American Tower (AMT) 10-Q 1 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 24, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	AMERICAN TOWER CORP /MA/
Entity Central Index Key	1,053,507
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		441,659,919

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 1,125,400	$ 802,100
Restricted cash	153,500	152,800
Short-term investments	389,400	1,000
Accounts receivable, net	557,900	513,600
Prepaid and other current assets	571,200	568,600
Total current assets	2,797,400	2,038,100
PROPERTY AND EQUIPMENT, net	11,294,800	11,101,000
GOODWILL	5,647,100	5,638,400
OTHER INTANGIBLE ASSETS, net	11,940,200	11,783,300
DEFERRED TAX ASSET	192,900	204,400
DEFERRED RENT ASSET	1,510,000	1,499,000
NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS	990,300	950,100
TOTAL	34,372,700	33,214,300
CURRENT LIABILITIES:
Accounts payable	118,700	142,900
Accrued expenses	825,400	854,300
Distributions payable	335,000	304,400
Accrued interest	131,000	166,900
Current portion of long-term obligations	2,803,200	774,800
Unearned revenue	331,400	268,800
Total current liabilities	4,544,700	2,512,100
NONCURRENT LIABILITIES
LONG-TERM OBLIGATIONS	18,568,800	19,430,300
ASSET RETIREMENT OBLIGATIONS	1,215,000	1,175,300
DEFERRED TAX LIABILITY	791,700	898,100
OTHER NON-CURRENT LIABILITIES	1,246,000	1,244,200
Total liabilities	26,366,200	25,260,000
COMMITMENTS AND CONTINGENCIES
REDEEMABLE NONCONTROLLING INTERESTS	1,065,200	1,126,200
EQUITY (shares in thousands):
Common stock: $.01 par value; 1,000,000 shares authorized; 450,505 and 437,729 shares issued; and 441,596 and 428,820 shares outstanding, respectively	4,500	4,400
Additional paid-in capital	10,224,000	10,247,500
Distributions in excess of earnings	(1,085,700)	(1,058,100)
Accumulated other comprehensive loss	(1,834,600)	(1,978,300)
Treasury stock (8,909 shares at cost)	(974,000)	(974,000)
Total American Tower Corporation equity	6,334,200	6,241,500
Noncontrolling interests	607,100	586,600
Total equity	6,941,300	6,828,100
TOTAL	34,372,700	33,214,300
Convertible Preferred Stock Subject to Mandatory Redemption | Preferred Stock - Series B
EQUITY (shares in thousands):
Preferred stock: $.01 par value: 20,000,000 shares authorized	$ 0	$ 0

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	450,505,000	437,729,000
Common stock, shares outstanding	441,596,000	428,820,000
Treasury stock, shares	8,909,000	8,909,000
Convertible Preferred Stock Subject to Mandatory Redemption
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Convertible Preferred Stock Subject to Mandatory Redemption | Preferred Stock - Series B
Class of Stock [Line Items]
Preferred stock, dividend rate percentage	5.50%	5.50%
Preferred stock, shares issued	0	1,375,000
Preferred stock, shares outstanding	0	1,375,000
Preferred stock, aggregate liquidation value	$ 0	$ 1.4

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
REVENUES:
Property	$ 1,710.4	$ 1,594.1
Services	31.4	22.1
Total operating revenues	1,741.8	1,616.2
Costs of operations (exclusive of items shown separately below):
Property (each including stock-based compensation expense of $0.7)	507.4	486.2
Services (including stock-based compensation expense of $0.3 and $0.2, respectively)	12.5	6.5
Depreciation, amortization and accretion	446.3	421.1
Selling, general, administrative and development expense (including stock-based compensation expense of $41.7 and $35.3, respectively)	204.9	164.8
Other operating expenses	167.8	6.2
Total operating expenses	1,338.9	1,084.8
OPERATING INCOME	402.9	531.4
OTHER INCOME (EXPENSE):
Loss on retirement of long-term obligations	0	(55.4)
Other income (including unrealized foreign currency gains of $24.9 and $28.0, respectively)	27.8	29.3
Total other expense	(153.7)	(197.2)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	249.2	334.2
Income tax benefit (provision)	31.1	(26.8)
NET INCOME	280.3	307.4
Net loss attributable to noncontrolling interests	4.9	8.7
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION STOCKHOLDERS	285.2	316.1
Dividends on preferred stock	(9.4)	(26.8)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 275.8	$ 289.3
NET INCOME PER COMMON SHARE AMOUNTS:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 0.63	$ 0.68
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 0.63	$ 0.67
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING (in thousands):
BASIC (in shares)	435,124	427,279
DILUTED (in shares)	438,520	430,199
DISTRIBUTIONS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.75	$ 0.62
TV Azteca
OTHER INCOME (EXPENSE):
Interest income, TV Azteca (each net of interest expense of $0.3)	$ 2.7	$ 2.7
Interest expense	(0.3)	(0.3)
Excluding TV Azteca
OTHER INCOME (EXPENSE):
Interest income	15.4	9.9
Interest expense	$ (199.6)	$ (183.7)

CONSOLIDATED STATEMENTS OF OPE5

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation expense	$ 42.7	$ 36.2
TV Azteca
Interest expense	0.3	0.3
Property
Stock-based compensation expense	0.7	0.7
Services
Stock-based compensation expense	0.3	0.2
Selling General Administrative and Development Expense
Stock-based compensation expense	41.7	35.3
Other Expense
Unrealized foreign currency gains	$ 24.9	$ 28

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 280.3	$ 307.4
Other comprehensive income (loss):
Changes in fair value of cash flow hedges, net of tax expense of $0	0	(0.1)
Reclassification of unrealized losses (gains) on cash flow hedges to net income, net of tax expense of $0	0.1	(0.1)
Adjustment to redeemable noncontrolling interest	78.8	0
Foreign currency translation adjustments, net of tax expense of $1.6 and $3.5, respectively	57.6	293.9
Other comprehensive income	136.5	293.7
Comprehensive income	416.8	601.1
Comprehensive loss (income) attributable to noncontrolling interests	12.1	(45.2)
Comprehensive income attributable to American Tower Corporation stockholders	$ 428.9	$ 555.9

CONSOLIDATED STATEMENTS OF COM7

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Changes in fair value of cash flow hedges, tax	$ 0	$ 0
Reclassification of unrealized gains on cash flow hedges to net income, tax	0	0
Foreign currency translation adjustments, tax expense	$ 1.6	$ 3.5

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 280.3	$ 307.4
Adjustments to reconcile net income to cash provided by operating activities
Depreciation, amortization and accretion	446.3	421.1
Stock-based compensation expense	42.7	36.2
Loss on early retirement of long-term obligations	0	55.4
Other non-cash items reflected in statements of operations	96.8	(45.3)
Increase in net deferred rent balances	(3.9)	(35.1)
Increase in assets	(95.4)	(40.3)
Increase (decrease) in liabilities	25	(21.2)
Cash provided by operating activities	791.8	678.2
CASH FLOWS FROM INVESTING ACTIVITIES
Payments for purchase of property and equipment and construction activities	(198.5)	(168.1)
Payments for acquisitions, net of cash acquired	(673.4)	(777.8)
Proceeds from sale of short-term investments and other non-current assets	84	3.8
Payments for short-term investments	478.1	0
Deposits and other	(14.6)	21.8
Cash used for investing activities	(1,280.6)	(920.3)
CASH FLOW FROM FINANCING ACTIVITIES
Borrowings under credit facilities	1,748.3	1,997
Proceeds from term loan	1,500	0
Proceeds from issuance of securities in securitization transaction	500	0
Repayments of notes payable, credit facilities, senior notes, secured debt and capital leases	(2,584.9)	(1,633.4)
(Distributions to) contributions from noncontrolling interest holders, net	(0.3)	265.4
Purchases of common stock	0	(147.2)
Proceeds from stock options	20	36.9
Distributions paid on common stock	(304.3)	(250.4)
Distributions paid on preferred stock	(18.9)	(26.8)
Payment for early retirement of long-term obligations	0	(61.8)
Deferred financing costs and other financing activities	(42.6)	(21.8)
Cash provided by financing activities	817.3	157.9
Net effect of changes in foreign currency exchange rates on cash and cash equivalents, and restricted cash	(4.5)	6
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH	324	(78.2)
CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH, BEGINNING OF PERIOD	954.9	936.5
CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH, END OF PERIOD	1,278.9	858.3
CASH PAID FOR INCOME TAXES (NET OF REFUNDS OF $4.7 AND $12.8, RESPECTIVELY)	24.7	23.1
CASH PAID FOR INTEREST	228.6	231
NON-CASH INVESTING AND FINANCING ACTIVITIES:
(Increase) decrease in accounts payable and accrued expenses for purchases of property and equipment and construction activities	(29.3)	10.1
Purchases of property and equipment under capital leases	$ 9.7	$ 11.9

CONDENSED CONSOLIDATED STATEME9

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Cash Flows [Abstract]
Income tax refunds	$ 4.7	$ 12.8

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Thousands, $ in Millions	Total	Preferred StockPreferred Stock - Series AConvertible Preferred Stock Subject to Mandatory Redemption	Preferred StockPreferred Stock - Series BConvertible Preferred Stock Subject to Mandatory Redemption	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Distributions in Excess of Earnings	Noncontrolling Interest
BALANCE at Dec. 31, 2016	$ 6,976.2	$ 0.1	$ 0	$ 4.3	$ (207.7)	$ 10,043.5	$ (1,999.3)	$ (1,077)	$ 212.3
BALANCE (shares) at Dec. 31, 2016		6,000	1,375	429,913	(2,810)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation related activity	50.5			$ 0		50.5
Stock-based compensation related activity (shares)				1,019
Treasury stock activity	(225)				$ (225)
Treasury stock activity (in shares)					(1,874)
Changes in fair value of cash flow hedges, net of tax	(0.1)						(0.1)		0
Reclassification of unrealized losses on cash flow hedges to net income	(0.1)						(0.1)		0
Foreign currency translation adjustment, net of tax	242.8						240.1		2.7
Impact of the revenue recognition standard adoption	314								314
Distributions to noncontrolling interest holders	(0.4)								(0.4)
Common stock distributions declared	(266)							(266)
Preferred stock dividends declared	(26.8)							(26.8)
Net income	319.8							316.1	3.7
BALANCE at Mar. 31, 2017	7,384.9	$ 0.1	$ 0	$ 4.3	$ (432.7)	10,094	(1,759.4)	(1,053.7)	532.3
BALANCE (shares) at Mar. 31, 2017		6,000	1,375	430,932	(4,684)
BALANCE at Dec. 31, 2017	6,828.1	$ 0	$ 0	$ 4.4	$ (974)	10,247.5	(1,978.3)	(1,058.1)	586.6
BALANCE (shares) at Dec. 31, 2017		0	1,375	437,729	(8,909)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation related activity	27.3			$ 0		27.3
Stock-based compensation related activity (shares)				756
Conversion of preferred stock	0		$ 0	$ 0.1		(0.1)
Conversion of preferred stock (shares)			(1,375)	12,020
Changes in fair value of cash flow hedges, net of tax	0						0		0
Reclassification of unrealized losses on cash flow hedges to net income	0.1						0.1		0
Foreign currency translation adjustment, net of tax	79.9						64.8		15.1
Adjustment to redeemable noncontrolling interest	28.1					(50.7)	78.8
Impact of the revenue recognition standard adoption	38.4							38.4	0
Distributions to noncontrolling interest holders	(0.3)								(0.3)
Common stock distributions declared	(332.3)							(332.3)
Preferred stock dividends declared	(18.9)							(18.9)
Net income	290.9							285.2	5.7
BALANCE at Mar. 31, 2018	$ 6,941.3	$ 0	$ 0	$ 4.5	$ (974)	$ 10,224	$ (1,834.6)	$ (1,085.7)	$ 607.1
BALANCE (shares) at Mar. 31, 2018		0	0	450,505	(8,909)

