable supplemental indenture. Bank Facilities Amendments to Bank Facilities —On February 10, 2021, the Company amended and restated its senior unsecured multicurrency revolving credit facility (as amended, the “2021 Multicurrency Credit Facility”) and its senior unsecured revolving credit facility (as amended, the “2021 Credit Facility”) and entered into an amendment agreement with respect to its $1.0 billion unsecured term loan, as amended and restated in December 2019 (as amended, the “2019 Term Loan”). These amendments, among other things, i. extend the maturity dates by one year to June 28, 2024 and January 31, 2026 for the 2021 Multicurrency Credit Facility and the 2021 Credit Facility, respectively, ii. increase the commitments under the 2021 Multicurrency Credit Facility and the 2021 Credit Facility to $4.1 billion and $2.9 billion, respectively, of which 1.3 billion EUR borrowed under the 2021 Multicurrency Credit Facility is to be reserved to finance the Pending Telxius Acquisition (as defined in note 14), iii. increase the maximum Revolving Loan Commitments, after giving effect to any Incremental Commitments (each as defined in the loan agreements for each of the 2021 Multicurrency Credit Facility and the 2021 Credit Facility) to $6.1 billion and $4.4 billion under the 2021 Multicurrency Credit Facility and the 2021 Credit Facility, respectively, iv. expand the sublimit for multicurrency borrowings under the 2021 Multicurrency Credit Facility from $1.0 billion to $3.0 billion and add a EUR borrowing option for the 2021 Credit Facility with a $1.5 billion sublimit, v. amend the limitation of the Company’s permitted ratio of Total Debt to Adjusted EBITDA (each as defined in each of the loan agreements for each of the facilities) to be no greater than 7.50 to 1.00 for the four fiscal quarters following the consummation of the Pending Telxius Acquisition, stepping down to 6.00 to 1.00 thereafter (with a further step up to 7.00 to 1.00 if the Company consummates a Qualified Acquisition (as defined in each of the loan agreements for the facilities)), vi. amend the limitation on indebtedness of, and guaranteed by, the Company’s subsidiaries to the greater of (a) $3.0 billion and (b) 50% of Adjusted EBITDA (as defined in each of the loan agreements for the facilities) of the Company and its subsidiaries on a consolidated basis and vii. increase the threshold for certain defaults with respect to judgments, attachments or acceleration of indebtedness from $400.0 million to $500.0 million. 2021 Multicurrency Credit Facility— During the three months ended March 31, 2021, the Company borrowed an aggregate of $1.8 billion and repaid an aggregate of $1.6 billion of revolving indebtedness under the 2021 Multicurrency Credit Facility. The Company used the borrowings to repay existing indebtedness, including the InSite Debt and its $750.0 million unsecured term loan due February 12, 2021 (the “2020 Term Loan”), and for general corporate purposes. 2021 Credit Facility— During the three months ended March 31, 2021, the Company borrowed an aggregate of $50.0 million and made no repayments of revolving indebtedness under the 2021 Credit Facility. The Company used the borrowings for general corporate purposes. Repayment of the 2020 Term Loan —On February 5, 2021, the Company repaid all amounts outstanding under the 2020 Term Loan with borrowings from the 2021 Multicurrency Credit Facility and cash on hand. 2021 Delayed Draw Term Loans —On February 10, 2021, the Company entered into (i) a 1.1 billion EUR (approximately $1.3 billion at the date of signing) unsecured term loan, the proceeds of which are to be used to fund the Pending Telxius Acquisition, with a maturity date that is 364 days from the date of the first draw thereunder and that bears interest at a rate based on the senior unsecured debt rating of the Company, which, based on the Company’s current debt ratings, is 1.000% above the Euro Interbank Offered Rate (“EURIBOR”) (the “2021 364-Day Delayed Draw Term Loan”) and (ii) an 825.0 million EUR (approximately $1.0 billion at the date of signing) unsecured term loan, the proceeds of which are to be used to fund the Pending Telxius Acquisition, with a maturity date that is three years from the date of the first draw thereunder and that bears interest at a rate based on the senior unsecured debt rating of the Company, which, based on the Company’s current debt ratings, is 1.125% above EURIBOR (the “2021 Three Year Delayed Draw Term Loan,” and, together with the 2021 364-Day Delayed Draw Term Loan, the “2021 Delayed Draw Term Loans”). The loan agreements for the 2021 Delayed Draw Term Loans contain certain reporting, information, financial and operating covenants and other restrictions (including limitations on additional debt, guaranties, sales of assets and liens) with which the Company must comply. Failure to comply with the financial and operating covenants of the loan agreements could not only prevent the Company from being able to borrow additional funds under the revolving credit facilities, but may constitute a default, which could result in, among other things, the amounts outstanding, including all accrued interest and unpaid fees, becoming immediately due and payable. Bridge Facility —In connection with entering into the Pending Telxius Acquisition, the Company entered into a commitment letter (the “Commitment Letter”), dated January 13, 2021, with Bank of America, N.A. and BofA Securities, Inc. (together, “BofA”) pursuant to which BofA has, with respect to bridge financing, committed to provide up to 7.5 billion EUR (approximately $9.1 billion at the date of signing) in bridge loans (the “Bridge Loan Commitment”) to ensure financing for the Pending Telxius Acquisition. Effective February 10, 2021, the Bridge Loan Commitment was reduced to 4.275 billion EUR (approximately $5.2 billion at the date of signing) as a result of an aggregate of 3.225 billion EUR (approximately $3.9 billion at the date of signing) of additional committed amounts under the 2021 Multicurrency Credit Facility, the 2021 Credit Facility and the 2021 Delayed Draw Term Loans, as described above. The Commitment Letter contains, and the credit agreement in respect of the Bridge Loan Commitment, if any, will contain, certain customary conditions to funding, including, without limitation, (i) the execution and delivery of definitive financing agreements for the Bridge Loan Commitment and (ii) other customary closing conditions set forth in the Commitment Letter. The Company will pay certain customary commitment fees and, in the event it makes any borrowings in connection with the Bridge Loan Commitment, funding and other fees. India Credit Facility —During the three months ended March 31, 2021, the Company entered into a working capital facility in India with a borrowing capacity of 1.0 billion Indian Rupees (“INR”) (approximately $13.7 million). The working capital facility is subject to annual renewal and bears interest at a rate equal to the one-month India Treasury Bill rate at the time of borrowing plus a spread. As of March 31, 2021, the Company has not borrowed under this facility. As of March 31, 2021, the key terms under the 2021 Multicurrency Credit Facility, the 2021 Credit Facility, the 2019 Term Loan, the 2021 364-Day Delayed Draw Term Loan, the 2021 Three Year Delayed Draw Term Loan and the Bridge Loan Commitment were as follows: Outstanding Principal Balance Undrawn letters of credit Maturity Date Current margin over LIBOR or EURIBOR (1) Current commitment fee (2) 2021 Multicurrency Credit Facility $ 270.0 $ 3.8 June 28, 2024 (3) 1.125 % 0.110 % 2021 Credit Facility $ 2,345.0 $ 0.8 January 31, 2026 (3) 1.125 % 0.110 % 2019 Term Loan $ 1,000.0 N/A January 31, 2025 1.125 % N/A 2021 364-Day Delayed Draw Term Loan — N/A N/A (4) 1.000 % 0.110 % 2021 Three Year Delayed Draw Term Loan — N/A N/A (4) 1.125 % 0.110 % Bridge Loan Commitment (5) — N/A N/A (5) 1.125 % 0.110 % _______________ (1) LIBOR, which means the London Interbank Offered Rate, applies to the 2021 Multicurrency Credit Facility, the 2021 Credit Facility and the 2019 Term Loan. EURIBOR, which means the Euro Interbank Offered Rate, applies to the 2021 Delayed Draw Term Loans and the Bridge Loan Commitment. (2) Fee on undrawn portion of each credit facility. (3) Subject to two optional renewal periods. (4) The maturity dates for the 2021 364-Day Delayed Draw Term Loan and the 2021 Three Year Delayed Draw Term Loan are 364 days and three years, respectively, from the date of the first borrowing under each facility. As of March 31, 2021, no borrowings were made under these facilities, and as such, no maturity dates have been set. The Company’s ability to borrow thereunder is subject to the occurrence of certain conditions related to the Pending Telxius Acquisition, as set forth in the agreements for the 2021 Delayed Draw Term Loans.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
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. Below are the three levels of inputs that may be used to measure fair value: Level 1 Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Items Measured at Fair Value on a Recurring Basis —The fair values of the Company’s financial assets and liabilities that are required to be measured on a recurring basis at fair value were as follows: March 31, 2021 December 31, 2020 Fair Value Measurements Using Fair Value Measurements Using Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets: Interest rate swap agreements — $ 24.5 — — $ 29.2 — Liabilities: Interest rate swap agreements — $ 0.0 — — $ 0.1 — Fair value of debt related to interest rate swap agreements (1) $ 26.3 — — $ 31.4 — — _______________ (1) Included in the carrying values of the corresponding debt obligations. During the three months ended March 31, 2021, the Company made no changes to the methods described in note 12 to its consolidated financial statements included in the 2020 Form 10-K that it used to measure the fair value of its interest rate swap agreements. Items Measured at Fair Value on a Nonrecurring Basis Assets Held and Used —The Company’s long-lived assets are recorded at amortized cost and, if impaired, are adjusted to fair value using Level 3 inputs. During the three months ended March 31, 2021 and 2020, the Company recorded $0.6 million and $3.7 million of impairments, respectively. There were no other items measured at fair value on a nonrecurring basis during the three months ended March 31, 2021 or 2020.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company provides for income taxes at the end of each interim period based on the estimated effective tax rate (“ETR”) for the full fiscal year. Cumulative adjustments to the Company’s estimate are recorded in the interim period in which a change in the estimated annual ETR is determined. Under the provisions of the Internal Revenue Code of 1986, as amended, the Company may deduct amounts distributed to stockholders against the income generated by its real estate investment trust (“REIT”) operations. The Company continues to be subject to income taxes on the income of its domestic taxable REIT subsidiaries and income taxes in foreign jurisdictions where it conducts operations. In addition, the Company is able to offset certain income by utilizing its net operating losses, subject to specified limitations. The Company 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 evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. The increase in the income tax provision during the three months ended March 31, 2021 as compared to the three months ended March 31, 2020 was primarily attributable to an increase in foreign earnings in the current period and higher benefits related to foreign exchange losses during the three months ended March 31, 2020. As of March 31, 2021 and December 31, 2020, the total unrecognized tax benefits that would impact the ETR, if recognized, were approximately $104.7 million and $105.9 million, respectively. The amount of unrecognized tax benefits during the three months ended March 31, 2021 includes (i) reductions due to foreign currency exchange rate fluctuations of $2.2 million, (ii) reductions to the Company’s prior year tax positions of $1.5 million and (iii) additions to the Company’s existing tax positions of $1.2 million. Unrecognized tax benefits are expected to change over the next 12 months if certain tax matters ultimately settle with the applicable taxing jurisdiction during this time frame, as described in note 13 to the Company’s consolidated financial statements included in the 2020 Form 10-K. The impact of the amount of these changes to previously recorded uncertain tax positions could range from zero to $34.2 million. The Company recorded the following penalties and income tax-related interest expense during the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 Penalties and income tax-related interest expense $ 3.7 $ 1.7

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION Summary of Stock-Based Compensation Plans —The Company maintains equity incentive plans that provide for the grant of stock-based awards to its directors, officers and employees. The 2007 Equity Incentive Plan, as amended (the “2007 Plan”), provides for the grant of non-qualified and incentive stock options, as well as restricted stock units, restricted stock and other stock-based awards. Exercise prices for non-qualified and incentive stock options are not less than the fair value of the underlying common stock on the date of grant. Equity awards typically vest ratably, generally over four years for time-based restricted stock units (“RSUs”) and stock options and three years for performance-based restricted stock units (“PSUs”). Stock options generally expire ten years from the date of grant. As of March 31, 2021, the Company had the ability to grant stock-based awards with respect to an aggregate of 5.9 million shares of common stock under the 2007 Plan. In addition, the Company maintains an employee stock purchase plan (the “ESPP”) pursuant to which eligible employees may purchase shares of the Company’s common stock on the last day of each bi-annual offering period at a 15% discount from the lower of the closing market value on the first or last day of such offering period. The offering periods run from June 1 through November 30 and from December 1 through May 31 of each year. During the three months ended March 31, 2021 and 2020, the Company recorded and capitalized the following stock-based compensation expense: Three Months Ended March 31, 2021 (1) 2020 (2) Stock-based compensation expense $ 38.0 $ 47.7 Total stock-based compensation expense $ 38.0 $ 47.7 _______________ (1) For the three months ended March 31, 2021, stock-based compensation expense consisted of $38.0 million included in selling, general, administrative and development expense. (2) For the three months ended March 31, 2020, stock-based compensation expense consisted of (i) $0.6 million included in Property costs of operations, (ii) $0.3 million included in Services costs of operations and (iii) $46.8 million included in selling, general, administrative and development expense. For the three months ended March 31, 2020, stock-based compensation expense capitalized as property and equipment was $0.5 million. Stock Options —As of March 31, 2021, total unrecognized compensation expense related to unvested stock options was less than $0.1 million, which is expected to be recognized over a weighted average period of less than one year. The Company’s option activity for the three months ended March 31, 2021 was as follows (shares disclosed in full amounts): Number of Options Outstanding as of January 1, 2021 2,016,261 Exercised (23,958) Forfeited — Expired — Outstanding as of March 31, 2021 1,992,303 Restricted Stock Units— As of March 31, 2021, total unrecognized compensation expense related to unvested RSUs granted under the 2007 Plan was $197.7 million and is expected to be recognized over a weighted average period of approximately three years. Vesting of RSUs is subject generally to the employee’s continued employment or death, disability or qualified retirement (each as defined in the applicable RSU award agreement). Performance-Based Restricted Stock Units— During the three months ended March 31, 2021, the Company’s Compensation Committee (the “Compensation Committee”) granted an aggregate of 92,312 PSUs (the “2021 PSUs”) to its executive officers and established the performance metrics for these awards. During the years ended December 31, 2020 and 2019, the Compensation Committee granted an aggregate of 110,925 PSUs (the “2020 PSUs”) and 114,823 PSUs (the “2019 PSUs”), respectively, to its executive officers and established the performance metrics for these awards. Threshold, target and maximum parameters were established for the metrics for a three three Restricted Stock Units and Performance-Based Restricted Stock Units —The Company’s RSU and PSU activity for the three months ended March 31, 2021 was as follows (shares disclosed in full amounts): RSUs PSUs Outstanding as of January 1, 2021 (1) 1,245,075 320,510 Granted (2) 538,239 92,312 Vested and Released (3) (547,567) (66,834) Forfeited (13,424) — Outstanding as of March 31, 2021 1,222,323 345,988 Vested and deferred as of March 31, 2021 (4) — 96,048 _______________ (1) PSUs consist of the target number of shares issuable at the end of the three-year performance period for the outstanding 2020 PSUs and the outstanding 2019 PSUs, or 70,739 and 86,889 shares, respectively, and the shares issuable at the end of the three-year performance period for the PSUs granted in 2018 (the “2018 PSUs”) based on achievement against the performance metrics for the three-year performance period, or 162,882 shares. (2) PSUs consist of the target number of shares issuable at the end of the three-year performance period for the 2021 PSUs, or 92,312 shares. (3) This includes 58,204 of previously vested and deferred RSUs. PSUs consist of shares vested pursuant to the 2018 PSUs. There are no additional shares to be earned related to the 2018 PSUs. (4) Vested and deferred PSUs are related to deferred compensation for certain former employees.

