American Tower (AMT) 10-Q 28 Oct 21 2021 Q3 Quarterly report Financial data

COVER

COVER - shares	9 Months Ended
	Sep. 30, 2021	Oct. 21, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 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 (in shares)		455,413,697
Entity Central Index Key	0001053507
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
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
0.450% Senior Notes due 2027
Document Information [Line Items]
Title of 12(b) Security	0.450% Senior Notes due 2027
Trading Symbol	AMT 27C
Security Exchange Name	NYSE
0.400% Senior Notes due 2027
Document Information [Line Items]
Title of 12(b) Security	0.400% Senior Notes due 2027
Trading Symbol	AMT 27D
Security Exchange Name	NYSE
0.500% Senior Notes due 2028
Document Information [Line Items]
Title of 12(b) Security	0.500% Senior Notes due 2028
Trading Symbol	AMT 28A
Security Exchange Name	NYSE
0.875% Senior Notes due 2029
Document Information [Line Items]
Title of 12(b) Security	0.875% Senior Notes due 2029
Trading Symbol	AMT 29B
Security Exchange Name	NYSE
0.950% Senior Notes due 2030
Document Information [Line Items]
Title of 12(b) Security	0.950% Senior Notes due 2030
Trading Symbol	AMT 30C
Security Exchange Name	NYSE
1.000% Senior Notes due 2032
Document Information [Line Items]
Title of 12(b) Security	1.000% Senior Notes due 2032
Trading Symbol	AMT 32
Security Exchange Name	NYSE
1.250% Senior Notes due 2033
Document Information [Line Items]
Title of 12(b) Security	1.250% Senior Notes due 2033
Trading Symbol	AMT 33
Security Exchange Name	NYSE

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 3,277.2	$ 1,746.3
Restricted cash	422.1	115.1
Accounts receivable, net	750.6	511.6
Prepaid and other current assets	592	532.6
Total current assets	5,041.9	2,905.6
PROPERTY AND EQUIPMENT, net	14,268.1	12,808.7
GOODWILL	10,480.8	7,282.7
OTHER INTANGIBLE ASSETS, net	18,768.4	13,839.8
DEFERRED TAX ASSET	150.2	123.1
DEFERRED RENT ASSET	2,403.3	2,084.3
RIGHT-OF-USE ASSET	9,021.9	7,789.2
NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS	395.4	400.1
TOTAL	60,530	47,233.5
CURRENT LIABILITIES:
Accounts payable	217.4	139.1
Accrued expenses	1,165.4	1,043.7
Distributions payable	602.2	544.6
Accrued interest	250.2	207.8
Current portion of operating lease liability	734.3	539.9
Current portion of long-term obligations	2,106.4	789.8
Unearned revenue	1,448.2	390.6
Total current liabilities	6,524.1	3,655.5
LONG-TERM OBLIGATIONS	31,439	28,497.7
OPERATING LEASE LIABILITY	7,863.2	6,884.4
ASSET RETIREMENT OBLIGATIONS	1,930.2	1,571.3
DEFERRED TAX LIABILITY	1,927.5	859.5
OTHER NON-CURRENT LIABILITIES	1,157.6	984.6
Total liabilities	50,841.6	42,453
COMMITMENTS AND CONTINGENCIES
REDEEMABLE NONCONTROLLING INTERESTS	211.4	212.1
EQUITY (shares in thousands):
Common stock: $.01 par value; 1,000,000 shares authorized; 466,324 and 455,245 shares issued; and 455,409 and 444,330 shares outstanding, respectively	4.7	4.6
Additional paid-in capital	12,081.3	10,473.7
Distributions in excess of earnings	(960.4)	(1,343)
Accumulated other comprehensive loss	(4,432)	(3,759.4)
Treasury stock (10,915 shares at cost)	(1,282.4)	(1,282.4)
Total American Tower Corporation equity	5,411.2	4,093.5
Noncontrolling interests	4,065.8	474.9
Total equity	9,477	4,568.4
TOTAL	$ 60,530	$ 47,233.5

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares shares in Thousands	Sep. 30, 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	1,000,000
Common stock, shares issued (in shares)	466,324	455,245
Common stock, shares outstanding (in shares)	455,409	444,330
Treasury stock, shares (in shares)	10,915	10,915

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
REVENUES:
Total operating revenues	$ 2,454.3	$ 2,012.9	$ 6,911.7	$ 5,919
Costs of operations (exclusive of items shown separately below):
Property	693.4	552.1	1,880	1,626.5
Depreciation, amortization and accretion	611.4	473.9	1,688.7	1,401.1
Selling, general, administrative and development expense	205.9	176	595.7	582.4
Other operating expenses	85.2	15.3	175.4	67.7
Total operating expenses	1,626.8	1,227.8	4,406.3	3,705.8
OPERATING INCOME	827.5	785.1	2,505.4	2,213.2
OTHER INCOME (EXPENSE):
Interest income	9.4	9.7	28.4	28.2
Interest expense	(226.1)	(190.9)	(646.8)	(597.4)
Loss on retirement of long-term obligations	0	(37.2)	(25.7)	(71.8)
Other income (expense) (including foreign currency gains (losses) of $180.5, $(49.4), $422.1, and $(152.7) respectively)	166.8	(64.5)	439.6	(170.8)
Total other expense	(49.9)	(282.9)	(204.5)	(811.8)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	777.6	502.2	2,300.9	1,401.4
Income tax provision	(51.4)	(39.3)	(174.5)	(71.5)
NET INCOME	726.2	462.9	2,126.4	1,329.9
Net (income) loss attributable to noncontrolling interests	(3.2)	1.5	(12.1)	(4.4)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 723	$ 464.4	$ 2,114.3	$ 1,325.5
NET INCOME PER COMMON SHARE AMOUNTS:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.59	$ 1.05	$ 4.70	$ 2.99
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.58	$ 1.04	$ 4.68	$ 2.97
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING (in thousands):
BASIC (in shares)	455,224	443,766	450,148	443,420
DILUTED (in shares)	456,977	446,156	451,981	446,008
Property
REVENUES:
Total operating revenues	$ 2,368.9	$ 1,987.6	$ 6,731.6	$ 5,854
Services
REVENUES:
Total operating revenues	85.4	25.3	180.1	65
Costs of operations (exclusive of items shown separately below):
Services	$ 30.9	$ 10.5	$ 66.5	$ 28.1

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Foreign currency (losses) gains	$ 180.5	$ (49.4)	$ 422.1	$ (152.7)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 726.2	$ 462.9	$ 2,126.4	$ 1,329.9
Other comprehensive income (loss):
Changes in fair value of cash flow hedges, each net of tax expense of $0	0	(0.1)	0	(0.2)
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	0	0.1	0.1	0.2
Foreign currency translation adjustments, net of tax expense (benefit) of $0.0, $(0.0), $(0.0) and $(0.0), respectively.	(622)	115	(826.9)	(1,222.7)
Other comprehensive (loss) income	(622)	115	(826.8)	(1,222.7)
Comprehensive income	104.2	577.9	1,299.6	107.2
Comprehensive loss (income) attributable to noncontrolling interests	89.7	(30.2)	94.6	(7.1)
Allocation of accumulated other comprehensive income (loss) resulting from purchases of noncontrolling interest and redeemable noncontrolling interests	0	0	47.5	(142.2)
Comprehensive income (loss) attributable to American Tower Corporation stockholders	$ 193.9	$ 547.7	$ 1,441.7	$ (42.1)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Changes in fair value of cash flow hedges, tax	$ 0	$ 0	$ 0	$ 0
Reclassification of unrealized gains on cash flow hedges to net income, tax	0	0	0	0
Foreign currency translation adjustments, tax expense (benefit)	$ 0	$ 0	$ 0	$ 0

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 2,126.4	$ 1,329.9
Adjustments to reconcile net income to cash provided by operating activities
Depreciation, amortization and accretion	1,688.7	1,401.1
Stock-based compensation expense	98	99
Loss on early retirement of long-term obligations	25.7	71.8
Other non-cash items reflected in statements of operations	(340.8)	248.1
Increase in net deferred rent balances	(324.3)	(178.9)
Right-of-use asset and Operating lease liability, net	13.9	0.2
Changes in unearned revenue	995.1	12
Increase in assets	(201.6)	(148.9)
Increase (decrease) in liabilities	59.9	(85.2)
Cash provided by operating activities	4,141	2,749.1
CASH FLOWS FROM INVESTING ACTIVITIES
Payments for purchase of property and equipment and construction activities	(916.7)	(668.8)
Payments for acquisitions, net of cash acquired	(9,595.3)	(333.6)
Proceeds from sale of short-term investments and other non-current assets	13.8	14.7
Payment for investments in equity securities	(25)	0
Deposits and other	(1.3)	17.1
Cash used for investing activities	(10,524.5)	(970.6)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings under credit facilities	7,666.9	5,380.4
Proceeds from issuance of senior notes, net	5,609.4	6,232.1
Proceeds from term loans	2,347	1,940
Repayments of notes payable, credit facilities, senior notes, secured debt, term loans and finance leases	(10,752.8)	(12,918.1)
Distributions to noncontrolling interest holders	(223.1)	(13.8)
Contributions from noncontrolling interest holders	3,078.2	0
Purchases of common stock	0	(56)
Proceeds from stock options and employee stock purchase plan	60.4	82.5
Distributions paid on common stock	(1,674.4)	(1,421.8)
Proceeds from the issuance of common stock, net	2,361.8	0
Payment for early retirement of long-term obligations	(61.9)	(68.2)
Deferred financing costs and other financing activities	(126.2)	(152.1)
Purchase of redeemable noncontrolling interest	(2.5)	(524.4)
Cash provided by (used for) financing activities	8,282.8	(1,519.4)
Net effect of changes in foreign currency exchange rates on cash and cash equivalents, and restricted cash	(61.4)	(106.9)
NET INCREASE IN CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH	1,837.9	152.2
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	3,699.3	1,730.2
CASH PAID FOR INCOME TAXES (NET OF REFUNDS OF $35.2 AND $24.2, RESPECTIVELY)	121.1	86
CASH PAID FOR INTEREST	576.9	643.4
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment under finance leases and perpetual easements	42.2	48.7
Decrease in accounts payable and accrued expenses for purchases of property and equipment and construction activities	(0.4)	(16.7)
Settlement of third-party debt	$ (9)	$ (5)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Statement of Cash Flows [Abstract]
Income tax refunds	$ 35.2	$ 24.2

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
Balance at beginning of period (shares) at Dec. 31, 2019		453,541	10,651
Balance at beginning of period 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)		1,526
Stock-based compensation related activity	102.8	$ 0		102.8
Issuance of common stock-stock purchase plan (in shares)		38
Issuance of common stock- stock purchase plan	6.9	$ 0		6.9
Treasury stock activity (shares)			(264)
Treasury stock activity	(56)		$ (56)
Changes in fair value of cash flow hedges, net of tax	(0.2)				(0.2)
Reclassification of unrealized losses on cash flow hedges to net income, net of tax	0.2				0.2
Foreign currency translation adjustment, net of tax	(1,204.3)				(1,225.4)		21.1
Distributions to noncontrolling interest holders	(1.9)						(1.9)
Purchase of redeemable noncontrolling interest	0			142.2	(142.2)
Common stock distributions declared	(1,477.5)					(1,477.5)
Net income	1,328.7					1,325.5	3.2
Balance at end of period (shares) at Sep. 30, 2020		455,105	10,915
Balance at end of period at Sep. 30, 2020	4,189.1	$ 4.5	$ (1,282.4)	10,369.6	(4,191.2)	(1,168.8)	457.4
Balance at beginning of period (shares) at Jun. 30, 2020		454,476	10,915
Balance at beginning of period at Jun. 30, 2020	4,060.3	$ 4.5	$ (1,282.4)	10,297.8	(4,274.5)	(1,125.1)	440
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation related activity (shares)		629
Stock-based compensation related activity	71.8	$ 0		71.8
Changes in fair value of cash flow hedges, net of tax	(0.1)				(0.1)
Reclassification of unrealized losses on cash flow hedges to net income, net of tax	0.1				0.1
Foreign currency translation adjustment, net of tax	102.2				83.3		18.9
Distributions to noncontrolling interest holders	(0.2)						(0.2)
Common stock distributions declared	(508.1)					(508.1)
Net income	463.1					464.4	(1.3)
Balance at end of period (shares) at Sep. 30, 2020		455,105	10,915
Balance at end of period at Sep. 30, 2020	4,189.1	$ 4.5	$ (1,282.4)	10,369.6	(4,191.2)	(1,168.8)	457.4
Balance at beginning of period (shares) at Dec. 31, 2020		455,245	10,915
Balance at beginning of period 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)		1,115
Stock-based compensation related activity	99.9	$ 0		99.9
Issuance of common stock-stock purchase plan (in shares)		38
Issuance of common stock- stock purchase plan	7.7	$ 0		7.7
Issuance of common stock (in shares)		9,900
Issuance of common stock	2,361.8	$ 0.1		2,361.7
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	0.1				0.1
Foreign currency translation adjustment, net of tax	(823.5)				(720.2)		(103.3)
Adjustment to noncontrolling interest	0			(648.4)	47.4		601
Contributions from noncontrolling interest holders	3,078.2						3,078.2
Distributions to noncontrolling interest holders	(215.3)			(214.9)			(0.4)
Redemption of noncontrolling interest (shares)		26
Redemption of noncontrolling interest	0	$ 0		1.7			(1.7)
Purchase of redeemable noncontrolling interest	0			(0.1)	0.1
Purchase of noncontrolling interest	10.2						10.2
Common stock distributions declared	(1,731.7)					(1,731.7)
Net income	2,121.2					2,114.3	6.9
Balance at end of period (shares) at Sep. 30, 2021		466,324	10,915
Balance at end of period at Sep. 30, 2021	9,477	$ 4.7	$ (1,282.4)	12,081.3	(4,432)	(960.4)	4,065.8
Balance at beginning of period (shares) at Jun. 30, 2021		465,946	10,915
Balance at beginning of period at Jun. 30, 2021	6,823.4	$ 4.7	$ (1,282.4)	12,019.8	(3,902.9)	(1,085)	1,069.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation related activity (shares)		378
Stock-based compensation related activity	61.5	$ 0		61.5
Changes in fair value of cash flow hedges, net of tax	0
Reclassification of unrealized losses on cash flow hedges to net income, net of tax	0
Foreign currency translation adjustment, net of tax	(622.3)				(529.1)		(93.2)
Contributions from noncontrolling interest holders	3,078.2						3,078.2
Distributions to noncontrolling interest holders	(0.1)						(0.1)
Purchase of noncontrolling interest	10.2						10.2
Common stock distributions declared	(598.4)					(598.4)
Net income	724.5					723	1.5
Balance at end of period (shares) at Sep. 30, 2021		466,324	10,915
Balance at end of period at Sep. 30, 2021	$ 9,477	$ 4.7	$ (1,282.4)	$ 12,081.3	$ (4,432)	$ (960.4)	$ 4,065.8

BASIS OF PRESENTATION AND SIGNI

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 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 September 30, 2021, the Company holds (i) a 92% controlling interest in ATC Telecom Infrastructure Private Limited (“ATC TIPL”), formerly Viom Networks Limited (“Viom”), in India, (ii) a 52% controlling interest in subsidiaries whose holdings consist of the Company’s operations in France, Germany, Poland and Spain (such subsidiaries collectively, “ATC Europe”) (Allianz and CDPQ (each as defined in note 12) hold the noncontrolling interests), and (iii) a 51% controlling interest in a joint venture whose holdings consist of the Company’s operations in Bangladesh (Confidence Tower Holdings Ltd. (“Confidence Group”) holds the noncontrolling interest). As of September 30, 2021, ATC Europe holds an 87% and an 83% controlling interest in subsidiaries that consist of the Company’s operations in Germany and Spain, respectively (PGGM holds the noncontrolling interests). See note 12 for a discussion of changes to the Company’s noncontrolling interests during the three and nine months ended September 30, 2021. 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 16. 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 nine months ended September 30, 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: Nine Months Ended September 30, 2021 2020 Cash and cash equivalents $ 3,277.2 $ 1,626.0 Restricted cash 422.1 104.2 Total cash, cash equivalents and restricted cash $ 3,699.3 $ 1,730.2 The increase in restricted cash during the nine months ended September 30, 2021 is due to advance payments from a tenant. 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 generally not accounted for as 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 generally require that the Company provide the tenant the right to use available capacity on 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 and nine months ended September 30, 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 September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 73.2 $ 2.6 $ 6.3 $ 2.1 $ 35.1 $ 119.3 Services revenue 85.4 — — — — 85.4 Total non-lease revenue $ 158.6 $ 2.6 $ 6.3 $ 2.1 $ 35.1 $ 204.7 Property lease revenue 1,158.0 310.9 251.1 173.7 355.9 2,249.6 Total revenue $ 1,316.6 $ 313.5 $ 257.4 $ 175.8 $ 391.0 $ 2,454.3 Three Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 72.0 $ 2.3 $ 3.6 $ 1.7 $ 26.7 $ 106.3 Services revenue 25.3 — — — — 25.3 Total non-lease revenue $ 97.3 $ 2.3 $ 3.6 $ 1.7 $ 26.7 $ 131.6 Property lease revenue 1,050.3 302.9 216.4 37.0 274.7 1,881.3 Total revenue $ 1,147.6 $ 305.2 $ 220.0 $ 38.7 $ 301.4 $ 2,012.9 Nine Months Ended September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 214.9 $ 6.8 $ 17.5 $ 6.0 $ 100.9 $ 346.1 Services revenue 180.1 — — — — 180.1 Total non-lease revenue $ 395.0 $ 6.8 $ 17.5 $ 6.0 $ 100.9 $ 526.2 Property lease revenue 3,481.0 886.3 723.6 302.2 992.4 6,385.5 Total revenue $ 3,876.0 $ 893.1 $ 741.1 $ 308.2 $ 1,093.3 $ 6,911.7 Nine Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 193.0 $ 6.8 $ 9.5 $ 4.8 $ 87.9 $ 302.0 Services revenue 65.0 — — — — 65.0 Total non-lease revenue $ 258.0 $ 6.8 $ 9.5 $ 4.8 $ 87.9 $ 367.0 Property lease revenue 3,106.7 856.3 642.0 103.1 843.9 5,552.0 Total revenue $ 3,364.7 $ 863.1 $ 651.5 $ 107.9 $ 931.8 $ 5,919.0 Property revenue for the three months ended September 30, 2021 and 2020 includes straight-line revenue of $99.6 million and $68.1 million, respectively. Property revenue for the nine months ended September 30, 2021 and 2020 includes straight-line revenue of $324.3 million and $178.9 million, respectively. Unearned revenue —Amounts billed upfront in connection with the execution of lease agreements are initially deferred and reflected in Unearned revenue in the consolidated balance sheets and recognized as revenue over the terms of the applicable lease arrangements. Amounts billed or received for services prior to being earned are deferred and reflected in Unearned revenue in the consolidated balance sheets until the criteria for recognition have been met. The increase in unearned revenue during the nine months ended September 30, 2021 is due to advance payments from a tenant. 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 September 30, 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	9 Months Ended
	Sep. 30, 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 September 30, 2021 December 31, 2020 Prepaid assets $ 89.6 $ 66.1 Prepaid income tax 91.6 143.7 Unbilled receivables 261.6 176.9 Value added tax and other consumption tax receivables 67.3 66.3 Other miscellaneous current assets 81.9 79.6 Prepaid and other current assets $ 592.0 $ 532.6