DESCRIPTION OF BUSINESS, BASIS

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES	DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) is one of the largest global real estate investment trusts and a leading independent owner, operator and developer of multitenant communications real estate. The Company’s primary business is the leasing of space on communications sites to wireless service providers, radio and television broadcast companies, wireless data providers, government agencies and municipalities and tenants in a number of other industries. The Company refers to this business as its property operations. Additionally, the Company offers tower-related services in the United States, which it refers to as its services operations. These services include site acquisition, zoning and permitting (“AZP”) and structural analysis, which primarily support the Company’s site leasing business, including the addition of new tenants and equipment on its sites. The Company’s portfolio primarily consists of towers that it owns and towers that it operates pursuant to long-term lease arrangements, as well as distributed antenna system (“DAS”) networks, which provide seamless coverage solutions in certain in-building and certain outdoor wireless environments. In addition to the communications sites in its portfolio, the Company manages rooftop and tower sites for property owners under various contractual arrangements. The Company also holds other telecommunications infrastructure, fiber and property interests that it leases primarily to communications service providers and third-party tower operators. American Tower Corporation is a holding company that conducts its operations through its directly and indirectly owned subsidiaries and joint ventures. ATC’s principal domestic operating subsidiaries are American Towers LLC and SpectraSite Communications, LLC. ATC conducts its international operations primarily through its subsidiary, American Tower International, Inc., which in turn conducts operations through its various international holding and operating subsidiaries and joint ventures. The Company operates as a real estate investment trust for U.S. federal income tax purposes (“REIT”). Accordingly, the Company generally is not required to pay U.S. federal income taxes on income generated by its REIT operations, including the income derived from leasing space on its towers, as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on earnings from its domestic taxable REIT subsidiaries (“TRSs”). In addition, the Company’s international assets and operations, regardless of their classification for U.S. tax purposes, continue to be subject to taxation in the foreign jurisdictions where those assets are held or those operations are conducted. The use of TRSs enables the Company to continue to engage in certain businesses while complying with REIT qualification requirements. The Company may, from time to time, change the election of previously designated TRSs to be included as part of the REIT. As of March 31, 2018 , the Company’s REIT-qualified businesses included its U.S. tower leasing business, its operations in Nigeria, most of its operations in Costa Rica and Mexico, a majority of its operations in Germany and a majority of its indoor DAS networks business and services segment. The accompanying consolidated and condensed consolidated financial statements have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission. 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, 2017 (the “ 2017 Form 10-K”). The results of operations for the three months ended March 31, 2018 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 or cost method, depending upon the Company’s ability to exercise significant influence over operating and financial policies. All intercompany accounts and transactions have been eliminated. As of March 31, 2018 , the Company holds (i) a 51% controlling interest, and MTN Group Limited holds a 49% noncontrolling interest, in each of two joint ventures, one in Ghana and one in Uganda, (ii) a 51% controlling interest, and PGGM holds a 49% noncontrolling interest, in a joint venture (“ATC Europe”) which primarily consists of operations in Germany and France, (iii) an approximate 75% controlling interest, and South African investors hold an approximate 25% noncontrolling interest, in a subsidiary of the Company in South Africa and (iv) a 63% controlling interest in ATC Telecom Infrastructure Private Limited (“ATC TIPL”), formerly Viom Networks Limited (“Viom”), in India. Significant Accounting Policies —The Company’s significant accounting policies are described in note 1 to the Company’s consolidated financial statements included in the 2017 Form 10-K. There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2018 , except the adoption of new revenue recognition guidance, as discussed below. Changes to Prior-Period Amounts —The Company is now disclosing its results in millions rather than thousands and, as a result, certain rounding adjustments have been made to prior-period amounts. 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 amount shown in the statement of cash flows is as follows: Three months ended March 31, 2018 2017 Cash and cash equivalents $ 1,125.4 $ 712.8 Restricted cash 153.5 145.5 Total cash and cash equivalents and restricted cash $ 1,278.9 $ 858.3 Revenue —The new revenue recognition accounting standard requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. On January 1, 2018, the Company adopted the new revenue recognition standard using the modified retrospective method applied to contracts that were not completed as of January 1, 2018. Results for reporting periods beginning January 1, 2018 are presented under the new standard, while prior-period amounts are not adjusted and continue to be reported in accordance with accounting under the previously applicable guidance. The Company recorded a net reduction to opening Distributions in excess of earnings in its consolidated balance sheet of $38.4 million as of January 1, 2018 due to the cumulative impact of adopting the new revenue recognition standard. The impact is primarily related to the Company’s site inspection revenue, which is now recognized at the point in time when the inspection service is completed. The impact to revenues for the three months ended March 31, 2018 as a result of applying the new standard was an increase of $2.6 million . The adoption of the new revenue recognition accounting standard did not have a material impact on the Company’s revenue recognition patterns. Most of the Company’s revenue is derived from leasing arrangements and is accounted for as lease revenue. A small portion of the Company’s revenue is either derived from non-lease performance obligations within the lease arrangements or from other agreements with its tenants. This revenue, designated non-lease revenue, is recognized when control of the promised goods or services is transferred to the tenants, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. Since most of the Company’s contracts are leases, costs are capitalized under the applicable lease accounting guidance. Costs incurred to obtain non-lease contracts that are capitalized primarily relate to DAS and are not material to the consolidated financial statements. The Company has excluded sales tax, value-added tax and similar taxes from non-lease revenue. Non-lease revenue is disaggregated by geography in a manner consistent with the Company’s business segments, which are discussed further in note 14 to the consolidated and condensed consolidated financial statements included in this Quarterly Report on Form 10-Q. A summary of non-lease revenue disaggregated by source and geography is as follows: Three Months Ended March 31, 2018 U.S. Asia EMEA Latin America Total Power and fuel pass-through revenue $ — $ 92.3 $ 34.9 $ 4.5 $ 131.7 Other non-lease revenue 67.7 1.9 0.6 23.7 93.9 Total non-lease property revenue $ 67.7 $ 94.2 $ 35.5 $ 28.2 $ 225.6 Services revenue 31.4 — — — 31.4 Total non-lease revenue $ 99.1 $ 94.2 $ 35.5 $ 28.2 $ 257.0 Property lease revenue 863.7 178.8 138.7 303.6 1,484.8 Total revenue $ 962.8 $ 273.0 $ 174.2 $ 331.8 $ 1,741.8 Power and fuel pass-through revenue —Most of the Company’s leasing arrangements outside of the U.S. require that the Company provide power to the communications site through an electrical grid connection, diesel fuel generators or other sources and permit the Company to pass through the costs of these services to its tenants. The Company recognizes revenue received in connection with such services as power and fuel pass-through revenue. Many arrangements require that the communications site has power for a specified percentage of time. In most such cases, if delivery of power falls below the specified service level, a corresponding reduction in revenue is recorded. The Company has determined that this performance obligation is satisfied over time for the duration of the arrangement. Other significant judgments related to this revenue stream are the (i) determination that the Company is a principal in these transactions and revenue is therefore recorded on a gross basis and (ii) service level related adjustments to revenue. Other non-lease revenue —Other non-lease revenue consists primarily of revenue generated from DAS, fiber and other property related revenue. DAS and fiber arrangements require that the Company provide the tenant the right to use the applicable communications infrastructure. Performance obligations are satisfied over time for the duration of the arrangements. Other property related revenue streams, which include site inspections, are not material on either an individual or consolidated basis. Services revenue —The Company offers tower-related services in the United States. These services include site AZP and structural analysis services. 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 incurred. Structural analysis services may have more than one performance obligation, contingent upon the number of contracted services. Revenue is recognized at the point in time the services are completed. Some of the Company’s contracts with tenants contain multiple performance obligations. For these arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price, which is typically based on the price charged to tenants. Information about receivables, contract assets and contract liabilities from contracts with tenants is as follows: January 1, 2018 March 31, 2018 Accounts receivable $ 222.2 $ 234.0 Prepaids and other current assets 79.7 73.3 Notes receivable and other non-current assets 24.2 23.5 Unearned revenue 26.6 33.3 Other non-current liabilities 68.5 65.2 The Company records unearned revenue when payments are received from tenants in advance of the completion of the Company’s performance obligations. Long-term unearned revenue is included in Other non-current liabilities. The increase in the Unearned revenue for the three months ended March 31, 2018 is due to payments received, offset by $17.9 million of revenue recognized in the three months ended March 31, 2018 that was included in the Unearned revenue balance as of January 1, 2018. There was $0.1 million of revenue recognized from Other non-current liabilities during the three months ended March 31, 2018. The Company records unbilled receivables, which are included in Prepaids and other current assets, when it has completed a performance obligation prior to its ability to bill under the customer arrangement. Other contract assets are included in Notes receivable and other non-current assets. The decrease in unbilled receivables and contract assets attributable to revenue recognized during the three months ended March 31, 2018 was less than $0.1 million . The Company does not disclose the value of unsatisfied performance obligations for agreements (i) with an original expected length of one year or less or (ii) for which it recognizes revenue at the amount to which it has the right to invoice for services performed. Accounting Standards Updates —In January 2016, the Financial Accounting Standards Board (the “FASB”) issued new guidance on the recognition and measurement of financial assets and financial liabilities. The guidance amends certain aspects of recognition, measurement, presentation and disclosure of financial instruments. This standard is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2017. The adoption of this guidance did not have a material impact on the Company’s financial statements. In February 2016, the FASB issued new guidance on the accounting for leases. The guidance amends the existing accounting standards for lease accounting, including the requirement that lessees recognize right of use assets and lease liabilities for leases with terms greater than twelve months in the statement of financial position. Under the new guidance, lessor accounting is largely unchanged. This guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018. The Company (i) has established a multidisciplinary team to assess and implement the new guidance, (ii) expects the guidance to have a material impact on its consolidated balance sheets due to the recording of right of use assets and lease liabilities for leases in which it is a lessee and which it currently treats as operating leases and (iii) continues to evaluate the impact of the new guidance. In January 2018, the FASB issued new guidance on the treatment of land easements. The guidance provides a practical expedient to not evaluate existing or expired land easements under the new lease accounting standards if those easements were not previously accounted for as leases under the existing lease guidance. The Company does not expect the adoption of this guidance to have a material impact on its financial statements or its adoption of the lease accounting guidance. In January 2017, the FASB issued new guidance on accounting for goodwill impairments. The guidance eliminates Step 2 from the goodwill impairment test and requires, among other things, recognition of an impairment loss when the carrying value of a reporting unit exceeds its fair value. The loss recognized is limited to the total amount of goodwill allocated to that reporting unit. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a material impact on its financial statements. In August 2017, the FASB issued new guidance on hedge and derivative accounting. The guidance simplifies accounting rules around hedge accounting and the disclosures of hedging arrangements. Among other things, the guidance eliminates the need to separately measure and report hedge ineffectiveness and generally requires the entire change in fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company does not expect the adoption of this guidance to have a material impact on its financial statements. In February 2018, the FASB issued new guidance on the treatment of tax effects that are presented in other comprehensive income. The guidance allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects as a result of the December 2017 legislation commonly referred to as the Tax Cuts and Jobs Act. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company does not expect the adoption of this guidance to have a material impact on its financial statements.

PREPAID AND OTHER CURRENT ASSET

PREPAID AND OTHER CURRENT ASSETS	3 Months Ended
	Mar. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID AND OTHER CURRENT ASSETS	PREPAID AND OTHER CURRENT ASSETS Prepaid and other current assets consisted of the following: As of March 31, 2018 December 31, 2017 Prepaid operating ground leases $ 150.6 $ 148.6 Prepaid income tax 136.5 136.5 Unbilled receivables 110.7 107.9 Value added tax and other consumption tax receivables 63.6 64.2 Prepaid assets 42.5 39.6 Other miscellaneous current assets 67.3 71.8 Prepaid and other current assets $ 571.2 $ 568.6

GOODWILL AND OTHER INTANGIBLE A

GOODWILL AND OTHER INTANGIBLE ASSETS	3 Months Ended
	Mar. 31, 2018
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. Asia EMEA Latin America Balance as of January 1, 2018 $ 3,379.2 $ 1,095.0 $ 404.9 $ 757.3 $ 2.0 $ 5,638.4 Effect of foreign currency translation — (21.9 ) 10.8 19.8 — 8.7 Balance as of March 31, 2018 $ 3,379.2 $ 1,073.1 $ 415.7 $ 777.1 $ 2.0 $ 5,647.1 The Company’s other intangible assets subject to amortization consisted of the following: As of March 31, 2018 As of December 31, 2017 Estimated Useful Gross Carrying Value Accumulated Amortization Net Book Value Gross Carrying Value Accumulated Amortization Net Book Value (years) Acquired network location intangibles (1) Up to 20 $ 4,922.5 $ (1,584.1 ) $ 3,338.4 $ 4,858.8 $ (1,525.3 ) $ 3,333.5 Acquired tenant-related intangibles 15-20 11,431.9 (2,883.7 ) 8,548.2 11,150.9 (2,754.7 ) 8,396.2 Acquired licenses and other intangibles 3-20 60.5 (10.2 ) 50.3 58.8 (8.1 ) 50.7 Economic Rights, TV Azteca 70 15.7 (12.4 ) 3.3 14.5 (11.6 ) 2.9 Total other intangible assets $ 16,430.6 $ (4,490.4 ) $ 11,940.2 $ 16,083.0 $ (4,299.7 ) $ 11,783.3 _______________ (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, or up to 20 years, as the Company considers these intangibles to be directly related to the tower assets. The acquired network location intangibles represent the value to the Company of the incremental revenue growth that could potentially be obtained from leasing the excess capacity on acquired communications sites. The acquired tenant-related intangibles typically represent the value to the Company of tenant contracts and relationships in place at the time of an acquisition or similar transaction, including assumptions regarding estimated renewals. The Company amortizes its acquired network location intangibles and tenant-related intangibles on a straight-line basis over their estimated useful lives. As of March 31, 2018 , the remaining weighted average amortization period of the Company’s intangible assets, excluding the TV Azteca Economic Rights detailed in note 5 to the Company’s consolidated financial statements included in the 2017 Form 10-K, was 15 years. Amortization of intangible assets for the three months ended March 31, 2018 and 2017 was $202.4 million and $183.2 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: Remainder of 2018 $ 620.6 2019 823.8 2020 804.1 2021 787.6 2022 783.1 2023 778.7

ACCRUED EXPENSES

ACCRUED EXPENSES	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consisted of the following: As of March 31, 2018 December 31, 2017 Accrued property and real estate taxes $ 156.9 $ 154.4 Amounts payable to tenants 62.0 60.8 Accrued rent 57.4 54.0 Payroll and related withholdings 54.1 82.2 Accrued pass-through costs 52.9 59.7 Accrued income tax payable 35.7 15.3 Accrued pass-through taxes 35.5 25.3 Accrued construction costs 21.9 31.9 Other accrued expenses 349.0 370.7 Total accrued expenses $ 825.4 $ 854.3