REDEEMABLE NONCONTROLLING INTER

REDEEMABLE NONCONTROLLING INTERESTS	3 Months Ended
	Mar. 31, 2021
Noncontrolling Interest [Abstract]
REDEEMABLE NONCONTROLLING INTERESTS	REDEEMABLE NONCONTROLLING INTERESTS India Redeemable Noncontrolling Interests —On April 21, 2016, the Company, through its wholly owned subsidiary, ATC Asia Pacific Pte. Ltd., acquired a 51% controlling ownership interest in ATC TIPL (formerly Viom), a telecommunications infrastructure company that owns and operates wireless communications towers and indoor DAS networks in India (the “Viom Acquisition”), which was subsequently merged with the Company’s existing India property operations. In connection with the Viom Acquisition, the Company, through one of its subsidiaries, entered into a shareholders agreement (the “Shareholders Agreement”) with Viom and the following remaining Viom shareholders: Tata Sons Limited (“Tata Sons”), Tata Teleservices Limited (“Tata Teleservices”), IDFC Private Equity Fund III (“IDFC”), Macquarie SBI Infrastructure Investments Pte Limited and SBI Macquarie Infrastructure Trust (together, “Macquarie,” and, collectively with Tata Sons, Tata Teleservices and IDFC, the “Remaining Shareholders”). The Shareholders Agreement also provides the Remaining Shareholders with put options, which allow them to sell outstanding shares of ATC TIPL to the Company, and the Company with call options, which allow it to buy the noncontrolling shares of ATC TIPL. The put options, which are not under the Company’s control, cannot be separated from the noncontrolling interests. As a result, the combination of the noncontrolling interests and the redemption feature requires classification as redeemable noncontrolling interests in the consolidated balance sheet, separate from equity. During the three months ended March 31, 2021, the Company made no changes to the methods of determining redemption value described in note 15 to its consolidated financial statements included in the 2020 Form 10-K. During the year ended December 31, 2020, the Company redeemed 100% of Tata Teleservices and Tata Sons’ remaining combined holdings of ATC TIPL for total consideration of INR 24.8 billion ($337.3 million at the date of redemption). As a result of the redemption, the Company’s controlling interest in ATC TIPL increased from 79% to 92% and the noncontrolling interest decreased from 21% to 8%. During the three months ended March 31, 2021, the Company entered into an agreement with Macquarie to redeem 100% of their combined holdings in ATC TIPL at a price of INR 175 per share, subject to certain adjustments. Accordingly, the Company expects to pay an amount equivalent to INR 12.9 billion (approximately $176.5 million) to redeem the shares in 2021, subject to regulatory approval. After the completion of the redemption, the Company will hold a 100% ownership interest in ATC TIPL. Other Redeemable Noncontrolling Interests —During the year ended December 31, 2020, the Company completed the acquisition of MTN Group Limited’s noncontrolling interests in each of the Company’s joint ventures in Ghana and Uganda for total consideration of approximately $524.4 million, including a net adjustment of $1.4 million made during the three months ended March 31, 2020, which resulted in an increase in the Company’s controlling interests in such joint ventures from 51% to 100%. In 2019, the Company, through a subsidiary of ATC Europe, entered into an agreement with its local partners in France to form Eure-et-Loir Réseaux Mobiles SAS (“Eure-et-Loir”), a telecommunications infrastructure company that owned and operated wireless communications towers in France. During the three months ended March 31, 2021, the Company liquidated its interests in Eure-et-Loir for total consideration of 2.2 million EUR (approximately $2.5 million at the date of redemption). The changes in Redeemable noncontrolling interests were as follows: Three Months Ended March 31, 2021 2020 Balance as of January 1, $ 212.1 $ 1,096.5 Net income attributable to noncontrolling interests 2.3 7.7 Adjustment to noncontrolling interest redemption value 1.2 (6.3) Purchase of redeemable noncontrolling interest (2.5) (524.4) Foreign currency translation adjustment attributable to noncontrolling interests (0.2) (32.1) Balance as of March 31, $ 212.9 $ 541.4

EQUITY

EQUITY	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
EQUITY	EQUITY Sales of Equity Securities —The Company receives proceeds from sales of its equity securities pursuant to the ESPP and upon exercise of stock options granted under the 2007 Plan. During the three months ended March 31, 2021, the Company received an aggregate of $1.9 million in proceeds upon exercises of stock options. 2020 “At the Market” Stock Offering Program —In August 2020, the Company established an “at the market” stock offering program through which it may issue and sell shares of its common stock having an aggregate gross sales price of up to $1.0 billion (the “2020 ATM Program”). Sales under the 2020 ATM Program may be made by means of ordinary brokers’ transactions on the New York Stock Exchange or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or, subject to specific instructions of the Company, at negotiated prices. The Company intends to use the net proceeds from any issuances under the 2020 ATM Program for general corporate purposes, which may include, among other things, the funding of acquisitions, additions to working capital and repayment or refinancing of existing indebtedness. As of March 31, 2021, the Company has not sold any shares of common stock under the 2020 ATM Program. Stock Repurchase Programs —In March 2011, the Company’s Board of Directors approved a stock repurchase program, pursuant to which the Company is authorized to repurchase up to $1.5 billion of its common stock (the “2011 Buyback”). In December 2017, the Board of Directors approved an additional stock repurchase program, pursuant to which the Company is authorized to repurchase up to $2.0 billion of its common stock (the “2017 Buyback,” and, together with the 2011 Buyback, the “Buyback Programs”). During the three months ended March 31, 2021, there were no repurchases under either of the Buyback Programs. As of March 31, 2021, the Company has repurchased a total of 14,361,283 shares of its common stock under the 2011 Buyback for an aggregate of $1.5 billion, including commissions and fees. As of March 31, 2021, the Company has not made any repurchases under the 2017 Buyback. Under the Buyback Programs, the Company is authorized to purchase shares from time to time through open market purchases, in privately negotiated transactions not to exceed market prices, and (with respect to such open market purchases) pursuant to plans adopted in accordance with Rule 10b5-1 under the Securities Exchange Act of 1934, as amended, in accordance with securities laws and other legal requirements and subject to market conditions and other factors. The Company expects to fund any further repurchases of its common stock through a combination of cash on hand, cash generated by operations and borrowings under its credit facilities. Repurchases under the Buyback Programs are subject to, among other things, the Company having available cash to fund the repurchases. Distributions —During the three months ended March 31, 2021, the Company declared or paid the following cash distributions (per share data reflects actual amounts): Declaration Date Payment Date Record Date Distribution per share Aggregate Payment Amount (1) Common Stock March 4, 2021 April 29, 2021 April 13, 2021 $ 1.24 $ 551.5 December 3, 2020 February 2, 2021 December 28, 2020 $ 1.21 $ 537.6 _______________ (1) Does not include amounts accrued for distributions payable related to unvested restricted stock units. During the three months ended March 31, 2020, the Company declared or paid the following cash distributions (per share data reflects actual amounts): Declaration Date Payment Date Record Date Distribution per share Aggregate Payment Amount (1) Common Stock March 12, 2020 April 29, 2020 April 14, 2020 $ 1.08 $ 478.8 December 11, 2019 January 14, 2020 December 27, 2019 $ 1.01 $ 447.3 _______________ (1) Does not include amounts accrued for distributions payable related to unvested restricted stock units. The Company accrues distributions on unvested restricted stock units, which are payable upon vesting. As of March 31, 2021, the amount accrued for distributions payable related to unvested restricted stock units was $7.6 million. During the three months ended March 31, 2021 and 2020, the Company paid $7.3 million and $7.6 million of distributions upon the vesting of restricted stock units, respectively. To maintain its qualification for taxation as a REIT, the Company expects to continue paying distributions, the amount, timing and frequency of which will be determined, and subject to adjustment, by the Company’s Board of Directors. Dividend to noncontrolling interest— The Company’s joint ventures may, from time to time, declare dividends. During the year ended December 31, 2020 , ATC Europe declared a dividend of 13.2 million EUR (approximately $16.2 million accrued as of December 31, 2020) payable in cash to the Company and PGGM in proportion to their respective equity interests in the joint venture. The dividend was paid on January 6, 2021. Purchase of Interests— During the three months ended March 31, 2021

EARNINGS PER COMMON SHARE

EARNINGS PER COMMON SHARE	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
EARNINGS PER COMMON SHARE	EARNINGS PER COMMON SHARE The following table sets forth basic and diluted net income per common share computational data (shares in thousands, except per share data): Three Months Ended March 31, 2021 2020 Net income attributable to American Tower Corporation common stockholders $ 645.0 $ 415.0 Basic weighted average common shares outstanding 444,486 443,055 Dilutive securities 1,808 2,777 Diluted weighted average common shares outstanding 446,294 445,832 Basic net income attributable to American Tower Corporation common stockholders per common share $ 1.45 $ 0.94 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 1.45 $ 0.93 Shares Excluded From Dilutive Effect —The following shares were not included in the computation of diluted earnings per share because the effect would be anti-dilutive (in thousands, on a weighted average basis): Three Months Ended March 31, 2021 2020 Restricted stock units — 86

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Litigation —The Company periodically becomes involved in various claims, lawsuits and proceedings that are incidental to its business. In the opinion of Company management, after consultation with counsel, there are no matters currently pending that would, in the event of an adverse outcome, materially impact the Company’s consolidated financial position, results of operations or liquidity. Verizon Transaction —In March 2015, the Company entered into an agreement with various operating entities of Verizon Communications Inc. (“Verizon”) that currently provides for the lease, sublease or management of approximately 11,250 wireless communications sites commencing March 27, 2015. The average term of the lease or sublease for all sites at the inception of the agreement was approximately 28 years, assuming renewals or extensions of the underlying ground leases for the sites. The Company has the option to purchase the leased sites in tranches, subject to the applicable lease, sublease or management rights upon its scheduled expiration. Each tower is assigned to an annual tranche, ranging from 2034 to 2047, which represents the outside expiration date for the sublease rights to the towers in that tranche. The purchase price for each tranche is a fixed amount stated in the lease for such tranche plus the fair market value of certain alterations made to the related towers. The aggregate purchase option price for the towers leased and subleased is approximately $5.0 billion. Verizon will occupy the sites as a tenant for an initial term of ten years with eight optional successive five-year terms; each such term shall be governed by standard master lease agreement terms established as a part of the transaction. AT&T Transaction —The Company has an agreement with SBC Communications Inc., a predecessor entity to AT&T Inc. (“AT&T”), that currently provides for the lease or sublease of approximately 2,100 towers commencing between December 2000 and August 2004. Substantially all of the towers are part of the securitization transactions completed in March 2013 and March 2018. The average term of the lease or sublease for all sites at the inception of the agreement was approximately 27 years, assuming renewals or extensions of the underlying ground leases for the sites. The Company has the option to purchase the sites subject to the applicable lease or sublease upon its expiration. Each tower is assigned to an annual tranche, ranging from 2013 to 2032, which represents the outside expiration date for the sublease rights to that tower. The purchase price for each site is a fixed amount stated in the lease for that site plus the fair market value of certain alterations made to the related tower by AT&T. As of March 31, 2021, the Company has purchased an aggregate of 331 of the subleased towers which are subject to the applicable agreement. The aggregate purchase option price for the remaining towers leased and subleased is $997.0 million and includes per annum accretion through the applicable expiration of the lease or sublease of a site. For all such sites, AT&T has the right to continue to lease the reserved space through June 30, 2025 at the then-current monthly fee, which shall escalate in accordance with the standard master lease agreement for the remainder of AT&T’s tenancy. Thereafter, AT&T shall have the right to renew such lease for up to five successive five-year terms. Other Contingencies —The Company is subject to income tax and other taxes in the geographic areas where it holds assets or operates, and periodically receives notifications of audits, assessments or other actions by taxing authorities. Taxing authorities may issue notices or assessments while audits are being conducted. In certain jurisdictions, taxing authorities may issue assessments with minimal examination. These notices and assessments do not represent amounts that the Company is obligated to pay and are often not reflective of the actual tax liability for which the Company will ultimately be liable. In the process of responding to assessments of taxes that the Company believes are not enforceable, the Company avails itself of both administrative and judicial remedies. The Company evaluates the circumstances of each notification or assessment based on the information available and, in those instances in which the Company does not anticipate a successful defense of positions taken in its tax filings, a liability is recorded in the appropriate amount based on the underlying assessment. On December 5, 2016, the Company received an income tax assessment of Essar Telecom Infrastructure Private Limited (“ETIPL”) from the India Income Tax Department (the “Tax Department”) for the fiscal year ending 2008 in the amount of INR 4.75 billion ($69.8 million on the date of assessment) related to capital contributions. The Company challenged the assessment before the Office of Commissioner of Income Tax - Appeals, which ruled in the Company’s favor in January 2018. However, the Tax Department has appealed this ruling at a higher appellate authority. The Company estimates that there is a more likely than not probability that the Company’s position will be sustained upon appeal. Accordingly, no liability has been recorded. Additionally, the assessment was made with respect to transactions that took place in the tax year commencing in 2007, prior to the Company’s acquisition of ETIPL. Under the Company’s definitive acquisition agreement with ETIPL, the seller is obligated to indemnify and defend the Company with respect to any tax-related liability that may arise from activities prior to March 31, 2010. Guaranties and Indemnifications — If the Company is unable to close the Pending Telxius Acquisition, the Company would be liable under the terms of the agreements to make certain payments to Telxius (each as defined below), which could be material.