LEASES

LEASES	9 Months Ended
	Sep. 30, 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 nine months ended September 30, 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 September 30, 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 September 30, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 1,648.0 2022 5,953.2 2023 6,611.2 2024 6,489.2 2025 6,044.5 Thereafter 34,158.8 Total $ 60,904.9 _______________ (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 and nine months ended September 30, 2021 and 2020. The Company leases certain land, rooftops and office space under operating leases and land and improvements, towers and vehicles under finance leases. As of September 30, 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 nine months ended September 30, 2021, other than leases acquired in connection with acquisitions, 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 nine months ended September 30, 2021. Information about other lease-related balances is as follows: As of September 30, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 9,021.9 $ 7,789.2 Current portion of lease liability $ 734.3 $ 539.9 Lease liability 7,863.2 6,884.4 Total operating lease liability $ 8,597.5 $ 7,424.3 The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of September 30, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.0 13.7 Weighted-average incremental borrowing rate 5.3 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Operating lease cost $ 295.6 $ 242.6 $ 815.3 $ 731.3 Variable lease costs not included in lease liability (1) 94.3 69.7 248.7 202.3 ______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (798.2) $ (732.8) Non-cash items: New operating leases (1) $ 1,607.2 $ 125.7 Operating lease modifications and reassessments $ 165.3 $ 573.2 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions, including $1.4 billion related to the Telxius Acquisition (as defined in note 6). As of September 30, 2021, the Company does not have material operating or financing leases that have not yet commenced. Maturities of operating lease liabilities as of September 30, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 285.9 2022 1,085.1 2023 1,042.2 2024 993.4 2025 936.1 Thereafter 7,509.8 Total lease payments 11,852.5 Less amounts representing interest (3,255.0) Total lease liability 8,597.5 Less current portion of lease liability 734.3 Non-current lease liability $ 7,863.2 _______________ (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 nine months ended September 30, 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 September 30, 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 September 30, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 1,648.0 2022 5,953.2 2023 6,611.2 2024 6,489.2 2025 6,044.5 Thereafter 34,158.8 Total $ 60,904.9 _______________ (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 and nine months ended September 30, 2021 and 2020. The Company leases certain land, rooftops and office space under operating leases and land and improvements, towers and vehicles under finance leases. As of September 30, 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 nine months ended September 30, 2021, other than leases acquired in connection with acquisitions, 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 nine months ended September 30, 2021. Information about other lease-related balances is as follows: As of September 30, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 9,021.9 $ 7,789.2 Current portion of lease liability $ 734.3 $ 539.9 Lease liability 7,863.2 6,884.4 Total operating lease liability $ 8,597.5 $ 7,424.3 The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of September 30, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.0 13.7 Weighted-average incremental borrowing rate 5.3 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Operating lease cost $ 295.6 $ 242.6 $ 815.3 $ 731.3 Variable lease costs not included in lease liability (1) 94.3 69.7 248.7 202.3 ______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (798.2) $ (732.8) Non-cash items: New operating leases (1) $ 1,607.2 $ 125.7 Operating lease modifications and reassessments $ 165.3 $ 573.2 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions, including $1.4 billion related to the Telxius Acquisition (as defined in note 6). As of September 30, 2021, the Company does not have material operating or financing leases that have not yet commenced. Maturities of operating lease liabilities as of September 30, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 285.9 2022 1,085.1 2023 1,042.2 2024 993.4 2025 936.1 Thereafter 7,509.8 Total lease payments 11,852.5 Less amounts representing interest (3,255.0) Total lease liability 8,597.5 Less current portion of lease liability 734.3 Non-current lease liability $ 7,863.2 _______________ (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 nine months ended September 30, 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 September 30, 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 September 30, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 1,648.0 2022 5,953.2 2023 6,611.2 2024 6,489.2 2025 6,044.5 Thereafter 34,158.8 Total $ 60,904.9 _______________ (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 and nine months ended September 30, 2021 and 2020. The Company leases certain land, rooftops and office space under operating leases and land and improvements, towers and vehicles under finance leases. As of September 30, 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 nine months ended September 30, 2021, other than leases acquired in connection with acquisitions, 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 nine months ended September 30, 2021. Information about other lease-related balances is as follows: As of September 30, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 9,021.9 $ 7,789.2 Current portion of lease liability $ 734.3 $ 539.9 Lease liability 7,863.2 6,884.4 Total operating lease liability $ 8,597.5 $ 7,424.3 The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of September 30, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.0 13.7 Weighted-average incremental borrowing rate 5.3 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Operating lease cost $ 295.6 $ 242.6 $ 815.3 $ 731.3 Variable lease costs not included in lease liability (1) 94.3 69.7 248.7 202.3 ______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (798.2) $ (732.8) Non-cash items: New operating leases (1) $ 1,607.2 $ 125.7 Operating lease modifications and reassessments $ 165.3 $ 573.2 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions, including $1.4 billion related to the Telxius Acquisition (as defined in note 6). As of September 30, 2021, the Company does not have material operating or financing leases that have not yet commenced. Maturities of operating lease liabilities as of September 30, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 285.9 2022 1,085.1 2023 1,042.2 2024 993.4 2025 936.1 Thereafter 7,509.8 Total lease payments 11,852.5 Less amounts representing interest (3,255.0) Total lease liability 8,597.5 Less current portion of lease liability 734.3 Non-current lease liability $ 7,863.2 _______________ (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	9 Months Ended
	Sep. 30, 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) (74.4) 9.5 — 3,177.6 322.4 — 3,435.1 Effect of foreign currency translation 2.4 (16.6) (3.3) (176.7) (42.8) — (237.0) Balance as of September 30, 2021 $ 4,678.8 $ 1,009.8 $ 622.3 $ 3,280.0 $ 887.9 $ 2.0 $ 10,480.8 _______________ (1) Europe and Latin America consist of additions and measurement period adjustments related to the Telxius Acquisition. U.S. & Canada consists of measurement period adjustments related to the InSite Acquisition. Asia-Pacific consists of $9.2 million of additions related to the Bangladesh acquisition (as discussed in note 15) and measurement period adjustments related to the InSite Acquisition. The Company’s other intangible assets subject to amortization consisted of the following: As of September 30, 2021 As of December 31, 2020 Estimated Useful Gross Accumulated Net Book Gross Accumulated Net Book Acquired network location intangibles (1) Up to 20 $ 6,329.5 $ (2,305.1) $ 4,024.4 $ 5,784.0 $ (2,117.6) $ 3,666.4 Acquired tenant-related intangibles Up to 20 19,471.9 (4,816.3) 14,655.6 14,322.5 (4,237.5) 10,085.0 Acquired licenses and other intangibles 3-20 99.9 (11.5) 88.4 97.8 (9.4) 88.4 Total other intangible assets $ 25,901.3 $ (7,132.9) $ 18,768.4 $ 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 September 30, 2021, the remaining weighted average amortization period of the Company’s intangible assets was 16 years. Amortization of intangible assets for the three and nine months ended September 30, 2021 was $318.0 million and $846.2 million, respectively. Amortization of intangible assets for the three and nine months ended September 30, 2020 was $215.1 million and $643.4 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 $ 318.0 2022 1,270.8 2023 1,237.8 2024 1,224.1 2025 1,196.7 2026 1,162.9

ACCRUED EXPENSES

ACCRUED EXPENSES	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consisted of the following: As of September 30, 2021 December 31, 2020 Accrued construction costs $ 96.3 $ 46.5 Accrued income tax payable 27.2 20.6 Accrued pass-through costs 76.1 67.1 Amounts payable for acquisitions 14.1 58.9 Amounts payable to tenants 78.7 66.4 Accrued property and real estate taxes 246.0 219.1 Accrued rent 77.8 82.6 Payroll and related withholdings 104.9 104.4 Other accrued expenses 444.3 378.1 Total accrued expenses $ 1,165.4 $ 1,043.7

LONG-TERM OBLIGATIONS

LONG-TERM OBLIGATIONS	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
LONG-TERM 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 September 30, 2021 December 31, 2020 Maturity Date 2020 Term Loan (1) (2) $ — $ 749.4 N/A 2021 Multicurrency Credit Facility (1) (3) 1,568.6 — June 28, 2024 2019 Term Loan (1) 496.3 996.1 January 31, 2025 2021 Credit Facility (1) — 2,295.0 January 31, 2026 2021 364-Day Delayed Draw Term Loan (1) (3) (4) 787.2 — May 28, 2022 2021 Three Year Delayed Draw Term Loan (1) (3) 955.1 — May 28, 2024 2.250% senior notes 601.6 605.1 January 15, 2022 4.70% senior notes (5) 699.6 699.0 March 15, 2022 3.50% senior notes 997.5 996.1 January 31, 2023 3.000% senior notes 714.9 721.9 June 15, 2023 0.600% senior notes 497.6 496.8 January 15, 2024 5.00% senior notes 1,001.0 1,001.3 February 15, 2024 3.375% senior notes 646.6 645.7 May 15, 2024 2.950% senior notes 644.3 643.1 January 15, 2025 2.400% senior notes 745.8 745.0 March 15, 2025 1.375% senior notes (6) 573.6 604.1 April 4, 2025 4.000% senior notes 745.2 744.3 June 1, 2025 1.300% senior notes 496.1 495.4 September 15, 2025 4.400% senior notes 497.5 497.1 February 15, 2026 1.600% senior notes 694.9 — April 15, 2026 1.950% senior notes (6) 574.2 605.2 May 22, 2026 1.450% senior notes 592.6 — September 15, 2026 3.375% senior notes 990.8 989.5 October 15, 2026 3.125% senior notes 398.2 397.9 January 15, 2027 2.750% senior notes 745.0 744.3 January 15, 2027 0.450% senior notes (6) 862.1 — January 15, 2027 3.55% senior notes 745.4 744.8 July 15, 2027 0.500% senior notes (6) 860.3 907.4 January 15, 2028 3.600% senior notes 694.1 693.4 January 15, 2028 1.500% senior notes 645.6 645.1 January 31, 2028 3.950% senior notes 591.3 590.6 March 15, 2029 0.875% senior notes (6) 862.3 — May 21, 2029 3.800% senior notes 1,634.7 1,633.5 August 15, 2029 2.900% senior notes 742.3 741.7 January 15, 2030 2.100% senior notes 740.9 740.2 June 15, 2030 1.875% senior notes 791.2 790.5 October 15, 2030 2.700% senior notes 693.6 — April 15, 2031 2.300% senior notes 690.8 — September 15, 2031 1.000% senior notes (6) 744.9 786.1 January 15, 2032 1.250% senior notes (6) 571.3 — May 21, 2033 3.700% senior notes 592.0 591.9 October 15, 2049 3.100% senior notes 1,037.9 1,037.7 June 15, 2050 2.950% senior notes 1,021.3 538.2 January 15, 2051 Total American Tower Corporation debt 31,186.2 26,113.4 Series 2013-2A securities (7) 1,297.8 1,296.6 March 15, 2023 Series 2018-1A securities (7) 495.1 494.6 March 15, 2028 Series 2015-2 notes (8) 522.6 522.1 June 16, 2025 InSite Debt (9) — 800.0 N/A Other subsidiary debt (10) 11.7 32.9 Various Total American Tower subsidiary debt 2,327.2 3,146.2 Finance lease obligations 32.0 27.9 Total 33,545.4 29,287.5 Less current portion of long-term obligations (2,106.4) (789.8) Long-term obligations $ 31,439.0 $ 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) As of September 30, 2021 reflects borrowings denominated in Euros (“EUR”). (4) Repaid in full on October 7, 2021 , as further discussed in note 17. (5) Repaid in full on October 18, 2021 , as further discussed in note 17. (6) Notes are denominated in EUR. (7) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (8) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (9) 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. (10) Includes (a) debt entered into by the Company’s Kenyan subsidiary in connection with an acquisition of sites in Kenya, which is denominated in 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 (b) U.S. subsidiary debt related to a seller-financed acquisition. As of December 31, 2020 also included the Colombian credit facility (the “Colombian Credit Facility”), which was denominated in Colombian Pesos and was fully repaid on its maturity date of April 24, 2021. As of September 30, 2021, no amounts remained outstanding under the Colombian Credit Facility. 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, (ii) $700.0 million aggregate principal amount of 4.70% senior unsecured notes due March 15, 2022 (the “4.70% Notes”) and (iii) 680.0 million EUR (approximately $787.2 million) in borrowings under the 2021 364-Day Delayed Draw Term Loan (as defined below). 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 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”). 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. 0.450% Senior Notes, 0.875% Senior Notes and 1.250% Senior Notes Offering— On May 21, 2021, the Company completed a registered public offering of 750.0 million EUR ($913.7 million at the date of issuance) aggregate principal amount of 0.450% senior unsecured notes due 2027 (the “0.450% Notes”), 750.0 million EUR ($913.7 million at the date of issuance) aggregate principal amount of 0.875% senior unsecured notes due 2029 (the “0.875% Notes”) and 500.0 million EUR ($609.1 million at the date of issuance) aggregate principal amount of 1.250% senior unsecured notes due 2033 (the “1.250% Notes”). The net proceeds from this offering were approximately 1,983.1 million EUR (approximately $2,415.8 million at the date of issuance) , after deducting commissions and estimated expenses. The Company used all of the net proceeds to fund its transaction with Telxius Telecom, S.A. (“Telxius,” and the acquisition, the “Telxius Acquisition”), as further described in note 15. 1.450% Senior Notes, 2.300% Senior Notes and 2.950% Senior Notes Offering —On September 27, 2021, the Company completed a registered public offering of $600.0 million aggregate principal amount of 1.450% senior unsecured notes due 2026 (the “1.450% Notes”), $700.0 million aggregate principal amount of 2.300% senior unsecured notes due 2031 (the “2.300% Notes”) and $500.0 million aggregate principal amount through a reopening of its 2.950% senior unsecured notes due 2051, originally issued on November 20, 2020 (the “2.950% Notes” and, collectively with the 1.600% Notes, the 2.700% Notes, the 0.450% Notes, the 0.875% Notes, the 1.250% Notes, the 1.450% Notes and the 2.300% Notes, the “Notes”). The net proceeds from this offering were approximately $1,765.1 million, after deducting commissions and estimated expenses. The Company used the net proceeds to repay existing indebtedness under the 2019 Term Loan (as defined below) and for general corporate purposes. 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 0.450% Notes (3) $ 913.7 May 21, 2021 January 15, 2027 0.450 % January 15, 2022 January 15 November 15, 2026 0.875% Notes (3) $ 913.7 May 21, 2021 May 21, 2029 0.875 % May 21, 2022 May 21 February 21, 2029 1.250% Notes (3) $ 609.1 May 21, 2021 May 21, 2033 1.250 % May 21, 2022 May 21 February 21, 2033 1.450% Notes $ 600.0 September 27, 2021 September 15, 2026 1.450 % March 15, 2022 March 15 and September 15 August 15, 2026 2.300% Notes $ 700.0 September 27, 2021 September 15, 2031 2.300 % March 15, 2022 March 15 and September 15 June 15, 2031 2.950% Notes (4) $ 1,050.0 September 27, 2021 January 15, 2051 2.950 % January 15, 2022 January 15 and July 15 July 15, 2050 ___________ (1) Accrued and unpaid interest on USD denominated notes 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. Interest on EUR denominated notes is payable in EUR annually and will be computed on the basis of the actual number of days in the period for which interest is being calculated and the actual number of days from and including the last date on which interest was paid on the notes, beginning on the issue date. (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. (3) The 0.450% Notes, the 0.875% Notes and the 1.250% Notes are denominated in EUR. Represents the dollar equivalent of the aggregate principal amount as of the issue date. (4) The initial 2.950% Notes were issued on November 20, 2020. The reopened 2.950% Notes were issued on September 27, 2021. If the Company undergoes a change of control and corresponding ratings decline, each as defined in the applicable 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 indentures contain 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. Subsequent to September 30, 2021, the Company completed a registered public offering of the 0.400% Notes and the 0.950% Notes, each as defined and further discussed in note 17. 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, 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 Telxius Acquisition, which began with the quarter ended June 30, 2021, 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 nine months ended September 30, 2021, the Company borrowed an aggregate of $4.6 billion, including an aggregate of 2.4 billion EUR ($2.9 billion as of the borrowing dates), and repaid an aggregate of $3.0 billion of revolving indebtedness, including an aggregate of 1.0 billion EUR ($1.2 billion as of the repayment date) primarily using proceeds from the ATC Europe Transactions (as defined in note 12), under the 2021 Multicurrency Credit Facility. The Company used the borrowings to fund the Telxius Acquisition, 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 nine months ended September 30, 2021, the Company borrowed an aggregate of $2.9 billion, including an aggregate of 1.2 billion EUR ($1.4 billion as of the borrowing dates), and repaid an aggregate of $5.2 billion of revolving indebtedness, including an aggregate of 1.2 billion EUR ($1.4 billion as of the repayment date) primarily using proceeds from the ATC Europe Transactions, under the 2021 Credit Facility. The Company used the borrowings to fund the Telxius Acquisition and 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 using borrowings from the 2021 Multicurrency Credit Facility and cash on hand. Repayment under the 2019 Term Loan— On September 27, 2021, the Company repaid $500.0 million of indebtedness under the 2019 Term Loan using proceeds from the issuance of the 1.450% Notes, the 2.300% Notes and the 2.950% Notes. 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 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 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”). On May 28, 2021, the Company borrowed 1.1 billion EUR ($1.3 billion as of the borrowing date) under the 2021 364-Day Delayed Draw Term Loan and 825.0 million EUR ($1.0 billion as of the borrowing date) under the 2021 Three Year Delayed Draw Term Loan. The Company used the borrowings to fund the Telxius Acquisition. On September 16, 2021, the Company repaid 420.0 million EUR ($494.2 million as of the repayment date) under the 2021 364-Day Delayed Draw Term Loan using proceeds from the ATC Europe Transactions. Subsequent to September 30, 2021, the Company repaid all remaining amounts outstanding under the 2021 364-Day Delayed Draw Term Loan, as further discussed in note 17. 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 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 had, 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 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 Bridge Loan Commitment was further reduced as a result of the May 2021 common stock offering, as further described in note 11. Effective May 24, 2021, upon receipt of the proceeds from the issuance of the 0.450% Notes, the 0.875% Notes and the 1.250% Notes, the Company determined that it had adequate cash resources and undrawn availability under its revolving credit facilities and the 2021 Delayed Draw Term Loans to fund the cash consideration payable in connection with the Telxius Acquisition and terminated the Commitment Letter. The Company did not make any borrowings under the Bridge Loan Commitment. India Credit Facilities —During the nine months ended September 30, 2021, the Company entered into two working capital facilities in India with an aggregate borrowing capacity of 1.95 billion Indian Rupees (“INR”) (approximately $26.3 million) and one overdraft facility with a borrowing capacity of INR 380.0 million (approximately $5.1 million). The working capital facilities are subject to annual renewals and bear interest at a rate equal to the one-month India Treasury Bill rate at the time of borrowing plus a spread. The overdraft facility bears interest at the Overnight Mumbai Inter-Bank Offer Rate (“MIBOR”) at the time of borrowing plus a spread. As of September 30, 2021, the Company has not borrowed under the facilities. As of September 30, 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 and the 2021 Three Year Delayed Draw Term Loan 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 1,568.6 $ 3.5 June 28, 2024 (3) 1.125 % 0.110 % 2021 Credit Facility — $ 0.9 January 31, 2026 (3) 1.125 % 0.110 % 2019 Term Loan 496.3 N/A January 31, 2025 1.125 % N/A 2021 364-Day Delayed Draw Term Loan 787.2 N/A May 28, 2022 1.000 % 0.110 % 2021 Three Year Delayed Draw Term Loan 955.1 N/A May 28, 2024 1.125 % 0.110 % _______________ (1) LIBOR applies to the USD denominated borrowings under the 2021 Multicurrency Credit Facility, the 2021 Credit Facility and the 2019 Term Loan. EURIBOR applies to the EUR denominated borrowings under the 2021 Multicurrency Credit Facility and the 2021 Credit Facility, and all of the borrowings under the 2021 Delayed Draw Term Loans. (2) Fee on undrawn portion of each credit facility.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 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: September 30, 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 — $ 17.5 — — $ 29.2 — Investments in equity securities (1) $ 50.5 — — — $ 6.0 — Liabilities: Fair value of debt related to interest rate swap agreements (2) $ 19.1 — — $ 31.4 — — _______________ (1) Investments in equity securities are recorded in Notes receivable and other non-current assets in the consolidated balance sheet at fair value. Unrealized holding gains and losses for equity securities are recorded in Other income (expense) in the consolidated statements of operations in the current period. During the three and nine months ended September 30, 2021, the Company recognized unrealized (losses) gains of $(9.9) million and $19.5 million, respectively, for equity securities held as of September 30, 2021. (2) Included in the carrying values of the corresponding debt obligations. During the nine months ended September 30, 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. On April 24, 2021, the interest rate swap agreement with certain lenders under the Colombian Credit Facility (the “Colombia Interest Rate Swap”) expired upon maturity of the underlying debt. As of September 30, 2021, there were no amounts outstanding under the Colombia Interest Rate Swap. 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. There were no material impairments during the three and nine months ended September 30, 2021 and 2020. There were no other items measured at fair value on a nonrecurring basis during the nine months ended September 30, 2021 or 2020.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 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 September 30, 2021 was primarily attributable to net additions to reserves for the Company’s existing tax positions. The increase in the income tax provision during the nine months ended September 30, 2021 was primarily attributable to increases in foreign earnings, net additions to reserves for the Company’s existing tax positions and changes in tax law in certain foreign jurisdictions in the current period. The income tax provision for the three and nine months ended September 30, 2020 includes a benefit related to the remeasurement of the Company’s net deferred tax liabilities in Kenya as a result of a change in tax rate. As of September 30, 2021 and December 31, 2020, the total unrecognized tax benefits that would impact the ETR, if recognized, were approximately $89.9 million and $105.9 million, respectively. The amount of unrecognized tax benefits during the three and nine months ended September 30, 2021 includes (i) additions to the Company’s existing tax positions of $12.9 million and $22.6 million, respectively, (ii) reductions due to foreign currency exchange rate fluctuations of $3.3 million and $2.9 million, respectively, (iii) reductions to the Company’s prior year tax positions of $21.6 million and $39.7 million, respectively, (iv) reductions due to statute of limitations of $1.6 million and $3.6 million, respectively, and (v) reductions to the Company’s prior year tax positions due to settlements of $8.8 million for each of the three and nine months ended September 30, 2021. 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 $24.7 million. The Company recorded the following penalties and income tax-related interest expense during the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Penalties and income tax-related interest expense (1) $ 9.6 $ 6.6 $ 43.1 $ 9.3 _______________ (1) Nine months ended September 30, 2021 reflects an increase of $16.6 million due to a reclassification of unrecognized tax benefits to penalties and income tax-related interest expense. As of September 30, 2021 and December 31, 2020, the total amount of accrued income tax related interest and penalties included in the consolidated balance sheets were $76.4 million and $34.4 million, respectively.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	9 Months Ended
	Sep. 30, 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 September 30, 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 and nine months ended September 30, 2021 and 2020, the Company recorded and capitalized the following stock-based compensation expense: Three Months Ended September 30, Nine Months Ended September 30, 2021 (1) 2020 (2) 2021 (1) 2020 (2) Stock-based compensation expense $ 28.1 $ 24.1 $ 98.0 $ 99.0 _______________ (1) For the three and nine months ended September 30, 2021, stock-based compensation expense consisted of $28.1 million and $98.0 million, respectively, included in selling, general, administrative and development expense. (2) For the three and nine months ended September 30, 2020, stock-based compensation expense consisted of (i) $0.4 million and $1.4 million, respectively, included in Property costs of operations, (ii) $0.3 million and $0.9 million, respectively, included in Services costs of operations and (iii) $23.4 million and $96.7 million, respectively, included in selling, general, administrative and development expense. For the three and nine months ended September 30, 2020, stock-based compensation expense capitalized as property and equipment was $0.4 million and $1.3 million, respectively. Stock Options —As of September 30, 2021, there was no unrecognized compensation expense related to unvested stock options. The Company’s option activity for the nine months ended September 30, 2021 was as follows (shares disclosed in full amounts): Number of Options Outstanding as of January 1, 2021 2,016,261 Exercised (629,515) Forfeited — Expired — Outstanding as of September 30, 2021 1,386,746 Restricted Stock Units— As of September 30, 2021, total unrecognized compensation expense related to unvested RSUs granted under the 2007 Plan was $149.9 million and is expected to be recognized over a weighted average period of approximately two 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 nine months ended September 30, 2021, the Company’s Compensation Committee (the “Compensation Committee”) granted an aggregate of 98,694 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-year performance period with respect to each of the 2021 PSUs, the 2020 PSUs and the 2019 PSUs and will be used to calculate the number of shares that will be issuable when each award vests, which may range from zero to 200% of the target amounts. At the end of each three-year performance period, the number of shares that vest will depend on the degree of achievement against the pre-established performance goals. PSUs will be paid out in common stock at the end of each performance period, subject generally to the executive’s continued employment or death, disability or qualified retirement (each as defined in the applicable PSU award agreement). PSUs will accrue dividend equivalents prior to vesting, which will be paid out only in respect of shares that actually vest. Restricted Stock Units and Performance-Based Restricted Stock Units —The Company’s RSU and PSU activity for the nine months ended September 30, 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) 546,698 98,694 Vested and Released (3) (564,397) (162,882) Forfeited (46,649) — Outstanding as of September 30, 2021 1,180,727 256,322 Vested and deferred as of September 30, 2021 (4) 17,121 — _______________ (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 98,694 shares. (3) This includes 58,204 and 96,048 of previously vested and deferred RSUs and PSUs, respectively. 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 RSUs are related to deferred compensation for certain former employees.

