American Tower (AMT) 10-K 27 Feb 19 2018 Q4 Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Feb. 20, 2019	Jun. 30, 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-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q4
Amendment Flag	false
Entity Common Stock, Shares Outstanding		441,134,906
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 63.1

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 1,208.7	$ 802.1
Restricted cash	96.2	152.8
Short-term investments	0	1
Accounts receivable, net	459	513.6
Prepaid and other current assets	621.2	568.6
Total current assets	2,385.1	2,038.1
PROPERTY AND EQUIPMENT, net	11,247.1	11,101
GOODWILL	5,501.9	5,638.4
OTHER INTANGIBLE ASSETS, net	11,174.3	11,783.3
DEFERRED TAX ASSET	157.7	204.4
DEFERRED RENT ASSET	1,581.7	1,499
NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS	962.6	950.1
TOTAL	33,010.4	33,214.3
CURRENT LIABILITIES:
Accounts payable	130.8	142.9
Accrued expenses	948.3	854.3
Distributions payable	377.4	304.4
Accrued interest	174.5	166.9
Current portion of long-term obligations	2,754.8	774.8
Unearned revenue	304.1	268.8
Total current liabilities	4,689.9	2,512.1
LONG-TERM OBLIGATIONS	18,405.1	19,430.3
ASSET RETIREMENT OBLIGATIONS	1,210	1,175.3
DEFERRED TAX LIABILITY	535.9	898.1
OTHER NON-CURRENT LIABILITIES	1,265.1	1,244.2
Total liabilities	26,106	25,260
COMMITMENTS AND CONTINGENCIES
REDEEMABLE NONCONTROLLING INTERESTS	1,004.8	1,126.2
EQUITY (shares in thousands):
Common stock: $.01 par value; 1,000,000 shares authorized; 451,617 and 437,729 shares issued; and 441,060 and 428,820 shares outstanding, respectively	4.5	4.4
Additional paid-in capital	10,380.8	10,247.5
Distributions in excess of earnings	(1,199.5)	(1,058.1)
Accumulated other comprehensive loss	(2,642.9)	(1,978.3)
Treasury stock (10,557 and 8,909 shares at cost, respectively)	(1,206.8)	(974)
Total American Tower Corporation equity	5,336.1	6,241.5
Noncontrolling interests	563.5	586.6
Total equity	5,899.6	6,828.1
TOTAL	33,010.4	33,214.3
Convertible Preferred Stock Subject to Mandatory Redemption | 5.50%, Series B, 1,375 shares issued, 0 and 1,375 shares outstanding; aggregate liquidation value of $0.0 and $1.4, respectively
EQUITY (shares in thousands):
Preferred stock: $.01 par value; 20,000 shares authorized;	0	0
Preferred stock | Convertible Preferred Stock Subject to Mandatory Redemption | 5.50%, Series B, 1,375 shares issued, 0 and 1,375 shares outstanding; aggregate liquidation value of $0.0 and $1.4, respectively
EQUITY (shares in thousands):
Total equity	$ 0	$ 0

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 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	451,617,000	437,729,000
Common stock, shares outstanding	441,060,000	428,820,000
Treasury stock, shares	10,557,000	8,909,000
Series B Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	5.50%	5.50%
Preferred stock, shares issued	1,375,000	1,375,000
Preferred stock, shares outstanding	0	1,375,000
Preferred stock, aggregate liquidation value	$ 0	$ 1.4
Preferred stock
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock | Series A Preferred Stock | 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, dividend rate, percentage	5.25%

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES:
Property	$ 7,314.7	$ 6,565.9	$ 5,713.1
Total operating revenues	7,440.1	6,663.9	5,785.7
OPERATING EXPENSES:
Property (including stock-based compensation expense of $2.4, $2.1 and $1.7, respectively)	2,128.7	2,022	1,762.7
Depreciation, amortization and accretion	2,110.8	1,715.9	1,525.6
Selling, general, administrative and development expense (including stock-based compensation expense of $134.2, $105.6, and $87.5, respectively)	733.2	637	543.4
Other operating expenses	513.3	256	73.3
Total operating expenses	5,535.1	4,665.5	3,932.7
OPERATING INCOME	1,905	1,998.4	1,853
OTHER INCOME (EXPENSE):
(Loss) gain on retirement of long-term obligations	(3.3)	(70.2)	1.2
Other income (expense) (including foreign currency (losses) gains of ($4.5), $26.4, and ($48.9), respectively)	23.8	31.3	(47.7)
Total other expense	(750.4)	(742.3)	(727.1)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	1,154.6	1,256.1	1,125.9
Income tax benefit (provision)	110.1	(30.7)	(155.5)
NET INCOME	1,264.7	1,225.4	970.4
Net (income) loss attributable to noncontrolling interests	(28.3)	13.5	(14)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION STOCKHOLDERS	1,236.4	1,238.9	956.4
Dividends on preferred stock	(9.4)	(87.4)	(107.1)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 1,227	$ 1,151.5	$ 849.3
NET INCOME PER COMMON SHARE AMOUNTS:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 2.79	$ 2.69	$ 2
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 2.77	$ 2.67	$ 1.98
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING:
BASIC (in shares)	439,606	428,181	425,143
DILUTED (in shares)	442,960	431,688	429,283
Services
REVENUES:
Services	$ 125.4	$ 98	$ 72.6
OPERATING EXPENSES:
Services (including stock-based compensation expense of $0.9, $0.8 and $0.7, respectively)	49.1	34.6	27.7
TV Azteca
OTHER INCOME (EXPENSE):
Interest (expense) income, TV Azteca, each net of interest expense of $1.2	(0.1)	10.8	10.9
Interest expense	(1.2)	(1.2)	(1.2)
Excluding TV Azteca
OTHER INCOME (EXPENSE):
Interest income	54.7	35.4	25.6
Interest expense	$ (825.5)	$ (749.6)	$ (717.1)

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation expense	$ 137.5	$ 108.5	$ 89.9
TV Azteca
Interest expense	1.2	1.2	1.2
Property
Stock-based compensation expense	2.4	2.1	1.7
Services
Stock-based compensation expense	0.9	0.8	0.7
Selling General Administrative And Development Expense
Stock-based compensation expense	134.2	105.6	87.5
Other Expense
Foreign currency gain (loss)	$ (4.5)	$ 26.4	$ (48.9)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 1,264.7	$ 1,225.4	$ 970.4
Other comprehensive (loss) income:
Changes in fair value of cash flow hedges, each net of tax expense of $0	(0.1)	(0.4)	(0.4)
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	0.3	(0.1)	(0.3)
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	78.8	0	0
Purchase of noncontrolling interest	0.5	0	0
Foreign currency translation adjustments, net of tax (benefit) expense of ($2.6), $1.0, and $3.8, respectively	(869.3)	144.4	(202.9)
Other comprehensive (loss) income	(789.8)	143.9	(203.6)
Comprehensive income	474.9	1,369.3	766.8
Comprehensive loss (income) attributable to non-controlling interest	96.9	(109.4)	18.2
Comprehensive income attributable to American Tower Corporation stockholders	$ 571.8	$ 1,259.9	$ 785

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net change in fair value of cash flow hedges, tax	$ 0	$ 0	$ 0
Reclassification of unrealized losses on cash flow hedges to net income, tax	0	0	0
Foreign currency translation adjustments, tax	$ (2.6)	$ 1	$ 3.8

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	South Africa	Preferred StockSeries A Preferred StockConvertible Preferred Stock Subject to Mandatory Redemption	Preferred StockSeries B Preferred StockConvertible Preferred Stock Subject to Mandatory Redemption	Common Stock	Treasury Stock	Additional Paid-in Capital	Additional Paid-in CapitalSouth Africa	Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) IncomeSouth Africa	Earnings (Distributions) in Excess of Distributions (Earnings)	Noncontrolling Interest	Noncontrolling InterestSouth Africa
BALANCE (shares) at Dec. 31, 2015			6,000,000	1,375,000	426,695,000	(2,810,000)
BALANCE at Dec. 31, 2015	$ 6,712.8		$ 0.1	$ 0	$ 4.3	$ (207.7)	$ 9,690.6		$ (1,837)		$ (998.5)	$ 61
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation related activity (shares)					1,959,000
Stock-based compensation related activity	155.1				$ 0		155.1
Issuance of common stock - stock purchase plan (shares)					88,000
Issuance of common stock—stock purchase plan	7.5				$ 0		7.5
Issuance of stock (shares)					1,171,000
Issuance of stock	120.8				$ 0		120.8
Changes in fair value of cash flow hedges, net of tax	(0.4)								(0.4)			0
Reclassification of unrealized gains on cash flow hedges to net income, net of tax	(0.3)								(0.3)			0
Foreign currency translation adjustment, net of tax	(179.4)								(170.7)		0	(8.7)
Contributions from noncontrolling interest	239.5						69.5		9.1			160.9
Adjustment to/purchase of noncontrolling interest	0
Distributions to noncontrolling interest	(1)											(1)
Common stock distributions declared	(927.8)										(927.8)
Preferred stock dividends declared	(107.1)										(107.1)
Net income	956.5										956.4	0.1
BALANCE (shares) at Dec. 31, 2016			6,000,000	1,375,000	429,913,000	(2,810,000)
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation related activity (shares)					2,121,000
Stock-based compensation related activity	195				$ 0		195
Issuance of common stock - stock purchase plan (shares)					93,000
Issuance of common stock—stock purchase plan	9				$ 0		9
Conversion of preferred stock (shares)			(6,000,000)	0	5,602,000
Conversion of preferred stock	0		$ (0.1)	$ 0	$ 0.1		0
Treasury stock activity (in shares)						(6,099,000)
Treasury stock activity	(766.3)					$ (766.3)
Changes in fair value of cash flow hedges, net of tax	(0.4)								(0.4)
Reclassification of unrealized gains on cash flow hedges to net income, net of tax	(0.1)								(0.1)
Foreign currency translation adjustment, net of tax	76.1								21.5			54.6
Contributions from noncontrolling interest	314.1						0		0			314.1
Adjustment to/purchase of noncontrolling interest	0
Distributions to noncontrolling interest	(14.3)											(14.3)
Common stock distributions declared	(1,128.6)										(1,128.6)
Preferred stock dividends declared	(91.4)										(91.4)
Net income	1,258.8										1,238.9	19.9
BALANCE (shares) at Dec. 31, 2017			0	1,375,000	437,729,000	(8,909,000)
BALANCE at Dec. 31, 2017	6,828.1		$ 0	$ 0	$ 4.4	$ (974)	10,247.5		(1,978.3)		(1,058.1)	586.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation related activity (shares)					1,782,000
Stock-based compensation related activity	190.4				$ 0		190.4
Issuance of common stock - stock purchase plan (shares)					86,000
Issuance of common stock—stock purchase plan	10.2				$ 0		10.2
Conversion of preferred stock (shares)			0	(1,375,000)	12,020,000
Conversion of preferred stock	0		$ 0	$ 0	$ 0.1		(0.1)
Treasury stock activity (in shares)						(1,648,000)
Treasury stock activity	(232.8)					$ (232.8)
Changes in fair value of cash flow hedges, net of tax	(0.1)								(0.1)
Reclassification of unrealized gains on cash flow hedges to net income, net of tax	0.3								0.3
Foreign currency translation adjustment, net of tax	(777.2)								(744.1)			(33.1)
Adjustment to/purchase of noncontrolling interest	28.1	$ (20.5)					(50.7)	$ (16.5)	78.8	$ 0.5			$ (4.5)
Distributions to noncontrolling interest	(15)											(15)
Common stock distributions declared	(1,397.3)										(1,397.3)
Preferred stock dividends declared	(18.9)										(18.9)
Net income	1,265.9										1,236.4	29.5
BALANCE (shares) at Dec. 31, 2018			0	0	451,617,000	(10,557,000)
BALANCE at Dec. 31, 2018	$ 5,899.6		$ 0	$ 0	$ 4.5	$ (1,206.8)	$ 10,380.8		$ (2,642.9)		$ (1,199.5)	$ 563.5