ACQUISITIONS

ACQUISITIONS	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS Impact of current year acquisitions —The Company typically acquires communications sites and other communications infrastructure assets from wireless carriers or other tower operators and subsequently integrates those sites and related assets into its existing portfolio of communications sites and related assets. The financial results of the Company’s acquisitions have been included in the Company’s consolidated statements of operations for the three months ended March 31, 2021 from the date of the respective acquisition. The date of acquisition, and by extension the point at which the Company begins to recognize the results of an acquisition, may depend on, among other things, the receipt of contractual consents, the commencement and extent of leasing arrangements and the timing of the transfer of title or rights to the assets, which may be accomplished in phases. Sites acquired from communications service providers may never have been operated as a business and may instead have been utilized solely by the seller as a component of its network infrastructure. An acquisition may or may not involve the transfer of business operations or employees. The Company evaluates each of its acquisitions under the accounting guidance framework to determine whether to treat an acquisition as an asset acquisition or a business combination. For those transactions treated as asset acquisitions, the purchase price is allocated to the assets acquired, with no recognition of goodwill. For those acquisitions accounted for as business combinations, the Company recognizes acquisition and merger related expenses in the period in which they are incurred and services are received; for transactions accounted for as asset acquisitions, these costs are capitalized as part of the purchase price. Acquisition and merger related costs may include finder’s fees, advisory, legal, accounting, valuation and other professional or consulting fees and general administrative costs directly related to completing the transaction. Integration costs include incremental and non-recurring costs necessary to convert data, retain employees and otherwise enable the Company to operate acquired businesses or assets efficiently. The Company records acquisition and merger related expenses for business combinations, as well as integration costs for all acquisitions, in Other operating expenses in the consolidated statements of operations. During the three months ended March 31, 2021 and 2020, the Company recorded acquisition and merger related expenses for business combinations and non-capitalized asset acquisition costs and integration costs as follows: Three Months Ended March 31, 2021 2020 Acquisition and merger related expenses $ 34.6 $ 7.6 Integration costs $ 16.6 $ 6.6 During the three months ended March 31, 2021, the Company also recorded benefits of $4.0 million related to pre-acquisition contingencies and settlements. The increase in acquisition and merger related costs during the three months ended March 31, 2021 was primarily associated with the Pending Telxius Acquisition (as defined below). 2021 Transactions The estimated aggregate impact of the acquisitions completed in 2021 on the Company’s revenues and gross margin for the three months ended March 31, 2021 was approximately $0.5 million and $0.4 million, respectively. The revenues and gross margin amounts also reflect incremental revenues from the addition of new tenants to such sites subsequent to the transaction date. Entel Acquisition —On December 19, 2019, the Company entered into a definitive agreement to acquire approximately 3,200 communications sites in Chile and Peru from Entel PCS Telecomunicaciones S.A. and Entel Peru S.A. for total consideration of approximately $0.8 billion (as of the date of signing). The Company completed the acquisition of approximately 2,400 communications sites in December 2019 and an additional 530 communications sites pursuant to this agreement during the year ended December 31, 2020. During the three months ended March 31, 2021, the Company completed the acquisition of an additional 50 communications sites pursuant to this agreement for an aggregate total purchase price of $14.7 million (as of the dates of acquisition), including value added tax, which are being accounted for as an acquisition of assets and are included in the table below. The remaining communications sites are expected to continue to close in tranches, subject to certain closing conditions. Other Acquisitions —During the three months ended March 31, 2021, the Company acquired a total of 66 communications sites as well as other communications infrastructure assets in the United States, Mexico and Peru, for an aggregate purchase price of $62.5 million. Of the aggregate purchase price, $4.0 million is reflected as a payable in the consolidated balance sheet as of March 31, 2021. These acquisitions were accounted for as asset acquisitions. The following table summarizes the allocations of the purchase prices for the fiscal year 2021 acquisitions based upon their estimated fair value at the date of acquisition: Allocation (1) Current assets $ 0.3 Property and equipment 22.5 Intangible assets (2): Tenant-related intangible assets 37.3 Network location intangible assets 15.7 Other intangible assets — Other non-current assets 5.8 Current liabilities (1.0) Deferred tax liability — Other non-current liabilities (3.4) Net assets acquired 77.2 Goodwill — Fair value of net assets acquired 77.2 Debt assumed — Purchase price $ 77.2 _______________ (1) Includes 12 sites in Peru held pursuant to long-term finance leases. (2) Tenant-related intangible assets and network location intangible assets are amortized on a straight-line basis generally over a 20 year period. Other Signed Acquisitions Orange Acquisition —On November 28, 2019, ATC France, a majority-owned subsidiary of the Company, entered into definitive agreements with Orange S.A. for the acquisition of up to approximately 2,000 communications sites in France over a period of up to five years for total consideration in the range of approximately 500.0 million EUR to 600.0 million EUR (approximately $550.5 million to $660.5 million at the date of signing) to be paid over the five-year term. The Company completed the acquisition of 564 of these sites during the year ended December 31, 2020. Subsequent to March 31, 2021, the Company completed the acquisition of an additional 81 communications sites. The remaining communications sites are expected to close in tranches, subject to customary closing conditions. Pending Telxius Acquisition —On January 13, 2021, the Company entered into two agreements with Telxius Telecom, S.A. (“Telxius”), a subsidiary of Telefónica, S.A., pursuant to which the Company expects to acquire Telxius’ European and Latin American tower divisions, comprising approximately 31,000 communications sites in Argentina, Brazil, Chile, Germany, Peru and Spain, for approximately 7.7 billion EUR (approximately $9.4 billion at the date of signing) (the “Pending Telxius Acquisition”), subject to certain adjustments. As of April 28, 2021, the Company has received all required government and regulatory approvals in Germany and Spain and expects to close on the majority of the European sites in the second quarter of 2021, with approximately 4,000 sites in Germany expected to close in the third quarter of 2021. The Latin American sites are expected to close either late in the second quarter or in the third quarter of 2021, subject to customary closing conditions, including government and regulatory approval. 2020 Transactions InSite Acquisition —On December 23, 2020, the Company acquired 100% of the outstanding units of IWG Holdings, LLC, the parent company of InSite, which owned, operated and managed approximately 3,000 communications sites in the U.S. and Canada. The portfolio included approximately 1,400 owned towers in the United States, over 200 owned towers in Canada and approximately 40 DAS networks in the United States. In addition, the portfolio included more than 600 land parcels under communications sites in the United States, Canada and Australia, as well as approximately 400 rooftop sites. The total consideration for the InSite Acquisition, including cash acquired, the repayment and assumption of certain debt held by InSite, was approximately $3.5 billion, subject to certain post-closing adjustments. The InSite Acquisition was accounted for as a business combination and is subject to post-closing adjustments. During the three months ended March 31, 2021, certain adjustments were made to reduce assets by $3.1 million and increase liabilities by $18.2 million with a corresponding increase in goodwill of $21.3 million and there were no other material post-closing adjustments. The full reconciliation and finalization of the assets acquired and liabilities assumed, including those subject to valuation, have not been completed and, as a result, there may be additional post-closing adjustments. Pro Forma Consolidated Results (Unaudited) The following table presents the unaudited pro forma financial results as if the 2021 acquisitions had occurred on January 1, 2020 and the 2020 acquisitions had occurred on January 1, 2019. The pro forma results do not include any anticipated cost synergies, costs or other integration impacts. Accordingly, such pro forma amounts are not necessarily indicative of the results that actually would have occurred had the transactions been completed on the date indicated, nor are they indicative of the future operating results of the Company. Three Months Ended March 31, 2021 2020 Pro forma revenues $ 2,158.9 $ 2,044.6 Pro forma net income attributable to American Tower Corporation common stockholders $ 644.9 $ 369.8 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 1.45 $ 0.83 Diluted net income attributable to American Tower Corporation common stockholders $ 1.45 $ 0.83

BUSINESS SEGMENTS

BUSINESS SEGMENTS	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
BUSINESS SEGMENTS	BUSINESS SEGMENTS The Company’s primary business is leasing space on multitenant 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. This business is referred to as the Company’s property operations. During the fourth quarter of 2020, as a result of the InSite Acquisition, the Company updated its reportable segments to rename U.S. property and Asia property to U.S. & Canada property and Asia-Pacific property, respectively. The Company continues to report its results in six segments – U.S. & Canada property, Asia-Pacific property, Africa property, Europe property, Latin America property and services. The change in reportable segment names is solely reflective of the inclusion of Canada and Australia in the Company’s business operations, as a result of the InSite Acquisition, and had no impact on the Company’s consolidated financial statements or historical segment financial information for any prior periods. As of March 31, 2021, the Company’s property operations consisted of the following: • U.S. & Canada: property operations in Canada and the United States; • Asia-Pacific: property operations in Australia and India; • Africa: property operations in Burkina Faso, Ghana, Kenya, Niger, Nigeria, South Africa and Uganda; • Europe: property operations in France, Germany and Poland; and • Latin America: property operations in Argentina, Brazil, Chile, Colombia, Costa Rica, Mexico, Paraguay and Peru. The Company’s services segment offers tower-related services in the United States, including AZP and structural analysis, which primarily support its site leasing business, including the addition of new tenants and equipment on its sites. The services segment is a strategic business unit that offers different services from, and requires different resources, skill sets and marketing strategies than, the property operating segments. The accounting policies applied in compiling segment information below are similar to those described in note 1 to the Company’s consolidated financial statements included in the 2020 Form 10-K and as updated in note 1 above. Among other factors, in evaluating financial performance in each business segment, management uses segment gross margin and segment operating profit. The Company defines segment gross margin as segment revenue less segment operating expenses excluding stock-based compensation expense recorded in costs of operations; Depreciation, amortization and accretion; Selling, general, administrative and development expense; and Other operating expenses. The Company defines segment operating profit as segment gross margin less Selling, general, administrative and development expense attributable to the segment, excluding stock-based compensation expense and corporate expenses. These measures of segment gross margin and segment operating profit are also before Interest income, Interest expense, Gain (loss) on retirement of long-term obligations, Other income (expense), Net income (loss) attributable to noncontrolling interests and Income tax benefit (provision). The categories of expenses indicated above, such as depreciation, have been excluded from segment operating performance as they are not considered in the review of information or the evaluation of results by management. There are no significant revenues resulting from transactions between the Company’s operating segments. All intercompany transactions are eliminated to reconcile segment results and assets to the consolidated statements of operations and consolidated balance sheets. Summarized financial information concerning the Company’s reportable segments for the three months ended March 31, 2021 and 2020 is shown in the following tables. The “Other” column (i) represents amounts excluded from specific segments, such as business development operations, stock-based compensation expense and corporate expenses included in Selling, general, administrative and development expense; Other operating expenses; Interest income; Interest expense; Gain (loss) on retirement of long-term obligations; and Other income (expense), and (ii) reconciles segment operating profit to Income from continuing operations before income taxes. Property Total Services Other Total Three Months Ended March 31, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,231.3 $ 281.4 $ 235.7 $ 44.6 $ 336.7 $ 2,129.7 $ 28.8 $ 2,158.5 Segment operating expenses 197.9 175.5 80.9 7.8 101.2 563.3 11.0 574.3 Segment gross margin 1,033.4 105.9 154.8 36.8 235.5 1,566.4 17.8 1,584.2 Segment selling, general, administrative and development expense (1) 39.3 7.1 18.9 5.6 23.3 94.2 4.2 98.4 Segment operating profit $ 994.1 $ 98.8 $ 135.9 $ 31.2 $ 212.2 $ 1,472.2 $ 13.6 $ 1,485.8 Stock-based compensation expense $ 38.0 38.0 Other selling, general, administrative and development expense 46.2 46.2 Depreciation, amortization and accretion 522.5 522.5 Other expense (2) 176.5 176.5 Income from continuing operations before income taxes $ 702.6 Total assets $ 27,331.9 $ 5,214.1 $ 4,905.4 $ 1,836.7 $ 7,127.2 $ 46,415.3 $ 59.4 $ 467.8 $ 46,942.5 _______________ (1) Segment selling, general, administrative and development expenses exclude stock-based compensation expense of $38.0 million. (2) Primarily includes interest expense. Property Total Services Other Total Three Months Ended March 31, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,089.9 $ 286.6 $ 225.5 $ 34.5 $ 336.7 $ 1,973.2 $ 19.9 $ 1,993.1 Segment operating expenses (1) 190.0 164.0 77.7 6.6 105.2 543.5 7.6 551.1 Segment gross margin 899.9 122.6 147.8 27.9 231.5 1,429.7 12.3 1,442.0 Segment selling, general, administrative and development expense (1) 42.0 32.6 17.1 5.5 26.6 123.8 3.5 127.3 Segment operating profit $ 857.9 $ 90.0 $ 130.7 $ 22.4 $ 204.9 $ 1,305.9 $ 8.8 $ 1,314.7 Stock-based compensation expense $ 47.7 47.7 Other selling, general, administrative and development expense 43.7 43.7 Depreciation, amortization and accretion 472.3 472.3 Other expense (2) 311.3 311.3 Income from continuing operations before income taxes $ 439.7 Total assets $ 22,486.9 $ 4,986.0 $ 4,510.3 $ 1,554.5 $ 6,739.0 $ 40,276.7 $ 29.0 $ 483.4 $ 40,789.1 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $0.9 million and $46.8 million, respectively. (2) Primarily includes interest expense.