REDEEMABLE NONCONTROLLING INTER

REDEEMABLE NONCONTROLLING INTERESTS	9 Months Ended
	Sep. 30, 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 nine months ended September 30, 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 nine months ended September 30, 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 (approximatel y $173.8 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 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 nine months ended September 30, 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: Nine Months Ended September 30, 2021 2020 Balance as of January 1, $ 212.1 $ 1,096.5 Net income attributable to noncontrolling interests 4.0 11.2 Adjustment to noncontrolling interest redemption value 1.2 (10.0) Purchase of redeemable noncontrolling interest (2.5) (524.4) Foreign currency translation adjustment attributable to noncontrolling interests (3.4) (18.4) Balance as of September 30, $ 211.4 $ 554.9 Dividend to noncontrolling interest— Certain of the Company’s subsidiaries may, from time to time, declare dividends. During the year ended December 31, 2020 , the subsidiary that primarily consisted of the Company’s operations in France, Germany and Poland (“Former 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 Former ATC Europe. The dividend was paid on January 6, 2021. Purchase of Interests— During the nine months ended September 30, 2021 , the Company purchased the remaining minority interests held in a subsidiary in the United States for total consideration of $6.0 million. The purchase price was settled with unregistered shares of the Company’s common stock, in lieu of cash. The Company now owns 100% of the subsidiary as a result of the purchase. Reorganization of European Interests— During the nine months ended September 30, 2021, in connection with the funding of the Telxius Acquisition, the Company completed a reorganization of its subsidiaries in Europe. As part of the reorganization, PGGM converted its previously held 49% noncontrolling interest in Former ATC Europe into noncontrolling interests in new subsidiaries, consisting of the Company's operations in Germany and Spain, inclusive of the assets acquired pursuant to the Telxius Acquisition. The reorganization included cash consideration paid to PGGM of 178.0 million EUR (approximately $214.9 million). The reorganization is reflected in the consolidated statements of equity as (i) a reduction in Additional Paid-in Capital of $648.4 million and (ii) an increase in Noncontrolling Interests of $601.0 million, and in the consolidated statements of comprehensive income (loss) as an increase in Comprehensive income attributable to American Tower Corporation stockholders of $47.4 million. CDPQ and Allianz Partnerships —During the nine months ended September 30, 2021, the Company entered into agreements with Caisse de dépôt et placement du Québec (“CDPQ”) and Allianz insurance companies and funds managed by Allianz Capital Partners GmbH, including the Allianz European Infrastructure Fund (collectively, “Allianz”), for CDPQ and Allianz to acquire 30% and 18% noncontrolling interests, respectively, in ATC Europe (the “ATC Europe Transactions”). The Company completed the ATC Europe Transactions during the three months ended September 2021 for total aggregate consideration of 2.6 billion EUR (approximately $3.1 billion at the date of closing). After the completion of the ATC Europe Transactions, the Company holds a 52% controlling ownership interest in ATC Europe. As of September 30, 2021, ATC Europe consists of the Company’s operations in France, Germany, Poland and Spain. The Company currently holds a 52% controlling interest in ATC Europe, with CDPQ and Allianz holding 30% and 18% noncontrolling interests, respectively. ATC Europe holds a 100% interest in the subsidiaries that consist of the Company’s operations in France and Poland and an 87% and an 83% controlling interest in the subsidiaries that consist of the Company’s operations in Germany and Spain, respectively, with PGGM holding a 13% and a 17% noncontrolling interest in each respective subsidiary. Bangladesh Partnership —During the three months ended September 30, 2021, the Company acquired a 51% controlling interest in Kirtonkhola Tower Bangladesh Limited (“KTBL”) for 900 million Bangladeshi Taka (“BDT”) (approximately $10.6 million at the date of closing) through a joint venture partnership with Confidence Group (which holds a 49% noncontrolling interest in KTBL). The changes in noncontrolling interests were as follows: Nine Months Ended September 30, 2021 Balance as of January 1, $ 474.9 ATC Europe Transactions (1) 3,078.2 Bangladesh partnership (2) 10.2 Adjustment to noncontrolling interest due to reorganization (3) 601.0 Redemption of noncontrolling interest (4) (1.7) Net income attributable to noncontrolling interests 6.9 Foreign currency translation adjustment attributable to noncontrolling interests, net of tax (103.3) Distributions to noncontrolling interest holders (0.4) Balance as of September 30, $ 4,065.8 _______________ (1) Represents the impact of contributions received from CDPQ and Allianz described above on Noncontrolling interests as of September 30, 2021. Reflected within Contributions from noncontrolling interest holders in the consolidated statements of equity. (2) Represents the impact of contributions made by the Company to establish the joint venture in Bangladesh described above on Noncontrolling interests as of September 30, 2021. Reflected within Purchase of noncontrolling interest in the consolidated statements of equity. (3) Represents the impact of the reorganization of European interests described above on Noncontrolling interests as of September 30, 2021.

EQUITY

EQUITY	9 Months Ended
	Sep. 30, 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 nine months ended September 30, 2021, the Company received an aggregate of $60.4 million in proceeds upon exercises of stock options and sales pursuant to the ESPP. 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 September 30, 2021, the Company has not sold any shares of common stock under the 2020 ATM Program. Common Stock Offering — On May 10, 2021, the Company completed a registered public offering of 9,000,000 shares of its common stock, par value $0.01 per share, at $244.75 per share. On May 10, 2021, the Company issued an additional 900,000 shares of its common stock in connection with the underwriters’ exercise in full of their over-allotment option. Aggregate net proceeds from this offering were approximately $2.4 billion after deducting underwriting discounts and estimated offering expenses. The Company used the net proceeds to finance the Telxius Acquisition. 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”). 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. During the nine months ended September 30, 2021, there were no repurchases under either of the Buyback Programs. As of September 30, 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 September 30, 2021, the Company has not made any repurchases under the 2017 Buyback. 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 nine months ended September 30, 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 September 16, 2021 October 15, 2021 September 28, 2021 $ 1.31 $ 596.6 May 27, 2021 July 9, 2021 June 18, 2021 $ 1.27 $ 577.8 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 nine months ended September 30, 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 September 10, 2020 October 16, 2020 September 28, 2020 $ 1.14 $ 506.4 May 19, 2020 July 10, 2020 June 19, 2020 $ 1.10 $ 487.9 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.

NONCONTROLLING INTEREST

NONCONTROLLING INTEREST	9 Months Ended
	Sep. 30, 2021
Noncontrolling Interest [Abstract]
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 nine months ended September 30, 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 nine months ended September 30, 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 (approximatel y $173.8 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 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 nine months ended September 30, 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: Nine Months Ended September 30, 2021 2020 Balance as of January 1, $ 212.1 $ 1,096.5 Net income attributable to noncontrolling interests 4.0 11.2 Adjustment to noncontrolling interest redemption value 1.2 (10.0) Purchase of redeemable noncontrolling interest (2.5) (524.4) Foreign currency translation adjustment attributable to noncontrolling interests (3.4) (18.4) Balance as of September 30, $ 211.4 $ 554.9 Dividend to noncontrolling interest— Certain of the Company’s subsidiaries may, from time to time, declare dividends. During the year ended December 31, 2020 , the subsidiary that primarily consisted of the Company’s operations in France, Germany and Poland (“Former 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 Former ATC Europe. The dividend was paid on January 6, 2021. Purchase of Interests— During the nine months ended September 30, 2021 , the Company purchased the remaining minority interests held in a subsidiary in the United States for total consideration of $6.0 million. The purchase price was settled with unregistered shares of the Company’s common stock, in lieu of cash. The Company now owns 100% of the subsidiary as a result of the purchase. Reorganization of European Interests— During the nine months ended September 30, 2021, in connection with the funding of the Telxius Acquisition, the Company completed a reorganization of its subsidiaries in Europe. As part of the reorganization, PGGM converted its previously held 49% noncontrolling interest in Former ATC Europe into noncontrolling interests in new subsidiaries, consisting of the Company's operations in Germany and Spain, inclusive of the assets acquired pursuant to the Telxius Acquisition. The reorganization included cash consideration paid to PGGM of 178.0 million EUR (approximately $214.9 million). The reorganization is reflected in the consolidated statements of equity as (i) a reduction in Additional Paid-in Capital of $648.4 million and (ii) an increase in Noncontrolling Interests of $601.0 million, and in the consolidated statements of comprehensive income (loss) as an increase in Comprehensive income attributable to American Tower Corporation stockholders of $47.4 million. CDPQ and Allianz Partnerships —During the nine months ended September 30, 2021, the Company entered into agreements with Caisse de dépôt et placement du Québec (“CDPQ”) and Allianz insurance companies and funds managed by Allianz Capital Partners GmbH, including the Allianz European Infrastructure Fund (collectively, “Allianz”), for CDPQ and Allianz to acquire 30% and 18% noncontrolling interests, respectively, in ATC Europe (the “ATC Europe Transactions”). The Company completed the ATC Europe Transactions during the three months ended September 2021 for total aggregate consideration of 2.6 billion EUR (approximately $3.1 billion at the date of closing). After the completion of the ATC Europe Transactions, the Company holds a 52% controlling ownership interest in ATC Europe. As of September 30, 2021, ATC Europe consists of the Company’s operations in France, Germany, Poland and Spain. The Company currently holds a 52% controlling interest in ATC Europe, with CDPQ and Allianz holding 30% and 18% noncontrolling interests, respectively. ATC Europe holds a 100% interest in the subsidiaries that consist of the Company’s operations in France and Poland and an 87% and an 83% controlling interest in the subsidiaries that consist of the Company’s operations in Germany and Spain, respectively, with PGGM holding a 13% and a 17% noncontrolling interest in each respective subsidiary. Bangladesh Partnership —During the three months ended September 30, 2021, the Company acquired a 51% controlling interest in Kirtonkhola Tower Bangladesh Limited (“KTBL”) for 900 million Bangladeshi Taka (“BDT”) (approximately $10.6 million at the date of closing) through a joint venture partnership with Confidence Group (which holds a 49% noncontrolling interest in KTBL). The changes in noncontrolling interests were as follows: Nine Months Ended September 30, 2021 Balance as of January 1, $ 474.9 ATC Europe Transactions (1) 3,078.2 Bangladesh partnership (2) 10.2 Adjustment to noncontrolling interest due to reorganization (3) 601.0 Redemption of noncontrolling interest (4) (1.7) Net income attributable to noncontrolling interests 6.9 Foreign currency translation adjustment attributable to noncontrolling interests, net of tax (103.3) Distributions to noncontrolling interest holders (0.4) Balance as of September 30, $ 4,065.8 _______________ (1) Represents the impact of contributions received from CDPQ and Allianz described above on Noncontrolling interests as of September 30, 2021. Reflected within Contributions from noncontrolling interest holders in the consolidated statements of equity. (2) Represents the impact of contributions made by the Company to establish the joint venture in Bangladesh described above on Noncontrolling interests as of September 30, 2021. Reflected within Purchase of noncontrolling interest in the consolidated statements of equity. (3) Represents the impact of the reorganization of European interests described above on Noncontrolling interests as of September 30, 2021.