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 1,264.7	$ 1,225.4	$ 970.4
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, amortization and accretion	2,110.8	1,715.9	1,525.6
Stock-based compensation expense	137.5	108.5	89.9
Loss (gain) on investments, unrealized foreign currency loss and other non-cash expense	47.3	(18)	127.4
Impairments, net loss on sale of long-lived assets, non-cash restructuring and merger related expenses	479.6	242.4	50.7
Loss (gain) on early retirement of long-term obligations	3.3	70.2	(1.2)
Amortization of deferred financing costs, debt discounts and premiums and other non-cash interest	22.1	20	17.7
Deferred income taxes	(303)	(86.6)	27
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	(32.1)	(191.1)	11.4
Prepaid and other assets	(101.7)	(179.9)	(80)
Deferred rent asset	(87.6)	(194.4)	(131.7)
Accounts payable and accrued expenses	69.3	95.8	(42.9)
Accrued interest	8.4	9.2	34.4
Unearned revenue	85.8	59.3	16.6
Deferred rent liability	57.9	62.3	67.8
Other non-current liabilities	(14)	(13.4)	18.6
Cash provided by operating activities	3,748.3	2,925.6	2,701.7
CASH FLOWS FROM INVESTING ACTIVITIES
Payments for purchase of property and equipment and construction activities	(913.2)	(803.6)	(682.5)
Payments for acquisitions, net of cash acquired	(1,881.4)	(2,007)	(1,411.3)
Payment for Verizon transaction	0	0	(4.7)
Proceeds from sales of short-term investments and other non-current assets	1,252.2	14.7	13.1
Payments for short-term investments	(1,154.3)	0	(0.8)
Deposits and other	(52.8)	(5)	(16.1)
Cash used for investing activities	(2,749.5)	(2,800.9)	(2,102.3)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings under credit facilities	3,263.3	5,359.4	2,446.8
Proceeds from issuance of senior notes, net	584.9	2,674	3,236.4
Proceeds from term loan	1,500	0	0
Proceeds from issuance of securities in securitization transaction	500	0	0
Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases	(4,884.8)	(6,484.4)	(5,093.7)
(Distributions to) contributions from noncontrolling interest holders, net	(14.4)	264.3	238.5
Purchases of common stock	(232.8)	(766.3)	0
Proceeds from stock options and stock purchase plan	98.9	119.7	92.5
Distributions paid on common stock	(1,323.5)	(1,073)	(886.1)
Distributions paid on preferred stock	(18.9)	(91.4)	(107.1)
Payment for early retirement of long-term obligations	(3.3)	(75.3)	(0.1)
Deferred financing costs and other financing activities	(56.6)	(40)	(26.5)
Purchase of noncontrolling interest	(20.5)	0	0
Cash used for financing activities	(607.7)	(113)	(99.3)
Net effect of changes in foreign currency exchange rates on cash and cash equivalents, and restricted cash	(41.1)	6.7	(26.5)
NET INCREASE IN CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH	350	18.4	473.6
CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH, BEGINNING OF YEAR	954.9	936.5	462.9
CASH AND CASH EQUIVALENTS, AND RESTRICTED CASH, END OF YEAR	$ 1,304.9	$ 954.9	$ 936.5