BASIS OF PRESENTATION AND SIG_2

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation—The accompanying consolidated and condensed 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	Reportable Segments — During the fourth quarter of 2020, as a result of the Company’s acquisition of InSite Wireless Group, LLC (“InSite,” and the acquisition, the “InSite Acquisition”), the Company updated its reportable segments to rename U.S. property and Asia property to U.S. & Canada property and Asia-Pacific property, respectively. The Company continues to report its results in six segments – U.S. & Canada property, Asia-Pacific property, Africa property, Europe property, Latin America property and services, which are discussed further in note 15. The change in reportable segment names is solely reflective of the inclusion of Canada and Australia in the Company’s business operations, as a result of the InSite Acquisition, and had no impact on the Company’s consolidated financial statements or historical segment financial information for any prior periods.
Revenue	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 distributed antenna system (“DAS”) networks and fiber and other related assets results from agreements with tenants that are not leases. 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. There were no material changes in the receivables, contract assets and contract liabilities from contracts with tenants for the three months ended March 31, 2021.
Accounting Standards Updates	Accounting Standards Updates In March 2020, the Financial Accounting Standards Board (the “FASB”) issued guidance to provide optional expedients and exceptions for applying accounting principles generally accepted in the United States to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The guidance applies only to contracts, hedging relationships and other transactions that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. The expedients and exceptions provided by the guidance do not apply to contract modifications made and hedging relationships entered into or evaluated after December 31, 2022, except for hedging relationships existing as of December 31, 2022 for which an entity has elected certain optional expedients that are retained through the end of the hedging relationship. In January 2021, the FASB issued additional guidance that clarifies that certain practical expedients and exceptions for contract modifications and hedge accounting apply to derivatives that are affected by reference rate reform. As of March 31, 2021, the Company has not modified any contracts as a result of reference rate reform and is evaluating the impact this standard may have on its financial statements.

BASIS OF PRESENTATION AND SIG_3

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reconciliation of Cash and Cash Equivalents and Restricted Cash	The reconciliation of cash and cash equivalents and restricted cash reported within the applicable balance sheet that sum to the total of the same such amounts shown in the statement of cash flows is as follows: Three Months Ended March 31, 2021 2020 Cash and cash equivalents $ 1,913.6 $ 1,326.0 Restricted cash 79.7 74.3 Total cash, cash equivalents and restricted cash $ 1,993.3 $ 1,400.3
Summary of Revenue Disaggregated by Source and Geography	A summary of revenue disaggregated by source and geography is as follows: Three Months Ended March 31, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 71.6 $ 2.5 $ 4.9 $ 2.2 $ 31.9 $ 113.1 Services revenue 28.8 — — — — 28.8 Total non-lease revenue $ 100.4 $ 2.5 $ 4.9 $ 2.2 $ 31.9 $ 141.9 Property lease revenue 1,159.7 278.9 230.8 42.4 304.8 2,016.6 Total revenue $ 1,260.1 $ 281.4 $ 235.7 $ 44.6 $ 336.7 $ 2,158.5 Three Months Ended March 31, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 58.6 $ 2.2 $ 2.9 $ 1.5 $ 32.9 $ 98.1 Services revenue 19.9 — — — — 19.9 Total non-lease revenue $ 78.5 $ 2.2 $ 2.9 $ 1.5 $ 32.9 $ 118.0 Property lease revenue 1,031.3 284.4 222.6 33.0 303.8 1,875.1 Total revenue $ 1,109.8 $ 286.6 $ 225.5 $ 34.5 $ 336.7 $ 1,993.1

PREPAID AND OTHER CURRENT ASS_2

PREPAID AND OTHER CURRENT ASSETS (Tables)	3 Months Ended
	Mar. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid and other current assets	Prepaid and other current assets consisted of the following: As of March 31, 2021 December 31, 2020 Prepaid assets $ 76.2 $ 66.1 Prepaid income tax 100.3 143.7 Unbilled receivables 160.8 176.9 Value added tax and other consumption tax receivables 58.1 66.3 Other miscellaneous current assets 95.2 79.6 Prepaid and other current assets $ 490.6 $ 532.6

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Schedule of Future Minimum Rental Receipts Expected Under Non-Cancellable Operating Lease Agreements	Future minimum rental receipts expected under non-cancellable operating lease agreements as of March 31, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 4,632.2 2022 5,976.8 2023 5,866.5 2024 5,755.9 2025 5,330.3 Thereafter 32,576.0 Total $ 60,137.7 _______________
Schedule of Information About Other Lease-related Balances	Information about other lease-related balances is as follows: As of March 31, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 7,719.9 $ 7,789.2 Current portion of lease liability $ 555.8 $ 539.9 Lease liability 6,812.9 6,884.4 Total operating lease liability $ 7,368.7 $ 7,424.3
Components of Operating Lease Cost	The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of March 31, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.6 13.7 Weighted-average incremental borrowing rate 5.6 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended March 31, 2021 2020 Operating lease cost $ 251.3 $ 250.7 Variable lease costs not included in lease liability (1) 69.3 61.4 _______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Three Months Ended March 31, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (244.9) $ (252.0) Non-cash items: New operating leases (1) $ 89.2 $ 50.1 Operating lease modifications and reassessments $ 85.7 $ 96.9 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions.
Maturity of Operating Lease Liabilities	Maturities of operating lease liabilities as of March 31, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 678.3 2022 874.6 2023 842.7 2024 805.2 2025 759.8 Thereafter 6,497.9 Total lease payments 10,458.5 Less amounts representing interest (3,089.8) Total lease liability 7,368.7 Less current portion of lease liability 555.8 Non-current lease liability $ 6,812.9 _______________ (1) Balances are translated at the applicable period-end exchange rate, which may impact comparability between periods.

GOODWILL AND OTHER INTANGIBLE_2

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying value of goodwill	The changes in the carrying value of goodwill for each of the Company’s business segments were as follows: Property Services Total U.S. & Canada Asia-Pacific Africa Europe Latin America Balance as of January 1, 2021 $ 4,750.8 $ 1,016.9 $ 625.6 $ 279.1 $ 608.3 $ 2.0 $ 7,282.7 Additions and adjustments (1) 21.3 (0.0) — — — — 21.3 Effect of foreign currency translation 4.2 (0.5) (3.4) (11.1) (30.8) — (41.6) Balance as of March 31, 2021 $ 4,776.3 $ 1,016.4 $ 622.2 $ 268.0 $ 577.5 $ 2.0 $ 7,262.4 _______________ (1) Consists of an aggregate of $21.3 million of measurement period adjustments related to the InSite Acquisition.
Intangible assets subject to amortization	The Company’s other intangible assets subject to amortization consisted of the following: As of March 31, 2021 As of December 31, 2020 Estimated Useful Gross Accumulated Net Book Gross Accumulated Net Book Acquired network location intangibles (1) Up to 20 $ 5,751.7 $ (2,171.1) $ 3,580.6 $ 5,784.0 $ (2,117.6) $ 3,666.4 Acquired tenant-related intangibles Up to 20 14,221.7 (4,379.6) 9,842.1 14,322.5 (4,237.5) 10,085.0 Acquired licenses and other intangibles 3-20 94.6 (10.0) 84.6 97.8 (9.4) 88.4 Total other intangible assets $ 20,068.0 $ (6,560.7) $ 13,507.3 $ 20,204.3 $ (6,364.5) $ 13,839.8 _______________ (1) Acquired network location intangibles are amortized over the shorter of the term of the corresponding ground lease, taking into consideration lease renewal options and residual value, generally up to 20 years, as the Company considers these intangibles to be directly related to the tower assets.
Expected future amortization expenses	Based on current exchange rates, the Company expects to record amortization expense as follows over the remaining current year and the five subsequent years: Fiscal Year Amount Remainder of 2021 $ 735.9 2022 975.8 2023 954.5 2024 944.9 2025 914.5 2026 873.2

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of accrued expenses	Accrued expenses consisted of the following: As of March 31, 2021 December 31, 2020 Accrued construction costs $ 37.8 $ 46.5 Accrued income tax payable 22.3 20.6 Accrued pass-through costs 78.3 67.1 Amounts payable for acquisitions 15.7 58.9 Amounts payable to tenants 63.5 66.4 Accrued property and real estate taxes 222.0 219.1 Accrued rent 81.0 82.6 Payroll and related withholdings 67.1 104.4 Other accrued expenses 357.1 378.1 Total accrued expenses $ 944.8 $ 1,043.7

LONG-TERM OBLIGATIONS (Tables)