LONG-TERM OBLIGATIONS

LONG-TERM OBLIGATIONS	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 December 31, 2017 Maturity Date 2018 Term Loan (1) $ 1,499.2 $ — March 29, 2019 2013 Credit Facility (1) 1,641.8 2,075.6 June 28, 2021 2013 Term Loan (1) 994.7 994.5 January 31, 2023 2014 Credit Facility (1) 600.0 495.0 January 31, 2023 3.40% senior notes 999.9 999.8 February 15, 2019 2.800% senior notes 746.7 746.3 June 1, 2020 5.050% senior notes 698.2 698.0 September 1, 2020 3.300% senior notes 746.3 746.0 February 15, 2021 3.450% senior notes 645.4 645.1 September 15, 2021 5.900% senior notes 498.0 497.8 November 1, 2021 2.250% senior notes 564.5 572.4 January 15, 2022 4.70% senior notes 696.9 696.7 March 15, 2022 3.50% senior notes 991.3 990.9 January 31, 2023 3.000% senior notes 682.4 692.5 June 15, 2023 5.00% senior notes 1,002.4 1,002.4 February 15, 2024 1.375% senior notes 605.1 589.1 April 4, 2025 4.000% senior notes 741.3 741.0 June 1, 2025 4.400% senior notes 495.8 495.6 February 15, 2026 3.375% senior notes 985.2 984.8 October 15, 2026 3.125% senior notes 397.1 397.1 January 15, 2027 3.55% senior notes 743.0 742.8 July 15, 2027 3.600% senior notes 691.3 691.1 January 15, 2028 Total American Tower Corporation debt 17,666.5 16,494.5 Series 2013-1A securities (2) — 499.8 N/A Series 2013-2A securities (3) 1,292.2 1,291.8 March 15, 2023 Series 2018-1A securities (3) 493.0 — March 15, 2028 Series 2015-1 notes (4) 348.2 348.0 June 15, 2020 Series 2015-2 notes (5) 520.3 520.1 June 16, 2025 India indebtedness (6) 518.6 512.6 Various India preference shares (7) 25.6 26.1 March 2, 2020 Shareholder loans (8) 101.8 100.6 Various Other subsidiary debt (1) (9) 239.6 246.1 Various Total American Tower subsidiary debt 3,539.3 3,545.1 Other debt, including capital lease obligations 166.2 165.5 Total 21,372.0 20,205.1 Less current portion of long-term obligations (2,803.2 ) (774.8 ) Long-term obligations $ 18,568.8 $ 19,430.3 _______________ (1) Accrues interest at a variable rate. (2) Repaid in full on the March 2018 payment date. (3) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (4) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2045. (5) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (6) Denominated in Indian Rupees (“INR”). Includes India working capital facility, remaining debt assumed by the Company in connection with the Viom Acquisition (as defined in note 9) and debt that has been entered into by ATC TIPL. (7) Mandatorily redeemable preference shares (the “Preference Shares”) classified as debt. The Preference Shares are to be redeemed on March 2, 2020 and have a dividend rate of 10.25% per annum. Denominated in INR. (8) Reflects balances owed to the Company’s joint venture partners in Ghana and Uganda. The Ghana loan is denominated in Ghanaian Cedi and the Uganda loan is denominated in Ugandan Shillings. (9) Includes the BR Towers debentures and the Brazil credit facility, which are denominated in Brazilian Reais and amortize through October 15, 2023 and January 15, 2022, respectively, the South African credit facility, which is denominated in South African Rand and amortizes through December 17, 2020 and the Colombian credit facility, which is denominated in Colombian Pesos and amortizes through April 24, 2021. Current portion of long-term obligations— The Company’s current portion of long-term obligations primarily includes (i) 14.6 billion INR ( $223.6 million ) of India indebtedness, (ii) $1.5 billion under its unsecured term loan entered into on March 29, 2018 (the “2018 Term Loan”) and (iii) $999.9 million under the 3.40% senior unsecured notes due 2019. 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 pay 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. Securitizations Secured Tower Revenue Securities, Series 2018-1, Subclass A and Series 2018-1, Subclass R— On March 29, 2018, the Company completed a securitization transaction (the “2018 Securitization”), in which the American Tower Trust I (the “Trust”) issued $500.0 million aggregate principal amount of Secured Tower Revenue Securities, Series 2018-1, Subclass A (the “Series 2018-1A Securities”). To satisfy the applicable risk retention requirements of Regulation RR promulgated under the Securities Exchange Act of 1934, as amended (the “Exchange Act” and, such requirements, the “Risk Retention Rules”), the Trust issued, and one of the Company’s affiliates purchased, $26.4 million aggregate principal amount of Secured Tower Revenue Securities, Series 2018-1, Subclass R (the “Series 2018-1R Securities” and, together with the Series 2018-1A Securities, the “2018 Securities”) to retain an “eligible horizontal residual interest” (as defined in the Risk Retention Rules) in an amount equal to at least 5% of the fair value of the 2018 Securities. The assets of the Trust consist of a nonrecourse loan (the “Loan”) made by the Trust to American Tower Asset Sub, LLC and American Tower Asset Sub II, LLC (together, the “AMT Asset Subs”). The AMT Asset Subs are jointly and severally liable under the Loan, which is secured primarily by mortgages on the AMT Asset Subs’ interests in 5,116 broadcast and wireless communications towers and related assets (the “Trust Sites”). The 2018 Securities correspond to components of the Loan made to the AMT Asset Subs pursuant to the Second Amended and Restated Loan and Security Agreement among the Trust and the AMT Asset Subs, dated as of March 29, 2018 (the “Loan Agreement”) and were issued in two separate subclasses of the same series. The 2018 Securities represent a pass-through interest in the components of the Loan corresponding to the 2018 Securities. The Series 2018-1A Securities have an interest rate of 3.652% and the Series 2018-1R Securities have an interest rate of 4.459% . The 2018 Securities have an expected life of approximately ten years with a final repayment date in March 2048. The debt service on the Loan will be paid solely from the cash flows generated from the operation of the Trust Sites held by the AMT Asset Subs. The AMT Asset Subs are required to make monthly payments of interest on the Loan. Subject to certain limited exceptions described below, no payments of principal will be required to be made on the components of the Loan corresponding to the 2018 Securities prior to the monthly payment date in March 2028, which is the anticipated repayment date for such components. The AMT Asset Subs may prepay the Loan at any time provided it is accompanied by applicable prepayment consideration. If the prepayment occurs within thirty-six months of the anticipated repayment date for the 2018 Securities, no prepayment consideration is due. The entire unpaid principal balance of the components of the Loan corresponding to the 2018 Securities will be due in March 2048. Under the Loan Agreement, the AMT Asset Subs are required to maintain reserve accounts, including for ground rents, real estate and personal property taxes and insurance premiums, and, in certain circumstances, to reserve a portion of advance rents from tenants on the Trust Sites. Based on the terms of the Loan Agreement, all rental cash receipts received each month are reserved for the succeeding month and held in an account controlled by the trustee and then released. The $88.8 million held in the reserve accounts as of March 31, 2018 is classified as restricted cash on the Company’s accompanying condensed consolidated balance sheet. The Secured Tower Revenue Securities, Series 2013-2A (the “Series 2013-2A Securities”) issued in a securitization transaction in March 2013 (the “2013 Securitization” and, together with the 2018 Securitization, the “Trust Securitizations”) remain outstanding and are subject to the terms of the Second Amended and Restated Trust and Servicing Agreement entered into in connection with the 2018 Securitization. The component of the Loan corresponding to the Series 2013-2A Securities also remains outstanding and is subject to the terms of the Loan Agreement. The Loan Agreement includes terms and conditions, including with respect to secured assets, substantially consistent with the First Amended and Restated Loan and Security Agreement dated as of March 15, 2013, and as further described in note 8 to the Company’s consolidated financial statements included in the 2017 Form 10-K. Bank Facilities 2013 Credit Facility— During the three months ended March 31, 2018 , the Company borrowed an aggregate of $620.0 million and repaid an aggregate of $1.1 billion of revolving indebtedness under its multicurrency senior unsecured revolving credit facility entered into in June 2013, as amended (the “2013 Credit Facility”). The Company used the borrowings to fund acquisitions and for general corporate purposes. 2014 Credit Facility— During the three months ended March 31, 2018 , the Company borrowed an aggregate of $1.1 billion and repaid an aggregate of $945.0 million of revolving indebtedness under its senior unsecured revolving credit facility entered into in January 2012 and amended and restated in September 2014, as further amended (the “2014 Credit Facility”). The Company used the borrowings to repay existing indebtedness, including the Secured Tower Revenue Securities, Series 2013-1A, and for general corporate purposes. 2018 Term Loan— During the three months ended March 31, 2018 , the Company entered into the 2018 Term Loan, the net proceeds of which were used to repay $1.1 billion of outstanding indebtedness under the 2013 Credit Facility and $445.0 million of outstanding indebtedness under the 2014 Credit Facility. The 2018 Term Loan matures on March 29, 2019. Any outstanding principal and accrued but unpaid interest will be due and payable in full at maturity. The 2018 Term Loan may be paid prior to maturity in whole or in part at the Company’s option without penalty or premium. The loan agreement for the 2018 Term Loan contains 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. Any failure to comply with the financial and operating covenants of the loan agreement 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. As of March 31, 2018 , the key terms under the 2013 Credit Facility, the 2014 Credit Facility, the Company’s unsecured term loan entered into in October 2013, as amended (the “2013 Term Loan”) and the 2018 Term Loan were as follows: Outstanding Principal Balance Undrawn letters of credit Maturity Date Current margin over LIBOR (1) Current commitment fee (2) 2013 Credit Facility $ 1,641.8 (3) $ 4.0 June 28, 2021 (4) 1.125 % 0.125 % 2014 Credit Facility $ 600.0 $ 6.3 January 31, 2023 (4) 1.250 % 0.150 % 2013 Term Loan $ 1,000.0 N/A January 31, 2023 1.250 % N/A 2018 Term Loan $ 1,500.0 N/A March 29, 2019 0.875 % N/A _______________ (1) LIBOR means the London Interbank Offered Rate. (2) Fee on undrawn portion of each credit facility. (3) Includes $140.0 million borrowed at the base rate of 4.750% plus a margin of 0.125% . (4) Subject to two optional renewal periods.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company determines the fair value of its financial instruments based on the fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. Below are the three levels of inputs that may be used to measure fair value: Level 1 Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Items Measured at Fair Value on a Recurring Basis —The fair values of the Company’s financial assets and liabilities that are required to be measured on a recurring basis at fair value were as follows: March 31, 2018 December 31, 2017 Fair Value Measurements Using Fair Value Measurements Using Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets: Short-term investments (1) $ — $ 389.4 — $ 1.0 — — Embedded derivative in lease agreement — — $ 12.2 — — $ 12.4 Liabilities: Interest rate swap agreements — $ 45.4 — — $ 29.0 — Acquisition-related contingent consideration — — $ 1.0 — — $ 10.1 Fair value of debt related to interest rate swap agreements $ (43.0 ) — — $ (24.5 ) — — _______________ (1) Consists of highly liquid investments with original maturities in excess of three months and mutual funds with a portfolio duration of less than 90 days. As of March 31, 2018, the Company had marketable securities with a cost basis of $386.7 million and recognized unrealized gains of $2.7 million on these securities. During the three months ended March 31, 2018 , the Company made no changes to the methods described in note 11 to its consolidated financial statements included in the 2017 Form 10-K that it used to measure the fair value of its interest rate swap agreements, the embedded derivative in one of its lease agreements and acquisition-related contingent consideration. The changes in fair value during the three months ended March 31, 2018 and 2017 were not material to the consolidated financial statements. As of March 31, 2018 , the Company estimated the value of all potential acquisition-related contingent consideration payments to be between zero and $1.0 million . 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 other items measured at fair value on a nonrecurring basis during the three months ended March 31, 2018 or 2017. On February 28, 2018, one of the Company’s tenants in Asia, Aircel Ltd. (“Aircel”), filed for bankruptcy protection with the National Company Law Tribunal of India. The bankruptcy process is expected to take at least several months to complete and the ultimate outcome has yet to be determined. The Company performed an impairment test based on current expectations of the impact of the bankruptcy on projected cash flows for assets related to Aircel. These assets consisted primarily of towers, which are assessed on an individual basis, network location intangibles, which relate directly to towers, and tenant-related intangibles. As a result, an impairment of $40.1 million was taken on the tower and network intangible assets. The Company also fully impaired the tenant-related intangible asset for Aircel, which resulted in an impairment of $107.3 million during the three months ended March 31, 2018. These impairments were recorded in Other operating expenses in the consolidated statements of operations. In October 2017, one of the Company’s tenants in Asia, Tata Teleservices Limited (“Tata Teleservices”), informed the Department of Telecommunications in India of its intent to exit the wireless telecommunications business and announced plans to transfer its business to another telecommunications provider. The Company considered the recent developments regarding these events, including ongoing negotiations with Tata Teleservices, when updating its impairment test for the Tata Teleservices tenant relationship, which did not result in an impairment since the estimated probability-weighted undiscounted cash flows were in excess of the carrying value of this asset. However, the Company will continue to monitor the status of these developments, as it is possible that the estimated future cash flows may differ from current estimates. Changes in estimated cash flows from Tata Teleservices could impact previously recorded tangible and intangible assets, including amounts originally recorded as tenant-related intangibles, which have a current net book value of $417.0 million as of March 31, 2018. Fair Value of Financial Instruments —The Company’s financial instruments for which the carrying value reasonably approximates fair value at March 31, 2018 and December 31, 2017 include cash and cash equivalents, restricted cash, accounts receivable and accounts payable. The Company’s estimates of fair value of its long-term obligations, including the current portion, are based primarily upon reported market values. For long-term debt not actively traded, fair value is estimated using either indicative price quotes or a discounted cash flow analysis using rates for debt with similar terms and maturities. As of March 31, 2018 and December 31, 2017 , the carrying value of long-term obligations, including the current portion, was $21.4 billion and $20.2 billion , respectively. As of March 31, 2018 , the fair value of long-term obligations, including the current portion, was $21.4 billion , of which $13.0 billion was measured using Level 1 inputs and $8.4 billion was measured using Level 2 inputs. As of December 31, 2017 , the fair value of long-term obligations, including the current portion, was $20.6 billion , of which $13.3 billion was measured using Level 1 inputs and $7.3 billion was measured using Level 2 inputs.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2018
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 REIT operations. The Company continues to be subject to income taxes on the income of its TRSs 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 change in the income tax benefit (provision) for the three months ended March 31, 2018 was primarily attributable to the tax effect of an increase in impairment charges and a one-time benefit for merger-related activity in the Company’s Asia property segment. As of March 31, 2018 and December 31, 2017 , the total unrecognized tax benefits that would impact the ETR, if recognized, were approximately $102.8 million and $105.8 million , respectively. The amount of unrecognized tax benefits during the three months ended March 31, 2018 includes additions of $2.1 million to the Company’s existing tax positions, reductions of $2.6 million due to a settlement with authorities and reductions of $1.7 million related to positions taken in prior years. 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 12 to the Company’s consolidated financial statements included in the 2017 Form 10-K. The impact of the amount of these changes to previously recorded uncertain tax positions could range from zero to $8.7 million . The Company recorded the following penalties and income tax-related interest expense during the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 Penalties and income tax-related interest expense $ 1.0 $ 1.3 As of March 31, 2018 and December 31, 2017 , the total amount of accrued income tax related interest and penalties included in the consolidated balance sheets was $28.9 million and $29.0 million , respectively.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [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 10 years from the date of grant. As of March 31, 2018 , the Company had the ability to grant stock-based awards with respect to an aggregate of 7.6 million shares of common stock under the 2007 Plan. In addition, the Company maintains an employee stock purchase plan (the “ESPP”) pursuant to which eligible employees may purchase shares of the Company’s common stock on the last day of each bi-annual offering period at a 15% discount from the lower of the closing market value on the first or last day of such offering period. The offering periods run from June 1 through November 30 and from December 1 through May 31 of each year. During the three months ended March 31, 2018 and 2017 , the Company recorded and capitalized the following stock-based compensation expense: Three Months Ended March 31, 2018 2017 Stock-based compensation expense $ 42.7 $ 36.2 Stock-based compensation expense capitalized as property and equipment $ 0.5 $ 0.5 Stock Options —As of March 31, 2018 , total unrecognized compensation expense related to unvested stock options was $10.0 million , which is expected to be recognized over a weighted average period of approximately two years . The Company’s option activity for the three months ended March 31, 2018 was as follows (shares disclosed in full amounts): Number of Options Outstanding as of January 1, 2018 5,557,561 Granted — Exercised (243,118 ) Forfeited — Expired — Outstanding as of March 31, 2018 5,314,443 Restricted Stock Units— As of March 31, 2018 , total unrecognized compensation expense related to unvested RSUs granted under the 2007 Plan was $166.1 million and is expected to be recognized over a weighted average period of approximately three years . Performance-Based Restricted Stock Units— During the three months ended March 31, 2018 , 2017 and 2016, the Company’s Compensation Committee granted an aggregate of 131,311 PSUs (the “2018 PSUs”), 154,520 PSUs (the “2017 PSUs”) and 169,340 PSUs (the “2016 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 the 2018 PSUs, the 2017 PSUs and the 2016 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. In the event of an executive’s death, disability or qualifying retirement, PSUs will be paid out pro rata in accordance with the terms of the applicable 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 three months ended March 31, 2018 was as follows (shares disclosed in full amounts): RSUs PSUs Outstanding as of January 1, 2018 (1) 1,742,725 444,031 Granted (2) 671,618 131,311 Vested (3) (644,022 ) (120,171 ) Forfeited (12,063 ) — Outstanding as of March 31, 2018 1,758,258 455,171 _______________ (1) PSUs consist of the target number of shares issuable at the end of the three -year performance period for the 2017 PSUs and the 2016 PSUs, or 154,520 and 169,340 shares, respectively, and the shares issuable at the end of the three-year vesting period for the PSUs granted in 2015 (the “2015 PSUs”), based on achievement against the performance metrics for the the first, second and third year’s performance periods, or 120,171 shares. (2) PSUs consist of the target number of shares issuable at the end of the three -year performance period for the 2018 PSUs, or 131,311 shares. (3) PSUs consist of shares vested pursuant to the 2015 PSUs. There are no additional shares to be earned related to the 2015 PSUs. During the three months ended March 31, 2018 , the Company recorded $8.8 million in stock-based compensation expense for equity awards in which the performance goals had been established and were probable of being achieved. The remaining unrecognized compensation expense related to these awards at March 31, 2018 was $41.8 million based on the Company’s current assessment of the probability of achieving the performance goals. The weighted average period over which the cost will be recognized is approximately two years .

REDEEMABLE NONCONTROLLING INTER

REDEEMABLE NONCONTROLLING INTERESTS	3 Months Ended
	Mar. 31, 2018
Noncontrolling Interest [Abstract]
REDEEMABLE NONCONTROLLING INTERESTS	REDEEMABLE NONCONTROLLING INTERESTS 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”). 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 Teleservices, IDFC Private Equity Fund III, Macquarie SBI Infrastructure Investments Pte Limited and SBI Macquarie Infrastructure Trust (collectively, the “Remaining Shareholders”). During the three months ended March 31, 2018, pursuant to the terms of the Shareholders Agreement, the Company received regulatory approval to merge its other wholly-owned India subsidiaries into ATC TIPL. As a result, the Company’s controlling interest in ATC TIPL increased from 51% to 63% , which resulted in an increase in the Company’s additional paid-in capital of $28.1 million . Similarly, the noncontrolling interest was reduced from 49% to 37% , and a corresponding adjustment to reduce the redeemable noncontrolling interest value by $28.1 million was recorded during the three months ended March 31, 2018. In addition, the Company reclassified $78.8 million of previously recorded accumulated other comprehensive loss to additional paid-in capital due to the change in ownership of ATC TIPL. The Shareholders Agreement also provides certain of 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. Given the provisions governing the put rights, the redeemable noncontrolling interests are recorded outside of permanent equity at their redemption value. The noncontrolling interests become redeemable after the passage of time, and therefore, the Company records the carrying amount of the noncontrolling interests at the greater of (i) the initial carrying amount, increased or decreased for the noncontrolling interests’ share of net income or loss and foreign currency translation adjustments, and (ii) the redemption value. If required, the Company will adjust the redeemable noncontrolling interests to redemption value on each balance sheet date with changes in redemption value recognized as an adjustment to Distributions in excess of earnings. Due to the impact of impairment charges on net income, the Company adjusted certain noncontrolling interests, which are subject to minimum redemption values, by $17.5 million for the three months ended March 31, 2018. The put options may be exercised, requiring the Company to purchase the Remaining Shareholders’ equity interests, on specified dates beginning April 1, 2018 through March 31, 2021. The changes in Redeemable noncontrolling interests for the three months ended March 31, 2018 and 2017 were as follows: Three Months Ended March 31, 2018 2017 Balance as of January 1, $ 1,126.2 $ 1,091.3 Net loss attributable to noncontrolling interests (28.1 ) (12.3 ) Adjustment to noncontrolling interest redemption value 17.5 — Adjustment to noncontrolling interest due to merger (28.1 ) — Foreign currency translation adjustment attributable to noncontrolling interests (22.3 ) 51.1 Balance as of March 31, $ 1,065.2 $ 1,130.1