BUSINESS AND SUMMARY OF SIGNIFI

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Business —American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) is one of the largest global real estate investment trusts and a leading independent owner, operator and developer of multitenant communications real estate. The Company’s primary business is the leasing of space on communications sites to wireless service providers, radio and television broadcast companies, wireless data providers, government agencies and municipalities and tenants in a number of other industries. The Company refers to this business as its property operations. Additionally, the Company offers tower-related services in the United States, which the Company refers to as its services operations. These services include site acquisition, zoning and permitting (“AZP”) and structural analysis, which primarily support the Company’s site leasing business, including the addition of new tenants and equipment on its sites. The Company’s portfolio primarily consists of towers that it owns and towers that it operates pursuant to long-term lease arrangements, as well as distributed antenna system (“DAS”) networks, which provide seamless coverage solutions in certain in-building and certain outdoor wireless environments. In addition to the communications sites in its portfolio, the Company manages rooftop and tower sites for property owners under various contractual arrangements. The Company also holds other telecommunications infrastructure, fiber and property interests that it leases primarily to communications service providers and third-party tower operators. American Tower Corporation is a holding company that conducts its operations through its directly and indirectly owned subsidiaries and joint ventures. ATC’s principal domestic operating subsidiaries are American Towers LLC and SpectraSite Communications, LLC. ATC conducts its international operations primarily through its subsidiary, American Tower International, Inc., which in turn conducts operations through its various international holding and operating subsidiaries and joint ventures. The Company operates as a real estate investment trust for U.S. federal income tax purposes (“REIT”). Accordingly, the Company generally is not required to pay U.S. federal income taxes on income generated by its REIT operations, including the income derived from leasing space on its towers, as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on earnings from its domestic taxable REIT subsidiaries (“TRSs”). In addition, the Company’s international assets and operations, regardless of their classification for U.S. tax purposes, continue to be subject to taxation in the jurisdictions where those assets are held or those operations are conducted. The use of TRSs enables the Company to continue to engage in certain businesses while complying with REIT qualification requirements. The Company may, from time to time, change the election of previously designated TRSs to be included as part of the REIT. As of December 31, 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. In January 2019, a majority of the Company’s operations in France became part of the REIT. Principles of Consolidation and Basis of Presentation —The accompanying consolidated financial statements include the accounts of the Company and those entities in which it has a controlling interest. Investments in entities that the Company does not control are accounted for using the equity 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 December 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 that primarily consists of the Company’s operations in Germany and France, (iii) an approximate 81% controlling interest, and South African investors hold an approximate 19% 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. During the year ended December 31, 2018, the Company purchased approximately 6% of the interest in a subsidiary of the Company in South Africa from one of its local partners for $20.5 million , which resulted in an increase in the Company’s controlling interest from approximately 75% to approximately 81% . The purchase is reflected in the consolidated statements of equity as a reduction of Additional paid-in capital of $16.5 million , a decrease in Accumulated other comprehensive loss of $0.5 million and a reduction in Noncontrolling interest of $4.5 million . Significant Accounting Policies and Use of Estimates —The preparation of financial statements in conformity with accounting principles generally accepted in the United States (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results may differ from those estimates, and such differences could be material to the accompanying consolidated financial statements. The significant estimates in the accompanying consolidated financial statements include impairment of long-lived assets (including goodwill), asset retirement obligations, revenue recognition, rent expense, income taxes and accounting for business combinations and acquisitions of assets. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued as additional evidence for certain estimates or to identify matters that require additional disclosure. Accounts Receivable and Deferred Rent Asset —The Company derives the largest portion of its revenues, corresponding accounts receivable and the related deferred rent asset from a relatively small number of tenants in the telecommunications industry, and 51% of its current-year revenues are derived from four tenants. The Company’s deferred rent asset is associated with non-cancellable tenant leases that contain fixed escalation clauses over the terms of the applicable lease in which revenue is recognized on a straight-line basis over the lease term. The Company mitigates its concentrations of credit risk with respect to notes and trade receivables and the related deferred rent assets by actively monitoring the creditworthiness of its borrowers and tenants. In recognizing tenant revenue, the Company assesses the collectibility of both the amounts billed and the portion recognized in advance of billing on a straight-line basis. This assessment takes tenant credit risk and business and industry conditions into consideration to ultimately determine the collectibility of the amounts billed. To the extent the amounts, based on management’s estimates, may not be collectible, recognition is deferred until such point as collectibility is determined to be reasonably assured. Any amounts that were previously recognized as revenue and subsequently determined to be uncollectible are charged to bad debt expense included in Selling, general, administrative and development expense in the accompanying consolidated statements of operations. Accounts receivable is reported net of allowances for doubtful accounts related to estimated losses resulting from a tenant’s inability to make required payments and allowances for amounts invoiced whose collectibility is not reasonably assured. These allowances are generally estimated based on payment patterns, days past due and collection history, and incorporate changes in economic conditions that may not be reflected in historical trends, such as tenants in bankruptcy, liquidation or reorganization. Receivables are written-off against the allowances when they are determined to be uncollectible. Such determination includes analysis and consideration of the particular conditions of the account. Changes in the allowances were as follows: Year Ended December 31, 2018 2017 2016 Balance as of January 1, $ 131.0 $ 45.9 $ 23.1 Current year increases 157.8 87.2 50.0 Write-offs, recoveries and other (1) (6.4 ) (2.1 ) (27.2 ) Balance as of December 31, $ 282.4 $ 131.0 $ 45.9 _______________ (1) Recoveries includes recognition of revenue resulting from collections of previously reserved amounts. Functional Currency —The functional currency of each of the Company’s foreign operating subsidiaries is normally the respective local currency, except for Costa Rica, where the functional currency is the U.S. Dollar. All foreign currency assets and liabilities held by the subsidiaries are translated into U.S. Dollars at the exchange rate in effect at the end of the applicable fiscal reporting period and all foreign currency revenues and expenses are translated at the average monthly exchange rates. Translation adjustments are reflected in equity as a component of Accumulated other comprehensive loss (“AOCL”) in the consolidated balance sheets and included as a component of Comprehensive income in the consolidated statements of comprehensive income. Gains and losses on foreign currency transactions are reflected in Other expense in the consolidated statements of operations. However, the effect from fluctuations in foreign currency exchange rates on intercompany debt for which repayment is not anticipated in the foreseeable future is reflected in AOCL in the consolidated balance sheets and included as a component of comprehensive income. The Company recorded the following net foreign currency losses: Year Ended December 31, 2018 2017 2016 Foreign currency losses recorded in AOCL $ 385.8 $ 51.6 $ 105.0 Foreign currency losses (gains) recorded in Other expense 4.5 (26.4 ) 48.9 Net foreign currency losses $ 390.3 $ 25.2 $ 153.9 Adoption of Highly Inflationary Accounting in Argentina —The Argentinean economy was deemed to be highly inflationary as of the second quarter of 2018 and, as a result, the Company adopted highly inflationary accounting as of July 1, 2018 for its subsidiary in Argentina. Under highly inflationary accounting, the functional currency of its subsidiary in Argentina is considered to be the U.S. Dollar. All monetary and non-monetary assets and liabilities were remeasured at the U.S. Dollar to Argentinean Peso exchange rate of 1 to 29.4 as of June 30, 2018. These amounts became the new basis for those assets and liabilities as of July 1, 2018. Non-monetary assets and liabilities, as well as the corresponding income statement activities such as depreciation, amortization and equity, will continue to be measured at the June 30, 2018 exchange rate. This change did not have a material impact on the Company’s financial statements as Argentina’s assets and revenue are less than 1% of consolidated assets and revenue, respectively. Cash and Cash Equivalents —Cash and cash equivalents include cash on hand, demand deposits and short-term investments with original maturities of three months or less. The Company maintains its deposits at high quality financial institutions and monitors the credit ratings of those institutions. Restricted Cash— Restricted cash includes cash pledged as collateral to secure obligations and all cash whose use is otherwise limited by contractual provisions. The reconciliation of cash and cash equivalents and restricted cash reported within the applicable balance sheet that sum to the total of the same such amounts shown in the statement of cash flows is as follows: Year Ended December 31, 2018 2017 2016 Cash and cash equivalents $ 1,208.7 $ 802.1 $ 787.2 Restricted cash 96.2 152.8 149.3 Total cash, cash equivalents and restricted cash $ 1,304.9 $ 954.9 $ 936.5 Short-Term Investments— Short-term investments consists of highly liquid investments with original maturities in excess of three months. Property and Equipment —Property and equipment is recorded at cost or, in the case of acquired properties, at estimated fair value on the date acquired. Cost for self-constructed towers includes direct materials and labor, capitalized interest and certain indirect costs associated with construction of the tower, such as transportation costs, employee benefits and payroll taxes. The Company begins the capitalization of costs during the pre-construction period, which is the period during which costs are incurred to evaluate the site, and continues to capitalize costs until the tower is substantially completed and ready for occupancy by a tenant. Labor and related costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were $55.0 million , $50.9 million and $47.7 million , respectively. Capitalized interest costs were not material for the years ended December 31, 2018 , 2017 and 2016 . Expenditures for repairs and maintenance are expensed as incurred. Augmentation and improvements that extend an asset’s useful life or enhance capacity are capitalized. Depreciation expense is recorded using the straight-line method over the assets’ estimated useful lives. Towers and related assets on leased land are depreciated over the shorter of the estimated useful life of the asset or the term of the corresponding ground lease, taking into consideration lease renewal options and residual value. Towers or assets acquired through capital leases are recorded net at the present value of future minimum lease payments or the fair value of the leased asset at the inception of the lease. Property and equipment and assets held under capital leases are amortized over the shorter of the applicable lease term or the estimated useful life of the respective assets for periods generally not exceeding twenty years. The Company reviews its tower portfolio for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company reviews other long-lived assets for impairment whenever events, changes in circumstances or other evidence indicate that the carrying amount of the Company’s assets may not be recoverable. The Company records impairment charges in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment. Goodwill and Other Intangible Assets —The Company reviews goodwill for impairment at least annually (as of December 31) or whenever events or circumstances indicate the carrying value of an asset may not be recoverable. Goodwill is recorded in the applicable segment and assessed for impairment at the reporting unit level. The Company utilizes the two-step impairment test and employs a discounted cash flow analysis when testing goodwill for impairment. The key assumptions utilized in the discounted cash flow analysis include current operating performance, terminal sales growth rate, management’s expectations of future operating results and cash requirements, the current weighted average cost of capital and an expected tax rate. Under the first step of the test, the Company compares the fair value of the reporting unit, as calculated under an income approach using future discounted cash flows, to the carrying amount of the applicable reporting unit. If the carrying amount exceeds the fair value, the Company conducts the second step of this test, in which the implied fair value of the applicable reporting unit’s goodwill is compared to the carrying amount of that goodwill. If the carrying amount of goodwill exceeds its implied fair value, an impairment loss would be recognized for the amount of the excess. During the years ended December 31, 2018 , 2017 and 2016 , no potential impairment was identified under the first step of the test, as the fair value of each of the reporting units was in excess of its carrying amount. Intangible assets that are separable from goodwill and are deemed to have a definite life are amortized over their useful lives, generally ranging from three to twenty years and are evaluated separately for impairment at least annually or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. The Company reviews its network location intangible assets for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company monitors its tenant-related intangible assets on a tenant by tenant basis for indicators of impairment, such as high levels of turnover or attrition, non-renewal of a significant number of contracts or the cancellation or termination of a relationship. The Company assesses recoverability by determining whether the carrying amount of the related assets will be recovered primarily through projected undiscounted future cash flows. If the Company determines that the carrying amount of an asset may not be recoverable, the Company measures any impairment loss based on the projected future discounted cash flows to be provided from the asset or available market information relative to the asset’s fair value, as compared to the asset’s carrying amount. The Company records impairment charges, which are discussed in note 16, in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment. Derivative Financial Instruments —Derivatives are recorded on the consolidated balance sheet at fair value. If a derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in AOCL, as well as a component of comprehensive income, and are recognized in the results of operations when the hedged item affects earnings. Changes in fair value of the ineffective portions of cash flow hedges are recognized in the results of operations. For derivative instruments that are designated and qualify as fair value hedges, changes in value of the derivatives are recorded in Other expense in the consolidated statements of operations in the current period, along with the offsetting gain or loss on the hedged item attributable to the hedged risk. For derivative instruments not designated as hedging instruments, changes in fair value are recognized in the results of operations in the period that the change occurs. The primary risks managed through the use of derivative instruments is interest rate risk, exposure to changes in the fair value of debt attributable to interest rate risk and currency risk. From time to time, the Company enters into interest rate swap agreements or foreign currency contracts to manage exposure to these risks. Under these agreements, the Company is exposed to counterparty credit risk to the extent that a counterparty fails to meet the terms of a contract. The Company’s exposure is limited to the current value of the contract at the time the counterparty fails to perform. The Company assesses, both at the inception of the hedge and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in cash flows or fair values of hedged items. The Company does not hold derivatives for trading purposes. Fair Value Measurements —The Company determines the fair value of its financial instruments based on the fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. Asset Retirement Obligations —When required, the Company recognizes the fair value of obligations to remove its tower assets and remediate the leased land upon which certain of its tower assets are located. Generally, the associated retirement costs are capitalized as part of the carrying amount of the related tower assets and depreciated over their estimated useful lives and the liability is accreted through the obligation’s estimated settlement date. Fair value estimates of asset retirement obligations generally involve discounting of estimated future cash flows associated with takedown costs. Periodic accretion of such liabilities due to the passage of time is included in Depreciation, amortization and accretion expense in the consolidated statements of operations. Adjustments are also made to the asset retirement obligation liability to reflect changes in the estimates of timing and amount of expected cash flows, with an offsetting adjustment made to the related long-lived tangible asset. The significant assumptions used in estimating the Company’s aggregate asset retirement obligation are: timing of tower removals; cost of tower removals; timing and number of land lease renewals; expected inflation rates; and credit-adjusted, risk-free interest rates that approximate the Company’s incremental borrowing rate. Income Taxes —As a REIT, the Company generally is not subject to U.S. federal income taxes on income generated by its REIT operations as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on certain earnings and continues to be subject to taxation in its foreign jurisdictions. Accordingly, the consolidated financial statements reflect provisions for federal, state, local and foreign income taxes. The Company recognizes deferred tax assets and liabilities for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, as well as operating loss and tax credit carryforwards. The Company measures deferred tax assets and liabilities using enacted tax rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities as a result of a change in tax rates is recognized in income in the period that includes the enactment date. The Company periodically reviews its deferred tax assets, and provides valuation allowances if, based on the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Valuation allowances would be reversed as a reduction to the provision for income taxes if related deferred tax assets are deemed realizable based on changes in facts and circumstances relevant to the assets’ recoverability. The Company classifies uncertain tax positions as non-current income tax liabilities in Other non-current liabilities in the consolidated balance sheet, unless expected to be paid within one year. The Company reports penalties and tax-related interest expense as a component of the income tax provision and interest income from tax refunds as a component of Other expense in the consolidated statements of operations. Other Comprehensive Income (Loss) —Other comprehensive income (loss) refers to items excluded from net income that are recorded as an adjustment to equity, net of tax. The Company’s other comprehensive income (loss) primarily consisted of changes in fair value of effective derivative cash flow hedges, foreign currency translation adjustments and reclassification of unrealized losses on effective derivative cash flow hedges. The AOCL balance included accumulated foreign currency translation losses of $2.6 billion , $2.0 billion and $2.0 billion for the years ended December 31, 2018 , 2017 and 2016 , respectively. Distributions —As a REIT, the Company must annually distribute to its stockholders an amount equal to at least 90% of its REIT taxable income (determined before the deduction for distributed earnings and excluding any net capital gain). Generally, the Company has distributed, and expects to continue to distribute, all or substantially all of its REIT taxable income after taking into consideration its utilization of net operating losses (“NOLs”). The amount, timing and frequency of future distributions will be at the sole discretion of the Board of Directors and will depend upon various factors, a number of which may be beyond the Company’s control, including the Company’s financial condition and operating cash flows, the amount required to maintain its qualification for taxation as a REIT and reduce any income and excise taxes that the Company otherwise would be required to pay, limitations on distributions in the Company’s existing and future debt and preferred equity instruments, the Company’s ability to utilize NOLs to offset the Company’s distribution requirements, limitations on its ability to fund distributions using cash generated through its TRSs and other factors that the Board of Directors may deem relevant. Acquisitions —For acquisitions that meet the definition of a business combination, the Company applies the acquisition method of accounting where assets acquired and liabilities assumed are recorded at fair value at the date of each acquisition, and the results of operations are included with those of the Company from the dates of the respective acquisitions. Any excess of the purchase price paid by the Company over the amounts recognized for assets acquired and liabilities assumed is recorded as goodwill. The Company continues to evaluate acquisitions for a period not to exceed one year after the applicable acquisition date of each transaction to determine whether any additional adjustments are needed to the allocation of the purchase price paid for the assets acquired and liabilities assumed. All other acquisitions are accounted for as asset acquisitions and the purchase price is allocated to the net assets acquired with no recognition of goodwill. The purchase price is not subsequently adjusted. The fair value of the assets acquired and liabilities assumed is typically determined by using either estimates of replacement costs or discounted cash flow valuation methods. When determining the fair value of tangible assets acquired, the Company must estimate the cost to replace the asset with a new asset taking into consideration such factors as age, condition and the economic useful life of the asset. When determining the fair value of intangible assets acquired and liabilities assumed, the Company must estimate the applicable discount rate and the timing and amount of future cash flows, including rate and terms of renewal and attrition. Revenue —The Company’s revenue from leasing arrangements, including fixed escalation clauses present in non-cancellable lease arrangements, is reported on a straight-line basis over the term of the respective leases when collectibility is probable. Escalation clauses tied to the Consumer Price Index or other inflation-based indices, and other incentives present in lease agreements with the Company’s tenants are excluded from the straight-line calculation. Total property straight-line revenues for the years ended December 31, 2018, 2017 and 2016 were $87.6 million , $194.4 million and $131.7 million , respectively. During the year ended December 31, 2018 the Company entered into agreements with one of its tenants in India, Tata Teleservices Limited (“Tata Teleservices”) and related entities (collectively, “Tata”), for a settlement and release of certain contractual lease obligations of Tata Teleservices for which the Company received a cash settlement payment of $345.5 million . The new revenue recognition accounting standard, which applies to revenue not recorded under the lease 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. For the year ended December 31, 2018, the impact of applying the new standard was an increase to revenue of $4.9 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 to enter into lease arrangements are capitalized under the applicable lease accounting guidance. Costs incurred to obtain non-lease contracts that are capitalized primarily relate to DAS networks and are not material to the consolidated financial statements. The Company has excluded sales tax, value-added tax and similar taxes from non-lease revenue. Non-lease revenue is disaggregated by geography in a manner consistent with the Company’s business segments, which are discussed further in note 20. A summary of non-lease revenue disaggregated by source and geography is as follows: Year Ended December 31, 2018 U.S. Asia EMEA Latin America Total Power and fuel pass-through revenue $ — $ 450.0 $ 140.3 $ 16.8 $ 607.1 Other non-lease revenue 273.2 7.0 1.3 102.1 383.6 Total non-lease property revenue $ 273.2 $ 457.0 $ 141.6 $ 118.9 $ 990.7 Services revenue 125.4 — — — 125.4 Total non-lease revenue $ 398.6 $ 457.0 $ 141.6 $ 118.9 $ 1,116.1 Property lease revenue 3,548.9 1,083.5 545.7 1,145.9 6,324.0 Total revenue $ 3,947.5 $ 1,540.5 $ 687.3 $ 1,264.8 $ 7,440.1 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, or otherwise charge for, these services. 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 networks, fiber and other property related revenue. DAS networks and fiber arrangements require that the Company provide the tenant the right to use the applicable communications infrastructure. Performance obligations are satisfied over time for the duration of the arrangements. Other prop