EARNINGS PER COMMON SHARE

EARNINGS PER COMMON SHARE	9 Months Ended
	Sep. 30, 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net income attributable to American Tower Corporation common stockholders $ 723.0 $ 464.4 $ 2,114.3 $ 1,325.5 Basic weighted average common shares outstanding 455,224 443,766 450,148 443,420 Dilutive securities 1,753 2,390 1,833 2,588 Diluted weighted average common shares outstanding 456,977 446,156 451,981 446,008 Basic net income attributable to American Tower Corporation common stockholders per common share $ 1.59 $ 1.05 $ 4.70 $ 2.99 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 1.58 $ 1.04 $ 4.68 $ 2.97 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Restricted stock units — 0 — 1

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 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 2,000 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 September 30, 2021, the Company has purchased an aggregate of approximately 400 of the subleased towers which are subject to the applicable agreement. The aggregate purchase option price for the remaining towers leased and subleased is $1.0 billion 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

ACQUISITIONS

ACQUISITIONS	9 Months Ended
	Sep. 30, 2021
Business Combination and Asset Acquisition [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 nine months ended September 30, 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 and systems, 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 and nine months ended September 30, 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Acquisition and merger related expenses $ 25.3 $ 0.7 $ 88.8 $ 11.1 Integration costs $ 6.9 $ 7.0 $ 32.9 $ 16.1 During the nine months ended September 30, 2021 and 2020, the Company also recorded benefits of $4.4 million and $4.6 million, respectively, related to pre-acquisition contingencies and settlements. The increase in acquisition and merger related costs during the three and nine months ended September 30, 2021 was primarily associated with the Telxius Acquisition. 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 September 30, 2021 was approximately $170.2 million and $91.3 million, respectively, and for the nine months ended September 30, 2021 was approximately $226.2 million and $116.2 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. Telxius Acquisition —On January 13, 2021, the Company entered into the Telxius Acquisition, pursuant to which the Company agreed 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), subject to certain adjustments. In June 2021, the Company completed the acquisition of nearly 20,000 communications sites in Germany and Spain, for total consideration of approximately 6.3 billion EUR (approximately $7.7 billion at the date of closing), subject to certain post-closing adjustments and over 7,000 communications sites in Brazil, Peru, Chile and Argentina, for total consideration of approximately 0.9 billion EUR (approximately $1.1 billion at the date of closing), subject to certain post-closing adjustments. On August 2, 2021, the Company completed the acquisition of the approximately 4,000 remaining communications sites in Germany pursuant to the Telxius Acquisition for 0.6 billion EUR (approximately $0.7 billion at the date of closing). Of the aggregate purchase price, 229.4 million EUR (approximately $265.6 million), including post-closing adjustments, of deferred payments are due in September 2025 and August 2026 and are reflected in Other non-current liabilities in the consolidated balance sheet as of September 30, 2021. The acquired operations in Germany and Spain are included in the Europe property segment and the acquired operations in Brazil, Peru, Chile and Argentina are included in the Latin America property segment. The Telxius Acquisition was accounted for as a business combination and is subject to post-closing adjustments. 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 nine months ended September 30, 2021, the Company completed the acquisition of an additional 156 communications sites pursuant to this agreement for an aggregate total purchase price of $44.5 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 in “Other.” The remaining communications sites are expected to continue to close in tranches, subject to certain closing conditions. Bangladesh Acquisition —During the three months ended September 30, 2021, the Company acquired a 51% controlling interest in KTBL for 900 million BDT (approximately $10.6 million at the date of closing) through a joint venture partnership with Confidence Group (which holds a 49% noncontrolling interest in KTBL). This acquisition is being accounted for as a business combination and is subject to post-closing adjustments. This acquisition is included in the table below in “Other.” Other Acquisitions —During the nine months ended September 30, 2021, the Company acquired a total of 718 communications sites as well as other communications infrastructure assets in the United States, France, Mexico, Nigeria, Peru and Poland, including 180 communications sites in connection with the Company’s agreement with Orange S.A. (“Orange”) as further described below, for an aggregate purchase price of $326.9 million. Of the aggregate purchase price, $8.5 million is reflected as a payable in the consolidated balance sheet as of September 30, 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: Telxius Acquisition Other (1) Current assets $ 289.0 $ 25.9 Property and equipment 1,417.7 119.2 Intangible assets (2): Tenant-related intangible assets 5,391.2 190.8 Network location intangible assets 675.8 55.9 Other intangible assets — — Other non-current assets 1,380.3 39.2 Current liabilities (331.9) (11.4) Deferred tax liability (1,227.5) — Other non-current liabilities (1,504.8) (36.6) Net assets acquired 6,089.8 383.0 Goodwill (3) 3,500.0 9.2 Fair value of net assets acquired 9,589.8 392.2 Debt assumed — — Noncontrolling interest — (10.2) Purchase price $ 9,589.8 $ 382.0 _______________ (1) Includes 21 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. (3) The Company expects goodwill to be partially deductible for tax purposes. Other Signed Acquisitions Orange Acquisition —On November 28, 2019, the Company entered into definitive agreements with Orange 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 communications sites during the year ended December 31, 2020. Subsequent to September 30, 2021, the Company completed the acquisition of an additional 157 of these communications sites. The remaining communications sites are expected to continue to close in tranches, subject to customary closing conditions. 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 nine months ended September 30, 2021, certain adjustments were made to increase assets by $6.8 million and reduce liabilities by $67.3 million, primarily related to deferred tax liabilities, with a corresponding decrease in goodwill of $74.1 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, to the extent available, are based on historical information, and accordingly may not fully reflect the current operations of the acquired business. In addition, 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Pro forma revenues $ 2,460.9 $ 2,203.1 $ 7,224.5 $ 6,460.1 Pro forma net income attributable to American Tower Corporation common stockholders $ 721.9 $ 392.1 $ 2,144.9 $ 1,106.4 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 1.59 $ 0.86 $ 4.72 $ 2.44 Diluted net income attributable to American Tower Corporation common stockholders $ 1.58 $ 0.86 $ 4.70 $ 2.43

BUSINESS SEGMENTS

BUSINESS SEGMENTS	9 Months Ended
	Sep. 30, 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 September 30, 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, Bangladesh, India and the Philippines; • Africa: property operations in Burkina Faso, Ghana, Kenya, Niger, Nigeria, South Africa and Uganda; • Europe: property operations in France, Germany, Poland and Spain; 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 and nine months ended September 30, 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 September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,231.2 $ 313.5 $ 257.4 $ 175.8 $ 391.0 $ 2,368.9 $ 85.4 $ 2,454.3 Segment operating expenses 221.4 187.1 88.2 73.0 123.7 693.4 30.9 724.3 Segment gross margin 1,009.8 126.4 169.2 102.8 267.3 1,675.5 54.5 1,730.0 Segment selling, general, administrative and development expense (1) 48.1 21.5 16.5 12.8 26.3 125.2 3.8 129.0 Segment operating profit $ 961.7 $ 104.9 $ 152.7 $ 90.0 $ 241.0 $ 1,550.3 $ 50.7 $ 1,601.0 Stock-based compensation expense $ 28.1 28.1 Other selling, general, administrative and development expense 48.8 48.8 Depreciation, amortization and accretion 611.4 611.4 Other expense (2) 135.1 135.1 Income from continuing operations before income taxes $ 777.6 Total assets $ 27,375.0 $ 5,164.2 $ 4,965.4 $ 12,123.2 $ 8,764.1 $ 58,391.9 $ 100.9 $ 2,037.2 $ 60,530.0 _______________ (1) Segment selling, general, administrative and development expenses exclude stock-based compensation expense of $28.1 million. (2) Primarily includes interest expense, partially offset by foreign currency gains. Property Total Services Other Total Three Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,122.3 $ 305.2 $ 220.0 $ 38.7 $ 301.4 $ 1,987.6 $ 25.3 $ 2,012.9 Segment operating expenses (1) 207.3 167.1 74.1 7.7 95.5 551.7 10.2 561.9 Segment gross margin 915.0 138.1 145.9 31.0 205.9 1,435.9 15.1 1,451.0 Segment selling, general, administrative and development expense (1) 38.3 24.1 18.5 5.3 20.9 107.1 4.2 111.3 Segment operating profit $ 876.7 $ 114.0 $ 127.4 $ 25.7 $ 185.0 $ 1,328.8 $ 10.9 $ 1,339.7 Stock-based compensation expense $ 24.1 24.1 Other selling, general, administrative and development expense 41.3 41.3 Depreciation, amortization and accretion 473.9 473.9 Other expense (2) 298.2 298.2 Income from continuing operations before income taxes $ 502.2 Total assets $ 22,610.8 $ 5,142.3 $ 4,645.3 $ 1,743.7 $ 6,855.4 $ 40,997.5 $ 35.1 $ 429.6 $ 41,462.2 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $0.7 million and $23.4 million, respectively. (2) Primarily includes interest expense. Property Total Services Other Total Nine Months Ended September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 3,695.9 $ 893.1 $ 741.1 $ 308.2 $ 1,093.3 $ 6,731.6 $ 180.1 $ 6,911.7 Segment operating expenses 631.1 546.4 254.8 110.7 337.0 1,880.0 66.5 1,946.5 Segment gross margin 3,064.8 346.7 486.3 197.5 756.3 4,851.6 113.6 4,965.2 Segment selling, general, administrative and development expense (1) 129.8 52.7 52.9 26.3 79.6 341.3 12.1 353.4 Segment operating profit $ 2,935.0 $ 294.0 $ 433.4 $ 171.2 $ 676.7 $ 4,510.3 $ 101.5 $ 4,611.8 Stock-based compensation expense $ 98.0 98.0 Other selling, general, administrative and development expense 144.3 144.3 Depreciation, amortization and accretion 1,688.7 1,688.7 Other expense (2) 379.9 379.9 Income from continuing operations before income taxes $ 2,300.9 _______________ (1) Segment selling, general, administrative and development expenses exclude stock-based compensation expense of $98.0 million. (2) Primarily includes interest expense, partially offset by foreign currency gains. Property Total Services Other Total Nine Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 3,299.7 $ 863.1 $ 651.5 $ 107.9 $ 931.8 $ 5,854.0 $ 65.0 $ 5,919.0 Segment operating expenses (1) 599.7 489.7 221.5 21.1 293.1 1,625.1 27.2 1,652.3 Segment gross margin 2,700.0 373.4 430.0 86.8 638.7 4,228.9 37.8 4,266.7 Segment selling, general, administrative and development expense (1) 117.6 90.2 56.4 15.6 67.8 347.6 9.8 357.4 Segment operating profit $ 2,582.4 $ 283.2 $ 373.6 $ 71.2 $ 570.9 $ 3,881.3 $ 28.0 $ 3,909.3 Stock-based compensation expense $ 99.0 99.0 Other selling, general, administrative and development expense 128.3 128.3 Depreciation, amortization and accretion 1,401.1 1,401.1 Other expense (2) 879.5 879.5 Income from continuing operations before income taxes $ 1,401.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $2.3 million and $96.7 million, respectively.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS Data Centers Acquisition— On October 5, 2021, the Company completed the acquisition of two multi-tenant data centers in the United States for total consideration of approximately $201 million. A preliminary purchase price allocation is not available due to the timing of the closing. 0.400% Senior Notes and 0.950% Senior Notes Offering— On October 5, 2021, the Company completed a registered public offering of 500.0 million EUR ($579.9 million at the date of issuance) aggregate principal amount of 0.400% senior unsecured notes due 2027 (the “0.400% Notes”) and 500.0 million EUR ($579.9 million at the date of issuance) aggregate principal amount of 0.950% senior unsecured notes due 2030 (the “0.950% Notes”). The net proceeds from this offering were approximately 987.7 million EUR (approximately $1,145.6 million at the date of issuance), after deducting commissions and estimated expenses. The Company used the net proceeds to repay EUR denominated existing indebtedness under the 2021 Multicurrency Credit Facility and the 2021 364-Day Delayed Draw Term Loan. The 0.400% Notes will mature on February 15, 2027 and bear interest at a rate of 0.400% per annum. The 0.950% Notes will mature on October 5, 2030 and bear interest at a rate of 0.950% per annum. Accrued and unpaid interest on the 0.400% Notes will be payable in EUR in arrears on February 15 of each year, beginning on February 15, 2022. Accrued and unpaid interest on the 0.950% Notes will be payable in EUR in arrears on October 5 of each year, beginning on October 5, 2022. Interest on the 0.400% Notes and the 0.950% Notes will accrue from October 5, 2021 and will be computed on the basis of the actual number of days in the period for which interest is being calculated and the actual number of days from and including the last date on which interest was paid on the notes, beginning on the issue date. The Company may redeem the 0.400% Notes and the 0.950% Notes at any time, in whole or in part, at a redemption price equal to 100% of the principal amount of the 0.400% Notes and the 0.950% Notes plus a make-whole premium, together with accrued interest to the redemption date. If the Company redeems the 0.400% Notes on or after December 15, 2026 or the 0.950% Notes on or after July 5, 2030, the Company will not be required to pay a make-whole premium. In addition, if the Company undergoes a change of control and corresponding ratings decline, each as defined in the supplemental indenture, it may be required to repurchase all of the 0.400% Notes and the 0.950% 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 0.400% Notes and the 0.950% 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 supplemental indenture. Repayment of the 2021 364-Day Delayed Draw Term Loan— On October 7, 2021, the Company repaid all amounts outstanding under the 2021 364-Day Delayed Draw Term Loan using proceeds from the issuance of the 0.400% Notes and the 0.950% Notes. Repayment of 4.70% Senior Notes— On October 18, 2021, the Company redeemed all of the 4.70% Notes at a price equal to 101.7270% of the principal amount, plus accrued and unpaid interest up to, but excluding October 18, 2021, for an aggregate redemption price of approximately $715.1 million, including $3.0 million in accrued and unpaid interest. The Company expects to record a loss on retirement of long-term obligations of approximately $12.4 million, which includes prepayment consideration of $12.1 million and the associated unamortized discount and deferred financing costs. The redemption was funded with cash on hand. Upon completion of this redemption, none of the 4.70% Notes remained outstanding.

BASIS OF PRESENTATION AND SIG_2

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 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.
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 16. 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 generally not accounted for as 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 generally require that the Company provide the tenant the right to use available capacity on 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 and nine months ended September 30, 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 September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 73.2 $ 2.6 $ 6.3 $ 2.1 $ 35.1 $ 119.3 Services revenue 85.4 — — — — 85.4 Total non-lease revenue $ 158.6 $ 2.6 $ 6.3 $ 2.1 $ 35.1 $ 204.7 Property lease revenue 1,158.0 310.9 251.1 173.7 355.9 2,249.6 Total revenue $ 1,316.6 $ 313.5 $ 257.4 $ 175.8 $ 391.0 $ 2,454.3 Three Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 72.0 $ 2.3 $ 3.6 $ 1.7 $ 26.7 $ 106.3 Services revenue 25.3 — — — — 25.3 Total non-lease revenue $ 97.3 $ 2.3 $ 3.6 $ 1.7 $ 26.7 $ 131.6 Property lease revenue 1,050.3 302.9 216.4 37.0 274.7 1,881.3 Total revenue $ 1,147.6 $ 305.2 $ 220.0 $ 38.7 $ 301.4 $ 2,012.9 Nine Months Ended September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 214.9 $ 6.8 $ 17.5 $ 6.0 $ 100.9 $ 346.1 Services revenue 180.1 — — — — 180.1 Total non-lease revenue $ 395.0 $ 6.8 $ 17.5 $ 6.0 $ 100.9 $ 526.2 Property lease revenue 3,481.0 886.3 723.6 302.2 992.4 6,385.5 Total revenue $ 3,876.0 $ 893.1 $ 741.1 $ 308.2 $ 1,093.3 $ 6,911.7 Nine Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 193.0 $ 6.8 $ 9.5 $ 4.8 $ 87.9 $ 302.0 Services revenue 65.0 — — — — 65.0 Total non-lease revenue $ 258.0 $ 6.8 $ 9.5 $ 4.8 $ 87.9 $ 367.0 Property lease revenue 3,106.7 856.3 642.0 103.1 843.9 5,552.0 Total revenue $ 3,364.7 $ 863.1 $ 651.5 $ 107.9 $ 931.8 $ 5,919.0 Property revenue for the three months ended September 30, 2021 and 2020 includes straight-line revenue of $99.6 million and $68.1 million, respectively. Property revenue for the nine months ended September 30, 2021 and 2020 includes straight-line revenue of $324.3 million and $178.9 million, respectively. Unearned revenue —Amounts billed upfront in connection with the execution of lease agreements are initially deferred and reflected in Unearned revenue in the consolidated balance sheets and recognized as revenue over the terms of the applicable lease arrangements. Amounts billed or received for services prior to being earned are deferred and reflected in Unearned revenue in the consolidated balance sheets until the criteria for recognition have been met. The increase in unearned revenue during the nine months ended September 30, 2021 is due to advance payments from a tenant.
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 September 30, 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)	9 Months Ended
	Sep. 30, 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: Nine Months Ended September 30, 2021 2020 Cash and cash equivalents $ 3,277.2 $ 1,626.0 Restricted cash 422.1 104.2 Total cash, cash equivalents and restricted cash $ 3,699.3 $ 1,730.2
Summary of Revenue Disaggregated by Source and Geography	A summary of revenue disaggregated by source and geography is as follows: Three Months Ended September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 73.2 $ 2.6 $ 6.3 $ 2.1 $ 35.1 $ 119.3 Services revenue 85.4 — — — — 85.4 Total non-lease revenue $ 158.6 $ 2.6 $ 6.3 $ 2.1 $ 35.1 $ 204.7 Property lease revenue 1,158.0 310.9 251.1 173.7 355.9 2,249.6 Total revenue $ 1,316.6 $ 313.5 $ 257.4 $ 175.8 $ 391.0 $ 2,454.3 Three Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 72.0 $ 2.3 $ 3.6 $ 1.7 $ 26.7 $ 106.3 Services revenue 25.3 — — — — 25.3 Total non-lease revenue $ 97.3 $ 2.3 $ 3.6 $ 1.7 $ 26.7 $ 131.6 Property lease revenue 1,050.3 302.9 216.4 37.0 274.7 1,881.3 Total revenue $ 1,147.6 $ 305.2 $ 220.0 $ 38.7 $ 301.4 $ 2,012.9 Nine Months Ended September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 214.9 $ 6.8 $ 17.5 $ 6.0 $ 100.9 $ 346.1 Services revenue 180.1 — — — — 180.1 Total non-lease revenue $ 395.0 $ 6.8 $ 17.5 $ 6.0 $ 100.9 $ 526.2 Property lease revenue 3,481.0 886.3 723.6 302.2 992.4 6,385.5 Total revenue $ 3,876.0 $ 893.1 $ 741.1 $ 308.2 $ 1,093.3 $ 6,911.7 Nine Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Total Non-lease property revenue $ 193.0 $ 6.8 $ 9.5 $ 4.8 $ 87.9 $ 302.0 Services revenue 65.0 — — — — 65.0 Total non-lease revenue $ 258.0 $ 6.8 $ 9.5 $ 4.8 $ 87.9 $ 367.0 Property lease revenue 3,106.7 856.3 642.0 103.1 843.9 5,552.0 Total revenue $ 3,364.7 $ 863.1 $ 651.5 $ 107.9 $ 931.8 $ 5,919.0

PREPAID AND OTHER CURRENT ASS_2

PREPAID AND OTHER CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of prepaid and other current assets	Prepaid and other current assets consisted of the following: As of September 30, 2021 December 31, 2020 Prepaid assets $ 89.6 $ 66.1 Prepaid income tax 91.6 143.7 Unbilled receivables 261.6 176.9 Value added tax and other consumption tax receivables 67.3 66.3 Other miscellaneous current assets 81.9 79.6 Prepaid and other current assets $ 592.0 $ 532.6

LEASES (Tables)