LONG-TERM OBLIGATIONS (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of long-term obligations and key terms	Outstanding amounts under the Company’s long-term obligations, reflecting discounts, premiums, debt issuance costs and fair value adjustments due to interest rate swaps consisted of the following: As of March 31, 2021 December 31, 2020 Maturity Date 2020 Term Loan (1) (2) $ — $ 749.4 N/A 2021 Multicurrency Credit Facility (1) 270.0 — June 28, 2024 2019 Term Loan (1) 995.8 996.1 January 31, 2025 2021 Credit Facility (1) 2,345.0 2,295.0 January 31, 2026 2.250% senior notes 604.0 605.1 January 15, 2022 4.70% senior notes 699.2 699.0 March 15, 2022 3.50% senior notes 996.5 996.1 January 31, 2023 3.000% senior notes 718.7 721.9 June 15, 2023 0.600% senior notes 497.1 496.8 January 15, 2024 5.00% senior notes 1,001.2 1,001.3 February 15, 2024 3.375% senior notes 646.0 645.7 May 15, 2024 2.950% senior notes 643.4 643.1 January 15, 2025 2.400% senior notes 745.3 745.0 March 15, 2025 1.375% senior notes (3) 580.2 604.1 April 4, 2025 4.000% senior notes 744.8 744.3 June 1, 2025 1.300% senior notes 495.6 495.4 September 15, 2025 4.400% senior notes 497.2 497.1 February 15, 2026 1.600% senior notes 694.4 — April 15, 2026 1.950% senior notes (3) 581.2 605.2 May 22, 2026 3.375% senior notes 989.9 989.5 October 15, 2026 3.125% senior notes 398.0 397.9 January 15, 2027 2.750% senior notes 744.5 744.3 January 15, 2027 3.55% senior notes 745.0 744.8 July 15, 2027 0.500% senior notes (3) 871.2 907.4 January 15, 2028 3.600% senior notes 693.6 693.4 January 15, 2028 1.500% senior notes 645.3 645.1 January 31, 2028 3.950% senior notes 590.8 590.6 March 15, 2029 3.800% senior notes 1,633.9 1,633.5 August 15, 2029 2.900% senior notes 741.9 741.7 January 15, 2030 2.100% senior notes 740.5 740.2 June 15, 2030 1.875% senior notes 790.8 790.5 October 15, 2030 2.700% senior notes 693.3 — April 15, 2031 1.000% senior notes (3) 754.5 786.1 January 15, 2032 3.700% senior notes 591.9 591.9 October 15, 2049 3.100% senior notes 1,037.8 1,037.7 June 15, 2050 2.950% senior notes 538.3 538.2 January 15, 2051 Total American Tower Corporation debt 26,956.8 26,113.4 Series 2013-2A securities (4) 1,297.0 1,296.6 March 15, 2023 Series 2018-1A securities (4) 494.8 494.6 March 15, 2028 Series 2015-2 notes (5) 522.2 522.1 June 16, 2025 InSite Debt (6) — 800.0 N/A Other subsidiary debt (7) 26.1 32.9 Various Total American Tower subsidiary debt 2,340.1 3,146.2 Finance lease obligations 29.9 27.9 Total 29,326.8 29,287.5 Less current portion of long-term obligations (1,336.5) (789.8) Long-term obligations $ 27,990.3 $ 28,497.7 _______________ (1) Accrues interest at a variable rate. (2) Repaid in full on February 5, 2021 using borrowings from the 2021 Multicurrency Credit Facility (as defined below) and cash on hand. (3) Notes are denominated in Euros (“EUR”). (4) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (5) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (6) Debt entered into by certain InSite subsidiaries acquired in connection with the InSite Acquisition (the “InSite Debt”). On January 15, 2021, all amounts outstanding under the InSite Debt were repaid. (7) Includes (a) the Colombian credit facility, which is denominated in Colombian Pesos (“COP”) and amortizes through April 24, 2021, (b) debt entered into by the Company’s Kenyan subsidiary in connection with an acquisition of sites in Kenya, which is denominated in U.S. Dollars (“USD”) and is payable either (i) in future installments subj ect to the satisfaction of specified conditions or (ii) three years from the note origination date, and (c) U.S. subsidiary debt related to a seller-financed acquisition. The key terms of the Notes are as follows: Senior Notes Aggregate Principal Amount (in millions) Issue Date and Interest Accrual Date Maturity Date Contractual Interest Rate First Interest Payment Interest Payments Due (1) Par Call Date (2) 1.600% Notes $ 700.0 March 29, 2021 April 15, 2026 1.600 % October 15, 2021 April 15 and October 15 March 15, 2026 2.700% Notes $ 700.0 March 29, 2021 April 15, 2031 2.700 % October 15, 2021 April 15 and October 15 January 15, 2031 ___________ (1) Accrued and unpaid interest is payable in USD semi-annually in arrears and will be computed from the issue date on the basis of a 360-day year comprised of twelve 30-day months. (2) The Company may redeem the Notes at any time, in whole or in part, at a redemption price equal to 100% of the principal amount of the Notes plus a make-whole premium, together with accrued interest to the redemption date. If the Company redeems the Notes on or after the par call date, the Company will not be required to pay a make-whole premium.
Schedule of line of credit facilities	As of March 31, 2021, the key terms under the 2021 Multicurrency Credit Facility, the 2021 Credit Facility, the 2019 Term Loan, the 2021 364-Day Delayed Draw Term Loan, the 2021 Three Year Delayed Draw Term Loan and the Bridge Loan Commitment were as follows: Outstanding Principal Balance Undrawn letters of credit Maturity Date Current margin over LIBOR or EURIBOR (1) Current commitment fee (2) 2021 Multicurrency Credit Facility $ 270.0 $ 3.8 June 28, 2024 (3) 1.125 % 0.110 % 2021 Credit Facility $ 2,345.0 $ 0.8 January 31, 2026 (3) 1.125 % 0.110 % 2019 Term Loan $ 1,000.0 N/A January 31, 2025 1.125 % N/A 2021 364-Day Delayed Draw Term Loan — N/A N/A (4) 1.000 % 0.110 % 2021 Three Year Delayed Draw Term Loan — N/A N/A (4) 1.125 % 0.110 % Bridge Loan Commitment (5) — N/A N/A (5) 1.125 % 0.110 % _______________ (1) LIBOR, which means the London Interbank Offered Rate, applies to the 2021 Multicurrency Credit Facility, the 2021 Credit Facility and the 2019 Term Loan. EURIBOR, which means the Euro Interbank Offered Rate, applies to the 2021 Delayed Draw Term Loans and the Bridge Loan Commitment. (2) Fee on undrawn portion of each credit facility. (3) Subject to two optional renewal periods. (4) The maturity dates for the 2021 364-Day Delayed Draw Term Loan and the 2021 Three Year Delayed Draw Term Loan are 364 days and three years, respectively, from the date of the first borrowing under each facility. As of March 31, 2021, no borrowings were made under these facilities, and as such, no maturity dates have been set. The Company’s ability to borrow thereunder is subject to the occurrence of certain conditions related to the Pending Telxius Acquisition, as set forth in the agreements for the 2021 Delayed Draw Term Loans.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Inputs used to measure fair value	Below are the three levels of inputs that may be used to measure fair value: Level 1 Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Schedule of fair value of assets and liabilities	The fair values of the Company’s financial assets and liabilities that are required to be measured on a recurring basis at fair value were as follows: March 31, 2021 December 31, 2020 Fair Value Measurements Using Fair Value Measurements Using Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets: Interest rate swap agreements — $ 24.5 — — $ 29.2 — Liabilities: Interest rate swap agreements — $ 0.0 — — $ 0.1 — Fair value of debt related to interest rate swap agreements (1) $ 26.3 — — $ 31.4 — — _______________

INCOME TAXES (Tables)

INCOME TAXES (Tables)	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of penalties and income tax-related interest expense	The Company recorded the following penalties and income tax-related interest expense during the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 Penalties and income tax-related interest expense $ 3.7 $ 1.7

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of stock-based compensation expenses	During the three months ended March 31, 2021 and 2020, the Company recorded and capitalized the following stock-based compensation expense: Three Months Ended March 31, 2021 (1) 2020 (2) Stock-based compensation expense $ 38.0 $ 47.7 Total stock-based compensation expense $ 38.0 $ 47.7 _______________ (1) For the three months ended March 31, 2021, stock-based compensation expense consisted of $38.0 million included in selling, general, administrative and development expense.
Summary of the company's option activity	The Company’s option activity for the three months ended March 31, 2021 was as follows (shares disclosed in full amounts): Number of Options Outstanding as of January 1, 2021 2,016,261 Exercised (23,958) Forfeited — Expired — Outstanding as of March 31, 2021 1,992,303
RSU and PSU activity	The Company’s RSU and PSU activity for the three months ended March 31, 2021 was as follows (shares disclosed in full amounts): RSUs PSUs Outstanding as of January 1, 2021 (1) 1,245,075 320,510 Granted (2) 538,239 92,312 Vested and Released (3) (547,567) (66,834) Forfeited (13,424) — Outstanding as of March 31, 2021 1,222,323 345,988 Vested and deferred as of March 31, 2021 (4) — 96,048 _______________ (1) PSUs consist of the target number of shares issuable at the end of the three-year performance period for the outstanding 2020 PSUs and the outstanding 2019 PSUs, or 70,739 and 86,889 shares, respectively, and the shares issuable at the end of the three-year performance period for the PSUs granted in 2018 (the “2018 PSUs”) based on achievement against the performance metrics for the three-year performance period, or 162,882 shares. (2) PSUs consist of the target number of shares issuable at the end of the three-year performance period for the 2021 PSUs, or 92,312 shares. (3) This includes 58,204 of previously vested and deferred RSUs. PSUs consist of shares vested pursuant to the 2018 PSUs. There are no additional shares to be earned related to the 2018 PSUs. (4) Vested and deferred PSUs are related to deferred compensation for certain former employees.

REDEEMABLE NONCONTROLLING INT_2

REDEEMABLE NONCONTROLLING INTERESTS (Tables)	3 Months Ended
	Mar. 31, 2021
Noncontrolling Interest [Abstract]
Changes in Redeemable noncontrolling interest	The changes in Redeemable noncontrolling interests were as follows: Three Months Ended March 31, 2021 2020 Balance as of January 1, $ 212.1 $ 1,096.5 Net income attributable to noncontrolling interests 2.3 7.7 Adjustment to noncontrolling interest redemption value 1.2 (6.3) Purchase of redeemable noncontrolling interest (2.5) (524.4) Foreign currency translation adjustment attributable to noncontrolling interests (0.2) (32.1) Balance as of March 31, $ 212.9 $ 541.4

EQUITY (Tables)

EQUITY (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of declared or paid cash distributions	During the three months ended March 31, 2021, the Company declared or paid the following cash distributions (per share data reflects actual amounts): Declaration Date Payment Date Record Date Distribution per share Aggregate Payment Amount (1) Common Stock March 4, 2021 April 29, 2021 April 13, 2021 $ 1.24 $ 551.5 December 3, 2020 February 2, 2021 December 28, 2020 $ 1.21 $ 537.6 _______________ (1) Does not include amounts accrued for distributions payable related to unvested restricted stock units. During the three months ended March 31, 2020, the Company declared or paid the following cash distributions (per share data reflects actual amounts): Declaration Date Payment Date Record Date Distribution per share Aggregate Payment Amount (1) Common Stock March 12, 2020 April 29, 2020 April 14, 2020 $ 1.08 $ 478.8 December 11, 2019 January 14, 2020 December 27, 2019 $ 1.01 $ 447.3 _______________

EARNINGS PER COMMON SHARE (Tabl

EARNINGS PER COMMON SHARE (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of earnings per basic and diluted by common class	The following table sets forth basic and diluted net income per common share computational data (shares in thousands, except per share data): Three Months Ended March 31, 2021 2020 Net income attributable to American Tower Corporation common stockholders $ 645.0 $ 415.0 Basic weighted average common shares outstanding 444,486 443,055 Dilutive securities 1,808 2,777 Diluted weighted average common shares outstanding 446,294 445,832 Basic net income attributable to American Tower Corporation common stockholders per common share $ 1.45 $ 0.94 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 1.45 $ 0.93
Schedule of antidilutive securities excluded from computation of earnings per share	The following shares were not included in the computation of diluted earnings per share because the effect would be anti-dilutive (in thousands, on a weighted average basis): Three Months Ended March 31, 2021 2020 Restricted stock units — 86

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Schedule of acquisition and merger related costs	During the three months ended March 31, 2021 and 2020, the Company recorded acquisition and merger related expenses for business combinations and non-capitalized asset acquisition costs and integration costs as follows: Three Months Ended March 31, 2021 2020 Acquisition and merger related expenses $ 34.6 $ 7.6 Integration costs $ 16.6 $ 6.6
Schedule of recognized identified assets acquired and liabilities assumed	The following table summarizes the allocations of the purchase prices for the fiscal year 2021 acquisitions based upon their estimated fair value at the date of acquisition: Allocation (1) Current assets $ 0.3 Property and equipment 22.5 Intangible assets (2): Tenant-related intangible assets 37.3 Network location intangible assets 15.7 Other intangible assets — Other non-current assets 5.8 Current liabilities (1.0) Deferred tax liability — Other non-current liabilities (3.4) Net assets acquired 77.2 Goodwill — Fair value of net assets acquired 77.2 Debt assumed — Purchase price $ 77.2 _______________ (1) Includes 12 sites in Peru held pursuant to long-term finance leases.
Schedule of pro forma information	The following table presents the unaudited pro forma financial results as if the 2021 acquisitions had occurred on January 1, 2020 and the 2020 acquisitions had occurred on January 1, 2019. The pro forma results do not include any anticipated cost synergies, costs or other integration impacts. Accordingly, such pro forma amounts are not necessarily indicative of the results that actually would have occurred had the transactions been completed on the date indicated, nor are they indicative of the future operating results of the Company. Three Months Ended March 31, 2021 2020 Pro forma revenues $ 2,158.9 $ 2,044.6 Pro forma net income attributable to American Tower Corporation common stockholders $ 644.9 $ 369.8 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 1.45 $ 0.83 Diluted net income attributable to American Tower Corporation common stockholders $ 1.45 $ 0.83

BUSINESS SEGMENTS (Tables)

BUSINESS SEGMENTS (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Summarized financial information concerning the company's reportable segments	Summarized financial information concerning the Company’s reportable segments for the three months ended March 31, 2021 and 2020 is shown in the following tables. The “Other” column (i) represents amounts excluded from specific segments, such as business development operations, stock-based compensation expense and corporate expenses included in Selling, general, administrative and development expense; Other operating expenses; Interest income; Interest expense; Gain (loss) on retirement of long-term obligations; and Other income (expense), and (ii) reconciles segment operating profit to Income from continuing operations before income taxes. Property Total Services Other Total Three Months Ended March 31, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,231.3 $ 281.4 $ 235.7 $ 44.6 $ 336.7 $ 2,129.7 $ 28.8 $ 2,158.5 Segment operating expenses 197.9 175.5 80.9 7.8 101.2 563.3 11.0 574.3 Segment gross margin 1,033.4 105.9 154.8 36.8 235.5 1,566.4 17.8 1,584.2 Segment selling, general, administrative and development expense (1) 39.3 7.1 18.9 5.6 23.3 94.2 4.2 98.4 Segment operating profit $ 994.1 $ 98.8 $ 135.9 $ 31.2 $ 212.2 $ 1,472.2 $ 13.6 $ 1,485.8 Stock-based compensation expense $ 38.0 38.0 Other selling, general, administrative and development expense 46.2 46.2 Depreciation, amortization and accretion 522.5 522.5 Other expense (2) 176.5 176.5 Income from continuing operations before income taxes $ 702.6 Total assets $ 27,331.9 $ 5,214.1 $ 4,905.4 $ 1,836.7 $ 7,127.2 $ 46,415.3 $ 59.4 $ 467.8 $ 46,942.5 _______________ (1) Segment selling, general, administrative and development expenses exclude stock-based compensation expense of $38.0 million. (2) Primarily includes interest expense. Property Total Services Other Total Three Months Ended March 31, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,089.9 $ 286.6 $ 225.5 $ 34.5 $ 336.7 $ 1,973.2 $ 19.9 $ 1,993.1 Segment operating expenses (1) 190.0 164.0 77.7 6.6 105.2 543.5 7.6 551.1 Segment gross margin 899.9 122.6 147.8 27.9 231.5 1,429.7 12.3 1,442.0 Segment selling, general, administrative and development expense (1) 42.0 32.6 17.1 5.5 26.6 123.8 3.5 127.3 Segment operating profit $ 857.9 $ 90.0 $ 130.7 $ 22.4 $ 204.9 $ 1,305.9 $ 8.8 $ 1,314.7 Stock-based compensation expense $ 47.7 47.7 Other selling, general, administrative and development expense 43.7 43.7 Depreciation, amortization and accretion 472.3 472.3 Other expense (2) 311.3 311.3 Income from continuing operations before income taxes $ 439.7 Total assets $ 22,486.9 $ 4,986.0 $ 4,510.3 $ 1,554.5 $ 6,739.0 $ 40,276.7 $ 29.0 $ 483.4 $ 40,789.1 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $0.9 million and $46.8 million, respectively. (2) Primarily includes interest expense.