PREPAID AND OTHER CURRENT ASSET

PREPAID AND OTHER CURRENT ASSETS	12 Months Ended
	Dec. 31, 2018
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid and Other Current Assets	PREPAID AND OTHER CURRENT ASSETS Prepaid and other current assets consisted of the following as of December 31,: 2018 2017 Prepaid operating ground leases $ 165.0 $ 148.6 Unbilled receivables 126.1 107.9 Prepaid income tax 125.1 136.5 Value added tax and other consumption tax receivables 86.3 64.2 Prepaid assets 40.5 39.6 Other miscellaneous current assets 78.2 71.8 Prepaids and other current assets $ 621.2 $ 568.6

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT Property and equipment (including assets held under capital leases) consisted of the following as of December 31,: Estimated Useful Lives (years) (1) 2018 2017 Towers Up to 20 $ 12,777.9 $ 12,500.5 Equipment (2) 2 - 20 1,667.3 1,423.0 Buildings and improvements 3 - 32 628.5 631.4 Land and improvements (3) Up to 20 2,285.4 2,112.9 Construction-in-progress 358.1 282.1 Total 17,717.2 16,949.9 Less accumulated depreciation (6,470.1 ) (5,848.9 ) Property and equipment, net $ 11,247.1 $ 11,101.0 _______________ (1) Assets on leased land are depreciated over the shorter of the estimated useful life of the asset or the term of the corresponding ground lease taking into consideration lease renewal options and residual value. (2) Includes fiber and DAS assets. (3) Estimated useful lives apply to improvements only. Depreciation expense for the years ended December 31, 2018 , 2017 and 2016 was $883.1 million , $835.5 million and $758.9 million , respectively. As of December 31, 2018 , property and equipment included $4,369.5 million and $1,016.2 million of capital lease assets with related equipment and improvements and accumulated depreciation, respectively. As of December 31, 2017 , property and equipment included $4,944.2 million and $1,370.4 million of capital lease assets with related equipment and improvements and accumulated depreciation, respectively. As of December 31, 2018 and 2017 , capital lease assets were primarily classified as towers and land and improvements.

GOODWILL AND OTHER INTANGIBLE A

GOODWILL AND OTHER INTANGIBLE ASSETS	12 Months Ended
	Dec. 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 the Company’s business segments were as follows: Property Services Total U.S. Asia EMEA Latin America Balance as of January 1, 2017 $ 3,379.2 $ 1,029.3 $ 150.5 $ 509.7 $ 2.0 $ 5,070.7 Additions (1) — 0.4 220.9 264.8 — 486.1 Effect of foreign currency translation — 65.3 33.5 (17.2 ) — 81.6 Balance as of January 1, 2018 $ 3,379.2 $ 1,095.0 $ 404.9 $ 757.3 $ 2.0 $ 5,638.4 Additions (2) 3.3 44.5 — 0.4 — 48.2 Effect of foreign currency translation — (94.0 ) (23.6 ) (67.1 ) — (184.7 ) Balance as of December 31, 2018 $ 3,382.5 $ 1,045.5 $ 381.3 $ 690.6 $ 2.0 $ 5,501.9 _______________ (1) Additions consist of $485.1 million resulting from 2017 acquisitions and $1.0 million from revisions to prior-year acquisitions due to measurement period adjustments. (2) Additions consist of $47.8 million resulting from 2018 acquisitions and $0.4 million from revisions to prior-year acquisitions due to measurement period adjustments. The Company’s other intangible assets subject to amortization consisted of the following: As of December 31, 2018 As of December 31, 2017 Estimated Useful Lives 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 $ 4,780.3 $ (1,704.9 ) $ 3,075.4 $ 4,858.8 $ (1,525.3 ) $ 3,333.5 Acquired tenant-related intangibles 15-20 11,156.5 (3,147.2 ) 8,009.3 11,150.9 (2,754.7 ) 8,396.2 Acquired licenses and other intangibles 3-20 104.1 (14.5 ) 89.6 58.8 (8.1 ) 50.7 Economic Rights, TV Azteca (2) 70 — — — 14.5 (11.6 ) 2.9 Total other intangible assets $ 16,040.9 $ (4,866.6 ) $ 11,174.3 $ 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. (2) As discussed in note 5, in conjunction with the extinguishment of a note from TV Azteca (as defined in note 5), the Company restructured the Economic Rights Agreement (as defined in note 5) and wrote off the corresponding asset. The intangible asset related to the Commercialization Rights (as defined in note 5) agreement with TV Azteca is included in Acquired licenses and other intangibles. 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 the estimated useful lives. As of December 31, 2018 , the remaining weighted average amortization period of the Company’s intangible assets was 15 years. Amortization of intangible assets for the years ended December 31, 2018 , 2017 and 2016 was $1,144.1 million , $785.9 million and $699.8 million , respectively. Amortization expense increased for the year ended December 31, 2018 because the Company entered into agreements with Tata for a settlement and release of certain contractual lease obligations of Tata Teleservices. As a result, the Company recorded $327.5 million of accelerated amortization related to the Tata tenant relationship, which was subsequently retired. Based on current exchange rates, the Company expects to record amortization expense as follows over the next five years: Year Ending December 31, 2019 $ 786.0 2020 765.8 2021 749.6 2022 745.1 2023 740.6