LEASES (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2021 were as follows: Fiscal Year Amount (1) Remainder of 2021 $ 1,648.0 2022 5,953.2 2023 6,611.2 2024 6,489.2 2025 6,044.5 Thereafter 34,158.8 Total $ 60,904.9 _______________
Schedule of Information About Other Lease-related Balances	Information about other lease-related balances is as follows: As of September 30, 2021 December 31, 2020 Operating leases: Right-of-use asset $ 9,021.9 $ 7,789.2 Current portion of lease liability $ 734.3 $ 539.9 Lease liability 7,863.2 6,884.4 Total operating lease liability $ 8,597.5 $ 7,424.3
Schedule of Components of Operating Lease Cost	The weighted-average remaining lease terms and incremental borrowing rates are as follows: As of September 30, 2021 December 31, 2020 Operating leases: Weighted-average remaining lease term (years) 13.0 13.7 Weighted-average incremental borrowing rate 5.3 % 5.6 % The following table sets forth the components of lease cost: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Operating lease cost $ 295.6 $ 242.6 $ 815.3 $ 731.3 Variable lease costs not included in lease liability (1) 94.3 69.7 248.7 202.3 ______________ (1) Includes property tax paid on behalf of the landlord. Supplemental cash flow information is as follows: Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ (798.2) $ (732.8) Non-cash items: New operating leases (1) $ 1,607.2 $ 125.7 Operating lease modifications and reassessments $ 165.3 $ 573.2 _______________ (1) Amount includes new operating leases and leases acquired in connection with acquisitions, including $1.4 billion related to the Telxius Acquisition (as defined in note 6).
Schedule of Maturity of Operating Lease Liabilities	Maturities of operating lease liabilities as of September 30, 2021 were as follows: Fiscal Year Operating Lease (1) Remainder of 2021 $ 285.9 2022 1,085.1 2023 1,042.2 2024 993.4 2025 936.1 Thereafter 7,509.8 Total lease payments 11,852.5 Less amounts representing interest (3,255.0) Total lease liability 8,597.5 Less current portion of lease liability 734.3 Non-current lease liability $ 7,863.2 _______________ (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)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of 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) (74.4) 9.5 — 3,177.6 322.4 — 3,435.1 Effect of foreign currency translation 2.4 (16.6) (3.3) (176.7) (42.8) — (237.0) Balance as of September 30, 2021 $ 4,678.8 $ 1,009.8 $ 622.3 $ 3,280.0 $ 887.9 $ 2.0 $ 10,480.8 _______________ (1) Europe and Latin America consist of additions and measurement period adjustments related to the Telxius Acquisition. U.S. & Canada consists of measurement period adjustments related to the InSite Acquisition. Asia-Pacific consists of $9.2 million of additions related to the Bangladesh acquisition (as discussed in note 15) and measurement period adjustments related to the InSite Acquisition.
Schedule of Other Intangible Assets Subject to Amortization	The Company’s other intangible assets subject to amortization consisted of the following: As of September 30, 2021 As of December 31, 2020 Estimated Useful Gross Accumulated Net Book Gross Accumulated Net Book Acquired network location intangibles (1) Up to 20 $ 6,329.5 $ (2,305.1) $ 4,024.4 $ 5,784.0 $ (2,117.6) $ 3,666.4 Acquired tenant-related intangibles Up to 20 19,471.9 (4,816.3) 14,655.6 14,322.5 (4,237.5) 10,085.0 Acquired licenses and other intangibles 3-20 99.9 (11.5) 88.4 97.8 (9.4) 88.4 Total other intangible assets $ 25,901.3 $ (7,132.9) $ 18,768.4 $ 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.
Schedule of 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 $ 318.0 2022 1,270.8 2023 1,237.8 2024 1,224.1 2025 1,196.7 2026 1,162.9

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: As of September 30, 2021 December 31, 2020 Accrued construction costs $ 96.3 $ 46.5 Accrued income tax payable 27.2 20.6 Accrued pass-through costs 76.1 67.1 Amounts payable for acquisitions 14.1 58.9 Amounts payable to tenants 78.7 66.4 Accrued property and real estate taxes 246.0 219.1 Accrued rent 77.8 82.6 Payroll and related withholdings 104.9 104.4 Other accrued expenses 444.3 378.1 Total accrued expenses $ 1,165.4 $ 1,043.7

LONG-TERM OBLIGATIONS (Tables)

LONG-TERM OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2021 December 31, 2020 Maturity Date 2020 Term Loan (1) (2) $ — $ 749.4 N/A 2021 Multicurrency Credit Facility (1) (3) 1,568.6 — June 28, 2024 2019 Term Loan (1) 496.3 996.1 January 31, 2025 2021 Credit Facility (1) — 2,295.0 January 31, 2026 2021 364-Day Delayed Draw Term Loan (1) (3) (4) 787.2 — May 28, 2022 2021 Three Year Delayed Draw Term Loan (1) (3) 955.1 — May 28, 2024 2.250% senior notes 601.6 605.1 January 15, 2022 4.70% senior notes (5) 699.6 699.0 March 15, 2022 3.50% senior notes 997.5 996.1 January 31, 2023 3.000% senior notes 714.9 721.9 June 15, 2023 0.600% senior notes 497.6 496.8 January 15, 2024 5.00% senior notes 1,001.0 1,001.3 February 15, 2024 3.375% senior notes 646.6 645.7 May 15, 2024 2.950% senior notes 644.3 643.1 January 15, 2025 2.400% senior notes 745.8 745.0 March 15, 2025 1.375% senior notes (6) 573.6 604.1 April 4, 2025 4.000% senior notes 745.2 744.3 June 1, 2025 1.300% senior notes 496.1 495.4 September 15, 2025 4.400% senior notes 497.5 497.1 February 15, 2026 1.600% senior notes 694.9 — April 15, 2026 1.950% senior notes (6) 574.2 605.2 May 22, 2026 1.450% senior notes 592.6 — September 15, 2026 3.375% senior notes 990.8 989.5 October 15, 2026 3.125% senior notes 398.2 397.9 January 15, 2027 2.750% senior notes 745.0 744.3 January 15, 2027 0.450% senior notes (6) 862.1 — January 15, 2027 3.55% senior notes 745.4 744.8 July 15, 2027 0.500% senior notes (6) 860.3 907.4 January 15, 2028 3.600% senior notes 694.1 693.4 January 15, 2028 1.500% senior notes 645.6 645.1 January 31, 2028 3.950% senior notes 591.3 590.6 March 15, 2029 0.875% senior notes (6) 862.3 — May 21, 2029 3.800% senior notes 1,634.7 1,633.5 August 15, 2029 2.900% senior notes 742.3 741.7 January 15, 2030 2.100% senior notes 740.9 740.2 June 15, 2030 1.875% senior notes 791.2 790.5 October 15, 2030 2.700% senior notes 693.6 — April 15, 2031 2.300% senior notes 690.8 — September 15, 2031 1.000% senior notes (6) 744.9 786.1 January 15, 2032 1.250% senior notes (6) 571.3 — May 21, 2033 3.700% senior notes 592.0 591.9 October 15, 2049 3.100% senior notes 1,037.9 1,037.7 June 15, 2050 2.950% senior notes 1,021.3 538.2 January 15, 2051 Total American Tower Corporation debt 31,186.2 26,113.4 Series 2013-2A securities (7) 1,297.8 1,296.6 March 15, 2023 Series 2018-1A securities (7) 495.1 494.6 March 15, 2028 Series 2015-2 notes (8) 522.6 522.1 June 16, 2025 InSite Debt (9) — 800.0 N/A Other subsidiary debt (10) 11.7 32.9 Various Total American Tower subsidiary debt 2,327.2 3,146.2 Finance lease obligations 32.0 27.9 Total 33,545.4 29,287.5 Less current portion of long-term obligations (2,106.4) (789.8) Long-term obligations $ 31,439.0 $ 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) As of September 30, 2021 reflects borrowings denominated in Euros (“EUR”). (4) Repaid in full on October 7, 2021 , as further discussed in note 17. (5) Repaid in full on October 18, 2021 , as further discussed in note 17. (6) Notes are denominated in EUR. (7) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (8) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (9) 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. (10) Includes (a) debt entered into by the Company’s Kenyan subsidiary in connection with an acquisition of sites in Kenya, which is denominated in 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 (b) U.S. subsidiary debt related to a seller-financed acquisition. As of December 31, 2020 also included the Colombian credit facility (the “Colombian Credit Facility”), which was denominated in Colombian Pesos and was fully repaid on its maturity date of April 24, 2021. As of September 30, 2021, no amounts remained outstanding under the Colombian 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 0.450% Notes (3) $ 913.7 May 21, 2021 January 15, 2027 0.450 % January 15, 2022 January 15 November 15, 2026 0.875% Notes (3) $ 913.7 May 21, 2021 May 21, 2029 0.875 % May 21, 2022 May 21 February 21, 2029 1.250% Notes (3) $ 609.1 May 21, 2021 May 21, 2033 1.250 % May 21, 2022 May 21 February 21, 2033 1.450% Notes $ 600.0 September 27, 2021 September 15, 2026 1.450 % March 15, 2022 March 15 and September 15 August 15, 2026 2.300% Notes $ 700.0 September 27, 2021 September 15, 2031 2.300 % March 15, 2022 March 15 and September 15 June 15, 2031 2.950% Notes (4) $ 1,050.0 September 27, 2021 January 15, 2051 2.950 % January 15, 2022 January 15 and July 15 July 15, 2050 ___________ (1) Accrued and unpaid interest on USD denominated notes 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. Interest on EUR denominated notes is payable in EUR annually and will be computed on the basis of the actual number of days in the period for which interest is being calculated and the actual number of days from and including the last date on which interest was paid on the notes, beginning on the issue date. (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. (3) The 0.450% Notes, the 0.875% Notes and the 1.250% Notes are denominated in EUR. Represents the dollar equivalent of the aggregate principal amount as of the issue date. (4) The initial 2.950% Notes were issued on November 20, 2020. The reopened 2.950% Notes were issued on September 27, 2021.
Schedule of line of credit facilities	As of September 30, 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 and the 2021 Three Year Delayed Draw Term Loan 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 1,568.6 $ 3.5 June 28, 2024 (3) 1.125 % 0.110 % 2021 Credit Facility — $ 0.9 January 31, 2026 (3) 1.125 % 0.110 % 2019 Term Loan 496.3 N/A January 31, 2025 1.125 % N/A 2021 364-Day Delayed Draw Term Loan 787.2 N/A May 28, 2022 1.000 % 0.110 % 2021 Three Year Delayed Draw Term Loan 955.1 N/A May 28, 2024 1.125 % 0.110 % _______________ (1) LIBOR applies to the USD denominated borrowings under the 2021 Multicurrency Credit Facility, the 2021 Credit Facility and the 2019 Term Loan. EURIBOR applies to the EUR denominated borrowings under the 2021 Multicurrency Credit Facility and the 2021 Credit Facility, and all of the borrowings under the 2021 Delayed Draw Term Loans. (2) Fee on undrawn portion of each credit facility.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 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: September 30, 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 — $ 17.5 — — $ 29.2 — Investments in equity securities (1) $ 50.5 — — — $ 6.0 — Liabilities: Fair value of debt related to interest rate swap agreements (2) $ 19.1 — — $ 31.4 — — _______________ (1) Investments in equity securities are recorded in Notes receivable and other non-current assets in the consolidated balance sheet at fair value. Unrealized holding gains and losses for equity securities are recorded in Other income (expense) in the consolidated statements of operations in the current period. During the three and nine months ended September 30, 2021, the Company recognized unrealized (losses) gains of $(9.9) million and $19.5 million, respectively, for equity securities held as of September 30, 2021. (2) Included in the carrying values of the corresponding debt obligations.

INCOME TAXES (Tables)

INCOME TAXES (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Penalties and income tax-related interest expense (1) $ 9.6 $ 6.6 $ 43.1 $ 9.3 _______________ (1) Nine months ended September 30, 2021 reflects an increase of $16.6 million due to a reclassification of unrecognized tax benefits to penalties and income tax-related interest expense.

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Summary of stock-based compensation expenses	During the three and nine months ended September 30, 2021 and 2020, the Company recorded and capitalized the following stock-based compensation expense: Three Months Ended September 30, Nine Months Ended September 30, 2021 (1) 2020 (2) 2021 (1) 2020 (2) Stock-based compensation expense $ 28.1 $ 24.1 $ 98.0 $ 99.0 _______________ (1) For the three and nine months ended September 30, 2021, stock-based compensation expense consisted of $28.1 million and $98.0 million, respectively, included in selling, general, administrative and development expense. (2) For the three and nine months ended September 30, 2020, stock-based compensation expense consisted of (i) $0.4 million and $1.4 million, respectively, included in Property costs of operations, (ii) $0.3 million and $0.9 million, respectively, included in Services costs of operations and (iii) $23.4 million and $96.7 million, respectively, included in selling, general, administrative and development expense. For the three and nine
Summary of the company's option activity	The Company’s option activity for the nine months ended September 30, 2021 was as follows (shares disclosed in full amounts): Number of Options Outstanding as of January 1, 2021 2,016,261 Exercised (629,515) Forfeited — Expired — Outstanding as of September 30, 2021 1,386,746
Schedule of RSU and PSU activity	The Company’s RSU and PSU activity for the nine months ended September 30, 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) 546,698 98,694 Vested and Released (3) (564,397) (162,882) Forfeited (46,649) — Outstanding as of September 30, 2021 1,180,727 256,322 Vested and deferred as of September 30, 2021 (4) 17,121 — _______________ (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 98,694 shares. (3) This includes 58,204 and 96,048 of previously vested and deferred RSUs and PSUs, respectively. 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 RSUs are related to deferred compensation for certain former employees.

REDEEMABLE NONCONTROLLING INT_2

REDEEMABLE NONCONTROLLING INTERESTS (Tables)	9 Months Ended
	Sep. 30, 2021
Noncontrolling Interest [Abstract]
Changes in Redeemable noncontrolling interest	The changes in Redeemable noncontrolling interests were as follows: Nine Months Ended September 30, 2021 2020 Balance as of January 1, $ 212.1 $ 1,096.5 Net income attributable to noncontrolling interests 4.0 11.2 Adjustment to noncontrolling interest redemption value 1.2 (10.0) Purchase of redeemable noncontrolling interest (2.5) (524.4) Foreign currency translation adjustment attributable to noncontrolling interests (3.4) (18.4) Balance as of September 30, $ 211.4 $ 554.9

EQUITY (Tables)

EQUITY (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Schedule of declared or paid cash distributions	During the nine months ended September 30, 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 September 16, 2021 October 15, 2021 September 28, 2021 $ 1.31 $ 596.6 May 27, 2021 July 9, 2021 June 18, 2021 $ 1.27 $ 577.8 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 nine months ended September 30, 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 September 10, 2020 October 16, 2020 September 28, 2020 $ 1.14 $ 506.4 May 19, 2020 July 10, 2020 June 19, 2020 $ 1.10 $ 487.9 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 _______________

NONCONTROLLING INTEREST (Tables

NONCONTROLLING INTEREST (Tables)	9 Months Ended
	Sep. 30, 2021
Noncontrolling Interest [Abstract]
Schedule of Changes in Noncontrolling Interests	The changes in noncontrolling interests were as follows: Nine Months Ended September 30, 2021 Balance as of January 1, $ 474.9 ATC Europe Transactions (1) 3,078.2 Bangladesh partnership (2) 10.2 Adjustment to noncontrolling interest due to reorganization (3) 601.0 Redemption of noncontrolling interest (4) (1.7) Net income attributable to noncontrolling interests 6.9 Foreign currency translation adjustment attributable to noncontrolling interests, net of tax (103.3) Distributions to noncontrolling interest holders (0.4) Balance as of September 30, $ 4,065.8 _______________ (1) Represents the impact of contributions received from CDPQ and Allianz described above on Noncontrolling interests as of September 30, 2021. Reflected within Contributions from noncontrolling interest holders in the consolidated statements of equity. (2) Represents the impact of contributions made by the Company to establish the joint venture in Bangladesh described above on Noncontrolling interests as of September 30, 2021. Reflected within Purchase of noncontrolling interest in the consolidated statements of equity. (3) Represents the impact of the reorganization of European interests described above on Noncontrolling interests as of September 30, 2021.

EARNINGS PER COMMON SHARE (Tabl

EARNINGS PER COMMON SHARE (Tables)	9 Months Ended
	Sep. 30, 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net income attributable to American Tower Corporation common stockholders $ 723.0 $ 464.4 $ 2,114.3 $ 1,325.5 Basic weighted average common shares outstanding 455,224 443,766 450,148 443,420 Dilutive securities 1,753 2,390 1,833 2,588 Diluted weighted average common shares outstanding 456,977 446,156 451,981 446,008 Basic net income attributable to American Tower Corporation common stockholders per common share $ 1.59 $ 1.05 $ 4.70 $ 2.99 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 1.58 $ 1.04 $ 4.68 $ 2.97
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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Restricted stock units — 0 — 1

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	9 Months Ended
	Sep. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Schedule of acquisition and merger related costs	During the three and nine months ended September 30, 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Acquisition and merger related expenses $ 25.3 $ 0.7 $ 88.8 $ 11.1 Integration costs $ 6.9 $ 7.0 $ 32.9 $ 16.1
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: Telxius Acquisition Other (1) Current assets $ 289.0 $ 25.9 Property and equipment 1,417.7 119.2 Intangible assets (2): Tenant-related intangible assets 5,391.2 190.8 Network location intangible assets 675.8 55.9 Other intangible assets — — Other non-current assets 1,380.3 39.2 Current liabilities (331.9) (11.4) Deferred tax liability (1,227.5) — Other non-current liabilities (1,504.8) (36.6) Net assets acquired 6,089.8 383.0 Goodwill (3) 3,500.0 9.2 Fair value of net assets acquired 9,589.8 392.2 Debt assumed — — Noncontrolling interest — (10.2) Purchase price $ 9,589.8 $ 382.0 _______________ (1) Includes 21 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. (3) The Company expects goodwill to be partially deductible for tax purposes.
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, to the extent available, are based on historical information, and accordingly may not fully reflect the current operations of the acquired business. In addition, 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Pro forma revenues $ 2,460.9 $ 2,203.1 $ 7,224.5 $ 6,460.1 Pro forma net income attributable to American Tower Corporation common stockholders $ 721.9 $ 392.1 $ 2,144.9 $ 1,106.4 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 1.59 $ 0.86 $ 4.72 $ 2.44 Diluted net income attributable to American Tower Corporation common stockholders $ 1.58 $ 0.86 $ 4.70 $ 2.43

BUSINESS SEGMENTS (Tables)