EQUITY

EQUITY	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
EQUITY	EQUITY Series B Preferred Stock —In March 2015, the Company issued 1,375,000 shares of its 5.50% Mandatory Convertible Preferred Stock, Series B, par value $0.01 per share (the “Series B Preferred Stock”). During the three months ended March 31, 2018, all outstanding shares of the Series B Preferred Stock converted at a rate of 8.7420 per share of Series B Preferred Stock, or 0.8742 per depositary share, each representing a 1/10th interest in a share of Series B Preferred Stock, into an aggregate of 12,020,064 shares of the Company’s common stock pursuant to the provisions of the Certificate of Designations governing the Series B Preferred Stock. The Company paid cash in lieu of fractional shares of the Company’s common stock. These payments were recorded as a reduction to Additional paid-in capital. On February 15, 2018, the Company paid the final dividend of $18.9 million to holders of the Series B Preferred Stock at the close of business on February 1, 2018. Sales of Equity Securities —The Company receives proceeds from the sale of its equity securities pursuant to the ESPP and upon exercise of stock options granted under its equity incentive plan. During the three months ended March 31, 2018 , the Company received an aggregate of $20.0 million in proceeds upon exercises of stock options. Stock Repurchase Program —In March 2011, the Board of Directors approved a stock repurchase program, pursuant to which the Company is authorized to repurchase up to $1.5 billion of its common stock (the “2011 Buyback”). In December 2017, the Board of Directors approved an additional stock repurchase program, pursuant to which the Company is authorized to repurchase up to $2.0 billion of its common stock (the “2017 Buyback” and, together with the 2011 Buyback, the “Buyback Programs”). During the three months ended March 31, 2018 , there were no repurchases under either program. As of March 31, 2018, the Company had repurchased a total of 12,356,054 shares of its common stock under the 2011 Buyback for an aggregate of $1.2 billion , including commissions and fees. 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 Exchange Act in accordance with securities laws and other legal requirements, and subject to market conditions and other factors. The Company expects to fund any further repurchases of its common stock through a combination of cash on hand, cash generated by operations and borrowings under its credit facilities. Purchases under the Buyback Programs are subject to the Company having available cash to fund repurchases. Distributions —During the three months ended March 31, 2018 , 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 December 6, 2017 January 16, 2018 December 28, 2017 $ 0.70 $ 300.2 March 8, 2018 April 27, 2018 April 11, 2018 $ 0.75 $ 331.2 Series B Preferred Stock January 22, 2018 February 15, 2018 February 1, 2018 $ 13.75 $ 18.9 _______________ (1) Does not include amounts accrued for distributions payable related to unvested restricted stock units. The Company accrues distributions on unvested restricted stock units, which are payable upon vesting. As of March 31, 2018 , the amount accrued for distributions payable related to unvested restricted stock units was $7.1 million . During the three months ended March 31, 2018 , the Company paid $4.1 million of distributions upon the vesting of restricted stock units. To maintain its qualification for taxation as a REIT, the Company expects to continue paying distributions, the amount, timing and frequency of which will be determined, and subject to adjustment, by the Company’s Board of Directors.

EARNINGS PER COMMON SHARE

EARNINGS PER COMMON SHARE	3 Months Ended
	Mar. 31, 2018
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, per share data reflects actual amounts): Three Months Ended March 31, 2018 2017 Net income attributable to American Tower Corporation stockholders $ 285.2 $ 316.1 Dividends on preferred stock (9.4 ) (26.8 ) Net income attributable to American Tower Corporation common stockholders 275.8 289.3 Basic weighted average common shares outstanding 435,124 427,279 Dilutive securities 3,396 2,920 Diluted weighted average common shares outstanding 438,520 430,199 Basic net income attributable to American Tower Corporation common stockholders per common share $ 0.63 $ 0.68 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 0.63 $ 0.67 Shares Excluded From Dilutive Effect —The following shares were not included in the computation of diluted earnings per share because the effect would be anti-dilutive (in thousands, on a weighted average basis): Three Months Ended March 31, 2018 2017 Restricted stock units 118 159 Stock options — 30 Preferred stock 5,904 17,547

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2018
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 2,340 towers commencing between December 2000 and August 2004. Substantially all of the towers are part of the Trust Securitizations. The average term of the lease or sublease for all sites at the inception of the agreement was approximately 27 years , assuming renewals or extensions of the underlying ground leases for the sites. The Company has the option to purchase the sites subject to the applicable lease or sublease upon its expiration. Each tower is assigned to an annual tranche, ranging from 2013 to 2032, which represents the outside expiration date for the sublease rights to that tower. The purchase price for each site is a fixed amount stated in the lease for that site plus the fair market value of certain alterations made to the related tower by AT&T. As of March 31, 2018 , the Company has purchased an aggregate of 88 of the subleased towers upon expiration of the applicable agreement. The aggregate purchase option price for the remaining towers leased and subleased is $851.1 million and will accrete at a rate of 10% per annum 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, 2020 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 four successive five -year terms. ALLTEL Transaction —In December 2000, the Company entered into an agreement with ALLTEL Communications, LLC, a predecessor entity to Verizon Wireless, to acquire towers through a 15 -year sublease agreement. Pursuant to the agreement, as amended, with Verizon Wireless, the Company acquired rights to approximately 1,800 towers in tranches between April 2001 and March 2002. The Company has the option to purchase each tower at the expiration of the applicable sublease. During the year ended December 31, 2016, the Company exercised the purchase options for 1,523 towers and provided notice to the tower owner, Verizon’s assignee, of its intent to exercise the purchase options related to the 243 remaining towers. As of March 31, 2018 , the purchase price per tower was $42,844 payable in cash or, at the tower owner’s option, with 769 shares of the Company’s common stock per tower. The aggregate cash purchase option price for the subleased towers was $10.4 million as of March 31, 2018 . Other Contingencies —The Company is subject to income tax and other taxes in the geographic areas where it operates, and periodically receives notifications of audits, assessments or other actions by taxing authorities. In certain jurisdictions, taxing authorities may issue preliminary notices or assessments while audits are being conducted. These preliminary notices or 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. The Company evaluates the circumstances of each notification or assessment based on the information available and records a liability for any potential outcome that is probable or more likely than not unfavorable if the liability is also reasonably estimable. 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 4.75 billion INR ( $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 may appeal this ruling at a higher appellate authority. The Company estimates that there is a more likely than not probability that the Company’s position will be sustained upon appeal. Accordingly, no liability has been recorded. Additionally, the assessment was made with respect to transactions that took place in the tax year commencing in 2007, prior to the Company’s acquisition of ETIPL. Under the Company’s definitive acquisition agreement of ETIPL, the seller is obligated to indemnify and defend the Company with respect to any tax-related liability that may arise from activities prior to March 31, 2010. Tenant Leases —The Company’s lease agreements with its tenants vary depending upon the region and the industry of the tenant, and generally have initial terms of ten years with multiple renewal terms at the option of the tenant. Future minimum rental receipts expected from tenants under non-cancellable operating lease agreements in effect at March 31, 2018 were as follows (in billions): Remainder of 2018 $ 4 2019 5 2020 5 2021 4 2022 3 Thereafter 11 Total $ 32 Lease Obligations —The Company leases certain land, office and tower space under operating leases that expire over various terms. Many of the leases contain renewal options with specified increases in lease payments upon exercise of the renewal option. Escalation clauses present in operating leases, excluding those tied to a consumer price index or other inflation-based indices, are recognized on a straight-line basis over the non-cancellable term of the leases. Future minimum rental payments under non-cancellable operating leases include payments for certain renewal periods at the Company’s option because failure to renew could result in a loss of the applicable communications sites and related revenues from tenant leases, thereby making it reasonably assured that the Company will renew the leases. Such payments at March 31, 2018 are as follows (in billions): Remainder of 2018 $ 1 2019 1 2020 1 2021 1 2022 1 Thereafter 6 Total $ 11

ACQUISITIONS

ACQUISITIONS	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS Impact of current year acquisitions —The Company typically acquires communications sites from wireless carriers or other tower operators and subsequently integrates those sites into its existing portfolio of communications sites. The financial results of the Company’s acquisitions have been included in the Company’s consolidated statements of operations for the three months ended March 31, 2018 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 the transaction. Integration costs include incremental and non-recurring costs necessary to convert data, retain employees and otherwise enable the Company to operate new businesses or assets efficiently. The Company records acquisition and merger related expenses for business combinations, as well as integration costs for all acquisitions, in Other operating expenses in the consolidated statements of operations. During the three months ended March 31, 2018 and 2017 , the Company recorded acquisition and merger related expenses for business combinations and non-capitalized asset acquisition costs and integration costs as follows: Three Months Ended March 31, 2018 2017 Acquisition and merger related expenses $ 1.4 $ 5.7 Integration costs $ 0.5 $ 4.6 2018 Transactions The estimated aggregate impact of the acquisitions completed in 2018 on the Company’s revenues and gross margin for the three months ended March 31, 2018 was approximately $0.9 million and $0.6 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. Vodafone Acquisition— On March 31, 2018, the Company acquired 10,238 communications sites from Vodafone India Limited and Vodafone Mobile Services Limited (together, “Vodafone”) for an aggregate total purchase price of 38.2 billion INR ( $586.9 million at the date of acquisition). This acquisition was accounted for as an asset acquisition. Other Acquisitions— During the three months ended March 31, 2018, the Company acquired a total of 338 communications sites in the United States, Colombia, Mexico, Paraguay and Peru for an aggregate purchase price of $93.2 million . Of the aggregate purchase price, $1.6 million is reflected in Accounts payable in the consolidated balance sheet as of March 31, 2018. These acquisitions were accounted for as asset acquisitions. The following table summarizes the allocations of the purchase prices for the fiscal year 2018 acquisitions based upon their estimated fair value at the date of acquisition: Asia Vodafone (1) (2) Other (1) (3) Current assets $ 16.6 $ 1.3 Non-current assets 9.9 1.1 Property and equipment 197.6 30.1 Intangible assets (4): Tenant-related intangible assets 326.1 42.5 Network location intangible assets 64.5 23.5 Current liabilities (15.8 ) (0.7 ) Other non-current liabilities (12.0 ) (4.6 ) Net assets acquired 586.9 93.2 Goodwill — — Fair value of net assets acquired 586.9 93.2 Debt assumed — — Purchase price $ 586.9 $ 93.2 _______________ (1) Accounted for as asset acquisitions. (2) Includes $1.3 million in acquisition and merger related expenses that were capitalized as part of the purchase price. (3) Includes 35 sites in Peru held pursuant to long-term capital leases. (4) Tenant-related intangible assets and network location intangible assets are amortized on a straight-line basis over periods of up to 20 years. Pro Forma Consolidated Results (Unaudited) The following table presents the unaudited pro forma financial results as if the 2018 acquisitions had occurred on January 1, 2017 and acquisitions completed in 2017 had occurred on January 1, 2016. The pro forma results do not include any anticipated cost synergies, costs or other integration impacts. Accordingly, such pro forma amounts are not necessarily indicative of the results that actually would have occurred had the transactions been completed on the date indicated, nor are they indicative of the future operating results of the Company. Three Months Ended March 31, 2018 2017 Pro forma revenues $ 1,780.3 $ 1,690.0 Pro forma net income attributable to American Tower Corporation common stockholders $ 275.8 $ 284.9 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 0.63 $ 0.67 Diluted net income attributable to American Tower Corporation common stockholders $ 0.63 $ 0.66 Other Signed Acquisitions Idea Cellular Limited —On November 13, 2017, the Company entered into an agreement with Idea Cellular Limited (“Idea”) and Idea’s subsidiary, Idea Cellular Infrastructure Services Limited (“ICISL”), to acquire 100% of the outstanding shares of ICISL, a telecommunications company that owns and operates approximately 9,900 communications sites in India, for cash consideration of approximately 40 billion INR ( $611.4 million at the date of signing), subject to certain adjustments (the “Idea Transaction”). Consummation of the Idea Transaction is subject to certain conditions, including regulatory approval. The Idea Transaction is expected to close in the second quarter of 2018.

BUSINESS SEGMENTS

BUSINESS SEGMENTS	3 Months Ended
	Mar. 31, 2018
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, which as of March 31, 2018 , consisted of the following: • U.S.: property operations in the United States; • Asia: property operations in India; • Europe, Middle East and Africa (“EMEA”): property operations in France, Germany, Ghana, Nigeria, South Africa and Uganda; and • Latin America: property operations in Argentina, Brazil, Chile, Colombia, Costa Rica, Mexico, Paraguay and Peru. The Company has applied the aggregation criteria to operations within the EMEA and Latin America property operating segments on a basis that is consistent with management’s review of information and performance evaluations of these regions. The Company’s services segment offers tower-related services in the United States, including site 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. 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. For reporting purposes, the Latin America property segment gross margin and segment operating profit also include Interest income, TV Azteca, net. These measures of segment gross margin and segment operating profit are also before Interest income, Interest expense, Gain (loss) on retirement of long-term obligations, Other income (expense), Net income (loss) attributable to noncontrolling interests and Income tax benefit (provision). The categories of expenses indicated above, such as depreciation, have been excluded from segment operating performance as they are not considered in the review of information or the evaluation of results by management. There are no significant revenues resulting from transactions between the Company’s operating segments. All intercompany transactions are eliminated to reconcile segment results and assets to the consolidated statements of operations and consolidated balance sheets. Summarized financial information concerning the Company’s reportable segments for the three months ended March 31, 2018 and 2017 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 Property Services Other Total Three Months Ended March 31, 2018 U.S. Asia EMEA Latin America Total segment revenues $ 931.4 $ 273.0 $ 174.2 $ 331.8 $ 1,710.4 $ 31.4 $ 1,741.8 Segment operating expenses (1) 186.3 157.9 59.1 103.4 506.7 12.2 518.9 Interest income, TV Azteca, net — — — 2.7 2.7 — 2.7 Segment gross margin 745.1 115.1 115.1 231.1 1,206.4 19.2 1,225.6 Segment selling, general, administrative and development expense (1) 35.4 44.2 16.8 24.6 121.0 3.5 124.5 Segment operating profit $ 709.7 $ 70.9 $ 98.3 $ 206.5 $ 1,085.4 $ 15.7 $ 1,101.1 Stock-based compensation expense $ 42.7 42.7 Other selling, general, administrative and development expense 38.7 38.7 Depreciation, amortization and accretion 446.3 446.3 Other expense (2) 324.2 324.2 Income from continuing operations before income taxes $ 249.2 Total assets $ 18,894.7 $ 5,796.8 $ 3,343.4 $ 6,084.1 $ 34,119.0 $ 47.0 $ 206.7 $ 34,372.7 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $1.0 million and $41.7 million , respectively. (2) Primarily includes interest expense and $147.4 million in impairment charges. Property Total Property Services Other Total Three Months Ended March 31, 2017 U.S. Asia EMEA Latin America Segment revenues $ 891.9 $ 275.5 $ 150.4 $ 276.3 $ 1,594.1 $ 22.1 $ 1,616.2 Segment operating expenses (1) 181.4 149.4 61.5 93.2 485.5 6.3 491.8 Interest income, TV Azteca, net — — — 2.7 2.7 — 2.7 Segment gross margin 710.5 126.1 88.9 185.8 1,111.3 15.8 1,127.1 Segment selling, general, administrative and development expense (1) 34.6 20.5 16.5 18.6 90.2 3.1 93.3 Segment operating profit $ 675.9 $ 105.6 $ 72.4 $ 167.2 $ 1,021.1 $ 12.7 $ 1,033.8 Stock-based compensation expense $ 36.2 36.2 Other selling, general, administrative and development expense 36.2 36.2 Depreciation, amortization and accretion 421.1 421.1 Other expense (2) 206.1 206.1 Income from continuing operations before income taxes $ 334.2 Total assets $ 18,768.4 $ 4,765.9 $ 3,054.5 $ 5,189.3 $ 31,778.1 $ 49.2 $ 230.1 $ 32,057.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $0.9 million and $35.3 million , respectively. (2) Primarily includes interest expense.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS Kenya —On April 3, 2018, the Company, through its recently formed Kenyan subsidiary, entered into a definitive agreement with Telkom Kenya Limited to acquire up to 723 communications sites in Kenya. The transaction is expected to close during the second half of 2018, subject to customary closing conditions, including the satisfaction of regulatory approvals.