NOTES RECEIVABLE AND OTHER NON-

NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS	12 Months Ended
	Dec. 31, 2018
Notes Receivable And Other Long Term Assets [Abstract]
Notes Receivable and Other Non-Current Assets	NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS Notes receivable and other non-current assets consisted of the following as of December 31,: 2018 2017 Long-term prepaid ground rent $ 607.5 $ 552.8 Notes receivable 1.0 83.7 Other miscellaneous assets 354.1 313.6 Notes receivable and other non-current assets $ 962.6 $ 950.1 TV Azteca Note Receivable —In 2000, the Company loaned TV Azteca, S.A. de C.V. (“TV Azteca”), the owner of a major national television network in Mexico, $119.8 million . The loan had an interest rate of 13.11% , payable quarterly, which at the time of issuance was determined to be below market and therefore a corresponding discount was recorded. The term of the loan was 70 years . The Company amortized the discount on the loan to Interest income, TV Azteca, net of interest expense on its consolidated statements of operations using the effective interest method over the term of the loan. As of December 31, 2017, the outstanding balance on the loan was $91.8 million , or $82.9 million , net of discount. On September 25, 2018, TV Azteca paid $59.5 million to extinguish this loan and simultaneously restructured its Economic Rights agreement, which the Company estimated had a fair value of $24.8 million . TV Azteca Economic Rights and Commercialization Rights —Simultaneous with the signing of the loan agreement in 2000, the Company also entered into a 70 -year Economic Rights Agreement with TV Azteca regarding space not used by TV Azteca on approximately 190 of its broadcast towers. In exchange for the issuance of the below market interest rate loan described above and the annual payment of $1.5 million to TV Azteca (under the Economic Rights Agreement), the Company had the right to market and lease the unused tower space on the broadcast towers (the “Economic Rights”). TV Azteca retained title to these towers and was responsible for their operation and maintenance. The Company was entitled to 100% of the revenues generated from leases with tenants on the unused space and was responsible for any incremental operating expenses associated with those tenants. The Company accounted for the annual payment of $1.5 million as a capital lease by initially recording an asset and a corresponding liability of $18.6 million . The capital lease asset also included the original discount on the note. The capital lease asset and original discount on the note aggregated $30.2 million at the time of the transaction and represented the cost to acquire the Economic Rights. The Economic Rights asset was recorded as an intangible asset and was being amortized over the 70 -year life of the Economic Rights Agreement. In conjunction with the note extinguishment described above, the Company restructured the Economic Rights Agreement into a Commercialization Rights agreement. Under this agreement, the Company has the exclusive right to commercialize available space on approximately 190 TV Azteca broadcast towers for the installation, licensing and operation of equipment for wireless telecommunications service, radio and television broadcasting on the towers (the “Commercialization Rights”) until September 2038, during which time the Company is entitled to all revenues derived from the Commercialization Rights. Subsequent to 2038, the Company is required to pay quarterly to TV Azteca a market rate of 25% of the gross revenues associated with the Commercialization Rights, and annually, TV Azteca has the right to repurchase the Commercialization Rights for the then-market price. As a result of entering into the Commercialization Rights agreement, the obligations under the capital lease were cancelled and the remaining capital lease liability of $14.1 million , the deferred financing costs of $1.5 million , and the net carrying value of the original Economic Rights asset of $3.0 million were written off, which resulted in a gain of $9.7 million that was recorded in Other income (expense).

ACQUISITIONS

ACQUISITIONS	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisitions	ACQUISITIONS 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 or rights acquired and liabilities assumed, with no recognition of goodwill. For those transactions treated as business combinations, the estimates of the fair value of the assets or rights acquired and liabilities assumed at the date of the applicable acquisition are subject to adjustment during the measurement period (up to one year from the particular acquisition date). The primary areas of the accounting for the acquisitions that are not yet finalized relate to the fair value of certain tangible and intangible assets acquired and liabilities assumed, which may include contingent consideration, residual goodwill and any related tax impact. The fair value of these net assets acquired are based on management’s estimates and assumptions, as well as other information compiled by management, including valuations that utilize customary valuation procedures and techniques. While the Company believes that such preliminary estimates provide a reasonable basis for estimating the fair value of assets acquired and liabilities assumed, it evaluates any necessary information prior to finalization of the fair value. During the measurement period for those acquisitions accounted for as business combinations, the Company will adjust assets or liabilities if new information is obtained about facts and circumstances that existed as of the acquisition date that, if known, would have resulted in the revised estimated values of those assets or liabilities as of that date. 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 year ended December 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. 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 acquired businesses or assets efficiently. The Company records acquisition and merger related expenses for business combinations, as well as integration costs for all acquisitions, in Other operating expenses in the consolidated statements of operations. During the years ended December 31, 2018 , 2017 and 2016 , the Company recorded the following acquisition and merger related expenses for business combinations and integration costs: Year Ended December 31, 2018 2017 2016 Acquisition and merger related expenses $ 14.1 $ 16.3 $ 15.9 Integration costs $ 16.1 $ 11.5 $ 9.9 The Company also recorded aggregate purchase price refunds of $22.2 million during the year ended December 31, 2017. The refunds primarily related to an acquisition in Brazil in 2014 for which the measurement period has closed. 2018 Transactions The estimated aggregate impact of the 2018 acquisitions on the Company’s revenues and gross margin for the year ended December 31, 2018 was approximately $232.2 million and $83.0 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. Idea Acquisition— On May 31, 2018, the Company acquired 100% of the outstanding shares of Idea Cellular Infrastructure Services Limited (“Idea”), a telecommunications company that owns and operates approximately 9,700 communications sites in India, for total consideration of approximately 42.8 billion Indian Rupees (“INR”) ( $635.5 million at the date of acquisition). This acquisition was accounted for as a business combination and is subject to post-closing adjustments. During the year ended December 31, 2018, the purchase price was reduced to approximately 42.2 billion INR ( $625.9 million at the date of acquisition). Vodafone Acquisition— On March 31, 2018, the Company acquired approximately 10,200 communications sites from Vodafone India Limited and Vodafone Mobile Services Limited (together, “Vodafone”) for an aggregate total purchase price of 38.3 billion INR ( $587.9 million at the date of acquisition). Of the aggregate purchase price, $1.1 million is reflected in Accounts payable in the consolidated balance sheet as of December 31, 2018. This acquisition was accounted for as an asset acquisition. Kenya Acquisition— On October 1, 2018, the Company acquired over 700 sites in Kenya from Telkom Kenya Limited for total consideration of $174.1 million , including value added tax. The Company issued a note for $51.8 million of the purchase price, which will be paid either in future installments subject to the satisfaction of specified conditions, or three years from the purchase date. This acquisition was accounted for as an asset acquisition. Other Acquisitions— During the year ended December 31, 2018, the Company acquired a total of 1,335 communications sites in the United States, Colombia, Mexico, Paraguay and Peru for an aggregate purchase price of $414.5 million . Of the aggregate purchase price, $11.8 million is reflected as a payable in the consolidated balance sheet as of December 31, 2018. The majority of these acquisitions were accounted for as asset acquisitions. On November 1, 2018, the Company acquired a portfolio of fiber assets and the right to use certain telecommunications poles in Brazil from Cia Energetica de Minas Gerais SA for total consideration of approximately 576.9 million Brazilian Reais (“BRL”) ( $155.8 million at the date of acquisition). This acquisition is included in “Other” in the table below and was accounted for as an asset acquisition. 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 EMEA Idea Vodafone (1) Kenya (2) Other (3) Preliminary Allocation Updated Allocation Current assets $ 100.7 $ 82.9 $ 15.1 $ 0.1 $ 3.6 Non-current assets 2.6 11.6 5.8 24.7 5.1 Property and equipment 161.2 161.2 194.6 51.2 271.5 Intangible assets (4): Tenant-related intangible assets 321.2 323.4 309.5 106.2 191.5 Network location intangible assets 82.9 83.5 88.5 25.6 91.5 Other intangible assets — — — — 28.7 Current liabilities (52.5 ) (47.4 ) (13.1 ) — (3.6 ) Deferred tax liability (20.7 ) (17.7 ) — (32.2 ) — Other non-current liabilities (10.5 ) (16.1 ) (12.5 ) (1.5 ) (21.3 ) Net assets acquired 584.9 581.4 587.9 174.1 567.0 Goodwill (5) 50.6 44.5 — — 3.3 Fair value of net assets acquired 635.5 625.9 587.9 174.1 570.3 Debt assumed — — — — — Purchase price $ 635.5 $ 625.9 $ 587.9 $ 174.1 $ 570.3 _______________ (1) Includes $1.3 million in acquisition and merger related expenses that were capitalized as part of the purchase price. (2) Includes $1.7 million in acquisition and merger related expenses that were capitalized as part of the purchase price. (3) Other includes 145 sites in Peru held pursuant to long-term capital leases. (4) Tenant-related intangible assets, network location intangible assets and other intangible assets are amortized on a straight-line basis over periods of up to 20 years. (5) The Company expects the majority of goodwill to be deductible for tax purposes. 2017 Transactions During the year ended December 31, 2018, post-closing adjustments impacted the following acquisition completed in 2017: Mexico Acquisition— On November 17, 2017, the Company acquired 100% of the outstanding shares of entities holding urban telecommunications assets in Mexico, including more than 50,000 concrete poles and approximately 2,100 route miles of fiber, for total initial consideration of $505.8 million , including value-added tax. During the year ended December 31, 2018, the purchase price was reduced to $499.7 million due to post-closing adjustments. The following table summarizes the preliminary and final allocation of the purchase price paid and the amounts of assets acquired and liabilities assumed for the acquisition based upon its estimated fair value at the date of acquisition. Balances are reflected in the accompanying consolidated balance sheet as of December 31, 2018. Latin America Mexico Preliminary Allocation (1) Final Allocation (2) Current assets $ 44.4 $ 42.5 Non-current assets — — Property and equipment 94.0 102.2 Intangible assets: Tenant-related intangible assets 153.3 138.0 Network location intangible assets — — Other intangible assets 22.0 20.3 Current liabilities (28.8 ) (27.2 ) Deferred tax liability (38.8 ) (36.2 ) Other non-current liabilities (4.5 ) (4.5 ) Net assets acquired 241.6 235.1 Goodwill (3) 264.2 264.6 Fair value of net assets acquired 505.8 499.7 Debt assumed — — Purchase price $ 505.8 $ 499.7 _______________ (1) As reported for the year ended December 31, 2017. (2) The allocation of the purchase price for the Mexico acquisition was finalized during the year ended December 31, 2018. (3) Primarily results from purchase accounting adjustments, which are not deductible for tax purposes. 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 the 2017 acquisitions 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 dates indicated, nor are they indicative of the future operating results of the Company. Year Ended December 31, 2018 2017 Pro forma revenues $ 7,610.6 $ 7,161.0 Pro forma net income attributable to American Tower Corporation common stockholders $ 1,218.2 $ 1,127.6 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 2.77 $ 2.63 Diluted net income attributable to American Tower Corporation common stockholders $ 2.75 $ 2.61 Acquisition-Related Contingent Consideration The Company may be required to pay additional consideration under certain agreements for the acquisition of communications sites if specific conditions are met or events occur. In Ghana, the Company may be required to pay additional consideration upon the conversion of certain barter agreements with other wireless carriers to cash-paying lease agreements. In the United States, the Company may be required to pay additional consideration if certain pre-designated tenant leases commence during a specified period of time. A summary of the value of the Company’s acquisition-related contingent consideration obligations are as follows: Year Ended December 31, 2018 Maximum potential value (1) Estimated value at December 31, 2018 Additions Settlements Change in Fair Value Ghana 0.6 0.6 — — 0.0 South Africa — — — (8.6 ) (0.5 ) United States 0.3 0.3 — (0.1 ) — Total $ 0.9 $ 0.9 $ — $ (8.7 ) $ (0.5 ) _______________ (1) The maximum potential value is based on exchange rates at December 31, 2018 . The minimum value could be zero . For more information regarding acquisition-related contingent consideration, see note 11.