BUSINESS SEGMENTS (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 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 September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,231.2 $ 313.5 $ 257.4 $ 175.8 $ 391.0 $ 2,368.9 $ 85.4 $ 2,454.3 Segment operating expenses 221.4 187.1 88.2 73.0 123.7 693.4 30.9 724.3 Segment gross margin 1,009.8 126.4 169.2 102.8 267.3 1,675.5 54.5 1,730.0 Segment selling, general, administrative and development expense (1) 48.1 21.5 16.5 12.8 26.3 125.2 3.8 129.0 Segment operating profit $ 961.7 $ 104.9 $ 152.7 $ 90.0 $ 241.0 $ 1,550.3 $ 50.7 $ 1,601.0 Stock-based compensation expense $ 28.1 28.1 Other selling, general, administrative and development expense 48.8 48.8 Depreciation, amortization and accretion 611.4 611.4 Other expense (2) 135.1 135.1 Income from continuing operations before income taxes $ 777.6 Total assets $ 27,375.0 $ 5,164.2 $ 4,965.4 $ 12,123.2 $ 8,764.1 $ 58,391.9 $ 100.9 $ 2,037.2 $ 60,530.0 _______________ (1) Segment selling, general, administrative and development expenses exclude stock-based compensation expense of $28.1 million. (2) Primarily includes interest expense, partially offset by foreign currency gains. Property Total Services Other Total Three Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 1,122.3 $ 305.2 $ 220.0 $ 38.7 $ 301.4 $ 1,987.6 $ 25.3 $ 2,012.9 Segment operating expenses (1) 207.3 167.1 74.1 7.7 95.5 551.7 10.2 561.9 Segment gross margin 915.0 138.1 145.9 31.0 205.9 1,435.9 15.1 1,451.0 Segment selling, general, administrative and development expense (1) 38.3 24.1 18.5 5.3 20.9 107.1 4.2 111.3 Segment operating profit $ 876.7 $ 114.0 $ 127.4 $ 25.7 $ 185.0 $ 1,328.8 $ 10.9 $ 1,339.7 Stock-based compensation expense $ 24.1 24.1 Other selling, general, administrative and development expense 41.3 41.3 Depreciation, amortization and accretion 473.9 473.9 Other expense (2) 298.2 298.2 Income from continuing operations before income taxes $ 502.2 Total assets $ 22,610.8 $ 5,142.3 $ 4,645.3 $ 1,743.7 $ 6,855.4 $ 40,997.5 $ 35.1 $ 429.6 $ 41,462.2 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $0.7 million and $23.4 million, respectively. (2) Primarily includes interest expense. Property Total Services Other Total Nine Months Ended September 30, 2021 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 3,695.9 $ 893.1 $ 741.1 $ 308.2 $ 1,093.3 $ 6,731.6 $ 180.1 $ 6,911.7 Segment operating expenses 631.1 546.4 254.8 110.7 337.0 1,880.0 66.5 1,946.5 Segment gross margin 3,064.8 346.7 486.3 197.5 756.3 4,851.6 113.6 4,965.2 Segment selling, general, administrative and development expense (1) 129.8 52.7 52.9 26.3 79.6 341.3 12.1 353.4 Segment operating profit $ 2,935.0 $ 294.0 $ 433.4 $ 171.2 $ 676.7 $ 4,510.3 $ 101.5 $ 4,611.8 Stock-based compensation expense $ 98.0 98.0 Other selling, general, administrative and development expense 144.3 144.3 Depreciation, amortization and accretion 1,688.7 1,688.7 Other expense (2) 379.9 379.9 Income from continuing operations before income taxes $ 2,300.9 _______________ (1) Segment selling, general, administrative and development expenses exclude stock-based compensation expense of $98.0 million. (2) Primarily includes interest expense, partially offset by foreign currency gains. Property Total Services Other Total Nine Months Ended September 30, 2020 U.S. & Canada Asia-Pacific Africa Europe Latin America Segment revenues $ 3,299.7 $ 863.1 $ 651.5 $ 107.9 $ 931.8 $ 5,854.0 $ 65.0 $ 5,919.0 Segment operating expenses (1) 599.7 489.7 221.5 21.1 293.1 1,625.1 27.2 1,652.3 Segment gross margin 2,700.0 373.4 430.0 86.8 638.7 4,228.9 37.8 4,266.7 Segment selling, general, administrative and development expense (1) 117.6 90.2 56.4 15.6 67.8 347.6 9.8 357.4 Segment operating profit $ 2,582.4 $ 283.2 $ 373.6 $ 71.2 $ 570.9 $ 3,881.3 $ 28.0 $ 3,909.3 Stock-based compensation expense $ 99.0 99.0 Other selling, general, administrative and development expense 128.3 128.3 Depreciation, amortization and accretion 1,401.1 1,401.1 Other expense (2) 879.5 879.5 Income from continuing operations before income taxes $ 1,401.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $2.3 million and $96.7 million, respectively.

BASIS OF PRESENTATION AND SIG_4

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - NARRATIVE (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)segment	Sep. 30, 2020USD ($)	Apr. 29, 2021	Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Number of reportable segments | segment			6
Straight-line revenue | $	$ 99.6	$ 68.1	$ 324.3	$ 178.9
ATC TIPL
Concentration Risk [Line Items]
Ownership percentage	92.00%		92.00%		100.00%	92.00%	79.00%
ATC Europe
Concentration Risk [Line Items]
Ownership percentage	52.00%		52.00%
Joint Venture - Bangladesh Operations
Concentration Risk [Line Items]
Ownership percentage	51.00%		51.00%
Germany | ATC Europe
Concentration Risk [Line Items]
Ownership percentage	87.00%		87.00%
Spain | ATC Europe
Concentration Risk [Line Items]
Ownership percentage	83.00%		83.00%

BASIS OF PRESENTATION AND SIG_5

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - CASH AND CASH EQUIVALENTS AND RESTRICTED CASH (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 3,277.2	$ 1,746.3	$ 1,626
Restricted cash	422.1	115.1	104.2
Total cash, cash equivalents and restricted cash	$ 3,699.3	$ 1,861.4	$ 1,730.2	$ 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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total non-lease revenue	$ 204.7	$ 131.6	$ 526.2	$ 367
Property lease revenue	2,249.6	1,881.3	6,385.5	5,552
Total revenue	$ 2,454.3	$ 2,012.9	$ 6,911.7	$ 5,919
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]	Total revenue	Total revenue	Total revenue	Total revenue
Non-lease property revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	$ 119.3	$ 106.3	$ 346.1	$ 302
Services revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	85.4	25.3	180.1	65
U.S. & Canada
Disaggregation of Revenue [Line Items]
Total non-lease revenue	158.6	97.3	395	258
Property lease revenue	1,158	1,050.3	3,481	3,106.7
Total revenue	1,316.6	1,147.6	3,876	3,364.7
U.S. & Canada | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	73.2	72	214.9	193
U.S. & Canada | Services revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	85.4	25.3	180.1	65
Asia-Pacific
Disaggregation of Revenue [Line Items]
Total non-lease revenue	2.6	2.3	6.8	6.8
Property lease revenue	310.9	302.9	886.3	856.3
Total revenue	313.5	305.2	893.1	863.1
Asia-Pacific | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	2.6	2.3	6.8	6.8
Asia-Pacific | Services revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	0	0	0	0
Africa
Disaggregation of Revenue [Line Items]
Total non-lease revenue	6.3	3.6	17.5	9.5
Property lease revenue	251.1	216.4	723.6	642
Total revenue	257.4	220	741.1	651.5
Africa | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	6.3	3.6	17.5	9.5
Africa | Services revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	0	0	0	0
Europe
Disaggregation of Revenue [Line Items]
Total non-lease revenue	2.1	1.7	6	4.8
Property lease revenue	173.7	37	302.2	103.1
Total revenue	175.8	38.7	308.2	107.9
Europe | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	2.1	1.7	6	4.8
Europe | Services revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	0	0	0	0
Latin America
Disaggregation of Revenue [Line Items]
Total non-lease revenue	35.1	26.7	100.9	87.9
Property lease revenue	355.9	274.7	992.4	843.9
Total revenue	391	301.4	1,093.3	931.8
Latin America | Non-lease property revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	35.1	26.7	100.9	87.9
Latin America | Services revenue
Disaggregation of Revenue [Line Items]
Total non-lease revenue	$ 0	$ 0	$ 0	$ 0

PREPAID AND OTHER CURRENT ASS_3

PREPAID AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid assets	$ 89.6	$ 66.1
Prepaid income tax	91.6	143.7
Unbilled receivables	261.6	176.9
Value added tax and other consumption tax receivables	67.3	66.3
Other miscellaneous current assets	81.9	79.6
Prepaid and other current assets	$ 592	$ 532.6

LEASES - MATURITIES OF MINIMUM

LEASES - MATURITIES OF MINIMUM RENTAL RECEIPTS EXPECTED UNDER NON-CANCELLABLE OPERATING LEASES (Details) $ in Millions	Sep. 30, 2021USD ($)
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Remainder of 2021	$ 1,648
2022	5,953.2
2023	6,611.2
2024	6,489.2
2025	6,044.5
Thereafter	34,158.8
Total	$ 60,904.9

LEASES - SCHEDULE OF INFORMATIO

LEASES - SCHEDULE OF INFORMATION ABOUT OTHER LEASE RELATED BALANCES (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Operating leases:
Right-of-use asset	$ 9,021.9	$ 7,789.2
Current portion of lease liability	734.3	539.9
Lease liability	7,863.2	6,884.4
Total lease liability	$ 8,597.5	$ 7,424.3

LEASES - SCHEDULE OF WEIGHTED A

LEASES - SCHEDULE OF WEIGHTED AVERAGE LEASE TERMS AND DISCOUNT RATES BY SEGMENT (Details)	Sep. 30, 2021	Dec. 31, 2020
Operating leases:
Weighted-average remaining lease term (years)	13 years	13 years 8 months 12 days
Weighted-average incremental borrowing rate	5.30%	5.60%

LEASES - LEASE COSTS (Details)

LEASES - LEASE COSTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease cost	$ 295.6	$ 242.6	$ 815.3	$ 731.3
Variable lease costs not included in lease liability	$ 94.3	$ 69.7	$ 248.7	$ 202.3

LEASES - SUPPLEMENTAL CASH FLOW

LEASES - SUPPLEMENTAL CASH FLOW INFOMATION (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ (798.2)	$ (732.8)
Non-cash items:
New operating leases	1,607.2	125.7
Operating lease modifications and reassessments	165.3	$ 573.2
Telxius Telecom S.A.
Non-cash items:
New operating leases	$ 1,400

LEASES - MATURITIES OF OPERATIN

LEASES - MATURITIES OF OPERATING AND FINANCE LEASE LIABILITIES (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Operating Lease
Remainder of 2021	$ 285.9
2022	1,085.1
2023	1,042.2
2024	993.4
2025	936.1
Thereafter	7,509.8
Total lease payments	11,852.5
Less amounts representing interest	(3,255)
Total lease liability	8,597.5	$ 7,424.3
Current portion of lease liability	734.3	539.9
Non-current lease liability	$ 7,863.2	$ 6,884.4

GOODWILL AND OTHER INTANGIBLE_3

GOODWILL AND OTHER INTANGIBLE ASSETS - CHANGES IN THE CARRYING VALUE OF GOODWILL (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 7,282.7
Additions and adjustments	3,435.1
Effect of foreign currency translation	(237)
Goodwill, ending balance	10,480.8
U.S. & Canada
Goodwill [Roll Forward]
Goodwill, beginning balance	4,750.8
Additions and adjustments	(74.4)
Effect of foreign currency translation	2.4
Goodwill, ending balance	4,678.8
Asia-Pacific
Goodwill [Roll Forward]
Goodwill, beginning balance	1,016.9
Additions and adjustments	9.5
Effect of foreign currency translation	(16.6)
Goodwill, ending balance	1,009.8
Asia-Pacific | Insite and Bangladesh Acquisitions
Goodwill [Roll Forward]
Additions and adjustments	9.2
Africa
Goodwill [Roll Forward]
Goodwill, beginning balance	625.6
Additions and adjustments	0
Effect of foreign currency translation	(3.3)
Goodwill, ending balance	622.3
Europe
Goodwill [Roll Forward]
Goodwill, beginning balance	279.1
Additions and adjustments	3,177.6
Effect of foreign currency translation	(176.7)
Goodwill, ending balance	3,280
Latin America
Goodwill [Roll Forward]
Goodwill, beginning balance	608.3
Additions and adjustments	322.4
Effect of foreign currency translation	(42.8)
Goodwill, ending balance	887.9
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	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 25,901.3	$ 20,204.3
Accumulated Amortization	(7,132.9)	(6,364.5)
Net Book Value	18,768.4	13,839.8
Acquired network location intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	6,329.5	5,784
Accumulated Amortization	(2,305.1)	(2,117.6)
Net Book Value	$ 4,024.4	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	$ 19,471.9	14,322.5
Accumulated Amortization	(4,816.3)	(4,237.5)
Net Book Value	$ 14,655.6	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	$ 99.9	97.8
Accumulated Amortization	(11.5)	(9.4)
Net Book Value	$ 88.4	$ 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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 318	$ 215.1	$ 846.2	$ 643.4
Weighted Average
Finite-Lived Intangible Assets [Line Items]
Remaining amortization period (in years)			16 years

GOODWILL AND OTHER INTANGIBLE_6

GOODWILL AND OTHER INTANGIBLE ASSETS - EXPECTED FUTURE AMORTIZATION EXPENSE (Details) $ in Millions	Sep. 30, 2021USD ($)
Fiscal Year
Remainder of 2021	$ 318
2022	1,270.8
2023	1,237.8
2024	1,224.1
2025	1,196.7
2026	$ 1,162.9

ACCRUED EXPENSES (Details)

ACCRUED EXPENSES (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued construction costs	$ 96.3	$ 46.5
Accrued income tax payable	27.2	20.6
Accrued pass-through costs	76.1	67.1
Amounts payable for acquisitions	14.1	58.9
Amounts payable to tenants	78.7	66.4
Accrued property and real estate taxes	246	219.1
Accrued rent	77.8	82.6
Payroll and related withholdings	104.9	104.4
Other accrued expenses	444.3	378.1
Total accrued expenses	$ 1,165.4	$ 1,043.7

LONG-TERM OBLIGATIONS - SCHEDUL

LONG-TERM OBLIGATIONS - SCHEDULE OF LONG-TERM OBLIGATIONS (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 27, 2021	May 21, 2021	Mar. 29, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Finance lease obligations	$ 32,000,000				$ 27,900,000
Total	33,545,400,000				29,287,500,000
Less current portion of long-term obligations	(2,106,400,000)				(789,800,000)
Long-term obligations	31,439,000,000				28,497,700,000
American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	31,186,200,000				26,113,400,000
American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	2,327,200,000				3,146,200,000
2020 Term Loan | Unsecured debt | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	0				749,400,000
2021 Multicurrency Credit Facility | Credit Facility | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	1,568,600,000				0
2019 Term Loan | Unsecured debt | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	496,300,000				996,100,000
2021 Credit Facility | Credit Facility | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	0				2,295,000,000
2021 364-Day Delayed Draw Term Loan | Unsecured debt | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	787,200,000				0
2021 Three Year Delayed Draw Term Loan | Unsecured debt | American Tower Corporation
Debt Instrument [Line Items]
Long-term debt	$ 955,100,000				0
2.250% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.25%
Long-term debt	$ 601,600,000				605,100,000
4.70% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	4.70%
Long-term debt	$ 699,600,000				699,000,000
3.50% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.50%
Long-term debt	$ 997,500,000				996,100,000
3.000% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.00%
Long-term debt	$ 714,900,000				721,900,000
0.600% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	0.60%
Long-term debt	$ 497,600,000				496,800,000
5.00% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	5.00%
Long-term debt	$ 1,001,000,000				1,001,300,000
3.375% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.375%
Long-term debt	$ 646,600,000				645,700,000
2.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.95%
Long-term debt	$ 644,300,000				643,100,000
2.400% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.40%
Long-term debt	$ 745,800,000				745,000,000
1.375% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.375%
Long-term debt	$ 573,600,000				604,100,000
4.000% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	4.00%
Long-term debt	$ 745,200,000				744,300,000
1.300% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.30%
Long-term debt	$ 496,100,000				495,400,000
4.400% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	4.40%
Long-term debt	$ 497,500,000				497,100,000
1.600% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.60%			1.60%
Long-term debt	$ 694,900,000				0
1.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.95%
Long-term debt	$ 574,200,000				605,200,000
1.450% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.45%	1.45%
Long-term debt	$ 592,600,000				0
3.375% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.375%
Long-term debt	$ 990,800,000				989,500,000
3.125% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.125%
Long-term debt	$ 398,200,000				397,900,000
2.750% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.75%
Long-term debt	$ 745,000,000				744,300,000
0.450% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	0.45%		0.45%
Long-term debt	$ 862,100,000				0
3.55% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.55%
Long-term debt	$ 745,400,000				744,800,000
0.500% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	0.50%
Long-term debt	$ 860,300,000				907,400,000
3.600% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.60%
Long-term debt	$ 694,100,000				693,400,000
1.500% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.50%
Long-term debt	$ 645,600,000				645,100,000
3.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.95%
Long-term debt	$ 591,300,000				590,600,000
0.875% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	0.875%		0.875%
Long-term debt	$ 862,300,000				0
3.800% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.80%
Long-term debt	$ 1,634,700,000				1,633,500,000
2.900% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.90%
Long-term debt	$ 742,300,000				741,700,000
2.100% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.10%
Long-term debt	$ 740,900,000				740,200,000
1.875% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.875%
Long-term debt	$ 791,200,000				790,500,000
2.700% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.70%			2.70%
Long-term debt	$ 693,600,000				0
2.300% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.30%	2.30%
Long-term debt	$ 690,800,000				0
1.000% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.00%
Long-term debt	$ 744,900,000				786,100,000
1.250% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	1.25%		1.25%
Long-term debt	$ 571,300,000				0
3.700% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.70%
Long-term debt	$ 592,000,000				591,900,000
3.100% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	3.10%
Long-term debt	$ 1,037,900,000				1,037,700,000
2.950% senior notes | Senior notes | American Tower Corporation
Debt Instrument [Line Items]
Debt interest rate	2.95%	2.95%
Long-term debt	$ 1,021,300,000				538,200,000
Series 2013-2A securities | Secured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	1,297,800,000				1,296,600,000
Series 2018-1A securities | Secured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	495,100,000				494,600,000
Series 2015-2 notes | Secured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	522,600,000				522,100,000
InSite Debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	0				800,000,000
Other subsidiary debt | Unsecured debt | American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt	$ 11,700,000				$ 32,900,000
Debt repayment period	3 years
Colombian Long Term Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit	$ 0

LONG-TERM OBLIGATIONS - CURRENT

LONG-TERM OBLIGATIONS - CURRENT PORTION OF LONG TERM DEBT (Details) $ in Millions	Feb. 10, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2021EUR (€)	May 28, 2021USD ($)	May 28, 2021EUR (€)	Feb. 10, 2021EUR (€)	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
Current portion of long-term obligations		$ 2,106.4					$ 789.8
2021 364-Day Delayed Draw Term Loan | Unsecured debt
Debt Instrument [Line Items]
Senior note public offering, amount	$ 1,300	787.2	€ 680,000,000	$ 1,300	€ 1,100,000,000	€ 1,100,000,000
Term	364 days
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%	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%	4.70%