DESCRIPTION OF BUSINESS, BASI26

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) is one of the largest global real estate investment trusts and a leading independent owner, operator and developer of multitenant communications real estate. The Company’s primary business is the leasing of space on communications sites to wireless service providers, radio and television broadcast companies, wireless data providers, government agencies and municipalities and tenants in a number of other industries. The Company refers to this business as its property operations. Additionally, the Company offers tower-related services in the United States, which it refers to as its services operations. These services include site acquisition, zoning and permitting (“AZP”) and structural analysis, which primarily support the Company’s site leasing business, including the addition of new tenants and equipment on its sites. The Company’s portfolio primarily consists of towers that it owns and towers that it operates pursuant to long-term lease arrangements, as well as distributed antenna system (“DAS”) networks, which provide seamless coverage solutions in certain in-building and certain outdoor wireless environments. In addition to the communications sites in its portfolio, the Company manages rooftop and tower sites for property owners under various contractual arrangements. The Company also holds other telecommunications infrastructure, fiber and property interests that it leases primarily to communications service providers and third-party tower operators. American Tower Corporation is a holding company that conducts its operations through its directly and indirectly owned subsidiaries and joint ventures. ATC’s principal domestic operating subsidiaries are American Towers LLC and SpectraSite Communications, LLC. ATC conducts its international operations primarily through its subsidiary, American Tower International, Inc., which in turn conducts operations through its various international holding and operating subsidiaries and joint ventures. The Company operates as a real estate investment trust for U.S. federal income tax purposes (“REIT”). Accordingly, the Company generally is not required to pay U.S. federal income taxes on income generated by its REIT operations, including the income derived from leasing space on its towers, as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on earnings from its domestic taxable REIT subsidiaries (“TRSs”). In addition, the Company’s international assets and operations, regardless of their classification for U.S. tax purposes, continue to be subject to taxation in the foreign jurisdictions where those assets are held or those operations are conducted. The use of TRSs enables the Company to continue to engage in certain businesses while complying with REIT qualification requirements. The Company may, from time to time, change the election of previously designated TRSs to be included as part of the REIT. As of March 31, 2018 , the Company’s REIT-qualified businesses included its U.S. tower leasing business, its operations in Nigeria, most of its operations in Costa Rica and Mexico, a majority of its operations in Germany and a majority of its indoor DAS networks business and services segment. The accompanying consolidated and condensed consolidated financial statements have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission. 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, 2017 (the “ 2017 Form 10-K”). The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the entire year.
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 or cost method, depending upon the Company’s ability to exercise significant influence over operating and financial policies. All intercompany accounts and transactions have been eliminated. As of March 31, 2018 , the Company holds (i) a 51% controlling interest, and MTN Group Limited holds a 49% noncontrolling interest, in each of two joint ventures, one in Ghana and one in Uganda, (ii) a 51% controlling interest, and PGGM holds a 49% noncontrolling interest, in a joint venture (“ATC Europe”) which primarily consists of operations in Germany and France, (iii) an approximate 75% controlling interest, and South African investors hold an approximate 25% noncontrolling interest, in a subsidiary of the Company in South Africa and (iv) a 63% controlling interest in ATC Telecom Infrastructure Private Limited (“ATC TIPL”), formerly Viom Networks Limited (“Viom”), in India.
Significant Accounting Policies	Significant Accounting Policies —The Company’s significant accounting policies are described in note 1 to the Company’s consolidated financial statements included in the 2017 Form 10-K. There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2018 , except the adoption of new revenue recognition guidance, as discussed below.
Revenue Recognition	The Company does not disclose the value of unsatisfied performance obligations for agreements (i) with an original expected length of one year or less or (ii) for which it recognizes revenue at the amount to which it has the right to invoice for services performed. The Company records unearned revenue when payments are received from tenants in advance of the completion of the Company’s performance obligations. Long-term unearned revenue is included in Other non-current liabilities. Power and fuel pass-through revenue —Most of the Company’s leasing arrangements outside of the U.S. require that the Company provide power to the communications site through an electrical grid connection, diesel fuel generators or other sources and permit the Company to pass through the costs of these services to its tenants. The Company recognizes revenue received in connection with such services as power and fuel pass-through revenue. Many arrangements require that the communications site has power for a specified percentage of time. In most such cases, if delivery of power falls below the specified service level, a corresponding reduction in revenue is recorded. The Company has determined that this performance obligation is satisfied over time for the duration of the arrangement. Other significant judgments related to this revenue stream are the (i) determination that the Company is a principal in these transactions and revenue is therefore recorded on a gross basis and (ii) service level related adjustments to revenue. Other non-lease revenue —Other non-lease revenue consists primarily of revenue generated from DAS, fiber and other property related revenue. DAS and fiber arrangements require that the Company provide the tenant the right to use the applicable communications infrastructure. Performance obligations are satisfied over time for the duration of the arrangements. Other property related revenue streams, which include site inspections, are not material on either an individual or consolidated basis. Services revenue —The Company offers tower-related services in the United States. These services include site AZP and structural analysis services. 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 incurred. Structural analysis services may have more than one performance obligation, contingent upon the number of contracted services. Revenue is recognized at the point in time the services are completed. Some of the Company’s contracts with tenants contain multiple performance obligations. For these arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price, which is typically based on the price charged to tenants. Revenue —The new revenue recognition accounting standard requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. On January 1, 2018, the Company adopted the new revenue recognition standard using the modified retrospective method applied to contracts that were not completed as of January 1, 2018. Results for reporting periods beginning January 1, 2018 are presented under the new standard, while prior-period amounts are not adjusted and continue to be reported in accordance with accounting under the previously applicable guidance. The Company recorded a net reduction to opening Distributions in excess of earnings in its consolidated balance sheet of $38.4 million as of January 1, 2018 due to the cumulative impact of adopting the new revenue recognition standard. The impact is primarily related to the Company’s site inspection revenue, which is now recognized at the point in time when the inspection service is completed. The impact to revenues for the three months ended March 31, 2018 as a result of applying the new standard was an increase of $2.6 million . The adoption of the new revenue recognition accounting standard did not have a material impact on the Company’s revenue recognition patterns. Most of the Company’s revenue is derived from leasing arrangements and is accounted for as lease revenue. A small portion of the Company’s revenue is either derived from non-lease performance obligations within the lease arrangements or from other agreements with its tenants. This revenue, designated non-lease revenue, is recognized when control of the promised goods or services is transferred to the tenants, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. Since most of the Company’s contracts are leases, costs are capitalized under the applicable lease accounting guidance. Costs incurred to obtain non-lease contracts that are capitalized primarily relate to DAS and are not material to the consolidated financial statements. The Company has excluded sales tax, value-added tax and similar taxes from non-lease revenue.
Accounting Standards Updates	Accounting Standards Updates —In January 2016, the Financial Accounting Standards Board (the “FASB”) issued new guidance on the recognition and measurement of financial assets and financial liabilities. The guidance amends certain aspects of recognition, measurement, presentation and disclosure of financial instruments. This standard is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2017. The adoption of this guidance did not have a material impact on the Company’s financial statements. In February 2016, the FASB issued new guidance on the accounting for leases. The guidance amends the existing accounting standards for lease accounting, including the requirement that lessees recognize right of use assets and lease liabilities for leases with terms greater than twelve months in the statement of financial position. Under the new guidance, lessor accounting is largely unchanged. This guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018. The Company (i) has established a multidisciplinary team to assess and implement the new guidance, (ii) expects the guidance to have a material impact on its consolidated balance sheets due to the recording of right of use assets and lease liabilities for leases in which it is a lessee and which it currently treats as operating leases and (iii) continues to evaluate the impact of the new guidance. In January 2018, the FASB issued new guidance on the treatment of land easements. The guidance provides a practical expedient to not evaluate existing or expired land easements under the new lease accounting standards if those easements were not previously accounted for as leases under the existing lease guidance. The Company does not expect the adoption of this guidance to have a material impact on its financial statements or its adoption of the lease accounting guidance. In January 2017, the FASB issued new guidance on accounting for goodwill impairments. The guidance eliminates Step 2 from the goodwill impairment test and requires, among other things, recognition of an impairment loss when the carrying value of a reporting unit exceeds its fair value. The loss recognized is limited to the total amount of goodwill allocated to that reporting unit. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a material impact on its financial statements. In August 2017, the FASB issued new guidance on hedge and derivative accounting. The guidance simplifies accounting rules around hedge accounting and the disclosures of hedging arrangements. Among other things, the guidance eliminates the need to separately measure and report hedge ineffectiveness and generally requires the entire change in fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company does not expect the adoption of this guidance to have a material impact on its financial statements. In February 2018, the FASB issued new guidance on the treatment of tax effects that are presented in other comprehensive income. The guidance allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects as a result of the December 2017 legislation commonly referred to as the Tax Cuts and Jobs Act. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company does not expect the adoption of this guidance to have a material impact on its financial statements.

DESCRIPTION OF BUSINESS, BASI27

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule 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 amount shown in the statement of cash flows is as follows: Three months ended March 31, 2018 2017 Cash and cash equivalents $ 1,125.4 $ 712.8 Restricted cash 153.5 145.5 Total cash and cash equivalents and restricted cash $ 1,278.9 $ 858.3
Summary of Non-lease disaggregated Revenue by Source and Geography	A summary of non-lease revenue disaggregated by source and geography is as follows: Three Months Ended March 31, 2018 U.S. Asia EMEA Latin America Total Power and fuel pass-through revenue $ — $ 92.3 $ 34.9 $ 4.5 $ 131.7 Other non-lease revenue 67.7 1.9 0.6 23.7 93.9 Total non-lease property revenue $ 67.7 $ 94.2 $ 35.5 $ 28.2 $ 225.6 Services revenue 31.4 — — — 31.4 Total non-lease revenue $ 99.1 $ 94.2 $ 35.5 $ 28.2 $ 257.0 Property lease revenue 863.7 178.8 138.7 303.6 1,484.8 Total revenue $ 962.8 $ 273.0 $ 174.2 $ 331.8 $ 1,741.8
Information About Receivables, Contract Assets and Contract Liabilities From Contracts with Tenants	Information about receivables, contract assets and contract liabilities from contracts with tenants is as follows: January 1, 2018 March 31, 2018 Accounts receivable $ 222.2 $ 234.0 Prepaids and other current assets 79.7 73.3 Notes receivable and other non-current assets 24.2 23.5 Unearned revenue 26.6 33.3 Other non-current liabilities 68.5 65.2

PREPAID AND OTHER CURRENT ASS28

PREPAID AND OTHER CURRENT ASSETS (Tables)	3 Months Ended
	Mar. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid and other current assets	Prepaid and other current assets consisted of the following: As of March 31, 2018 December 31, 2017 Prepaid operating ground leases $ 150.6 $ 148.6 Prepaid income tax 136.5 136.5 Unbilled receivables 110.7 107.9 Value added tax and other consumption tax receivables 63.6 64.2 Prepaid assets 42.5 39.6 Other miscellaneous current assets 67.3 71.8 Prepaid and other current assets $ 571.2 $ 568.6

GOODWILL AND OTHER INTANGIBLE29

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying value of goodwill	The changes in the carrying value of goodwill for each of the Company’s business segments were as follows: Property Services Total U.S. Asia EMEA Latin America Balance as of January 1, 2018 $ 3,379.2 $ 1,095.0 $ 404.9 $ 757.3 $ 2.0 $ 5,638.4 Effect of foreign currency translation — (21.9 ) 10.8 19.8 — 8.7 Balance as of March 31, 2018 $ 3,379.2 $ 1,073.1 $ 415.7 $ 777.1 $ 2.0 $ 5,647.1
Intangible assets subject to amortization	The Company’s other intangible assets subject to amortization consisted of the following: As of March 31, 2018 As of December 31, 2017 Estimated Useful Gross Carrying Value Accumulated Amortization Net Book Value Gross Carrying Value Accumulated Amortization Net Book Value (years) Acquired network location intangibles (1) Up to 20 $ 4,922.5 $ (1,584.1 ) $ 3,338.4 $ 4,858.8 $ (1,525.3 ) $ 3,333.5 Acquired tenant-related intangibles 15-20 11,431.9 (2,883.7 ) 8,548.2 11,150.9 (2,754.7 ) 8,396.2 Acquired licenses and other intangibles 3-20 60.5 (10.2 ) 50.3 58.8 (8.1 ) 50.7 Economic Rights, TV Azteca 70 15.7 (12.4 ) 3.3 14.5 (11.6 ) 2.9 Total other intangible assets $ 16,430.6 $ (4,490.4 ) $ 11,940.2 $ 16,083.0 $ (4,299.7 ) $ 11,783.3 _______________ (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, or up to 20 years, as the Company considers these intangibles to be directly related to the tower assets.
Expected future amortization expenses	Based on current exchange rates, the Company expects to record amortization expense as follows over the remaining current year and the five subsequent years: Remainder of 2018 $ 620.6 2019 823.8 2020 804.1 2021 787.6 2022 783.1 2023 778.7

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Schedule of accrued expenses	Accrued expenses consisted of the following: As of March 31, 2018 December 31, 2017 Accrued property and real estate taxes $ 156.9 $ 154.4 Amounts payable to tenants 62.0 60.8 Accrued rent 57.4 54.0 Payroll and related withholdings 54.1 82.2 Accrued pass-through costs 52.9 59.7 Accrued income tax payable 35.7 15.3 Accrued pass-through taxes 35.5 25.3 Accrued construction costs 21.9 31.9 Other accrued expenses 349.0 370.7 Total accrued expenses $ 825.4 $ 854.3

LONG-TERM OBLIGATIONS (Tables)

LONG-TERM OBLIGATIONS (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of long-term obligations	Outstanding amounts under the Company’s long-term obligations, reflecting discounts, premiums, debt issuance costs and fair value adjustments due to interest rate swaps consisted of the following: As of March 31, 2018 December 31, 2017 Maturity Date 2018 Term Loan (1) $ 1,499.2 $ — March 29, 2019 2013 Credit Facility (1) 1,641.8 2,075.6 June 28, 2021 2013 Term Loan (1) 994.7 994.5 January 31, 2023 2014 Credit Facility (1) 600.0 495.0 January 31, 2023 3.40% senior notes 999.9 999.8 February 15, 2019 2.800% senior notes 746.7 746.3 June 1, 2020 5.050% senior notes 698.2 698.0 September 1, 2020 3.300% senior notes 746.3 746.0 February 15, 2021 3.450% senior notes 645.4 645.1 September 15, 2021 5.900% senior notes 498.0 497.8 November 1, 2021 2.250% senior notes 564.5 572.4 January 15, 2022 4.70% senior notes 696.9 696.7 March 15, 2022 3.50% senior notes 991.3 990.9 January 31, 2023 3.000% senior notes 682.4 692.5 June 15, 2023 5.00% senior notes 1,002.4 1,002.4 February 15, 2024 1.375% senior notes 605.1 589.1 April 4, 2025 4.000% senior notes 741.3 741.0 June 1, 2025 4.400% senior notes 495.8 495.6 February 15, 2026 3.375% senior notes 985.2 984.8 October 15, 2026 3.125% senior notes 397.1 397.1 January 15, 2027 3.55% senior notes 743.0 742.8 July 15, 2027 3.600% senior notes 691.3 691.1 January 15, 2028 Total American Tower Corporation debt 17,666.5 16,494.5 Series 2013-1A securities (2) — 499.8 N/A Series 2013-2A securities (3) 1,292.2 1,291.8 March 15, 2023 Series 2018-1A securities (3) 493.0 — March 15, 2028 Series 2015-1 notes (4) 348.2 348.0 June 15, 2020 Series 2015-2 notes (5) 520.3 520.1 June 16, 2025 India indebtedness (6) 518.6 512.6 Various India preference shares (7) 25.6 26.1 March 2, 2020 Shareholder loans (8) 101.8 100.6 Various Other subsidiary debt (1) (9) 239.6 246.1 Various Total American Tower subsidiary debt 3,539.3 3,545.1 Other debt, including capital lease obligations 166.2 165.5 Total 21,372.0 20,205.1 Less current portion of long-term obligations (2,803.2 ) (774.8 ) Long-term obligations $ 18,568.8 $ 19,430.3 _______________ (1) Accrues interest at a variable rate. (2) Repaid in full on the March 2018 payment date. (3) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (4) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2045. (5) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (6) Denominated in Indian Rupees (“INR”). Includes India working capital facility, remaining debt assumed by the Company in connection with the Viom Acquisition (as defined in note 9) and debt that has been entered into by ATC TIPL. (7) Mandatorily redeemable preference shares (the “Preference Shares”) classified as debt. The Preference Shares are to be redeemed on March 2, 2020 and have a dividend rate of 10.25% per annum. Denominated in INR. (8) Reflects balances owed to the Company’s joint venture partners in Ghana and Uganda. The Ghana loan is denominated in Ghanaian Cedi and the Uganda loan is denominated in Ugandan Shillings. (9) Includes the BR Towers debentures and the Brazil credit facility, which are denominated in Brazilian Reais and amortize through October 15, 2023 and January 15, 2022, respectively, the South African credit facility, which is denominated in South African Rand and amortizes through December 17, 2020 and the Colombian credit facility, which is denominated in Colombian Pesos and amortizes through April 24, 2021.
Schedule of line of credit facilities	As of March 31, 2018 , the key terms under the 2013 Credit Facility, the 2014 Credit Facility, the Company’s unsecured term loan entered into in October 2013, as amended (the “2013 Term Loan”) and the 2018 Term Loan were as follows: Outstanding Principal Balance Undrawn letters of credit Maturity Date Current margin over LIBOR (1) Current commitment fee (2) 2013 Credit Facility $ 1,641.8 (3) $ 4.0 June 28, 2021 (4) 1.125 % 0.125 % 2014 Credit Facility $ 600.0 $ 6.3 January 31, 2023 (4) 1.250 % 0.150 % 2013 Term Loan $ 1,000.0 N/A January 31, 2023 1.250 % N/A 2018 Term Loan $ 1,500.0 N/A March 29, 2019 0.875 % N/A _______________ (1) LIBOR means the London Interbank Offered Rate. (2) Fee on undrawn portion of each credit facility. (3) Includes $140.0 million borrowed at the base rate of 4.750% plus a margin of 0.125% . (4) Subject to two optional renewal periods.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of fair value	The fair values of the Company’s financial assets and liabilities that are required to be measured on a recurring basis at fair value were as follows: March 31, 2018 December 31, 2017 Fair Value Measurements Using Fair Value Measurements Using Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets: Short-term investments (1) $ — $ 389.4 — $ 1.0 — — Embedded derivative in lease agreement — — $ 12.2 — — $ 12.4 Liabilities: Interest rate swap agreements — $ 45.4 — — $ 29.0 — Acquisition-related contingent consideration — — $ 1.0 — — $ 10.1 Fair value of debt related to interest rate swap agreements $ (43.0 ) — — $ (24.5 ) — — _______________ (1) Consists of highly liquid investments with original maturities in excess of three months and mutual funds with a portfolio duration of less than 90 days.