ACCRUED EXPENSES

ACCRUED EXPENSES	12 Months Ended
	Dec. 31, 2018
Accrued Liabilities, Current [Abstract]
Accrued Expenses	ACCRUED EXPENSES Accrued expenses consisted of the following as of December 31,: 2018 2017 Accrued property and real estate taxes $ 169.7 $ 154.4 Amounts payable to tenants 93.5 60.8 Payroll and related withholdings 90.4 82.2 Accrued pass-through costs 71.2 59.7 Accrued rent 61.4 54.0 Accrued income tax payable 57.9 15.3 Accrued construction costs 41.5 31.9 Accrued pass-through taxes 2.2 25.3 Other accrued expenses 360.5 370.7 Accrued expenses $ 948.3 $ 854.3

LONG-TERM OBLIGATIONS

LONG-TERM OBLIGATIONS	12 Months Ended
	Dec. 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 December 31,: 2018 2017 Contractual Interest Rate (1) Maturity Date (1) 2018 Term Loan (2)(3) $ 1,499.8 $ — 3.405 % March 29, 2019 2013 Credit Facility (2) 1,875.0 2,075.6 3.616 % June 28, 2022 2013 Term Loan (2) 994.8 994.5 3.655 % January 31, 2024 2014 Credit Facility (2) — 495.0 3.655 % January 31, 2024 3.40% senior notes (4) 1,000.0 999.8 3.400 % February 15, 2019 2.800% senior notes 747.8 746.3 2.800 % June 1, 2020 5.050% senior notes 698.7 698.0 5.050 % September 1, 2020 3.300% senior notes 747.2 746.0 3.300 % February 15, 2021 3.450% senior notes 646.3 645.1 3.450 % September 15, 2021 5.900% senior notes 498.4 497.8 5.900 % November 1, 2021 2.250% senior notes 572.7 572.4 2.250 % January 15, 2022 4.70% senior notes 697.4 696.7 4.700 % March 15, 2022 3.50% senior notes 992.6 990.9 3.500 % January 31, 2023 3.000% senior notes 687.5 692.5 3.000 % June 15, 2023 5.00% senior notes 1,002.1 1,002.4 5.000 % February 15, 2024 1.375% senior notes 564.0 589.1 1.375 % April 4, 2025 4.000% senior notes 742.1 741.0 4.000 % June 1, 2025 4.400% senior notes 496.1 495.6 4.400 % February 15, 2026 1.950% senior notes 566.0 — 1.950 % May 22, 2026 3.375% senior notes 986.3 984.8 3.375 % October 15, 2026 3.125% senior notes 397.3 397.1 3.125 % January 15, 2027 3.55% senior notes 743.5 742.8 3.550 % July 15, 2027 3.600% senior notes 691.9 691.1 3.600 % January 15, 2028 Total American Tower Corporation debt 17,847.5 16,494.5 Series 2013-1A Securities (5) — 499.8 N/A N/A Series 2013-2A Securities (6) 1,293.4 1,291.8 3.070 % March 15, 2023 Series 2018-1A Securities (6) 493.5 — 3.652 % March 15, 2028 Series 2015-1 Notes (7) 348.8 348.0 2.350 % June 15, 2020 Series 2015-2 Notes (8) 520.8 520.1 3.482 % June 16, 2025 India indebtedness (9) 240.1 512.6 8.40% - 8.95% Various India preference shares (10) 23.9 26.1 10.250 % March 2, 2020 Shareholder loans (11) 59.9 100.6 Various Various Other subsidiary debt (12) 152.5 246.1 Various Various Total American Tower subsidiary debt 3,132.9 3,545.1 Other debt, including capital lease obligations 179.5 165.5 Total 21,159.9 20,205.1 Less current portion long-term obligations (2,754.8 ) (774.8 ) Long-term obligations $ 18,405.1 $ 19,430.3 _______________ (1) Represents the interest rate or maturity date as of December 31, 2018; interest rate does not reflect the impact of interest rate swap agreements. (2) Accrues interest at a variable rate. Interest rates on outstanding balances are calculated using a weighted average. (3) Repaid in full subsequent to December 31, 2018. For more information see note 23. (4) Repaid in full on the maturity date in February 2019 with borrowings from the 2013 Credit Facility and the 2014 Credit Facility (each defined below). (5) Repaid in full on the March 2018 payment date. (6) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (7) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2045. (8) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (9) Denominated in INR. Includes India working capital facilities, remaining debt assumed by the Company in connection with the Viom Acquisition (as defined in note 14) and debt that has been entered into by ATC TIPL. (10) Mandatorily redeemable preference shares (the “Preference Shares”) denominated in INR and classified as debt. The Company intends to redeem these shares on March 2, 2019. (11) Reflects balances owed to the Company’s joint venture partners in Ghana and Uganda. The Ghana loan is denominated in Ghanaian Cedi (“GHS”) and the Uganda loan is denominated in Ugandan Shillings (“UGX”). On August 30, 2018, the Company repaid the remaining 127.2 billion UGX ( $33.8 million ) under the Uganda loan, including principal and accrued unpaid interest. As a result, no amounts were outstanding under the Uganda loan as of December 31, 2018. (12) Includes the BR Towers Debentures (as defined below) and the Brazil Credit Facility (as defined below), which are denominated in BRL and have an original amortization through October 15, 2023 and January 15, 2022, respectively, the South African Credit Facility (as defined below), which is denominated in South African Rand (“ZAR”) and amortizes through December 17, 2020, the Colombian Credit Facility (as defined below), which is denominated in Colombian Pesos (“COP”) and amortizes through April 24, 2021, the Kenya Debt (as defined below), which is denominated in U.S. Dollars (“USD”) and is payable either (i) in future installments subject to the satisfaction of specified conditions or (ii) three years from the note origination date, and U.S. subsidiary debt related to a seller-financed acquisition. In October 2018, the Company repaid the BR Towers Debentures in full, including any accrued and unpaid interest. Current portion of long-term obligations —The Company’s current portion of long-term obligations primarily includes (i) $1.5 billion under its secured term loan entered into on March 29, 2018 (the “2018 Term Loan”), (ii) $1.0 billion under the 3.40% senior unsecured notes due 2019, (iii) 7.1 billion INR ( $101.9 million ) of India indebtedness, (iv) 294.4 million GHS ( $59.9 million ) of the shareholder loan owed to the Company’s joint venture partner in Ghana and (v) 1.67 billion INR ( $23.9 million ) of the Preference Shares classified as debt. American Tower Corporation Debt Bank Facilities —In November 2018, the Company entered into amendment agreements with respect to (A) its multicurrency senior unsecured revolving credit facility entered into in June 2013, as amended (the “2013 Credit Facility”), (B) its senior unsecured revolving credit facility entered into in January 2012, as amended and restated in September 2014, as further amended (the “2014 Credit Facility”) and (C) its unsecured term loan entered into in October 2013, as amended (the “2013 Term Loan”), to, among other things, (i) extend the maturity dates by one year, (ii) increase the commitments under each of the 2013 Credit Facility and the 2014 Credit Facility by $100.0 million to $2.85 billion and $2.1 billion , respectively, (iii) increase the maximum Revolving Loan Commitments, after giving effect to any Incremental Commitments (each as defined in the applicable loan agreement) to $4.5 billion and $3.25 billion under the 2013 Credit Facility and the 2014 Credit Facility, respectively, (iv) amend the limitation on indebtedness of, and guaranteed by, the Company’s subsidiaries to the greater of (x) $2.5 billion and (y) 50% of Adjusted EBITDA (as defined in the applicable loan agreement) of the Company and its subsidiaries on a consolidated basis, (v) increase the threshold for certain defaults with respect to judgments, attachments or acceleration of indebtedness from $300.0 million to $400.0 million and (vi) add provisions regarding the establishment of an alternative rate of interest in the event that the London Interbank Offered Rate (“LIBOR”) is no longer available. In addition, the amendments to the 2014 Credit Facility and the 2013 Term Loan reduce the Applicable Margins (as defined in the applicable loan agreement) to conform to the Applicable Margins in the 2013 Credit Facility (as defined therein). 2013 Credit Facility— The Company has the ability to borrow up to $2.85 billion under the 2013 Credit Facility, which includes a $1.0 billion sublimit for multicurrency borrowings, a $200.0 million sublimit for letters of credit and a $50.0 million sublimit for swingline loans. During the year ended December 31, 2018 , the Company borrowed an aggregate of $2.1 billion and repaid an aggregate of $2.3 billion of revolving indebtedness under the 2013 Credit Facility. The Company primarily used the borrowings to fund acquisitions, repay existing indebtedness and for general corporate purposes. 2014 Credit Facility— The Company has the ability to borrow up to $2.1 billion under the 2014 Credit Facility, which includes a $200.0 million sublimit for letters of credit and a $50.0 million sublimit for swingline loans. During the year ended December 31, 2018 , the Company borrowed an aggregate of $1.1 billion and repaid an aggregate of $1.5 billion of revolving indebtedness under the 2014 Credit Facility. The Company used the borrowings to repay existing indebtedness, including the Secured Tower Revenue Securities, Series 2013-1A (the “Series 2013-1A Securities”), to fund acquisitions and for general corporate purposes. 2018 Term Loan— On March 29, 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 2013 Credit Facility, the 2014 Credit Facility, the 2013 Term Loan and the 2018 Term Loan do not require amortization of principal and may be paid prior to maturity in whole or in part at the Company’s option without penalty or premium. The Company has the option of choosing either a defined base rate or LIBOR as the applicable base rate for borrowings under the 2013 Credit Facility, the 2014 Credit Facility, the 2013 Term Loan and the 2018 Term Loan. The interest rates on the 2013 Credit Facility, 2014 Credit Facility and 2013 Term Loan range between 0.875% to 1.750% above LIBOR for LIBOR based borrowings or up to 0.750% above the defined base rate for base rate borrowings, in each case based upon the Company’s debt ratings. The interest rate on the 2018 Term Loan ranges between 0.625% to 1.500% above LIBOR for LIBOR based borrowings or up to 0.500% above the defined base rate for base rate borrowings, in each case based upon the Company’s debt ratings. As of December 31, 2018 , the key terms under the 2013 Credit Facility, the 2014 Credit Facility, the 2013 Term Loan and 2018 Term loan were as follows: Outstanding Principal Balance Undrawn letters of credit Maturity Date Current margin over LIBOR Current commitment fee (1) 2013 Credit Facility $ 1,875.0 (2) $ 3.8 June 28, 2022 (3) 1.125 % 0.125 % 2014 Credit Facility $ — $ 6.2 January 31, 2024 (3) 1.125 % 0.125 % 2013 Term Loan $ 1,000.0 (2) N/A January 31, 2024 1.125 % N/A 2018 Term Loan $ 1,500.0 (2) N/A March 29, 2019 0.875 % N/A _______________ (1) Fee on undrawn portion of each credit facility. (2) Borrowed at LIBOR. (3) Subject to two optional renewal periods. The agreements for the 2013 Credit Facility, the 2014 Credit Facility, the 2013 Term Loan and the 2018 Term Loan contain certain reporting, information, financial and operating covenants and other restrictions (including limitations on additional debt, guaranties, sales of assets and liens) with which the Company must comply. Any failure to comply with the financial and operating covenants of the loan agreements may constitute a default, which could result in, among other things, the amounts outstanding under the applicable agreement, including all accrued interest and unpaid fees, becoming immediately due and payable. Senior Notes 1.950% Senior Notes Offering— On May 22, 2018, the Company completed a registered public offering of 500.0 million Euros (“EUR”) ( $589.0 million at the date of issuance) aggregate principal amount of 1.950% senior unsecured notes due 2026 (the “ 1.950% Notes”). The net proceeds from this offering were approximately 493.2 million EUR (approximately $581.0 million at the date of issuance), after deducting commissions and estimated expenses. The Company used the net proceeds to repay existing indebtedness under the 2013 Credit Facility. The 1.950% Notes will mature on May 22, 2026 and bear interest at a rate of 1.950% per annum. Accrued and unpaid interest on the 1.950% Notes will be payable in EUR in arrears on May 22 of each year, beginning on May 22, 2019. Interest on the 1.950% Notes will be computed on the basis of the actual number of days in the period for which interest is being calculated and the actual number of days from and including the last date on which interest was paid on the 1.950% Notes and commenced accruing on May 22, 2018. The following table outlines key terms related to the Company ’ s outstanding senior notes as of December 31, 2018 : Adjustments to Principal Amount (1) Aggregate Principal Amount 2018 2017 Interest payments due (2) Issue Date Par Call Date (3) 3.40% Notes (4) 1,000.0 — (0.2 ) February 15 and August 15 August 19, 2013 N/A 2.800% Notes 750.0 (2.2 ) (3.7 ) June 1 and December 1 May 7, 2015 May 1, 2020 5.050% Notes 700.0 (1.3 ) (2.0 ) March 1 and September 1 August 16, 2010 N/A 3.300% Notes 750.0 (2.8 ) (4.0 ) February 15 and August 15 January 12, 2016 January 15, 2021 3.450% Notes 650.0 (3.7 ) (4.9 ) March 15 and September 15 August 7, 2014 N/A 5.900% Notes 500.0 (1.6 ) (2.2 ) May 1 and November 1 October 6, 2011 N/A 2.250% Notes (5) 600.0 (27.3 ) (27.6 ) January 15 and July 15 September 30, 2016 N/A 4.70% Notes 700.0 (2.6 ) (3.3 ) March 15 and September 15 March 12, 2012 N/A 3.50% Notes 1,000.0 (7.4 ) (9.1 ) January 31 and July 31 January 8, 2013 N/A 3.000% Notes (6) 700.0 (12.5 ) (7.5 ) June 15 and December 15 December 8, 2017 N/A 5.00% Notes (4) 1,000.0 2.1 2.4 February 15 and August 15 August 19, 2013 N/A 1.375% Notes (7) 573.3 (9.3 ) (11.1 ) April 4 April 6, 2017 January 4, 2025 4.000% Notes 750.0 (7.9 ) (9.0 ) June 1 and December 1 May 7, 2015 March 1, 2025 4.400% Notes 500.0 (3.9 ) (4.4 ) February 15 and August 15 January 12, 2016 November 15, 2025 1.950% Notes (7) 573.3 (7.3 ) — May 22 May 22, 2018 February 22, 2026 3.375% Notes 1,000.0 (13.7 ) (15.2 ) April 15 and October 15 May 13, 2016 July 15, 2026 3.125% Notes 400.0 (2.7 ) (2.9 ) January 15 and July 15 September 30, 2016 October 15, 2026 3.55% Notes 750.0 (6.5 ) (7.2 ) January 15 and July 15 June 30, 2017 April 15, 2027 3.600% Notes 700.0 (8.1 ) (8.9 ) January 15 and July 15 December 8, 2017 October 15, 2027 _______________ (1) Includes unamortized discounts, premiums and debt issuance costs and fair value adjustments due to interest rate swaps. (2) Interest payments are due semi-annually for each series of senior notes, except for the 1.375% Notes and the 1.950% Notes, for which interest payments are due annually. (3) The Company will not be required to pay a make-whole premium if redeemed on or after the par call date. (4) The original issue date for the 3.40% Notes and the 