LONG-TERM OBLIGATIONS - INSITE

LONG-TERM OBLIGATIONS - INSITE DEBT (Details) - USD ($) $ in Millions	Jan. 15, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Loss on retirement of long-term obligations		$ 0	$ 37.2	$ 25.7	$ 71.8
Insite Acquisition | InSite Debt
Debt Instrument [Line Items]
Debt instrument, repurchased amount	$ 826.4
Accrued and unpaid interest	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, $ in Millions	Oct. 05, 2021USD ($)	Sep. 27, 2021USD ($)	May 21, 2021USD ($)	May 21, 2021EUR (€)	Mar. 29, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Oct. 05, 2021EUR (€)	May 21, 2021EUR (€)
Debt Instrument [Line Items]
Proceeds from term loans						$ 2,347	$ 1,940
Debt redemption price rate (as a percent)						101.00%
Maximum adjusted EBITDA						3.5
Subsequent Event
Debt Instrument [Line Items]
Debt redemption price rate (as a percent)	101.00%
Maximum adjusted EBITDA	3.5							3.5
American Tower Corporation | 1.600% senior notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate					1.60%	1.60%
Senior note public offering, amount					$ 700
Debt redemption price rate (as a percent)					100.00%
American Tower Corporation | 2.700% senior notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate					2.70%	2.70%
Senior note public offering, amount					$ 700
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 loans					$ 1,386.3
American Tower Corporation | 0.450% Senior Notes due 2027 | Senior notes
Debt Instrument [Line Items]
Debt interest rate			0.45%			0.45%			0.45%
Senior note public offering, amount			$ 913.7						€ 750
Debt redemption price rate (as a percent)			100.00%	100.00%
American Tower Corporation | 0.875% Senior Notes due 2029 | Senior notes
Debt Instrument [Line Items]
Debt interest rate			0.875%			0.875%			0.875%
Senior note public offering, amount			$ 913.7						€ 750
Debt redemption price rate (as a percent)			100.00%	100.00%
American Tower Corporation | 1.250% Senior Notes due 2033 | Senior notes
Debt Instrument [Line Items]
Debt interest rate			1.25%			1.25%			1.25%
Senior note public offering, amount			$ 609.1						€ 500
Debt redemption price rate (as a percent)			100.00%	100.00%
American Tower Corporation | 2026, 2027, 2029, 2031, and 2033 Notes | Senior notes
Debt Instrument [Line Items]
Proceeds from term loans			$ 2,415.8	€ 1,983.1
American Tower Corporation | 1.450% senior notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		1.45%				1.45%
Senior note public offering, amount		$ 600
Debt redemption price rate (as a percent)		100.00%
American Tower Corporation | 2.300% senior notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		2.30%				2.30%
Senior note public offering, amount		$ 700
Debt redemption price rate (as a percent)		100.00%
American Tower Corporation | Reopened 2.950% Senior Notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		2.95%
Senior note public offering, amount		$ 500
American Tower Corporation | 2.950% senior notes | Senior notes
Debt Instrument [Line Items]
Debt interest rate		2.95%				2.95%
Senior note public offering, amount		$ 1,050
Debt redemption price rate (as a percent)		100.00%
American Tower Corporation | 2026, 2027, 2029, 2031, 2033 and 2051 Notes | Senior notes
Debt Instrument [Line Items]
Proceeds from term loans		$ 1,765.1
American Tower Corporation | 0.400% Senior Notes due 2027 | Senior notes | Subsequent Event
Debt Instrument [Line Items]
Debt interest rate	0.40%							0.40%
Senior note public offering, amount	$ 579.9							€ 500
Debt redemption price rate (as a percent)	100.00%
American Tower Corporation | 0.950% Senior Notes due 2030 | Senior notes | Subsequent Event
Debt Instrument [Line Items]
Debt interest rate	0.95%							0.95%
Senior note public offering, amount	$ 579.9							€ 500
Debt redemption price rate (as a percent)	100.00%

LONG-TERM DEBT OBLIGATIONS - SC

LONG-TERM DEBT OBLIGATIONS - SCHEDULE OF KEY TERMS (Details) € in Millions, $ in Millions	Sep. 27, 2021USD ($)	May 21, 2021EUR (€)	Mar. 29, 2021USD ($)	Sep. 30, 2021	May 21, 2021USD ($)	Nov. 20, 2020
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]
Contractual Interest Rate			1.60%	1.60%
Aggregate Principal Amount			$ 700
Debt redemption price rate (as a percent)			100.00%
Senior Notes | 2.700% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate			2.70%	2.70%
Aggregate Principal Amount			$ 700
Debt redemption price rate (as a percent)			100.00%
Senior Notes | 0.450% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate		0.45%		0.45%	0.45%
Aggregate Principal Amount		€ 750			$ 913.7
Debt redemption price rate (as a percent)		100.00%
Senior Notes | 0.875% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate		0.875%		0.875%	0.875%
Aggregate Principal Amount		€ 750			$ 913.7
Debt redemption price rate (as a percent)		100.00%
Senior Notes | 1.250% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate		1.25%		1.25%	1.25%
Aggregate Principal Amount		€ 500			$ 609.1
Debt redemption price rate (as a percent)		100.00%
Senior Notes | 1.450% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate	1.45%			1.45%
Aggregate Principal Amount	$ 600
Debt redemption price rate (as a percent)	100.00%
Senior Notes | 2.300% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate	2.30%			2.30%
Aggregate Principal Amount	$ 700
Debt redemption price rate (as a percent)	100.00%
Senior Notes | 2.950% senior notes | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate	2.95%			2.95%
Aggregate Principal Amount	$ 1,050
Debt redemption price rate (as a percent)	100.00%
Senior Notes | Initial 2.950% Senior Notes, Due 2051 | American Tower Corporation
Debt Instrument [Line Items]
Contractual Interest Rate						2.95%

LONG-TERM OBLIGATIONS - BANK FA

LONG-TERM OBLIGATIONS - BANK FACILITIES (Details)	Sep. 30, 2021USD ($)	Feb. 10, 2021USD ($)	Feb. 10, 2021EUR (€)
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
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) $ in Millions, € in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2021EUR (€)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Line of Credit Facility [Line Items]
Borrowings under credit facilities			$ 7,666.9	$ 5,380.4
Repayment of credit facilities			10,752.8	$ 12,918.1
American Tower Corporation | Credit Facility | 2021 Multicurrency Credit Facility
Line of Credit Facility [Line Items]
Borrowings under credit facilities	$ 2,900	€ 2.4	4,600
Repayment of indebtedness under credit facility			3,000
Repayment of credit facilities	1,200	1
American Tower Corporation | Credit Facility | InSite Debt and 2020 Term Loan
Line of Credit Facility [Line Items]
Repayment of indebtedness under credit facility			750
American Tower Corporation | Credit Facility | 2021 Credit Facility
Line of Credit Facility [Line Items]
Borrowings under credit facilities	1,400	1.2	2,900
Repayment of indebtedness under credit facility			$ 5,200
Repayment of credit facilities	$ 1,400	€ 1.2

LONG-TERM OBLIGATIONS - REPAYME

LONG-TERM OBLIGATIONS - REPAYMENT OF TERM LOANS (Details) - USD ($) $ in Millions	Sep. 27, 2021	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Repayment of term loans		$ 10,752.8	$ 12,918.1
American Tower Corporation | 2019 Term Loan | Unsecured debt
Debt Instrument [Line Items]
Repayment of term loans	$ 500
American Tower Corporation | 1.450% senior notes | Senior notes
Debt Instrument [Line Items]
Contractual Interest Rate	1.45%	1.45%
American Tower Corporation | 2.300% senior notes | Senior notes
Debt Instrument [Line Items]
Contractual Interest Rate	2.30%	2.30%
American Tower Corporation | 2.950% senior notes | Senior notes
Debt Instrument [Line Items]
Contractual Interest Rate	2.95%	2.95%

LONG-TERM OBLIGATIONS - 2021 DE

LONG-TERM OBLIGATIONS - 2021 DELAYED DRAW TERM LOANS (Details) $ in Millions	Sep. 16, 2021USD ($)	Sep. 16, 2021EUR (€)	Feb. 10, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021EUR (€)	May 28, 2021USD ($)	May 28, 2021EUR (€)	Feb. 10, 2021EUR (€)
Debt Instrument [Line Items]
Repayment of term loans				$ 10,752.8	$ 12,918.1
2021 364-Day Delayed Draw Term Loan | Unsecured debt
Debt Instrument [Line Items]
Senior note public offering, amount			$ 1,300	$ 787.2		€ 680,000,000	$ 1,300	€ 1,100,000,000	€ 1,100,000,000
Term			364 days
Repayment of term loans	$ 494.2	€ 420,000,000
2021 364-Day Delayed Draw Term Loan | Unsecured debt | 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 | Unsecured debt
Debt Instrument [Line Items]
Senior note public offering, amount			$ 1,000				$ 1,000	€ 825,000,000	€ 825,000,000
Term			3 years
2021 Three Year Delayed Draw Term Loan | Unsecured debt | 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) $ in Billions	Sep. 30, 2021	May 21, 2021	Feb. 10, 2021USD ($)	Feb. 10, 2021EUR (€)	Jan. 13, 2021USD ($)	Jan. 13, 2021EUR (€)
American Tower Corporation | 0.450% Senior Notes due 2027 | Senior notes
Line of Credit Facility [Line Items]
Contractual Interest Rate	0.45%	0.45%
American Tower Corporation | 0.875% Senior Notes due 2029 | Senior notes
Line of Credit Facility [Line Items]
Contractual Interest Rate	0.875%	0.875%
American Tower Corporation | 1.250% Senior Notes due 2033 | Senior notes
Line of Credit Facility [Line Items]
Contractual Interest Rate	1.25%	1.25%
Credit Facility
Line of Credit Facility [Line Items]
Line of credit maximum borrowing capacity			$ 3.9	€ 3,225,000,000
Credit Facility | 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 - INDIA C

LONG-TERM OBLIGATIONS - INDIA CREDIT FACILITY (Details) - 9 months ended Sep. 30, 2021 - India Credit Facility $ in Millions	USD ($)debt_instrument	INR (₨)
Working Capital Facility
Line of Credit Facility [Line Items]
Number of credit facilities	2
Line of credit maximum borrowing capacity	$ 26.3	₨ 1,950,000,000
Overdraft Facility
Line of Credit Facility [Line Items]
Number of credit facilities	1
Line of credit maximum borrowing capacity	$ 5.1	₨ 380,000,000

LONG-TERM OBLIGATIONS - SCHED_2

LONG-TERM OBLIGATIONS - SCHEDULE OF LINES OF CREDIT (Details) - American Tower Corporation $ in Millions	9 Months Ended
	Sep. 30, 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	$ 1,568.6
Undrawn letters of credit	$ 3.5
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	$ 0
Undrawn letters of credit	$ 0.9
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	$ 496.3
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	$ 787.2
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	$ 955.1
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%

FAIR VALUE MEASUREMENTS - ASSET

FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED AT FAIR VALUE ON A RECURRING BASIS (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Liabilities:
Unrealized gains (losses) for equity securities	$ (9.9)	$ 19.5
Fair Value, Measurements, Recurring | Level 1
Assets:
Investments in equity securities	50.5	50.5	$ 0
Fair Value, Measurements, Recurring | Level 1 | Interest rate swap agreements
Assets:
Fair value of assets	0	0	0
Liabilities:
Fair value of debt related to interest rate swap	19.1	19.1	31.4
Fair Value, Measurements, Recurring | Level 2
Assets:
Investments in equity securities	0	0	6
Fair Value, Measurements, Recurring | Level 2 | Interest rate swap agreements
Assets:
Fair value of assets	17.5	17.5	29.2
Liabilities:
Fair value of debt related to interest rate swap	0	0	0
Fair Value, Measurements, Recurring | Level 3
Assets:
Investments in equity securities	0	0	0
Fair Value, Measurements, Recurring | Level 3 | Interest rate swap agreements
Assets:
Fair value of assets	0	0	0
Liabilities:
Fair value of debt related to interest rate swap	$ 0	$ 0	$ 0

FAIR VALUE MEASUREMENTS - NARRA

FAIR VALUE MEASUREMENTS - NARRATIVE (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term obligations	$ 33,545.4	$ 29,287.5
Interest rate swap agreements | Colombian Long Term Credit Facility | Credit Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements	0
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	34,800	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	28,600	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	$ 6,200	$ 7,400

INCOME TAXES - NARRATIVE (Detai

INCOME TAXES - NARRATIVE (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact the ETR	$ 89,900,000	$ 89,900,000	$ 105,900,000
Unrecognized tax benefits, increase resulting from current period tax positions	12,900,000	22,600,000
Unrecognized tax benefits, decrease due to foreign currency translation	3,300,000	2,900,000
Unrecognized tax benefits, decrease resulting from prior period tax positions	21,600,000	39,700,000
Unrecognized tax benefits, decrease due to statute of limitations	1,600,000	3,600,000
Unrecognized tax benefits, decrease from settlements	8,800,000	8,800,000
Unrecognized tax benefits, income tax penalties and interest accrued	76,400,000	76,400,000	$ 34,400,000
Minimum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	0	0
Maximum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	$ 24,700,000	$ 24,700,000

INCOME TAXES - SCHEDULE OF PENA

INCOME TAXES - SCHEDULE OF PENALTIES AND INCOME TAX RELATED EXPENSES (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Penalties and income tax-related interest expense	$ 9.6	$ 6.6	$ 43.1	$ 9.3
Reclassification of unrecognized tax benefits			$ 16.6

STOCK-BASED COMPENSATION - NARR

STOCK-BASED COMPENSATION - NARRATIVE (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	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%
Unrecognized compensation expense	$ 0		$ 0
Stock-based compensation expense	28,100,000	$ 24,100,000	$ 98,000,000	$ 99,000,000
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected weighted average recognition period			2 years
Units granted (in shares)			546,698
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years		3 years	3 years
Unrecognized compensation expense	7,500,000		$ 7,500,000
Expected weighted average recognition period			2 years
Units granted (in shares)			98,694
Stock-based compensation expense	$ 6,800,000		$ 16,400,000
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%
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		5,900,000
2007 Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Unrecognized compensation expense	$ 149,900,000		$ 149,900,000
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]
Vesting period			3 years
Units granted (in shares)			98,694
2020 PSUs | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Units granted (in shares)					110,925
2019 PSUs | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Units granted (in shares)						114,823

STOCK-BASED COMPENSATION - SUMM

STOCK-BASED COMPENSATION - SUMMARY OF STOCK-BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 28.1	$ 24.1	$ 98	$ 99
Amount capitalized		0.4		1.3
Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 28.1	23.4	$ 98	96.7
Property costs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense		0.4		1.4
Services
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense		$ 0.3		$ 0.9

STOCK-BASED COMPENSATION - SU_2

STOCK-BASED COMPENSATION - SUMMARY OF THE COMPANY'S OPTION ACTIVITY (Details)	9 Months Ended
	Sep. 30, 2021shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding at beginning of period (in shares)	2,016,261
Options exercised (in shares)	(629,515)
Options forfeited (in shares)	0
Options expired (in shares)	0
Options outstanding at end of period (in shares)	1,386,746

STOCK-BASED COMPENSATION - SU_3

STOCK-BASED COMPENSATION - SUMMARY OF THE COMPANY'S RESTRICTED STOCK UNIT ACTIVITY (Details) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
RSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Units outstanding at beginning of period (in shares)	1,245,075
Units granted (in shares)	546,698
Units vested (in shares)	(564,397)
Units forfeited (in shares)	(46,649)
Units outstanding at end of period (in shares)	1,180,727	1,245,075
Units vested and deferred (in shares)	17,121
Units previously vested and deferred (in shares)	58,204
PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Units outstanding at beginning of period (in shares)	320,510
Units granted (in shares)	98,694
Units vested (in shares)	(162,882)
Units forfeited (in shares)	0
Units outstanding at end of period (in shares)	256,322	320,510
Units vested and deferred (in shares)	0
Vesting period	3 years	3 years	3 years
Units previously vested and deferred (in shares)	96,048
2018 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Units outstanding at end of period (in shares)	162,882
Vesting period	3 years
2019 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Units granted (in shares)			114,823
Units outstanding at end of period (in shares)	86,889
Vesting period	3 years
2020 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Units granted (in shares)		110,925
Units outstanding at end of period (in shares)	70,739
Vesting period	3 years
2021 PSUs | PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Units granted (in shares)	98,694
Vesting period	3 years

REDEEMABLE NONCONTROLLING INT_3

REDEEMABLE NONCONTROLLING INTERESTS - NARRATIVE (Details) $ / shares in Units, € in Millions, $ in Millions, ₨ in Billions	3 Months Ended	9 Months Ended				12 Months Ended
	Mar. 31, 2020USD ($)	Sep. 30, 2021INR (₨)	Sep. 30, 2021USD ($)$ / shares	Sep. 30, 2021EUR (€)	Sep. 30, 2020USD ($)	Dec. 31, 2020INR (₨)	Dec. 31, 2020USD ($)	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 percentage			92.00%			92.00%	92.00%	100.00%	79.00%
Noncontrolling ownership interest percentage						8.00%	8.00%		21.00%
Ghana and Uganda Subsidiaries
Noncontrolling Interest [Line Items]
Purchase of redeemable noncontrolling interest							$ 524.4
Ownership 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						₨ 24.8	$ 337.3
Macquarie | ATC TIPL
Noncontrolling Interest [Line Items]
Percentage of ownership before transaction		100.00%	100.00%	100.00%
Purchase of redeemable noncontrolling interest		₨ 12.9	$ 173.8
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	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 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	4	11.2
Adjustment to noncontrolling interest redemption value	1.2	(10)
Purchase of redeemable noncontrolling interest	(2.5)	(524.4)
Foreign currency translation adjustment attributable to noncontrolling interests	(3.4)	(18.4)
Balance as of September 30,	$ 211.4	$ 554.9	$ 212.1

EQUITY - NARRATIVE (Details)

EQUITY - NARRATIVE (Details) - USD ($)	May 10, 2021	Aug. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2017	Mar. 31, 2011
Class of Stock [Line Items]
Proceeds from stock options and employee stock purchase plan			$ 60,400,000
Stock offering, value (up to)		$ 1,000,000,000
Common stock, par value (in usd per share)	$ 0.01		$ 0.01		$ 0.01
Price per share (in usd per share)	$ 244.75
Treasury stock repurchased				$ 56,000,000
Accrued dividend RSU			$ 10,900,000
Paid dividend RSU			$ 7,500,000	$ 7,800,000
Over-Allotment Option
Class of Stock [Line Items]
Stock offerings (in shares)	900,000
Public Stock Offering
Class of Stock [Line Items]
Stock offerings (in shares)	9,000,000
Proceeds from sale of stock	$ 2,400,000,000
2020 ATM Program
Class of Stock [Line Items]
Stock offerings (in shares)			0
2011 Buyback
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,500,000,000
Treasury stock activity (in 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)			0

EQUITY - DISTRIBUTIONS (Details

EQUITY - DISTRIBUTIONS (Details) - USD ($) $ / shares in Units, $ in Millions

Oct. 15, 2021

Sep. 16, 2021

Jul. 09, 2021

May 27, 2021

Apr. 29, 2021

Mar. 04, 2021

Feb. 02, 2021

Dec. 03, 2020

Oct. 16, 2020

Sep. 10, 2020

Jul. 10, 2020

May 19, 2020

Apr. 29, 2020

Mar. 12, 2020

Jan. 14, 2020

Dec. 11, 2019

Sep. 30, 2021

Sep. 30, 2020

Dividends Payable [Line Items]

Aggregate Payment Amount on common stock

$ 1,674.4

$ 1,421.8

Common Stock

Dividends Payable [Line Items]

Distribution per share, common stock (in dollars per share)

$ 1.31

$ 1.27

$ 1.24

$ 1.21

$ 1.14

$ 1.10

$ 1.08

$ 1.01

Aggregate Payment Amount on common stock

$ 577.8

$ 551.5

$ 537.6

$ 506.4

$ 487.9

$ 478.8

$ 447.3

Common Stock | Subsequent Event

Dividends Payable [Line Items]