INCOME TAXES (Tables)

INCOME TAXES (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of penalties and income tax-related interest expense	The Company recorded the following penalties and income tax-related interest expense during the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 Penalties and income tax-related interest expense $ 1.0 $ 1.3

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of stock-based compensation expenses	During the three months ended March 31, 2018 and 2017 , the Company recorded and capitalized the following stock-based compensation expense: Three Months Ended March 31, 2018 2017 Stock-based compensation expense $ 42.7 $ 36.2 Stock-based compensation expense capitalized as property and equipment $ 0.5 $ 0.5
Summary of the company's option activity	The Company’s option activity for the three months ended March 31, 2018 was as follows (shares disclosed in full amounts): Number of Options Outstanding as of January 1, 2018 5,557,561 Granted — Exercised (243,118 ) Forfeited — Expired — Outstanding as of March 31, 2018 5,314,443
Summary of the company's restricted stock unit activity	The Company’s RSU and PSU activity for the three months ended March 31, 2018 was as follows (shares disclosed in full amounts): RSUs PSUs Outstanding as of January 1, 2018 (1) 1,742,725 444,031 Granted (2) 671,618 131,311 Vested (3) (644,022 ) (120,171 ) Forfeited (12,063 ) — Outstanding as of March 31, 2018 1,758,258 455,171 _______________ (1) PSUs consist of the target number of shares issuable at the end of the three -year performance period for the 2017 PSUs and the 2016 PSUs, or 154,520 and 169,340 shares, respectively, and the shares issuable at the end of the three-year vesting period for the PSUs granted in 2015 (the “2015 PSUs”), based on achievement against the performance metrics for the the first, second and third year’s performance periods, or 120,171 shares. (2) PSUs consist of the target number of shares issuable at the end of the three -year performance period for the 2018 PSUs, or 131,311 shares. (3) PSUs consist of shares vested pursuant to the 2015 PSUs. There are no additional shares to be earned related to the 2015 PSUs.

REDEEMABLE NONCONTROLLING INT35

REDEEMABLE NONCONTROLLING INTERESTS (Tables)	3 Months Ended
	Mar. 31, 2018
Noncontrolling Interest [Abstract]
Changes in redeemable noncontrolling interest	The changes in Redeemable noncontrolling interests for the three months ended March 31, 2018 and 2017 were as follows: Three Months Ended March 31, 2018 2017 Balance as of January 1, $ 1,126.2 $ 1,091.3 Net loss attributable to noncontrolling interests (28.1 ) (12.3 ) Adjustment to noncontrolling interest redemption value 17.5 — Adjustment to noncontrolling interest due to merger (28.1 ) — Foreign currency translation adjustment attributable to noncontrolling interests (22.3 ) 51.1 Balance as of March 31, $ 1,065.2 $ 1,130.1

EQUITY (Tables)

EQUITY (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Schedule of declared or paid cash distributions	During the three months ended March 31, 2018 , 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 December 6, 2017 January 16, 2018 December 28, 2017 $ 0.70 $ 300.2 March 8, 2018 April 27, 2018 April 11, 2018 $ 0.75 $ 331.2 Series B Preferred Stock January 22, 2018 February 15, 2018 February 1, 2018 $ 13.75 $ 18.9 _______________ (1) Does not include amounts accrued for distributions payable related to unvested restricted stock units.

EARNINGS PER COMMON SHARE (Tabl

EARNINGS PER COMMON SHARE (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of basic and diluted net income per common share	The following table sets forth basic and diluted net income per common share computational data (shares in thousands, per share data reflects actual amounts): Three Months Ended March 31, 2018 2017 Net income attributable to American Tower Corporation stockholders $ 285.2 $ 316.1 Dividends on preferred stock (9.4 ) (26.8 ) Net income attributable to American Tower Corporation common stockholders 275.8 289.3 Basic weighted average common shares outstanding 435,124 427,279 Dilutive securities 3,396 2,920 Diluted weighted average common shares outstanding 438,520 430,199 Basic net income attributable to American Tower Corporation common stockholders per common share $ 0.63 $ 0.68 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 0.63 $ 0.67
Schedule of antidilutive securities excluded from computation of earnings per share	The following shares were not included in the computation of diluted earnings per share because the effect would be anti-dilutive (in thousands, on a weighted average basis): Three Months Ended March 31, 2018 2017 Restricted stock units 118 159 Stock options — 30 Preferred stock 5,904 17,547

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Future minimum rental receipts under operating lease agreements	Future minimum rental receipts expected from tenants under non-cancellable operating lease agreements in effect at March 31, 2018 were as follows (in billions): Remainder of 2018 $ 4 2019 5 2020 5 2021 4 2022 3 Thereafter 11 Total $ 32
Future minimum rental payments under non-cancelable operating leases	Future minimum rental payments under non-cancellable operating leases include payments for certain renewal periods at the Company’s option because failure to renew could result in a loss of the applicable communications sites and related revenues from tenant leases, thereby making it reasonably assured that the Company will renew the leases. Such payments at March 31, 2018 are as follows (in billions): Remainder of 2018 $ 1 2019 1 2020 1 2021 1 2022 1 Thereafter 6 Total $ 11

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Schedule of acquisition and merger related costs	During the three months ended March 31, 2018 and 2017 , the Company recorded acquisition and merger related expenses for business combinations and non-capitalized asset acquisition costs and integration costs as follows: Three Months Ended March 31, 2018 2017 Acquisition and merger related expenses $ 1.4 $ 5.7 Integration costs $ 0.5 $ 4.6
Schedule of allocation of purchase for acquisitions	The following table summarizes the allocations of the purchase prices for the fiscal year 2018 acquisitions based upon their estimated fair value at the date of acquisition: Asia Vodafone (1) (2) Other (1) (3) Current assets $ 16.6 $ 1.3 Non-current assets 9.9 1.1 Property and equipment 197.6 30.1 Intangible assets (4): Tenant-related intangible assets 326.1 42.5 Network location intangible assets 64.5 23.5 Current liabilities (15.8 ) (0.7 ) Other non-current liabilities (12.0 ) (4.6 ) Net assets acquired 586.9 93.2 Goodwill — — Fair value of net assets acquired 586.9 93.2 Debt assumed — — Purchase price $ 586.9 $ 93.2 _______________ (1) Accounted for as asset acquisitions. (2) Includes $1.3 million in acquisition and merger related expenses that were capitalized as part of the purchase price. (3) Includes 35 sites in Peru held pursuant to long-term capital leases. (4) Tenant-related intangible assets and network location intangible assets are amortized on a straight-line basis over periods of up to 20 years.
Schedule of pro forma information	The following table presents the unaudited pro forma financial results as if the 2018 acquisitions had occurred on January 1, 2017 and acquisitions completed in 2017 had occurred on January 1, 2016. The pro forma results do not include any anticipated cost synergies, costs or other integration impacts. Accordingly, such pro forma amounts are not necessarily indicative of the results that actually would have occurred had the transactions been completed on the date indicated, nor are they indicative of the future operating results of the Company. Three Months Ended March 31, 2018 2017 Pro forma revenues $ 1,780.3 $ 1,690.0 Pro forma net income attributable to American Tower Corporation common stockholders $ 275.8 $ 284.9 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 0.63 $ 0.67 Diluted net income attributable to American Tower Corporation common stockholders $ 0.63 $ 0.66

BUSINESS SEGMENTS (Tables)

BUSINESS SEGMENTS (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Summarized financial information concerning the company's reportable segments	Property Total Property Services Other Total Three Months Ended March 31, 2018 U.S. Asia EMEA Latin America Total segment revenues $ 931.4 $ 273.0 $ 174.2 $ 331.8 $ 1,710.4 $ 31.4 $ 1,741.8 Segment operating expenses (1) 186.3 157.9 59.1 103.4 506.7 12.2 518.9 Interest income, TV Azteca, net — — — 2.7 2.7 — 2.7 Segment gross margin 745.1 115.1 115.1 231.1 1,206.4 19.2 1,225.6 Segment selling, general, administrative and development expense (1) 35.4 44.2 16.8 24.6 121.0 3.5 124.5 Segment operating profit $ 709.7 $ 70.9 $ 98.3 $ 206.5 $ 1,085.4 $ 15.7 $ 1,101.1 Stock-based compensation expense $ 42.7 42.7 Other selling, general, administrative and development expense 38.7 38.7 Depreciation, amortization and accretion 446.3 446.3 Other expense (2) 324.2 324.2 Income from continuing operations before income taxes $ 249.2 Total assets $ 18,894.7 $ 5,796.8 $ 3,343.4 $ 6,084.1 $ 34,119.0 $ 47.0 $ 206.7 $ 34,372.7 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $1.0 million and $41.7 million , respectively. (2) Primarily includes interest expense and $147.4 million in impairment charges. Property Total Property Services Other Total Three Months Ended March 31, 2017 U.S. Asia EMEA Latin America Segment revenues $ 891.9 $ 275.5 $ 150.4 $ 276.3 $ 1,594.1 $ 22.1 $ 1,616.2 Segment operating expenses (1) 181.4 149.4 61.5 93.2 485.5 6.3 491.8 Interest income, TV Azteca, net — — — 2.7 2.7 — 2.7 Segment gross margin 710.5 126.1 88.9 185.8 1,111.3 15.8 1,127.1 Segment selling, general, administrative and development expense (1) 34.6 20.5 16.5 18.6 90.2 3.1 93.3 Segment operating profit $ 675.9 $ 105.6 $ 72.4 $ 167.2 $ 1,021.1 $ 12.7 $ 1,033.8 Stock-based compensation expense $ 36.2 36.2 Other selling, general, administrative and development expense 36.2 36.2 Depreciation, amortization and accretion 421.1 421.1 Other expense (2) 206.1 206.1 Income from continuing operations before income taxes $ 334.2 Total assets $ 18,768.4 $ 4,765.9 $ 3,054.5 $ 5,189.3 $ 31,778.1 $ 49.2 $ 230.1 $ 32,057.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $0.9 million and $35.3 million , respectively. (2) Primarily includes interest expense.

DESCRIPTION OF BUSINESS, BASI41

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended
	Mar. 31, 2018joint_venture
Concentration Risk [Line Items]
Number of joint ventures the Company has a controlling interest in	2
Ghana
Concentration Risk [Line Items]
Number of joint ventures the Company has a controlling interest in	1
Uganda
Concentration Risk [Line Items]
Number of joint ventures the Company has a controlling interest in	1
ATC Europe
Concentration Risk [Line Items]
Ownership interest (as a percent)	51.00%
Noncontrolling interest, ownership percentage by noncontrolling owners	49.00%
ATC, TIPL
Concentration Risk [Line Items]
Ownership interest (as a percent)	63.00%
Corporate Joint Venture | Ghana
Concentration Risk [Line Items]
Ownership interest (as a percent)	51.00%
Noncontrolling interest, ownership percentage by noncontrolling owners	49.00%
Corporate Joint Venture | South Africa
Concentration Risk [Line Items]
Ownership interest (as a percent)	75.00%
Noncontrolling interest, ownership percentage by noncontrolling owners	25.00%

DESCRIPTION OF BUSINESS, BASI42

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 1,125.4	$ 802.1	$ 712.8
Restricted cash	153.5	152.8	145.5
Total cash and cash equivalents and restricted cash	$ 1,278.9	$ 954.9	$ 858.3	$ 936.5

DESCRIPTION OF BUSINESS, BASI43

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Distributions in excess of earnings	$ 1,085.7		$ 1,058.1
Impact on revenue as a result ofd applying new standard	1,741.8
Unearned revenue recognized	17.9
Revenue recognized	0.1
Decrease in contract assets attributable to revenue recognized (less than)	0.1
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Distributions in excess of earnings		$ 38.4
Impact on revenue as a result ofd applying new standard	$ 2.6

DESCRIPTION OF BUSINESS, BASI44

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	$ 1,741.8
U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	962.8
Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	273
EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	174.2
Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	331.8
Power and fuel pass-through revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	131.7
Power and fuel pass-through revenue | U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0
Power and fuel pass-through revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	92.3
Power and fuel pass-through revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	34.9
Power and fuel pass-through revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	4.5
Other non-lease revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	93.9
Other non-lease revenue | U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	67.7
Other non-lease revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	1.9
Other non-lease revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0.6
Other non-lease revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	23.7
Total non-lease property revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	225.6
Total non-lease property revenue | U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	67.7
Total non-lease property revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	94.2
Total non-lease property revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	35.5
Total non-lease property revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	28.2
Services revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	31.4
Services revenue | U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	31.4
Services revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0
Services revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0
Services revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0
Total non-lease revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	257
Total non-lease revenue | U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	99.1
Total non-lease revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	94.2
Total non-lease revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	35.5
Total non-lease revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	28.2
Property lease revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	1,484.8
Property lease revenue | U.S.
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	863.7
Property lease revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	178.8
Property lease revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	138.7
Property lease revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	$ 303.6

DESCRIPTION OF BUSINESS, BASI45

DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Information About Receivables, Contract Assets and Contract Liabilities From Contract With Tenants (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Contract Assets And Liabilities From Contracts With Customers [Line Items]
Prepaid and other current assets	$ 571,200		$ 568,600
Notes receivable and other non-current assets	990,300		950,100
Other non-current liabilities	1,246,000		$ 1,244,200
Non-lease revenue
Schedule of Contract Assets And Liabilities From Contracts With Customers [Line Items]
Accounts receivable	234,000	$ 222,200
Prepaid and other current assets	73,300	79,700
Notes receivable and other non-current assets	23,500	24,200
Unearned revenue	33,300	26,600
Other non-current liabilities	$ 65,200	$ 68,500

PREPAID AND OTHER CURRENT ASS46

PREPAID AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid operating ground leases	$ 150,600	$ 148,600
Prepaid income tax	136,500	136,500
Unbilled receivables	110,700	107,900
Value added tax and other consumption tax receivables	63,600	64,200
Prepaid assets	42,500	39,600
Other miscellaneous current assets	67,300	71,800
Prepaid and other current assets	$ 571,200	$ 568,600