5.00% Notes was August 19, 2013. The issue date for the reopened 3.40% Notes and the reopened 5.00% Notes was January 10, 2014. The 3.40% Notes were repaid on February 15, 2019. (5) Includes $24.3 million and $23.7 million fair value adjustment due to interest rate swaps in 2018 and 2017, respectively. (6) Includes $7.0 million and $0.8 million fair value adjustment due to interest rate swaps in 2018 and 2017, respectively. (7) Notes are denominated in EUR. The Company may redeem each series of senior notes at any time, subject to the terms of the applicable supplemental indenture, in whole or in part, at a redemption price equal to 100% of the principal amount of the notes plus a make-whole premium, together with accrued interest to the redemption date. In addition, if the Company undergoes a change of control and corresponding ratings decline, each as defined in the applicable supplemental indenture, it may be required to repurchase all of the applicable notes at a purchase price equal to 101% of the principal amount of such notes, plus accrued and unpaid interest (including additional interest, if any), up to but not including the repurchase date. The notes rank equally with all of the Company’s other senior unsecured debt and are structurally subordinated to all existing and future indebtedness and other obligations of its subsidiaries. Each applicable supplemental indenture for the notes contains certain covenants that restrict the Company’s ability to merge, consolidate or sell assets and its (together with its subsidiaries’) ability to incur liens. These covenants are subject to a number of exceptions, including that the Company and its subsidiaries may incur certain liens on assets, mortgages or other liens securing indebtedness if the aggregate amount of such liens does not exceed 3.5 x Adjusted EBITDA, as defined in the applicable supplemental indenture. American Tower Subsidiary Debt The Company has several securitizations in place. Cash flows generated by the sites that secure the securitized debt 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 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. Repayment of Series 2013-1A Securities. On the March 2018 payment date, the Company repaid the $500.0 million aggregate principal amount outstanding under the Series 2013-1A Securities pursuant to the terms of the agreements governing such securities. The repayment was funded with borrowings under the 2014 Credit Facility and cash on hand. American Tower Secured Revenue Notes, Series 2015-1, Class A and Series 2015-2, Class A —In May 2015, GTP Acquisition Partners I, LLC (“GTP Acquisition Partners”), one of the Company’s wholly owned subsidiaries, refinanced existing debt with cash on hand and proceeds from a private issuance (the “2015 Securitization”) of $350.0 million of American Tower Secured Revenue Notes, Series 2015-1, Class A (the “Series 2015-1 Notes”) and $525.0 million of American Tower Secured Revenue Notes, Series 2015-2, Class A (the “Series 2015-2 Notes,” and together with the Series 2015-1 Notes, the “2015 Notes”). The 2015 Notes are secured by (i) mortgages, deeds of trust and deeds to secure debt on substantially all of the 3,556 communications sites (the “2015 Secured Sites”) owned by GTP Acquisition Partners and its subsidiaries (the “GTP Entities”) and their operating cash flows, (ii) a security interest in substantially all of the personal property and fixtures of the GTP Entities, including GTP Acquisition Partners’ equity interests in its subsidiaries and (iii) the rights of the GTP Entities under a management agreement. American Tower Holding Sub II, LLC, whose only material assets are its equity interests in GTP Acquisition Partners, has guaranteed repayment of the 2015 Notes and pledged its equity interests in GTP Acquisition Partners as security for such payment obligations. The 2015 Notes were issued by GTP Acquisition Partners pursuant to a Third Amended and Restated Indenture and related series supplements, each dated as of May 29, 2015 (collectively, the “2015 Indenture”), between the GTP Entities and The Bank of New York Mellon, as trustee. The effective weighted average life and interest rate of the 2015 Notes was 8.1 years and 3.029% , respectively, as of the date of issuance. Secured Tower Revenue Securities, Series 2013-2A , 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 Secured Tower Revenue Securities, Series 2013-2A (the “Series 2013-2A Securities” and, together with the 2018 Securities the “Trust 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 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 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. 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. 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 Loan is secured by (1) mortgages, deeds of trust and deeds to secure debt on substantially all of the Trust Sites and their operating cash flows, (2) a security interest in substantially all of the AMT Asset Subs’ personal property and fixtures and (3) the AMT Asset Subs’ rights under that certain management agreement among the AMT Asset Subs and SpectraSite Communications, LLC entered into in March 2013. American Tower Holding Sub, LLC (the “Guarantor”), whose only material assets are its equity interests in each of the AMT Asset Subs, and American Tower Guarantor Sub, LLC whose only material asset is its equity interests in the Guarantor, have each guaranteed repayment of the Loan and pledged their equity interests in their respective subsidiary or subsidiaries as security for such payment obligations. Under the terms of the Loan Agreement and 2015 Indenture, amounts due will be paid from the cash flows generated by the Trust Sites or the 2015 Secured Sites, respectively, which must be deposited into certain reserve accounts, and thereafter distributed solely pursuant to the terms of the Loan Agreement or 2015 Indenture, as applicable. On a monthly basis, after payment of all required amounts under the Loan Agreement or 2015 Indenture, as applicable, including interest payments, subject to the conditions described below, the excess cash flows generated from the operation of such assets are released to the AMT Asset Subs or GTP Acquisition Partners, as applicable, which can then be distributed to, and used by, the Company. In order to distribute any excess cash flow to the Company, the AMT Asset Subs and GTP Acquisition Partners must each maintain a specified debt service coverage ratio (the “DSCR”), which is generally calculated as the ratio of the net cash flow (as defined in the applicable agreement) to the amount of interest, servicing fees and trustee fees required to be paid over the succeeding 12 months on the principal amount of the Loan or the 2015 Notes, as applicable, that will be outstanding on the payment date following such date of determination. If the DSCR were equal to or below 1.30 x (the “Cash Trap DSCR”) for any quarter, then all cash flow in excess of amounts required to make debt service payments, fund required reserves, pay management fees and budgeted operating expenses and make other payments required under the applicable transaction documents, referred to as excess cash flow, will be deposited into a reserve account (the “Cash Trap Reserve Account”) instead of being released to the AMT Asset Subs or GTP Acquisition Partners, as applicable. The funds in the Cash Trap Reserve Account will not be released to the AMT Asset Subs or GTP Acquisition Partners, as applicable, unless the DSCR exceeds the Cash Trap DSCR for two consecutive calendar quarters. Additionally, an “amortization period” commences if, as of the end of any calendar quarter, the DSCR is equal to or below 1.15 x (the “Minimum DSCR”) and will continue to exist until the DSCR exceeds the Minimum DSCR for two consecutive calendar quarters. With respect to the Trust Securities, an “amortization period” also commences if, on the anticipated repayment date the component of the Loan corresponding to the applicable subclass of the Trust Securities has not been repaid in full, provided that such amortization period shall apply with respect to such component that has not been repaid in full. If either series of the 2015 Notes have not been repaid in full on the applicable anticipated repayment date, additional interest will accrue on the unpaid principal balance of the applicable series of the 2015 Notes, and such series will begin to amortize on a monthly basis from excess cash flow. During an amortization period, all excess cash flow and any amounts in the applicable Cash Trap Reserve Account would be applied to pay the principal of the Loan or the 2015 Notes, as applicable, on each monthly payment date. The Loan and the 2015 Notes may be prepaid in whole or in part at any time, provided such payment is accompanied by the applicable prepayment consideration. If the prepayment occurs within 12 months of the anticipated repayment date with respect to the Series 2015-1 Notes, 18 months of the anticipated repayment date with respect to the Series 2013-2A Securities or the Series 2015-2 Notes, or 36 months of the anticipated repayment date with respect to the Series 2018 Securities, no prepayment consideration is due. The Loan Agreement and the 2015 Indenture include operating covenants and other restrictions customary for transactions subject to rated securitizations. Among other things, the AMT Asset Subs and the GTP Entities, as applicable, are prohibited from incurring other indebtedness for borrowed money or further encumbering their assets subject to customary carve-outs for ordinary course trade payables and permitted encumbrances (as defined in the Loan Agreement or the 2015 Indenture, as applicable). The organizational documents of the AMT Asset Subs and the GTP Entities contain provisions consistent with rating agency securitization criteria for special purpose entities, including the requirement that they maintain independent directors. The Loan Agreement and the 2015 Indenture also contain certain covenants that require the AMT Asset Subs or GTP Acquisition Partners, as applicable, to provide the respective trustee with regular financial reports and operating budgets, promptly notify such trustee of events of default and material breaches under the Loan Agreement and other agreements related to the Trust Sites or the 2015 Indenture and other agreements related to the 2015 Secured Sites, as applicable, and allow the applicable trustee reasonable access to the sites, including the right to conduct site investigations. A failure to comply with the covenants in the Loan Agreement or the 2015 Indenture could prevent the AMT Asset Subs or GTP Acquisition Partners, as applicable, from distributing excess cash flow to the Company. Furthermore, if the AMT Asset Subs or GTP Acquisition Partners were to default on the Loan or a series of the 2015 Notes, the applicable trustee may seek to foreclose upon or otherwise convert the ownership of all or any portion of the Trust Sites or the 2015 Secured Sites, respectively, in which case the Company could lose the revenue associated with those assets. With respect to the 2015 Notes, upon the occurrence and during an event of default, the applicable trustee may, in its discretion or at the direction of holders of more than 50% of the aggregate outstanding principal of any series of the 2015 Notes, declare such series of 2015 Notes immediately due and payable, in which case any excess cash flow would need to be used to pay holders of such notes. Further, under the Loan Agreement and the 2015 Indenture, the AMT Asset Subs or GTP Acquisition Partners, respectively, are required to maintain reserve accounts, including for ground rents, real estate and personal property taxes and insurance premiums, and, under the 2015 Indenture and in certain circumstances under the Loan Agreement, to reserve a portion of advance rents from tenants on the Trust Sites. Based on the terms of the Loan Agreement and the 2015 Indenture, all rental cash receipts received for each month are reserved for the succeeding month and held in an account controlled by the applicable trustee and then released. The $63.3 million held in the reserve accounts with respect to the Trust Securitizations and the $16.8 million held in the reserve accounts with respect to the 2015 Securitization as of December 31, 2018 are classified as Restricted cash on the Company’s accompanying consolidated balance sheets. India Indebtedness— Amounts outstanding and key terms of the India indebtedness consisted of the following as of December 31, 2018 (in millions, except percentages): Amount Outstanding (INR) Amount Outstanding (USD) Interest Rate (Range) Maturity Date (Range) Term loans (1) 16,751 $ 240.1 8.75% - 8.95% January 1, 2019 - November 30, 2024 Working capital facilities (2) — $ — 8.40% - 8.75% March 18, 2019 - October 23, 2019 _______________ (1) In January 2019, the Company repaid approximately 5.0 billion INR ($ 72.0 million ) of India indebtedness. (2) 5.7 billion INR ( $81.8 million ) of borrowing capacity as of December 31, 2018. The India indebtedness includes several term loans, with maturities ranging from 1 to 10 years, which are generally secured by the borrower’s short-term and long-term assets. Each of the term loans bear interest at the applicable bank’s Marginal Cost of Funds based Lending Rate (as defined in the applicable agreement), plus a spread. Interest rates on the term loans are fixed until certain reset dates. Generally, the term loans can be repaid without penalty on the reset dates; repayments at dates other than the reset dates are subject to prepayment penalties, typically of 1% to 2% . Scheduled repayment terms include either ratable or staggered amortization with repayments typically commencing between 6 and 36 months after the initial disbursement of funds. The India indebtedness also includes several working capital facilities, most of which are subject to annual renewal, and which are generally secured by the borrower’s short-term and long-term assets. The working capital facilities bear interest at rates that consist of the applicable bank’s Marginal Cost of Funds based Lending Rate (as defined in the applicable agreement), plus a spread. Generally, the working capital facilities are payable on demand prior to maturity. Preference Shares— On March 2, 2017, ATC TIPL issued 166,666,666 Preference Shares and used the proceeds to redeem the preference shares previously issued by Viom. As of December 31, 2018 , ATC TIPL had 166,666,666 Preference Shares outstanding, which are required to be redeemed in cash. Accordingly, the Company recognized debt of 1.67 billion INR ( $23.9 million ) related t