Aggregate Payment Amount on common stock

$ 596.6

NONCONTROLLING INTEREST - NARRA

NONCONTROLLING INTEREST - NARRATIVE (Details) € in Millions, ৳ in Millions, $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2021EUR (€)	Sep. 30, 2021BDT (৳)	Sep. 30, 2021USD ($)	Sep. 30, 2021EUR (€)	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)
Noncontrolling Interest [Line Items]
Adjustment to noncontrolling interest				$ 0
KTBL Acquisition
Noncontrolling Interest [Line Items]
Percentage of interests acquired	51.00%	51.00%	51.00%	51.00%	51.00%
Purchase price	$ 10.6		৳ 900
Additional Paid-in Capital
Noncontrolling Interest [Line Items]
Adjustment to noncontrolling interest				$ (648.4)
Noncontrolling Interests
Noncontrolling Interest [Line Items]
Adjustment to noncontrolling interest				601
Accumulated Other Comprehensive Loss
Noncontrolling Interest [Line Items]
Adjustment to noncontrolling interest				47.4
Subsidiary Interest
Noncontrolling Interest [Line Items]
Payments to acquire noncontrolling interest				$ 6
Ownership percentage	100.00%	100.00%	100.00%	100.00%	100.00%
ATC Europe
Noncontrolling Interest [Line Items]
Payments to acquire noncontrolling interest				$ 214.9	€ 178
Ownership percentage	52.00%	52.00%	52.00%	52.00%	52.00%
Ownership percentage by noncontrolling owners	49.00%	49.00%	49.00%	49.00%	49.00%
Germany
Noncontrolling Interest [Line Items]
Ownership percentage by noncontrolling owners	13.00%	13.00%	13.00%	13.00%	13.00%
Spain
Noncontrolling Interest [Line Items]
Ownership percentage by noncontrolling owners	17.00%	17.00%	17.00%	17.00%	17.00%
ATC Europe
Noncontrolling Interest [Line Items]
Dividends						$ 16.2	€ 13.2
ATC Europe | France And Poland
Noncontrolling Interest [Line Items]
Ownership percentage	100.00%	100.00%	100.00%	100.00%	100.00%
ATC Europe | Germany
Noncontrolling Interest [Line Items]
Ownership percentage	87.00%	87.00%	87.00%	87.00%	87.00%
ATC Europe | Spain
Noncontrolling Interest [Line Items]
Ownership percentage	83.00%	83.00%	83.00%	83.00%	83.00%
CDPQ | ATC Europe
Noncontrolling Interest [Line Items]
Ownership interest acquired				30.00%	30.00%
Allianz | ATC Europe
Noncontrolling Interest [Line Items]
Ownership interest acquired				18.00%	18.00%
CDPQ & Allianz | ATC Europe
Noncontrolling Interest [Line Items]
Payments to acquire noncontrolling interest	$ 3,100	€ 2,600
Confidence Group | KTBL
Noncontrolling Interest [Line Items]
Ownership percentage by noncontrolling owners	49.00%	49.00%	49.00%	49.00%	49.00%

NONCONTROLLING INTEREST - SCHED

NONCONTROLLING INTEREST - SCHEDULE OF CHANGES IN NONCONTROLLING INTEREST (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at beginning of period	$ 6,823.4	$ 4,060.3	$ 4,568.4	$ 5,490.4
ATC Europe Transactions	3,078.2		3,078.2
Bangladesh partnership	10.2		10.2
Adjustment to noncontrolling interest due to reorganization			0
Redemption of noncontrolling interest			0
Net income attributable to noncontrolling interests	724.5	463.1	2,121.2	1,328.7
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	(622.3)	102.2	(823.5)	(1,204.3)
Distributions to noncontrolling interest holders	(0.1)	(0.2)	(215.3)	(1.9)
Balance at end of period	9,477	4,189.1	9,477	4,189.1
Noncontrolling Interests
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at beginning of period	1,069.2	440	474.9	435
ATC Europe Transactions	3,078.2		3,078.2
Bangladesh partnership	10.2		10.2
Adjustment to noncontrolling interest due to reorganization			601
Redemption of noncontrolling interest			(1.7)
Net income attributable to noncontrolling interests	1.5	(1.3)	6.9	3.2
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	(93.2)	18.9	(103.3)	21.1
Distributions to noncontrolling interest holders	(0.1)	(0.2)	(0.4)	(1.9)
Balance at end of period	$ 4,065.8	$ 457.4	4,065.8	$ 457.4
Noncontrolling Interests | ATC Europe Transaction
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
ATC Europe Transactions			3,078.2
Noncontrolling Interests | Bangladesh partnership
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Bangladesh partnership			$ 10.2

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income attributable to American Tower Corporation common stockholders, basic	$ 723	$ 464.4	$ 2,114.3	$ 1,325.5
Net income attributable to American Tower Corporation common stockholders, diluted	$ 723	$ 464.4	$ 2,114.3	$ 1,325.5
Basic weighted average common shares outstanding (in shares)	455,224	443,766	450,148	443,420
Dilutive securities (in shares)	1,753	2,390	1,833	2,588
Diluted weighted average common shares outstanding (in shares)	456,977	446,156	451,981	446,008
Basic net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 1.59	$ 1.05	$ 4.70	$ 2.99
Diluted net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 1.58	$ 1.04	$ 4.68	$ 2.97

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from dilutive effect (in shares)	0	0	0	1

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) ₨ in Millions, $ in Millions	Dec. 05, 2016USD ($)	Dec. 05, 2016INR (₨)	Mar. 27, 2015USD ($)communicationsSiterenewalPeriod	Sep. 30, 2021USD ($)communicationsSiterenewalPeriod	Dec. 31, 2000communicationsSite
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 | communicationsSite			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 | communicationsSite				400	2,000
Aggregate purchase option price for towers | $				$ 1,000
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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Combination and Asset Acquisition [Abstract]
Acquisition and merger related expenses	$ 25.3	$ 0.7	$ 88.8	$ 11.1
Integration costs	$ 6.9	$ 7	$ 32.9	$ 16.1

ACQUISITIONS - NARRATIVE (Detai

ACQUISITIONS - NARRATIVE (Details) € in Millions, ৳ in Millions, $ in Millions	Sep. 30, 2021USD ($)communicationSite	Sep. 30, 2021EUR (€)	Aug. 02, 2021USD ($)communicationSite	Aug. 02, 2021EUR (€)communicationSite	Jan. 13, 2021USD ($)communicationSite	Jan. 13, 2021EUR (€)communicationSite	Dec. 23, 2020USD ($)networkcommunicationSitelandParceltower	Dec. 31, 2019USD ($)communicationSite	Nov. 28, 2019USD ($)communicationSite	Nov. 28, 2019EUR (€)communicationSite	Jun. 30, 2021USD ($)communicationSite	Jun. 30, 2021EUR (€)communicationSite	Sep. 30, 2021USD ($)communicationSite	Sep. 30, 2021BDT (৳)	Sep. 30, 2021USD ($)communicationSite	Sep. 30, 2020USD ($)	Oct. 28, 2021communicationSite	Dec. 31, 2020USD ($)communicationSite	Dec. 19, 2019communicationSite
Business Acquisition [Line Items]
Payment received related to acquisition | $															$ 4.4	$ 4.6
Estimated aggregate impact of acquisitions completed, revenue | $													$ 170.2		226.2
Estimated aggregate impact of acquisitions completed, gross margin | $													91.3		116.2
Accounts payable | $	$ 217.4												$ 217.4		$ 217.4			$ 139.1
KTBL | Confidence Group
Business Acquisition [Line Items]
Ownership percentage by noncontrolling owners	49.00%												49.00%		49.00%
Telxius Telecom S.A.
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite					31,000	31,000
Purchase price			$ 700	€ 600	$ 9,400	€ 7,700					$ 9,589.8
Telxius Telecom S.A. | Other non-current liabilities
Business Acquisition [Line Items]
Purchase price	$ 265.6	€ 229.4
Telxius Telecom S.A. | Telxius European Tower Division
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite											20,000	20,000
Purchase price											$ 7,700	€ 6,300
Telxius Telecom S.A. | Telxius Latin America Tower Division
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite											7,000	7,000
Purchase price											$ 1,100	€ 900
Telxius Telecom S.A. | GERMANY
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite			4,000	4,000
Insite Acquisition
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite							3,000
Purchase price | $							$ 3,500
Percentage of interests acquired							100.00%
Number of land parcels under communication sites | landParcel							600
Adjustment to assets | $															$ 6.8
Adjustment to liabilities | $															67.3
Adjustments to goodwill | $															$ 74.1
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
KTBL Acquisition
Business Acquisition [Line Items]
Purchase price													$ 10.6	৳ 900
Percentage of interests acquired	51.00%												51.00%		51.00%
Entel Acquisition
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite																			3,200
Aggregate purchase price | $								$ 800							$ 44.5
Entel Acquisition | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite	156							2,400					156		156			530
Other Acquisitions 2021 | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite	718												718		718
Aggregate purchase price | $															$ 326.9
Accounts payable | $	$ 8.5												$ 8.5		$ 8.5
Orange S.A. | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communicationSite	180								2,000	2,000			180		180			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																	157
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) communicationSite in Thousands, $ in Millions, € in Billions	Aug. 02, 2021USD ($)	Aug. 02, 2021EUR (€)	Jan. 13, 2021USD ($)communicationSite	Jan. 13, 2021EUR (€)communicationSite	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)site	Dec. 31, 2020USD ($)
Telxius Acquisition
Goodwill						$ 10,480.8	$ 7,282.7
Other
Goodwill						$ 10,480.8	$ 7,282.7
Telxius Telecom S.A.
Telxius Acquisition
Current assets					$ 289
Property and equipment					1,417.7
Other non-current assets					1,380.3
Current liabilities					(331.9)
Deferred tax liability					(1,227.5)
Other non-current liabilities					(1,504.8)
Net assets acquired					6,089.8
Goodwill					3,500
Fair value of net assets acquired					9,589.8
Debt assumed					0
Noncontrolling interest					0
Purchase price	$ 700	€ 0.6	$ 9,400	€ 7.7	9,589.8
Other
Goodwill					3,500
Number of sites acquired | communicationSite			31	31
Estimated Useful Lives (years)						20 years
Tenant-related intangible assets | Telxius Telecom S.A.
Telxius Acquisition
Intangibles assets					5,391.2
Network location intangible assets | Telxius Telecom S.A.
Telxius Acquisition
Intangibles assets					675.8
Other intangible assets | Telxius Telecom S.A.
Telxius Acquisition
Intangibles assets					$ 0
Acquisitions 2021
Telxius Acquisition
Goodwill						$ 9.2
Other
Current assets						25.9
Property and equipment						119.2
Other non-current assets						39.2
Current liabilities						(11.4)
Deferred tax liability						0
Other non-current liabilities						(36.6)
Net assets acquired						383
Goodwill						9.2
Fair value of net assets acquired						392.2
Debt assumed						0
Noncontrolling interest						(10.2)
Purchase price						$ 382
Estimated Useful Lives (years)						20 years
Acquisitions 2021 | Peru
Other
Number of sites acquired | site						21
Acquisitions 2021 | Tenant-related intangible assets
Other
Intangible assets						$ 190.8
Acquisitions 2021 | Network location intangible assets
Other
Intangible assets						55.9
Acquisitions 2021 | Other intangible assets
Other
Intangible assets						$ 0

ACQUISITIONS - PRO FORMA INFORM

ACQUISITIONS - PRO FORMA INFORMATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Combination and Asset Acquisition [Abstract]
Pro forma revenues	$ 2,460.9	$ 2,203.1	$ 7,224.5	$ 6,460.1
Pro forma net income attributable to American Tower Corporation common stockholders	$ 721.9	$ 392.1	$ 2,144.9	$ 1,106.4
Pro forma net income per common share amounts:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.59	$ 0.86	$ 4.72	$ 2.44
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 1.58	$ 0.86	$ 4.70	$ 2.43

BUSINESS SEGMENTS (Details)

BUSINESS SEGMENTS (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)segment	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			6
Segment revenues	$ 2,454.3	$ 2,012.9	$ 6,911.7	$ 5,919
Segment selling, general, administrative and development expense	205.9	176	595.7	582.4
OPERATING INCOME	827.5	785.1	2,505.4	2,213.2
Stock-based compensation expense	28.1	24.1	98	99
Depreciation, amortization and accretion	611.4	473.9	1,688.7	1,401.1
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	777.6	502.2	2,300.9	1,401.4
Total assets	60,530	41,462.2	60,530	41,462.2	$ 47,233.5
Operating Expense
Segment Reporting Information [Line Items]
Stock-based compensation expense		0.7		2.3
Selling, General and Administrative Expenses
Segment Reporting Information [Line Items]
Stock-based compensation expense	28.1	23.4	98	96.7
Operating Segments
Segment Reporting Information [Line Items]
Segment revenues	2,454.3	2,012.9	6,911.7	5,919
Segment operating expenses	724.3	561.9	1,946.5	1,652.3
Segment gross margin	1,730	1,451	4,965.2	4,266.7
Segment selling, general, administrative and development expense	129	111.3	353.4	357.4
OPERATING INCOME	1,601	1,339.7	4,611.8	3,909.3
Operating Segments | Property
Segment Reporting Information [Line Items]
Segment revenues	2,368.9	1,987.6	6,731.6	5,854
Segment operating expenses	693.4	551.7	1,880	1,625.1
Segment gross margin	1,675.5	1,435.9	4,851.6	4,228.9
Segment selling, general, administrative and development expense	125.2	107.1	341.3	347.6
OPERATING INCOME	1,550.3	1,328.8	4,510.3	3,881.3
Total assets	58,391.9	40,997.5	58,391.9	40,997.5
Operating Segments | U.S. & Canada
Segment Reporting Information [Line Items]
Segment revenues	1,231.2	1,122.3	3,695.9	3,299.7
Segment operating expenses	221.4	207.3	631.1	599.7
Segment gross margin	1,009.8	915	3,064.8	2,700
Segment selling, general, administrative and development expense	48.1	38.3	129.8	117.6
OPERATING INCOME	961.7	876.7	2,935	2,582.4
Total assets	27,375	22,610.8	27,375	22,610.8
Operating Segments | Asia-Pacific
Segment Reporting Information [Line Items]
Segment revenues	313.5	305.2	893.1	863.1
Segment operating expenses	187.1	167.1	546.4	489.7
Segment gross margin	126.4	138.1	346.7	373.4
Segment selling, general, administrative and development expense	21.5	24.1	52.7	90.2
OPERATING INCOME	104.9	114	294	283.2
Total assets	5,164.2	5,142.3	5,164.2	5,142.3
Operating Segments | Africa
Segment Reporting Information [Line Items]
Segment revenues	257.4	220	741.1	651.5
Segment operating expenses	88.2	74.1	254.8	221.5
Segment gross margin	169.2	145.9	486.3	430
Segment selling, general, administrative and development expense	16.5	18.5	52.9	56.4
OPERATING INCOME	152.7	127.4	433.4	373.6
Total assets	4,965.4	4,645.3	4,965.4	4,645.3
Operating Segments | Europe
Segment Reporting Information [Line Items]
Segment revenues	175.8	38.7	308.2	107.9
Segment operating expenses	73	7.7	110.7	21.1
Segment gross margin	102.8	31	197.5	86.8
Segment selling, general, administrative and development expense	12.8	5.3	26.3	15.6
OPERATING INCOME	90	25.7	171.2	71.2
Total assets	12,123.2	1,743.7	12,123.2	1,743.7
Operating Segments | Latin America
Segment Reporting Information [Line Items]
Segment revenues	391	301.4	1,093.3	931.8
Segment operating expenses	123.7	95.5	337	293.1
Segment gross margin	267.3	205.9	756.3	638.7
Segment selling, general, administrative and development expense	26.3	20.9	79.6	67.8
OPERATING INCOME	241	185	676.7	570.9
Total assets	8,764.1	6,855.4	8,764.1	6,855.4
Operating Segments | Services
Segment Reporting Information [Line Items]
Segment revenues	85.4	25.3	180.1	65
Segment operating expenses	30.9	10.2	66.5	27.2
Segment gross margin	54.5	15.1	113.6	37.8
Segment selling, general, administrative and development expense	3.8	4.2	12.1	9.8
OPERATING INCOME	50.7	10.9	101.5	28
Total assets	100.9	35.1	100.9	35.1
Other
Segment Reporting Information [Line Items]
Segment selling, general, administrative and development expense	48.8	41.3	144.3	128.3
Stock-based compensation expense	28.1	24.1	98	99
Depreciation, amortization and accretion	611.4	473.9	1,688.7	1,401.1
Other expense	135.1	298.2	379.9	879.5
Total assets	$ 2,037.2	$ 429.6	$ 2,037.2	$ 429.6

Subsequent Events (Details)

Subsequent Events (Details)	Oct. 18, 2021USD ($)	Oct. 05, 2021USD ($)dataCenter	Oct. 05, 2021EUR (€)	Feb. 10, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Oct. 05, 2021EUR (€)dataCenter	Sep. 30, 2021EUR (€)	May 28, 2021USD ($)	May 28, 2021EUR (€)	Feb. 10, 2021EUR (€)
Subsequent Event [Line Items]
Proceeds from term loans							$ 2,347,000,000	$ 1,940,000,000
Debt redemption price rate (as a percent)							101.00%
Maximum adjusted EBITDA					3.5		3.5			3.5
Loss on retirement of long-term obligations					$ 0	$ 37,200,000	$ 25,700,000	$ 71,800,000
Unsecured debt | 2021 364-Day Delayed Draw Term Loan
Subsequent Event [Line Items]
Senior note public offering, amount				$ 1,300,000,000	$ 787,200,000		$ 787,200,000			€ 680,000,000	$ 1,300,000,000	€ 1,100,000,000	€ 1,100,000,000
Term				364 days
American Tower Corporation | Senior notes | 4.70% senior notes
Subsequent Event [Line Items]
Contractual Interest Rate					4.70%		4.70%			4.70%
Subsequent Event
Subsequent Event [Line Items]
Debt redemption price rate (as a percent)		101.00%	101.00%
Maximum adjusted EBITDA		3.5							3.5
Subsequent Event | American Tower Corporation | Senior notes | 0.400% Senior Notes due 2027
Subsequent Event [Line Items]
Contractual Interest Rate		0.40%							0.40%
Senior note public offering, amount		$ 579,900,000							€ 500,000,000
Debt redemption price rate (as a percent)		100.00%	100.00%
Subsequent Event | American Tower Corporation | Senior notes | 0.950% Senior Notes due 2030
Subsequent Event [Line Items]
Contractual Interest Rate		0.95%							0.95%
Senior note public offering, amount		$ 579,900,000							€ 500,000,000
Debt redemption price rate (as a percent)		100.00%	100.00%
Subsequent Event | American Tower Corporation | Senior notes | 2027 and 2030 Notes
Subsequent Event [Line Items]
Proceeds from term loans		$ 1,145,600,000	€ 987,700,000
Subsequent Event | American Tower Corporation | Senior notes | 4.70% senior notes
Subsequent Event [Line Items]
Debt redemption price rate (as a percent)	101.727%
Debt instrument, repurchased amount	$ 715,100,000
Accrued and unpaid interest	3,000,000
Loss on retirement of long-term obligations	12,400,000
Prepayment consideration	12,100,000
Notes outstanding	$ 0
Subsequent Event | Data Centers Acquisition
Subsequent Event [Line Items]
Number of multi-tenant data centers acquired | dataCenter		2							2
Aggregate purchase price		$ 201,000,000