GOODWILL AND OTHER INTANGIBLE47

GOODWILL AND OTHER INTANGIBLE ASSETS - CHANGES IN THE CARRYING VALUE OF GOODWILL (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 5,638.4
Effect of foreign currency translation	8.7
Goodwill, ending balance	5,647.1
Property | U.S.
Goodwill [Roll Forward]
Goodwill, beginning balance	3,379.2
Effect of foreign currency translation	0
Goodwill, ending balance	3,379.2
Property | Asia
Goodwill [Roll Forward]
Goodwill, beginning balance	1,095
Effect of foreign currency translation	(21.9)
Goodwill, ending balance	1,073.1
Property | EMEA
Goodwill [Roll Forward]
Goodwill, beginning balance	404.9
Effect of foreign currency translation	10.8
Goodwill, ending balance	415.7
Property | Latin America
Goodwill [Roll Forward]
Goodwill, beginning balance	757.3
Effect of foreign currency translation	19.8
Goodwill, ending balance	777.1
Services
Goodwill [Roll Forward]
Goodwill, beginning balance	2
Effect of foreign currency translation	0
Goodwill, ending balance	$ 2

GOODWILL AND OTHER INTANGIBLE48

GOODWILL AND OTHER INTANGIBLE ASSETS - INTANGIBLE ASSETS SUBJECT TO AMORTIZATION (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 16,430.6	$ 16,083
Accumulated Amortization	(4,490.4)	(4,299.7)
Net Book Value	11,940.2	11,783.3
Acquired network location intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	4,922.5	4,858.8
Accumulated Amortization	(1,584.1)	(1,525.3)
Net Book Value	$ 3,338.4	$ 3,333.5
Acquired network location intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives	20 years	20 years
Acquired tenant-related intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 11,431.9	$ 11,150.9
Accumulated Amortization	(2,883.7)	(2,754.7)
Net Book Value	$ 8,548.2	8,396.2
Acquired tenant-related intangibles | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives	15 years
Acquired tenant-related intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives	20 years
Acquired licenses and other intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 60.5	58.8
Accumulated Amortization	(10.2)	(8.1)
Net Book Value	$ 50.3	50.7
Acquired licenses and other intangibles | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives	3 years
Acquired licenses and other intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Lives	20 years
Economic Rights, TV Azteca
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 15.7	14.5
Accumulated Amortization	(12.4)	(11.6)
Net Book Value	$ 3.3	$ 2.9
Estimated Useful Lives	70 years

GOODWILL AND OTHER INTANGIBLE49

GOODWILL AND OTHER INTANGIBLE ASSETS - NARRATIVE (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 202.4	$ 183.2
Weighted Average
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, remaining amortization period			15 years

GOODWILL AND OTHER INTANGIBLE50

GOODWILL AND OTHER INTANGIBLE ASSETS - EXPECTED FUTURE AMORTIZATION EXPENSE (Details) $ in Millions	Mar. 31, 2018USD ($)
Fiscal Year
Remainder of 2018	$ 620.6
2,019	823.8
2,020	804.1
2,021	787.6
2,022	783.1
2,023	$ 778.7

ACCRUED EXPENSES (Details)

ACCRUED EXPENSES (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued property and real estate taxes	$ 156.9	$ 154.4
Amounts payable to tenants	62	60.8
Accrued rent	57.4	54
Payroll and related withholdings	54.1	82.2
Accrued pass-through costs	52.9	59.7
Accrued income tax payable	35.7	15.3
Accrued pass-through taxes	35.5	25.3
Accrued construction costs	21.9	31.9
Other accrued expenses	349	370.7
Total accrued expenses	$ 825.4	$ 854.3

LONG-TERM OBLIGATIONS - SCHEDUL

LONG-TERM OBLIGATIONS - SCHEDULE OF LONG-TERM OBLIGATIONS (Details) - USD ($) $ in Millions	Mar. 02, 2017	Mar. 31, 2018	Mar. 29, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Other debt, including capital lease obligations		$ 166.2		$ 165.5
Total		21,372		20,205.1
Less current portion long-term obligations		(2,803.2)		(774.8)
Long-term obligations		18,568.8		19,430.3
American Tower Corporation
Debt Instrument [Line Items]
Long-term debt		17,666.5		16,494.5
American Tower subsidiary
Debt Instrument [Line Items]
Long-term debt		3,539.3		3,545.1
2018 Term Loan
Debt Instrument [Line Items]
Long-term debt		1,499.2	$ 1,500	0
2013 Credit Facility | Credit Facility
Debt Instrument [Line Items]
Line of credit		1,641.8		2,075.6
2013 Term Loan | Unsecured debt
Debt Instrument [Line Items]
Long-term debt		994.7		994.5
2014 Credit Facility | Credit Facility
Debt Instrument [Line Items]
Line of credit		600		495
3.40% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 999.9		999.8
Long-term debt, stated interest rate (as a percent)		3.40%
2.800% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 746.7		746.3
Long-term debt, stated interest rate (as a percent)		2.80%
5.050% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 698.2		698
Long-term debt, stated interest rate (as a percent)		5.05%
3.300% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 746.3		746
Long-term debt, stated interest rate (as a percent)		3.30%
3.450% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 645.4		645.1
Long-term debt, stated interest rate (as a percent)		3.45%
5.900% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 498		497.8
Long-term debt, stated interest rate (as a percent)		5.90%
2.250% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 564.5		572.4
Long-term debt, stated interest rate (as a percent)		2.25%
4.70% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 696.9		696.7
Long-term debt, stated interest rate (as a percent)		4.70%
3.50% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 991.3		990.9
Long-term debt, stated interest rate (as a percent)		3.50%
3.000% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 682.4		692.5
Long-term debt, stated interest rate (as a percent)		3.00%
5.00% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 1,002.4		1,002.4
Long-term debt, stated interest rate (as a percent)		5.00%
1.375% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 605.1		589.1
Long-term debt, stated interest rate (as a percent)		1.375%
4.000% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 741.3		741
Long-term debt, stated interest rate (as a percent)		4.00%
4.400% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 495.8		495.6
Long-term debt, stated interest rate (as a percent)		4.40%
3.375% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 985.2		984.8
Long-term debt, stated interest rate (as a percent)		3.375%
3.125% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 397.1		397.1
Long-term debt, stated interest rate (as a percent)		3.125%
3.55% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 743		742.8
Long-term debt, stated interest rate (as a percent)		3.55%
3.600% senior notes | Senior notes
Debt Instrument [Line Items]
Long-term debt		$ 691.3		691.1
Long-term debt, stated interest rate (as a percent)		3.60%
Series 2013-1A and 2A securities | Secured debt | Series 2013-1A securities
Debt Instrument [Line Items]
Long-term debt		$ 0		499.8
Series 2013-1A and 2A securities | Secured debt | Series 2013-2A securities
Debt Instrument [Line Items]
Long-term debt		1,292.2		1,291.8
Series 2018-1A securities | Secured debt | Series 2018-1A securities
Debt Instrument [Line Items]
Long-term debt		493		0
Long-term debt, stated interest rate (as a percent)			3.652%
Series 2015-1 notes | Secured debt
Debt Instrument [Line Items]
Long-term debt		348.2		348
Series 2015-2 notes | Secured debt
Debt Instrument [Line Items]
Long-term debt		520.3		520.1
India indebtedness | Unsecured debt
Debt Instrument [Line Items]
Long-term debt		518.6		512.6
India preference shares | Mandatorily redeemable preferred stock
Debt Instrument [Line Items]
Long-term debt		25.6		26.1
Preferred stock, dividend rate percentage	10.25%
Shareholder loans | Unsecured debt
Debt Instrument [Line Items]
Long-term debt		101.8		100.6
Other subsidiary debt | Unsecured debt
Debt Instrument [Line Items]
Long-term debt		$ 239.6		$ 246.1

LONG-TERM OBLIGATIONS - NARRATI

LONG-TERM OBLIGATIONS - NARRATIVE (Details) $ in Millions, ₨ in Billions	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Mar. 31, 2018INR (₨)	Mar. 29, 2018USD ($)	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 2,803.2				$ 774.8
Restricted Cash	88.8
Borrowings under credit facilities	1,748.3	$ 1,997
2018 Term Loan
Debt Instrument [Line Items]
Long-term Debt	1,499.2			$ 1,500	0
Outstanding Principal Balance	1,500
2013 Credit Facility | Credit Facility
Debt Instrument [Line Items]
Outstanding Principal Balance	1,641.8
Borrowings under credit facilities	620
Repayment of indebtedness under credit facility	1,100
2014 Credit Facility | Credit Facility
Debt Instrument [Line Items]
Outstanding Principal Balance	600
Borrowings under credit facilities	1,100
Repayment of indebtedness under credit facility	945
Repayments of Long-term Lines of Credit	445
Viom Transaction
Debt Instrument [Line Items]
Current portion of long-term obligations	223.6		₨ 14.6
Senior notes | 3.40% senior notes
Debt Instrument [Line Items]
Long-term Debt	$ 999.9				999.8
Long-term debt, stated interest rate (as a percent)	3.40%		3.40%
Series 2018-1A securities | Secured debt | Series 2018-1A securities
Debt Instrument [Line Items]
Long-term Debt	$ 493				$ 0
Long-term debt, stated interest rate (as a percent)				3.652%
Outstanding Principal Balance				$ 500
Series 2018-1R securities | Secured debt | Series 2018-1A securities
Debt Instrument [Line Items]
Long-term debt, stated interest rate (as a percent)				4.459%
Series 2018-1R securities | Affiliate | Secured debt | Series 2018-1A securities
Debt Instrument [Line Items]
Outstanding Principal Balance				$ 26.4

LONG-TERM OBLIGATIONS - SCHED54

LONG-TERM OBLIGATIONS - SCHEDULE OF LINES OF CREDIT (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)renewal_period
2013 Credit Facility | Credit Facility
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 1,641.8
Undrawn letters of credit	$ 4
Current commitment fee (as a percent)	0.125%
Borrowings on line of credit	$ 140
Line of Credit Facility, Interest Rate at Period End	4.75%
2013 Credit Facility | Credit Facility | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.125%
2013 Credit Facility | Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.125%
2014 Credit Facility | Credit Facility
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 600
Undrawn letters of credit	$ 6.3
Current commitment fee (as a percent)	0.15%
Optional renewal periods | renewal_period	2
2014 Credit Facility | Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
2013 Term Loan | Unsecured debt
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 1,000
2013 Term Loan | Unsecured debt | LIBOR
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
2018 Term Loan
Line of Credit Facility [Line Items]
Outstanding Principal Balance	$ 1,500
2018 Term Loan | LIBOR
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.875%

FAIR VALUE MEASUREMENTS - ASSET

FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED AT FAIR VALUE ON A RECURRING BASIS (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Short-term investments	$ 389.4	$ 1
Fair Value, Measurements, Recurring | Level 1
Assets:
Short-term investments	0	1
Embedded derivative in lease agreement	0	0
Liabilities:
Acquisition-related contingent consideration	0	0
Fair Value, Measurements, Recurring | Level 1 | Interest rate swap agreements
Liabilities:
Interest rate swap agreements	0	0
Fair value of debt related to interest rate swap agreements	(43)	(24.5)
Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term investments	389.4	0
Embedded derivative in lease agreement	0	0
Liabilities:
Acquisition-related contingent consideration	0	0
Fair Value, Measurements, Recurring | Level 2 | Interest rate swap agreements
Liabilities:
Interest rate swap agreements	45.4	29
Fair value of debt related to interest rate swap agreements	0	0
Fair Value, Measurements, Recurring | Level 3
Assets:
Short-term investments	0	0
Embedded derivative in lease agreement	12.2	12.4
Liabilities:
Acquisition-related contingent consideration	1	10.1
Fair Value, Measurements, Recurring | Level 3 | Interest rate swap agreements
Liabilities:
Interest rate swap agreements	0	0
Fair value of debt related to interest rate swap agreements	$ 0	$ 0

FAIR VALUE MEASUREMENTS - NARRA

FAIR VALUE MEASUREMENTS - NARRATIVE (Details) - USD ($)	Feb. 28, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		$ 386,700,000
Marketable securities, unrealized gain		2,700,000
Business combination, contingent consideration arrangements, range of outcomes, value, low		0
Business combination, contingent consideration arrangements, range of outcomes, value, high		1,000,000
Tenant-related intangibles net book value		11,940,200,000	$ 11,783,300,000
Debt, long-term and short-term, combined amount		21,372,000,000	20,205,100,000
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value		21,400,000,000	20,600,000,000
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		13,000,000,000	13,300,000,000
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		8,400,000,000	7,300,000,000
Tenant-related intangible assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tenant-related intangibles net book value		8,548,200,000	$ 8,396,200,000
Tata Teleservices Limited | Tenant-related intangible assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tenant-related intangibles net book value		$ 417,000,000
Tower and network | Aircel, Asia
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of intangible assets	$ 40,100,000
Tenant-related intangible assets | Aircel, Asia
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of intangible assets	$ 107,300,000

INCOME TAXES - NARRATIVE (Detai

INCOME TAXES - NARRATIVE (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact the ETR	$ 102,800,000	$ 105,800,000
Unrecognized tax benefits, increase resulting from current period tax positions	2,100,000
Unrecognized tax benefits, reduction due to a settlements with authorities	2,600,000
Unrecognized tax benefits, reduction due to positions taken in prior period	1,700,000
Unrecognized tax benefits, income tax penalties and interest accrued	28,900,000	$ 29,000,000
Minimum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	0
Maximum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	$ 8,700,000

INCOME TAXES - SCHEDULE OF PEN

INCOME TAXES - SCHEDULE OF PENALTIES AND INCOME TAX RELATED EXPENSES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Penalties and income tax-related interest expense	$ 1	$ 1.3

STOCK-BASED COMPENSATION - NARR

STOCK-BASED COMPENSATION - NARRATIVE (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP, discount rate (as a percent)	15.00%
Performance grant, shares granted based on first, Ssecond and third year's performance period (in shares)					120,171
Stock-based compensation expense	$ 42.7	$ 36.2
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 166.1
Expected recognition of stock award compensation expense weighted average period in years	3 years
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years		3 years
Total unrecognized compensation expense	$ 41.8
Expected recognition of stock award compensation expense weighted average period in years	2 years
Performance grant, shares granted (in shares)	131,311	154,520	154,520	169,340
Stock-based compensation expense	$ 8.8
Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential target shares	0.00%
Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential target shares	200.00%
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 10
Expected recognition of stock award compensation expense weighted average period in years	2 years
2007 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issuable under stock incentive plan	7,600,000
2007 Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
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

STOCK-BASED COMPENSATION - SUMM

STOCK-BASED COMPENSATION - SUMMARY OF STOCK-BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense	$ 42.7	$ 36.2
Stock-based compensation expense capitalized as property and equipment	$ 0.5	$ 0.5

STOCK-BASED COMPENSATION - SU61

STOCK-BASED COMPENSATION - SUMMARY OF THE COMPANY'S OPTION ACTIVITY (Details) - Employee Stock Option	3 Months Ended
	Mar. 31, 2018shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding as of beginning of period (in shares)	5,557,561
Granted (in shares)	0
Exercised (in shares)	(243,118)
Forfeited (in shares)	0
Expired (in shares)	0
Outstanding as of end of period (in shares)	5,314,443

STOCK-BASED COMPENSATION - SU62

STOCK-BASED COMPENSATION - SUMMARY OF THE COMPANY'S RESTRICTED STOCK UNIT ACTIVITY (Details) - shares	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
RSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Outstanding as of beginning of period (in shares)	1,742,725
Granted (in shares)	671,618
Vested (in shares)	(644,022)
Forfeited (in shares)	(12,063)
Outstanding as of end of period (in shares)	1,758,258		1,742,725
PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Outstanding as of beginning of period (in shares)	444,031
Granted (in shares)	131,311
Vested (in shares)	(120,171)
Forfeited (in shares)	0
Outstanding as of end of period (in shares)	455,171		444,031
Vesting period	3 years		3 years
Three year performance grant, shares granted (in shares)	131,311	154,520	154,520	169,340