BASIS OF PRESENTATION AND SIG_4

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Details) - segment	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Number of reportable segments	6
ATC Europe
Concentration Risk [Line Items]
Ownership interest percentage	51.00%
Noncontrolling interest, ownership percentage by noncontrolling owners (as a percent)	49.00%
ATC, TIPL
Concentration Risk [Line Items]
Ownership interest percentage	92.00%	92.00%	79.00%
Noncontrolling interest, ownership percentage by noncontrolling owners (as a percent)		8.00%	21.00%

BASIS OF PRESENTATION AND SIG_5

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - CASH AND CASH EQUIVALENTS AND RESTRICTED CASH (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 1,913.6	$ 1,746.3	$ 1,326
Restricted cash	79.7	115.1	74.3
Total cash, cash equivalents and restricted cash	$ 1,993.3	$ 1,861.4	$ 1,400.3	$ 1,578

BASIS OF PRESENTATION AND SIG_6

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - SUMMARY OF REVENUE DISAGGREGATED BY SOURCE AND GEOGRAPHY (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 141.9	$ 118
Property lease revenue	2,016.6	1,875.1
Total operating revenues	2,158.5	1,993.1
Non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	113.1	98.1
Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	28.8	19.9
U.S. & Canada
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	100.4	78.5
Property lease revenue	1,159.7	1,031.3
Total operating revenues	1,260.1	1,109.8
U.S. & Canada | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	71.6	58.6
U.S. & Canada | Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	28.8	19.9
Asia-Pacific
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2.5	2.2
Property lease revenue	278.9	284.4
Total operating revenues	281.4	286.6
Asia-Pacific | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2.5	2.2
Asia-Pacific | Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Africa
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4.9	2.9
Property lease revenue	230.8	222.6
Total operating revenues	235.7	225.5
Africa | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4.9	2.9
Africa | Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Europe
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2.2	1.5
Property lease revenue	42.4	33
Total operating revenues	44.6	34.5
Europe | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2.2	1.5
Europe | Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	31.9	32.9
Property lease revenue	304.8	303.8
Total operating revenues	336.7	336.7
Latin America | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	31.9	32.9
Latin America | Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 0	$ 0

PREPAID AND OTHER CURRENT ASS_3

PREPAID AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid assets	$ 76.2	$ 66.1
Prepaid income tax	100.3	143.7
Unbilled receivables	160.8	176.9
Value added tax and other consumption tax receivables	58.1	66.3
Other miscellaneous current assets	95.2	79.6
Prepaid and other current assets	$ 490.6	$ 532.6

LEASES - MATURITIES OF MINIMUM

LEASES - MATURITIES OF MINIMUM RENTAL RECEIPTS EXPECTED UNDER NON-CANCELLABLE OPERATING LEASES (Details) $ in Millions	Mar. 31, 2021USD ($)
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Remainder of 2021	$ 4,632.2
2022	5,976.8
2023	5,866.5
2024	5,755.9
2025	5,330.3
Thereafter	32,576
Total	$ 60,137.7

LEASES - SCHEDULE OF INFORMATIO

LEASES - SCHEDULE OF INFORMATION ABOUT OTHER LEASE RELATED BALANCES (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Operating leases:
Right-of-use asset	$ 7,719.9	$ 7,789.2
Current portion of lease liability	555.8	539.9
Lease liability	6,812.9	6,884.4
Total lease liability	$ 7,368.7	$ 7,424.3

LEASES - SCHEDULE OF WEIGHTED A

LEASES - SCHEDULE OF WEIGHTED AVERAGE LEASE TERMS AND DISCOUNT RATES BY SEGMENT (Details)	Mar. 31, 2021	Dec. 31, 2020
Operating leases:
Weighted-average remaining lease term (years)	13 years 7 months 6 days	13 years 8 months 12 days
Weighted-average incremental borrowing rate	5.60%	5.60%

LEASES - LEASE COSTS (Details)

LEASES - LEASE COSTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 251.3	$ 250.7
Variable lease costs not included in lease liability	$ 69.3	$ 61.4

LEASES - SUPPLEMENTAL CASH FLOW

LEASES - SUPPLEMENTAL CASH FLOW INFOMATION (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ (244.9)	$ (252)
Non-cash items:
New operating leases	89.2	50.1
Operating lease modifications and reassessments	$ 85.7	$ 96.9

LEASES - MATURITIES OF OPERATIN

LEASES - MATURITIES OF OPERATING AND FINANCE LEASE LIABILITIES (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Operating Lease
Remainder of 2021	$ 678.3
2022	874.6
2023	842.7
2024	805.2
2025	759.8
Thereafter	6,497.9
Total lease payments	10,458.5
Less amounts representing interest	(3,089.8)
Total lease liability	7,368.7	$ 7,424.3
Less current portion of lease liability	(555.8)	(539.9)
Non-current lease liability	$ 6,812.9	$ 6,884.4

GOODWILL AND OTHER INTANGIBLE_3

GOODWILL AND OTHER INTANGIBLE ASSETS - CHANGES IN THE CARRYING VALUE OF GOODWILL (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 7,282.7
Additions and adjustments	21.3
Effect of foreign currency translation	(41.6)
Goodwill, ending balance	7,262.4
Property, US
Goodwill [Roll Forward]
Goodwill, beginning balance	4,750.8
Additions and adjustments	21.3
Effect of foreign currency translation	4.2
Goodwill, ending balance	4,776.3
Property, Asia
Goodwill [Roll Forward]
Goodwill, beginning balance	1,016.9
Additions and adjustments	0
Effect of foreign currency translation	(0.5)
Goodwill, ending balance	1,016.4
Property, Africa
Goodwill [Roll Forward]
Goodwill, beginning balance	625.6
Additions and adjustments	0
Effect of foreign currency translation	(3.4)
Goodwill, ending balance	622.2
Property, Europe
Goodwill [Roll Forward]
Goodwill, beginning balance	279.1
Additions and adjustments	0
Effect of foreign currency translation	(11.1)
Goodwill, ending balance	268
Property, Latin America
Goodwill [Roll Forward]
Goodwill, beginning balance	608.3
Additions and adjustments	0
Effect of foreign currency translation	(30.8)
Goodwill, ending balance	577.5
Services
Goodwill [Roll Forward]
Goodwill, beginning balance	2
Additions and adjustments	0
Effect of foreign currency translation	0
Goodwill, ending balance	$ 2

GOODWILL AND OTHER INTANGIBLE_4

GOODWILL AND OTHER INTANGIBLE ASSETS - INTANGIBLE ASSETS SUBJECT TO AMORTIZATION (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 20,068	$ 20,204.3
Accumulated Amortization	(6,560.7)	(6,364.5)
Net Book Value	13,507.3	13,839.8
Acquired network location intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	5,751.7	5,784
Accumulated Amortization	(2,171.1)	(2,117.6)
Net Book Value	$ 3,580.6	3,666.4
Acquired network location intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives (years)	20 years
Acquired tenant-related intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 14,221.7	14,322.5
Accumulated Amortization	(4,379.6)	(4,237.5)
Net Book Value	$ 9,842.1	10,085
Acquired tenant-related intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives (years)	20 years
Acquired licenses and other intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 94.6	97.8
Accumulated Amortization	(10)	(9.4)
Net Book Value	$ 84.6	$ 88.4
Acquired licenses and other intangibles | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives (years)	3 years
Acquired licenses and other intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives (years)	20 years

GOODWILL AND OTHER INTANGIBLE_5

GOODWILL AND OTHER INTANGIBLE ASSETS - NARRATIVE (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 253.4	$ 217.5
Weighted Average
Finite-Lived Intangible Assets [Line Items]
Remaining amortization period (in years)	15 years

GOODWILL AND OTHER INTANGIBLE_6

GOODWILL AND OTHER INTANGIBLE ASSETS - EXPECTED FUTURE AMORTIZATION EXPENSE (Details) $ in Millions	Mar. 31, 2021USD ($)
Fiscal Year
Remainder of 2021	$ 735.9
2022	975.8
2023	954.5
2024	944.9
2025	914.5
2026	$ 873.2

ACCRUED EXPENSES (Details)

ACCRUED EXPENSES (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued construction costs	$ 37.8	$ 46.5
Accrued income tax payable	22.3	20.6
Accrued pass-through costs	78.3	67.1
Amounts payable for acquisitions	15.7	58.9
Amounts payable to tenants	63.5	66.4
Accrued property and real estate taxes	222	219.1
Accrued rent	81	82.6
Payroll and related withholdings	67.1	104.4
Other accrued expenses	357.1	378.1
Total accrued expenses	$ 944.8	$ 1,043.7

LONG-TERM OBLIGATIONS - SCHEDUL

LONG-TERM OBLIGATIONS - SCHEDULE OF LONG-TERM OBLIGATIONS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 29, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Finance lease obligations	$ 29.9		$ 27.9
Total	29,326.8		29,287.5
Less current portion of long-term obligations	(1,336.5)		(789.8)
Long-term obligations	27,990.3		28,497.7
American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	26,956.8		26,113.4
American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	2,340.1		3,146.2
2020 Term Loan | Unsecured debt | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	0		749.4
2021 Multicurrency Credit Facility | Credit Facility | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	270		0
2019 Term Loan | Unsecured debt | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	995.8		996.1
Credit Facility 2021 | Credit Facility | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	$ 2,345		2,295
2.250% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.25%
Long-term debt	$ 604		605.1
4.70% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	4.70%
Long-term debt	$ 699.2		699
3.50% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.50%
Long-term debt	$ 996.5		996.1
3.000% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.00%
Long-term debt	$ 718.7		721.9
0.600% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	0.60%
Long-term debt	$ 497.1		496.8
5.00% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	5.00%
Long-term debt	$ 1,001.2		1,001.3
3.375% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.375%
Long-term debt	$ 646		645.7
2.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.95%
Long-term debt	$ 643.4		643.1
2.400% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.40%
Long-term debt	$ 745.3		745
1.375% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.375%
Long-term debt	$ 580.2		604.1
4.000% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	4.00%
Long-term debt	$ 744.8		744.3
1.300% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.30%
Long-term debt	$ 495.6		495.4
4.400% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	4.40%
Long-term debt	$ 497.2		497.1
1.600% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate		1.60%
Long-term debt	$ 694.4		0
1.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.95%
Long-term debt	$ 581.2		605.2
3.375% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.375%
Long-term debt	$ 989.9		989.5
3.125% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.125%
Long-term debt	$ 398		397.9
2.750% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.75%
Long-term debt	$ 744.5		744.3
3.55% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.55%
Long-term debt	$ 745		744.8
0.500% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	0.50%
Long-term debt	$ 871.2		907.4
3.600% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.60%
Long-term debt	$ 693.6		693.4
1.500% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.50%
Long-term debt	$ 645.3		645.1
3.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.95%
Long-term debt	$ 590.8		590.6
3.800% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.80%
Long-term debt	$ 1,633.9		1,633.5
2.900% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.90%
Long-term debt	$ 741.9		741.7
2.100% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.10%
Long-term debt	$ 740.5		740.2
1.875% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.875%
Long-term debt	$ 790.8		790.5
2.700% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate		2.70%
Long-term debt	$ 693.3		0
1.000% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.00%
Long-term debt	$ 754.5		786.1
3.700% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.70%
Long-term debt	$ 591.9		591.9
3.100% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.10%
Long-term debt	$ 1,037.8		1,037.7
2.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.95%
Long-term debt	$ 538.3		538.2
Series 2013-2A securities | Secured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	1,297		1,296.6
Series 2018-1A securities | Secured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	494.8		494.6
Series 2015-2 notes | Secured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	522.2		522.1
Insite Debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	0		800
Other subsidiary debt | Unsecured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	$ 26.1		$ 32.9
Debt repayment period	3 years

LONG-TERM OBLIGATIONS - CURRENT

LONG-TERM OBLIGATIONS - CURRENT PORTION OF LONG TERM DEBT (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 1,336.5	$ 789.8
American Tower Corporation | 2.250% senior notes | Senior notes
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 600
Debt interest rate	2.25%
American Tower Corporation | 4.70% senior notes | Senior notes
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 700
Debt interest rate	4.70%

LONG-TERM OBLIGATIONS - INSITE

LONG-TERM OBLIGATIONS - INSITE DEBT (Details) - USD ($) $ in Millions	Jan. 15, 2021	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Loss on retirement of long-term obligations		$ (25.7)	$ (34.6)
Insite Acquisition | Insite Debt
Debt Instrument [Line Items]
Debt Instrument, repurchase amount	$ 826.4
Interest expense	2.3
Loss on retirement of long-term obligations	$ 25.7

LONG-TERM OBLIGATIONS - OFFERIN

LONG-TERM OBLIGATIONS - OFFERINGS OF SENIOR NOTES (Details) $ in Millions	Mar. 29, 2021USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)
Debt Instrument [Line Items]
Proceeds from term loan		$ 0	$ 750
Debt redemption price rate (as a percent)		101.00%
Maximum adjusted EBITDA		3.5
American Tower Corporation | 1.600% senior notes | Senior notes
Debt Instrument [Line Items]
Senior note public offering, amount	$ 700
Debt interest rate	1.60%
Debt redemption price rate (as a percent)	100.00%
American Tower Corporation | 2.700% senior notes | Senior notes
Debt Instrument [Line Items]
Senior note public offering, amount	$ 700
Debt interest rate	2.70%
Debt redemption price rate (as a percent)	100.00%
American Tower Corporation | 2026 and 2031 Notes | Senior notes
Debt Instrument [Line Items]
Proceeds from term loan	$ 1,386.3

LONG-TERM DEBT OBLIGATIONS - SC

LONG-TERM DEBT OBLIGATIONS - SCHEDULE OF KEY TERMS (Details) - USD ($) $ in Millions	Mar. 29, 2021	Mar. 31, 2021
Debt Instrument [Line Items]
Debt, interest accrual period		360 days
Debt redemption price rate (as a percent)		101.00%
Senior Notes | 1.600% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Aggregate Principal Amount	$ 700
Contractual Interest Rate	1.60%
Debt redemption price rate (as a percent)	100.00%
Senior Notes | 2.700% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Aggregate Principal Amount	$ 700
Contractual Interest Rate	2.70%
Debt redemption price rate (as a percent)	100.00%

LONG-TERM OBLIGATIONS - BANK FA

LONG-TERM OBLIGATIONS - BANK FACILITIES (Details)	Feb. 10, 2021EUR (€)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Feb. 10, 2021USD ($)	Feb. 10, 2021EUR (€)
Line of Credit Facility [Line Items]
Borrowings under credit facilities		$ 1,870,000,000	$ 2,642,300,000
Credit Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				$ 3,900,000,000	€ 3,225,000,000
Credit Facility | Credit Facility 2019
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity		1,000,000,000
Credit Facility | 2021 Multicurrency Credit Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				$ 6,100,000,000
Total debt to adjusted EBITDA ratio, maximum				7.50	7.50
Total debt to adjusted EBITDA ratio, step down				6	6
Total debt to adjusted EBITDA ratio, after a qualified acquisition				7	7
Limitation of indebtedness guaranteed by subsidiaries				$ 3,000,000,000
Limitation of indebtedness guaranteed by subsidiaries rate				50.00%	50.00%
Default threshold		400,000,000		$ 500,000,000
Credit Facility | 2021 Multicurrency Credit Facility | Line of Credit
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				4,100,000,000
Borrowings under credit facilities | €	€ 1,300,000,000
Credit Facility | 2021 Credit Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				$ 4,400,000,000
Total debt to adjusted EBITDA ratio, maximum				7.50	7.50
Total debt to adjusted EBITDA ratio, step down				6	6
Total debt to adjusted EBITDA ratio, after a qualified acquisition				7	7
Limitation of indebtedness guaranteed by subsidiaries				$ 3,000,000,000
Limitation of indebtedness guaranteed by subsidiaries rate				50.00%	50.00%
Credit Facility | 2021 Credit Facility | Line of Credit
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				$ 2,900,000,000
Letter of Credit | 2021 Multicurrency Credit Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity		$ 1,000,000,000		$ 3,000,000,000
Letter of Credit | 2021 Credit Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity | €					€ 1,500,000,000

LONG-TERM OBLIGATIONS - CREDIT

LONG-TERM OBLIGATIONS - CREDIT FACILITIES (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Line of Credit Facility [Line Items]
Borrowings under credit facilities	$ 1,870,000,000	$ 2,642,300,000
American Tower Corporation | Credit Facility | 2021 Multicurrency Credit Facility
Line of Credit Facility [Line Items]
Repayment of indebtedness under credit facility	1,600,000,000
Borrowings under credit facilities	1,800,000,000
American Tower Corporation | Credit Facility | InSite Debt and 2020 Term Loan
Line of Credit Facility [Line Items]
Repayment of indebtedness under credit facility	750,000,000
American Tower Corporation | Credit Facility | 2021 Credit Facility
Line of Credit Facility [Line Items]
Repayment of indebtedness under credit facility	0
Borrowings under credit facilities	$ 50,000,000

LONG-TERM OBLIGATIONS - 2021 DE

LONG-TERM OBLIGATIONS - 2021 DELAYED DRAW TERM LOANS (Details) - Feb. 10, 2021 - Unsecured debt $ in Billions	USD ($)	EUR (€)
2021 364-Day Delayed Draw Term Loan
Debt Instrument [Line Items]
Senior note public offering, amount	$ 1.3	€ 1,100,000,000
Debt Instrument, Term	364 days
2021 364-Day Delayed Draw Term Loan | Euro Interbank Offered Rate (EURIBOR)
Debt Instrument [Line Items]
Current margin over LIBOR (as a percent)	1.00%
2021 Three Year Delayed Draw Term Loan
Debt Instrument [Line Items]
Senior note public offering, amount	$ 1	€ 825,000,000
Debt Instrument, Term	3 years
2021 Three Year Delayed Draw Term Loan | Euro Interbank Offered Rate (EURIBOR)
Debt Instrument [Line Items]
Current margin over LIBOR (as a percent)	1.125%

LONG-TERM OBLIGATIONS - BRIDGE

LONG-TERM OBLIGATIONS - BRIDGE FACILITY (Details) - Credit Facility $ in Billions	Feb. 10, 2021USD ($)	Feb. 10, 2021EUR (€)	Jan. 13, 2021USD ($)	Jan. 13, 2021EUR (€)
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity	$ 3.9	€ 3,225,000,000
Bridge Loan
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity	$ 5.2	€ 4,275,000,000	$ 9.1	€ 7,500,000,000

LONG-TERM OBLIGATIONS - SCHED_2

LONG-TERM OBLIGATIONS - SCHEDULE OF LINES OF CREDIT (Details) - American Tower Corporation $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)renewalPeriod
Credit Facility
Line of Credit Facility [Line Items]
Optional renewal periods | renewalPeriod	2
2021 Multicurrency Credit Facility | Credit Facility
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 270
Undrawn letters of credit	$ 3.8
Current commitment fee (as a percent)	0.11%
2021 Multicurrency Credit Facility | Credit Facility | Current margin over LIBOR
Line of Credit Facility [Line Items]
Current margin over LIBOR (as a percent)	1.125%
2021 Credit Facility | Credit Facility
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 2,345
Undrawn letters of credit	$ 0.8
Current commitment fee (as a percent)	0.11%
2021 Credit Facility | Credit Facility | Current margin over LIBOR
Line of Credit Facility [Line Items]
Current margin over LIBOR (as a percent)	1.125%
2019 Term Loan | Unsecured debt
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 1,000
2019 Term Loan | Unsecured debt | Current margin over LIBOR
Line of Credit Facility [Line Items]
Current margin over LIBOR (as a percent)	1.125%
2021 364-Day Delayed Draw Term Loan
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 0
Current commitment fee (as a percent)	0.11%
2021 364-Day Delayed Draw Term Loan | Current margin over LIBOR
Line of Credit Facility [Line Items]
Current margin over LIBOR (as a percent)	1.00%
2021 Three Year Delayed Draw Term Loan
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 0
Current commitment fee (as a percent)	0.11%
2021 Three Year Delayed Draw Term Loan | Current margin over LIBOR
Line of Credit Facility [Line Items]
Current margin over LIBOR (as a percent)	1.125%
Bridge Loan
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 0
Current commitment fee (as a percent)	0.11%
Bridge Loan | Current margin over LIBOR
Line of Credit Facility [Line Items]
Current margin over LIBOR (as a percent)	1.125%

LONG-TERM OBLIGATIONS - INDIA C

LONG-TERM OBLIGATIONS - INDIA CREDIT FACILITY (Details) - Mar. 31, 2021	USD ($)	INR (₨)
India Credit Facility | Working Capital Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity	$ 13,700,000	₨ 1,000,000,000

FAIR VALUE MEASUREMENTS - ASSET

FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED AT FAIR VALUE ON A RECURRING BASIS (Details) - Fair Value, Measurements, Recurring - Interest rate swap agreements - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Level 1
Assets:
Interest rate swap agreements	$ 0	$ 0
Liabilities:
Interest rate swap agreements	0	0
Fair value of debt related to interest rate swap	26.3	31.4
Level 2
Assets:
Interest rate swap agreements	24.5	29.2
Liabilities:
Interest rate swap agreements	0	0.1
Fair value of debt related to interest rate swap	0	0
Level 3
Assets:
Interest rate swap agreements	0	0
Liabilities:
Interest rate swap agreements	0	0
Fair value of debt related to interest rate swap	$ 0	$ 0

FAIR VALUE MEASUREMENTS - NARRA

FAIR VALUE MEASUREMENTS - NARRATIVE (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	$ 0.6	$ 3.7
Long-term obligations	29,326.8		$ 29,287.5
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	30,400		31,400
Estimate of Fair Value Measurement | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	24,300		24,000
Estimate of Fair Value Measurement | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 6,100		$ 7,400

INCOME TAXES - NARRATIVE (Detai

INCOME TAXES - NARRATIVE (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact the ETR	$ 104,700,000	$ 105,900,000
Unrecognized tax benefits, decrease resulting from prior period tax positions	1,500,000
Unrecognized tax benefits, increase resulting from current period tax positions	1,200,000
Unrecognized tax benefits, income tax penalties and interest accrued	37,100,000	$ 34,400,000
Unrecognized tax benefits, decrease from foreign currency exchange rate fluctuations	2,200,000
Minimum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	0
Maximum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	$ 34,200,000

INCOME TAXES - SCHEDULE OF PENA

INCOME TAXES - SCHEDULE OF PENALTIES AND INCOME TAX RELATED EXPENSES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Penalties and income tax-related interest expense	$ 3.7	$ 1.7

STOCK-BASED COMPENSATION - NARR

STOCK-BASED COMPENSATION - NARRATIVE (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP, discount rate (as a percent)	15.00%
Total unrecognized compensation expense	$ 0.1
Stock-based compensation expense	$ 38	$ 47.7
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected recognition of stock award compensation expense weighted average period ( less than one year for stock options)	3 years
Granted (in shares)	538,239
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years	3 years	3 years	3 years	3 years	3 years
Total unrecognized compensation expense	$ 20.8
Expected recognition of stock award compensation expense weighted average period ( less than one year for stock options)	3 years
Granted (in shares)	92,312				110,925	114,823
Stock-based compensation expense	$ 1.5
Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential target shares	0.00%
Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential target shares	200.00%
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected recognition of stock award compensation expense weighted average period ( less than one year for stock options)	1 year
2007 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issuable under stock incentive plan (in shares)	5,900,000
2007 Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Total unrecognized compensation expense	$ 197.7
2007 Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
2007 Plan | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
2021 PSUs | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	92,312

STOCK-BASED COMPENSATION - SUMM

STOCK-BASED COMPENSATION - SUMMARY OF STOCK-BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 38	$ 47.7
Amount capitalized		0.5
Property costs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense		0.6
Services
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense		0.3
Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 38	$ 46.8

STOCK-BASED COMPENSATION - SU_2

STOCK-BASED COMPENSATION - SUMMARY OF THE COMPANY'S OPTION ACTIVITY (Details)	3 Months Ended
	Mar. 31, 2021shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding as of January 1, 2020 (in shares)	2,016,261
Exercised (in shares)	(23,958)
Forfeited (in shares)	0
Expired (in shares)	0
Outstanding as of September 30, 2020 (in shares)	1,992,303

STOCK-BASED COMPENSATION - SU_3

STOCK-BASED COMPENSATION - SUMMARY OF THE COMPANY'S RESTRICTED STOCK UNIT ACTIVITY (Details) - shares	3 Months Ended				12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
RSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	1,245,075
Granted (in shares)	538,239
Vested (in shares)	(547,567)
Forfeited (in shares)	(13,424)
Ending balance (in shares)	1,222,323				1,245,075
Vested and deferred as of September 30, 2020 (in shares)	0						58,204
PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	320,510
Granted (in shares)	92,312				110,925	114,823
Vested (in shares)	(66,834)
Forfeited (in shares)	0
Ending balance (in shares)	345,988				320,510
Vested and deferred as of September 30, 2020 (in shares)	96,048
Vesting period	3 years	3 years	3 years	3 years	3 years	3 years
2020 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	70,739
Ending balance (in shares)					70,739
2019 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	86,889
Ending balance (in shares)					86,889
2018 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	162,882
Ending balance (in shares)					162,882

REDEEMABLE NONCONTROLLING INT_3

REDEEMABLE NONCONTROLLING INTERESTS - NARRATIVE (Details) $ / shares in Units, € in Millions, $ in Millions, ₨ in Billions	3 Months Ended				12 Months Ended
	Mar. 31, 2021USD ($)$ / shares	Mar. 31, 2021INR (₨)	Mar. 31, 2021EUR (€)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2020INR (₨)	Apr. 29, 2021	Dec. 31, 2019	Apr. 21, 2016
Noncontrolling Interest [Line Items]
Purchase of redeemable noncontrolling interest	$ 2.5			$ 524.4
ATC, TIPL
Noncontrolling Interest [Line Items]
Ownership interest percentage	92.00%				92.00%	92.00%		79.00%
Noncontrolling interest, ownership percentage by noncontrolling owners (as a percent)					8.00%	8.00%		21.00%
ATC, TIPL | Subsequent Event
Noncontrolling Interest [Line Items]
Ownership interest percentage							100.00%
Ghana and Uganda Subsidiaries
Noncontrolling Interest [Line Items]
Purchase of redeemable noncontrolling interest	$ 524.4
Ownership interest percentage	100.00%				51.00%	51.00%
Payments for repurchase of redeemable noncontrolling interest, interest portion	$ 1.4
Eure-et-Loir
Noncontrolling Interest [Line Items]
Purchase of redeemable noncontrolling interest	$ 2.5		€ 2.2
Tata Teleservices Limited
Noncontrolling Interest [Line Items]
Percentage of ownership before transaction					100.00%	100.00%
Purchase of redeemable noncontrolling interest					$ 337.3	₨ 24.8
Macquarie | ATC, TIPL
Noncontrolling Interest [Line Items]
Percentage of ownership before transaction	100.00%	100.00%	100.00%
Purchase of redeemable noncontrolling interest	$ 176.5	₨ 12.9
Temporary equity, redemption price per share (in dollars per share) | $ / shares	$ 175
Viom Transaction
Noncontrolling Interest [Line Items]
Percentage of interests acquired									51.00%