REDEEMABLE NONCONTROLLING INT63

REDEEMABLE NONCONTROLLING INTERESTS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Apr. 21, 2016
Noncontrolling Interest [Line Items]
Adjustments to additional paid in capital, Increase in carrying amount of redeemable preferred stock	$ (28.1)
Decrease in noncontrolling Interest	28.1	$ 0
Adjustment to noncontrolling interest redemption value	$ 17.5	$ 0
Viom Transaction
Noncontrolling Interest [Line Items]
Percentage of interests acquired	63.00%		51.00%
Adjustments to additional paid in capital, Increase in carrying amount of redeemable preferred stock	$ 28.1
Noncontrolling interest, ownership percentage by noncontrolling owners	37.00%		49.00%
Decrease in noncontrolling Interest	$ 28.1
Adjustments to additional paid in capital, reclassified from other comprehensive loss	78.8
Adjustment to noncontrolling interest redemption value	$ 17.5

REDEEMABLE NONCONTROLLING INT64

REDEEMABLE NONCONTROLLING INTERESTS - Changes in Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes In Redeemable Noncontrolling Interests [Roll Forward]
Balance as of January 1,	$ 1,126.2	$ 1,091.3
Net loss attributable to noncontrolling interests	(28.1)	(12.3)
Adjustment to noncontrolling interest redemption value	17.5	0
Adjustment to noncontrolling interest due to merger	(28.1)	0
Foreign currency translation adjustment attributable to noncontrolling interests	(22.3)	51.1
Balance as of March 31,	$ 1,065.2	$ 1,130.1

EQUITY - NARRATIVE (Details)

EQUITY - NARRATIVE (Details) - USD ($)	Feb. 15, 2018	Mar. 31, 2015	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 31, 2011
Class of Stock [Line Items]
Proceeds from stock options			$ 20,000,000	$ 36,900,000
Stock repurchased (in shares)			8,909,000		8,909,000
Stock repurchased			$ 974,000,000		$ 974,000,000
Accrued dividend RSU			7,100,000
Dividends Declared and Paid
Class of Stock [Line Items]
Paid dividend RSU			$ 4,100,000
2011 Buyback
Class of Stock [Line Items]
Stock repurchase program, authorized amount						$ 1,500,000,000
Stock repurchased (in shares)			12,356,054
Stock repurchased			$ 1,200,000,000
2017 Buyback
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 2,000,000,000
Preferred Stock - Series B
Class of Stock [Line Items]
Depository shares, percentage of preferred shares (in shares)	0.1
Convertible Preferred Stock Subject to Mandatory Redemption
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share)			$ 0.01		$ 0.01
Convertible Preferred Stock Subject to Mandatory Redemption | Preferred Stock - Series B
Class of Stock [Line Items]
Preferred stock, dividend rate percentage (in percent)			5.50%		5.50%
Convertible Preferred Stock Subject to Mandatory Redemption | Preferred Stock - Series B | Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		1,375,000
Preferred stock, dividend rate percentage (in percent)		5.50%
Preferred stock, par value (in dollars per share)		$ 0.01
Conversion factor, preferred stock (in shares)	8.7420
Conversion factor, depository shares, preferred stock	0.8742
Conversion of preferred stock (shares)	12,020,064		(1,375,000)
Dividends paid to holder of Series B Preferred Stock	$ 18,900,000

EQUITY - DISTRIBUTIONS (Details

EQUITY - DISTRIBUTIONS (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 27, 2018	Mar. 08, 2018	Feb. 15, 2018	Jan. 22, 2018	Jan. 16, 2018	Dec. 06, 2017	Mar. 31, 2018	Mar. 31, 2017
Dividends Payable [Line Items]
Distribution per common share (in dollars per share)							$ 0.75	$ 0.62
Aggregate Payment Amount on common stock							$ 304.3	$ 250.4
Aggregate Payment Amount on preferred stock							$ 18.9	$ 26.8
Common Stock
Dividends Payable [Line Items]
Distribution per common share (in dollars per share)		$ 0.75				$ 0.70
Aggregate Payment Amount on common stock					$ 300.2
Preferred Stock - Series B | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Distribution per preferred share (in dollars per share)				$ 13.75
Aggregate Payment Amount on preferred stock			$ 18.9
Subsequent Event | Common Stock
Dividends Payable [Line Items]
Aggregate Payment Amount on common stock	$ 331.2

EARNINGS PER COMMON SHARE - SCH

EARNINGS PER COMMON SHARE - SCHEDULE OF BASIC AND DILUTED NET INCOME PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to American Tower Corporation Stockholders	$ 285.2	$ 316.1
Dividends on preferred stock	(9.4)	(26.8)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 275.8	$ 289.3
Basic weighted average common shares outstanding (in shares)	435,124	427,279
Dilutive securities (in shares)	3,396	2,920
Diluted weighted average common shares outstanding (in shares)	438,520	430,199
Basic net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 0.63	$ 0.68
Diluted net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 0.63	$ 0.67

EARNINGS PER COMMON SHARE - S68

EARNINGS PER COMMON SHARE - SCHEDULE OF SHARES EXCLUDED FROM COMPUTATION OF EARNINGS PER SHARE (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from dilutive effect	118	159
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from dilutive effect	0	30
Preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from dilutive effect	5,904	17,547

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - NARRATIVE (Details) ₨ in Millions	Dec. 05, 2016USD ($)	Dec. 05, 2016INR (₨)	Mar. 27, 2015USD ($)communications_siterenewal_period	Dec. 31, 2000tower	Mar. 31, 2018USD ($)renewal_periodtowershares	Dec. 31, 2017tower	Dec. 31, 2016tower
Loss Contingencies [Line Items]
Foreign income tax assessment	$ 69,800,000	₨ 4,750
Lessor agreements, term of contract					10 years
Verizon Transaction
Loss Contingencies [Line Items]
Capital leased assets, number of units (in number of communication sites or towers) | communications_site			11,250
Right to lease, weighted average term			28 years
Aggregate purchase option price for towers | $			$ 5,000,000,000
Customer lease, initial term			10 years
Successive terms to renew lease (in numbers of terms) | renewal_period			8
Renewal term			5 years
AT&T Transaction
Loss Contingencies [Line Items]
Capital leased assets, number of units (in number of communication sites or towers)						2,340
Aggregate purchase option price for towers | $					$ 851,100,000
Successive terms to renew lease (in numbers of terms) | renewal_period					4
Renewal term					5 years
Operating lease, term of contract						27 years
Number of communications sites acquired (in number of towers)					88
Purchase price accretion rate (per year)					10.00%
ALLTEL Transaction
Loss Contingencies [Line Items]
Capital leased assets, number of units (in number of communication sites or towers)				1,800
Aggregate purchase option price for towers | $					$ 10,400,000
Number of communications sites acquired (in number of towers)							1,523
Average lease term (in years)				15 years
Number of remaining towers					243
Cash purchase price per tower | $					$ 42,844
Purchase price of tower in shares of common stock (in shares) | shares					769

COMMITMENTS AND CONTINGENCIES70

COMMITMENTS AND CONTINGENCIES - FUTURE MINIMUM RENTAL RECEIPTS UNDER OPERATING LEASE AGREEMENTS (Details) $ in Billions	Mar. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Remainder of 2018	$ 4
2,019	5
2,020	5
2,021	4
2,022	3
Thereafter	11
Total	$ 32

COMMITMENTS AND CONTINGENCIES71

COMMITMENTS AND CONTINGENCIES - FUTURE MINIMUM RENTAL PAYMENTS UNDER NON-CANCELABLE OPERATING LEASES (Details) $ in Billions	Mar. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Remainder of 2018	$ 1
2,019	1
2,020	1
2,021	1
2,022	1
Thereafter	6
Total	$ 11

ACQUISITIONS - SCHEDULE OF MERG

ACQUISITIONS - SCHEDULE OF MERGER AND ACQUISITION RELATED COSTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Business Combinations [Abstract]
Acquisition and merger related expenses	$ 1.4	$ 5.7
Integration costs	$ 0.5	$ 4.6

ACQUISITIONS - NARRATIVE (Detai

ACQUISITIONS - NARRATIVE (Details) $ in Millions, ₨ in Billions	Mar. 31, 2018USD ($)site	Mar. 31, 2018INR (₨)	Nov. 17, 2017USD ($)communications_site	Nov. 17, 2017INR (₨)communications_site	Mar. 31, 2018USD ($)site	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Revenue of acquiree since acquisition date					$ 0.9
Business combination gross margin					0.6
Accounts payable	$ 118.7				$ 118.7	$ 142.9
Idea Cellular Limited
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | communications_site			9,900	9,900
Total consideration			$ 611.4	₨ 40
Percentage of interests acquired			100.00%	100.00%
Vodafone
Business Acquisition [Line Items]
Purchase price	$ 586.9
Vodafone | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | site	10,238				10,238
Total consideration	$ 586.9	₨ 38.2
Other Acquisitions
Business Acquisition [Line Items]
Purchase price					$ 93.2
Accounts payable	$ 1.6				$ 1.6
Other Acquisitions | Communication Sites
Business Acquisition [Line Items]
Number of communications sites acquired (in number of towers) | site	338				338
Purchase price					$ 93.2

ACQUISITIONS - SCHEDULE OF PREL

ACQUISITIONS - SCHEDULE OF PRELIMINARY ALLOCATION OF THE PURCHASE PRICE (Details) $ in Millions	Mar. 31, 2018USD ($)site	Mar. 31, 2018USD ($)site	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Asset Acquisition:
Current assets	$ 2,797.4	$ 2,797.4		$ 2,038.1
Property and equipment	11,294.8	11,294.8		11,101
Intangible assets	11,940.2	11,940.2		11,783.3
Current liabilities	(4,544.7)	(4,544.7)		(2,512.1)
Other non-current liabilities	(1,246)	(1,246)		(1,244.2)
Goodwill	5,647.1	5,647.1		5,638.4
Acquisition and merger related expenses		1.4	$ 5.7
Tenant-related intangible assets
Asset Acquisition:
Intangible assets	8,548.2	$ 8,548.2		8,396.2
Tenant-related intangible assets | Maximum
Asset Acquisition:
Estimated useful lives		20 years
Network location intangible assets
Asset Acquisition:
Intangible assets	3,338.4	$ 3,338.4		$ 3,333.5
Network location intangible assets | Maximum
Asset Acquisition:
Estimated useful lives		20 years		20 years
Vodafone
Asset Acquisition:
Current assets	16.6	$ 16.6
Non-current assets	9.9	9.9
Property and equipment	197.6	197.6
Current liabilities	(15.8)	(15.8)
Other non-current liabilities	(12)	(12)
Net assets acquired	586.9	586.9
Goodwill	0	0
Fair value of net assets acquired	586.9	586.9
Debt assumed	0
Purchase price	586.9
Acquisition and merger related expenses	1.3
Vodafone | Tenant-related intangible assets
Asset Acquisition:
Intangible assets	326.1	$ 326.1
Vodafone | Tenant-related intangible assets | Maximum
Asset Acquisition:
Estimated useful lives		20 years
Vodafone | Network location intangible assets
Asset Acquisition:
Intangible assets	64.5	$ 64.5
Vodafone | Network location intangible assets | Maximum
Asset Acquisition:
Estimated useful lives		20 years
Other
Asset Acquisition:
Current assets	1.3	$ 1.3
Non-current assets	1.1	1.1
Property and equipment	30.1	30.1
Current liabilities	(0.7)	(0.7)
Other non-current liabilities	(4.6)	(4.6)
Net assets acquired	93.2	93.2
Goodwill	0	0
Fair value of net assets acquired	93.2	93.2
Debt assumed		0
Purchase price		93.2
Other | Tenant-related intangible assets
Asset Acquisition:
Intangible assets	42.5	$ 42.5
Other | Tenant-related intangible assets | Maximum
Asset Acquisition:
Estimated useful lives		20 years
Other | Network location intangible assets
Asset Acquisition:
Intangible assets	$ 23.5	$ 23.5
Other | Network location intangible assets | Maximum
Asset Acquisition:
Estimated useful lives		20 years
Communication Sites | Vodafone
Asset Acquisition:
Number of sites acquired | site	10,238	10,238
Communication Sites | Other
Asset Acquisition:
Purchase price		$ 93.2
Number of sites acquired | site	338	338
Communication Sites | Other | PERU
Asset Acquisition:
Number of sites acquired | site	35	35

ACQUISITIONS - PRO FORMA INFORM

ACQUISITIONS - PRO FORMA INFORMATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Business Combinations [Abstract]
Pro forma revenues	$ 1,780.3	$ 1,690
Pro forma net income attributable to American Tower Corporation common stockholders	$ 275.8	$ 284.9
Pro forma net income per common share amounts:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 0.63	$ 0.67
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 0.63	$ 0.66

BUSINESS SEGMENTS (Details)

BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total segment revenues	$ 1,741.8	$ 1,616.2
Segment operating expenses	518.9	491.8
Segment gross margin	1,225.6	1,127.1
Segment selling, general, administrative and development expense	124.5	93.3
Segment operating profit	1,101.1	1,033.8
Stock-based compensation expense	42.7	36.2
Other selling, general, administrative and development expense	38.7	36.2
Depreciation, amortization and accretion	446.3	421.1
Other expense	324.2	206.1
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	249.2	334.2
Total assets	34,372.7	32,057.4	$ 33,214.3
Impairment charges	147.4
Operating Expense
Segment Reporting Information [Line Items]
Stock-based compensation expense	1	0.9
Selling General Administrative and Development Expense
Segment Reporting Information [Line Items]
Stock-based compensation expense	41.7	35.3
TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	2.7	2.7
Operating Segments | Property
Segment Reporting Information [Line Items]
Total segment revenues	1,710.4	1,594.1
Segment operating expenses	506.7	485.5
Segment gross margin	1,206.4	1,111.3
Segment selling, general, administrative and development expense	121	90.2
Segment operating profit	1,085.4	1,021.1
Total assets	34,119	31,778.1
Operating Segments | Property | TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	2.7	2.7
Operating Segments | Property | U.S.
Segment Reporting Information [Line Items]
Total segment revenues	931.4	891.9
Segment operating expenses	186.3	181.4
Segment gross margin	745.1	710.5
Segment selling, general, administrative and development expense	35.4	34.6
Segment operating profit	709.7	675.9
Total assets	18,894.7	18,768.4
Operating Segments | Property | U.S. | TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	0	0
Operating Segments | Property | Asia
Segment Reporting Information [Line Items]
Total segment revenues	273	275.5
Segment operating expenses	157.9	149.4
Segment gross margin	115.1	126.1
Segment selling, general, administrative and development expense	44.2	20.5
Segment operating profit	70.9	105.6
Total assets	5,796.8	4,765.9
Operating Segments | Property | Asia | TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	0	0
Operating Segments | Property | EMEA
Segment Reporting Information [Line Items]
Total segment revenues	174.2	150.4
Segment operating expenses	59.1	61.5
Segment gross margin	115.1	88.9
Segment selling, general, administrative and development expense	16.8	16.5
Segment operating profit	98.3	72.4
Total assets	3,343.4	3,054.5
Operating Segments | Property | EMEA | TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	0	0
Operating Segments | Property | Latin America
Segment Reporting Information [Line Items]
Total segment revenues	331.8	276.3
Segment operating expenses	103.4	93.2
Segment gross margin	231.1	185.8
Segment selling, general, administrative and development expense	24.6	18.6
Segment operating profit	206.5	167.2
Total assets	6,084.1	5,189.3
Operating Segments | Property | Latin America | TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	2.7	2.7
Operating Segments | Services
Segment Reporting Information [Line Items]
Total segment revenues	31.4	22.1
Segment operating expenses	12.2	6.3
Segment gross margin	19.2	15.8
Segment selling, general, administrative and development expense	3.5	3.1
Segment operating profit	15.7	12.7
Total assets	47	49.2
Operating Segments | Services | TV Azteca
Segment Reporting Information [Line Items]
Interest income, TV Azteca, net	0	0
Other
Segment Reporting Information [Line Items]
Stock-based compensation expense	42.7	36.2
Other selling, general, administrative and development expense	38.7	36.2
Depreciation, amortization and accretion	446.3	421.1
Other expense	324.2	206.1
Total assets	$ 206.7	$ 230.1

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details)	Apr. 03, 2018site
Subsequent Event | Telkom Kenya Limited | Kenya
Subsequent Event [Line Items]
Number of sites acquired	723