REDEEMABLE NONCONTROLLING INT_4

REDEEMABLE NONCONTROLLING INTERESTS - CHANGE IN REDEEMABLE NONCONTROLLING INTEREST (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Balance as of January 1,	$ 212.1	$ 1,096.5	$ 1,096.5
Net income attributable to noncontrolling interests	2.3	7.7
Adjustment to noncontrolling interest redemption value	1.2	(6.3)
Purchase of redeemable noncontrolling interest	(2.5)	(524.4)
Foreign currency translation adjustment attributable to noncontrolling interests	(0.2)	(32.1)
Balance as of March 31,	$ 212.9	$ 541.4	$ 212.1

EQUITY - NARRATIVE (Details)

EQUITY - NARRATIVE (Details) € in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Aug. 31, 2020USD ($)	Mar. 31, 2021USD ($)shares	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Dec. 31, 2017USD ($)	Mar. 31, 2011USD ($)
Class of Stock [Line Items]
Proceeds from stock options		$ 1,900,000	$ 11,100,000
Stock offering, value (up to)	$ 1,000,000,000
Treasury stock repurchased			45,100,000
Accrued dividend RSU		7,600,000
Paid dividend RSU		7,300,000	$ 7,600,000
Payments to acquire noncontrolling interest		$ 6,000,000
Subsidiary Interest
Class of Stock [Line Items]
Ownership interest percentage		100.00%
ATC Europe
Class of Stock [Line Items]
Dividends				$ 16,200,000	€ 13.2
2020 ATM Program
Class of Stock [Line Items]
Stock offerings (in shares) | shares		0
2011 Buyback
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,500,000,000
Treasury stock activity (in shares) | shares		14,361,283
Treasury stock repurchased		$ 1,500,000,000
2017 Buyback
Class of Stock [Line Items]
Stock repurchase program, authorized amount						$ 2,000,000,000
Treasury stock activity (in shares) | shares		0

EQUITY - DISTRIBUTIONS (Details

EQUITY - DISTRIBUTIONS (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 29, 2021	Mar. 04, 2021	Feb. 02, 2021	Dec. 03, 2020	Mar. 12, 2020	Jan. 14, 2020	Dec. 11, 2019	Mar. 31, 2021	Mar. 31, 2020	Apr. 29, 2020
Dividends Payable [Line Items]
Aggregate Payment Amount on common stock								$ 544.9	$ 454.9
Common Stock
Dividends Payable [Line Items]
Distribution per share, common stock (in dollars per share)		$ 1.24		$ 1.21	$ 1.08		$ 1.01
Aggregate Payment Amount on common stock			$ 537.6			$ 447.3				$ 478.8
Common Stock | Subsequent Event
Dividends Payable [Line Items]
Aggregate Payment Amount on common stock	$ 551.5

EARNINGS PER COMMON SHARE - SCH

EARNINGS PER COMMON SHARE - SCHEDULE OF EARNINGS PER BASIC AND DILUTED BY COMMON CLASS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income attributable to American Tower Corporation common stockholders	$ 645	$ 415
Basic weighted average common shares outstanding (in shares)	444,486	443,055
Dilutive securities (in shares)	1,808	2,777
Diluted weighted average common shares outstanding (in shares)	446,294	445,832
Basic net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 1.45	$ 0.94
Diluted net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 1.45	$ 0.93

EARNINGS PER COMMON SHARE - S_2

EARNINGS PER COMMON SHARE - SCHEDULE OF SHARES EXCLUDED FROM COMPUTATION OF EARNINGS PER SHARE (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from dilutive effect (in shares)	0	86

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - NARRATIVE (Details) ₨ in Millions, $ in Millions	Dec. 05, 2016USD ($)	Dec. 05, 2016INR (₨)	Mar. 27, 2015USD ($)communications_siterenewalPeriod	Mar. 31, 2021USD ($)communications_siterenewalPeriod	Dec. 31, 2000communications_site
INDIA
Loss Contingencies [Line Items]
Foreign income tax assessment	$ 69.8	₨ 4,750
Verizon Transaction
Loss Contingencies [Line Items]
Leased assets, number of communication sites | communications_site			11,250
Right to lease, weighted average term			28 years
Aggregate purchase option price for towers | $			$ 5,000
Customer lease, initial term			10 years
Successive terms to renew lease (in numbers of terms) | renewalPeriod			8
Lease renewal term			5 years
AT&T Transaction
Loss Contingencies [Line Items]
Leased assets, number of communication sites | communications_site				331	2,100
Aggregate purchase option price for towers | $				$ 997
Successive terms to renew lease (in numbers of terms) | renewalPeriod				5
Lease renewal term				5 years
Operating lease, term of contract				27 years

ACQUISITIONS - SCHEDULE OF MERG

ACQUISITIONS - SCHEDULE OF MERGER AND ACQUISITION RELATED COSTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Business Combinations [Abstract]
Acquisition and merger related expenses	$ 34.6	$ 7.6
Integration costs	$ 16.6	$ 6.6

ACQUISITIONS - NARRATIVE (Detai

ACQUISITIONS - NARRATIVE (Details) € in Millions, $ in Millions	Jan. 13, 2021USD ($)communicationSite	Jan. 13, 2021EUR (€)communicationSite	Dec. 23, 2020USD ($)networkcommunicationSitelandParceltower	Dec. 31, 2019USD ($)communicationSite	Nov. 28, 2019USD ($)communicationSite	Nov. 28, 2019EUR (€)communicationSite	Mar. 31, 2021USD ($)communicationSite	Apr. 29, 2021communicationSite	Dec. 31, 2020USD ($)communicationSite	Dec. 19, 2019communicationSite
Business Acquisition [Line Items]
Payment received related to acquisition							$ 4
Estimated aggregate impact of acquisitions completed, revenue							0.5
Estimated aggregate impact of acquisitions completed, gross margin							0.4
Accounts payable							130.1		$ 139.1
Telxius Telecom S.A.
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite	31,000	31,000
Consideration transferred	$ 9,400	€ 7,700
Insite Acquisition
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite			3,000
Percentage of interests acquired			100.00%
Number of land parcels under communication sites | landParcel			600
Consideration transferred			$ 3,500
Adjustment to assets							3.1
Adjustment to liabilities							18.2
Increase to goodwill							21.3
Insite Acquisition | U.S.
Business Acquisition [Line Items]
Number of broadcast and wireless communications towers | tower			1,400
Number of DAS networks | network			40
Number of rooftop sites | communicationSite			400
Insite Acquisition | CANADA
Business Acquisition [Line Items]
Number of broadcast and wireless communications towers | tower			200
Entel Acquisition
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite										3,200
Aggregate purchase price				$ 800			$ 14.7
Entel Acquisition | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite				2,400			50		530
Other Acquisitions 2021 | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite							66
Aggregate purchase price							$ 62.5
Accounts payable							$ 4
Orange S.A. | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite					2,000	2,000	564
Purchase, period to be paid over					5 years	5 years
Orange S.A. | Communication Sites | Subsequent Event
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite								81
Orange S.A. | Communication Sites | Minimum
Business Acquisition [Line Items]
Aggregate purchase price					$ 550.5	€ 500
Orange S.A. | Communication Sites | Maximum
Business Acquisition [Line Items]
Aggregate purchase price					$ 660.5	€ 600

ACQUISITIONS - SUMMARY OF ALLOC

ACQUISITIONS - SUMMARY OF ALLOCATION OF THE PURCHASE PRICE (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)site	Dec. 31, 2020USD ($)
Asset Acquisition:
Goodwill	$ 7,262.4	$ 7,282.7
Acquisitions 2021
Asset Acquisition:
Current assets	0.3
Property and equipment	22.5
Other non-current assets	5.8
Current liabilities	(1)
Deferred tax liability	0
Other non-current liabilities	(3.4)
Net assets acquired	77.2
Goodwill	0
Fair value of net assets acquired	77.2
Debt assumed	0
Purchase price	$ 77.2
Estimated Useful Lives (years)	20 years
Acquisitions 2021 | Peru
Asset Acquisition:
Number of sites acquired | site	12
Acquisitions 2021 | Tenant-related intangible assets
Asset Acquisition:
Intangible assets	$ 37.3
Acquisitions 2021 | Network location intangible assets
Asset Acquisition:
Intangible assets	15.7
Acquisitions 2021 | Other intangible assets
Asset Acquisition:
Intangible assets	$ 0

ACQUISITIONS - PRO FORMA INFORM

ACQUISITIONS - PRO FORMA INFORMATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Business Combinations [Abstract]
Pro forma revenues	$ 2,158.9	$ 2,044.6
Pro forma net income attributable to American Tower Corporation common stockholders	$ 644.9	$ 369.8
Pro forma net income per common share amounts:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.45	$ 0.83
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.45	$ 0.83

BUSINESS SEGMENTS (Details)

BUSINESS SEGMENTS (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	6
Segment revenues	$ 2,158.5	$ 1,993.1
Segment selling, general, administrative and development expense	182.6	217.8
OPERATING INCOME	828.7	736.8
Stock-based compensation expense	38	47.7
Depreciation, amortization and accretion	522.5	472.3
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	702.6	439.7
Total assets	46,942.5	40,789.1	$ 47,233.5
Operating Expense
Segment Reporting Information [Line Items]
Stock-based compensation expense		0.9
Selling, General and Administrative Expenses
Segment Reporting Information [Line Items]
Stock-based compensation expense	38	46.8
Operating Segments
Segment Reporting Information [Line Items]
Segment revenues	2,158.5	1,993.1
Segment operating expenses	574.3	551.1
Segment gross margin	1,584.2	1,442
Segment selling, general, administrative and development expense	98.4	127.3
OPERATING INCOME	1,485.8	1,314.7
Operating Segments | Property
Segment Reporting Information [Line Items]
Segment revenues	2,129.7	1,973.2
Segment operating expenses	563.3	543.5
Segment gross margin	1,566.4	1,429.7
Segment selling, general, administrative and development expense	94.2	123.8
OPERATING INCOME	1,472.2	1,305.9
Total assets	46,415.3	40,276.7
Operating Segments | Property, US
Segment Reporting Information [Line Items]
Segment revenues	1,231.3	1,089.9
Segment operating expenses	197.9	190
Segment gross margin	1,033.4	899.9
Segment selling, general, administrative and development expense	39.3	42
OPERATING INCOME	994.1	857.9
Total assets	27,331.9	22,486.9
Operating Segments | Property, Asia
Segment Reporting Information [Line Items]
Segment revenues	281.4	286.6
Segment operating expenses	175.5	164
Segment gross margin	105.9	122.6
Segment selling, general, administrative and development expense	7.1	32.6
OPERATING INCOME	98.8	90
Total assets	5,214.1	4,986
Operating Segments | Property, Africa
Segment Reporting Information [Line Items]
Segment revenues	235.7	225.5
Segment operating expenses	80.9	77.7
Segment gross margin	154.8	147.8
Segment selling, general, administrative and development expense	18.9	17.1
OPERATING INCOME	135.9	130.7
Total assets	4,905.4	4,510.3
Operating Segments | Property, Europe
Segment Reporting Information [Line Items]
Segment revenues	44.6	34.5
Segment operating expenses	7.8	6.6
Segment gross margin	36.8	27.9
Segment selling, general, administrative and development expense	5.6	5.5
OPERATING INCOME	31.2	22.4
Total assets	1,836.7	1,554.5
Operating Segments | Property, Latin America
Segment Reporting Information [Line Items]
Segment revenues	336.7	336.7
Segment operating expenses	101.2	105.2
Segment gross margin	235.5	231.5
Segment selling, general, administrative and development expense	23.3	26.6
OPERATING INCOME	212.2	204.9
Total assets	7,127.2	6,739
Operating Segments | Services
Segment Reporting Information [Line Items]
Segment revenues	28.8	19.9
Segment operating expenses	11	7.6
Segment gross margin	17.8	12.3
Segment selling, general, administrative and development expense	4.2	3.5
OPERATING INCOME	13.6	8.8
Total assets	59.4	29
Other
Segment Reporting Information [Line Items]
Segment selling, general, administrative and development expense	46.2	43.7
Stock-based compensation expense	38	47.7
Depreciation, amortization and accretion	522.5	472.3
Other expense	176.5	311.3
Total assets	$ 467.8	$ 483.4

Uncategorized Items - amt-20210

Label	Element	Value
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	us-gaap_AdjustmentsToAdditionalPaidInCapitalIncreaseInCarryingAmountOfRedeemablePreferredStock	$ 0
AOCI Attributable to Parent [Member]
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	us-gaap_AdjustmentsToAdditionalPaidInCapitalIncreaseInCarryingAmountOfRedeemablePreferredStock	142,200,000
Additional Paid-in Capital [Member]
Adjustments to Additional Paid in Capital, Increase in Carrying Amount of Redeemable Preferred Stock	us-gaap_AdjustmentsToAdditionalPaidInCapitalIncreaseInCarryingAmountOfRedeemablePreferredStock	$ (142,200,000)