OTHER NON-CURRENT LIABILITIES

OTHER NON-CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2018
Other Liabilities, Noncurrent [Abstract]
Other Non-Current Liabilities	OTHER NON-CURRENT LIABILITIES Other non-current liabilities consisted of the following as of December 31,: 2018 2017 Deferred rent liability $ 506.7 $ 467.0 Unearned revenue 504.6 509.2 Other miscellaneous liabilities 253.8 268.0 Other non-current liabilities $ 1,265.1 $ 1,244.2

ASSET RETIREMENT OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS The changes in the carrying amount of the Company’s asset retirement obligations were as follows: 2018 2017 Beginning balance as of January 1, $ 1,175.3 $ 965.5 Additions 39.6 33.4 Accretion expense 83.6 94.5 Revisions in estimates (1) (81.5 ) 86.6 Settlements (7.0 ) (4.7 ) Balance as of December 31, $ 1,210.0 $ 1,175.3 _______________ (1) Revisions in estimates include a decrease to the liability of $49.4 million and an increase to the liability of $13.0 million related to foreign currency translation for the years ended December 31, 2018 and 2017, respectively. As of December 31, 2018 , the estimated undiscounted future cash outlay for asset retirement obligations was $2.7 billion .

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 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 value of the Company’s financial assets and liabilities that are required to be measured on a recurring basis at fair value was as follows: December 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) $ — — — $ 1.0 — — Embedded derivative in lease agreement — — $ 11.5 — — $ 12.4 Liabilities: Interest rate swap agreements — $ 33.8 — — $ 29.0 — Acquisition-related contingent consideration — — $ 0.9 — — $ 10.1 Fair value of debt related to interest rate swap agreements $ (31.3 ) — — $ (24.5 ) — — Redeemable noncontrolling interests — — $ 1,004.8 — — $ 1,126.2 _______________ (1) Consists of highly liquid investments with original maturities in excess of three months. Interest Rate Swap Agreements The fair value of the Company’s interest rate swap agreements is determined using pricing models with inputs that are observable in the market or can be derived principally from, or corroborated by, observable market data. For derivative instruments that are designated and qualify as fair value hedges, changes in the value of the derivatives are recognized in the consolidated statement of operations in the current period, along with the offsetting gain or loss on the hedged item attributable to the hedged risk. For derivative instruments that are designated and qualify as cash flow hedges, the Company records the change in fair value for the effective portion of the cash flow hedges in AOCL in the consolidated balance sheets and reclassifies a portion of the value from AOCL into Interest expense on a quarterly basis as the cash flows from the hedged item affects earnings. The Company records the settlement of interest rate swap agreements in (Loss) gain on retirement of long-term obligations in the consolidated statements of operations in the period in which the settlement occurs. The Company entered into three interest rate swap agreements with an aggregate notional value of $500.0 million related to the 3.000% senior unsecured notes due 2021 (the “ 3.000% Notes”). These interest rate swaps, which were designated as fair value hedges at inception, were entered into to hedge against changes in fair value of the 3.000% Notes resulting from changes in interest rates. The interest rate swap agreements require the Company to pay interest at a variable interest rate of one-month LIBOR plus applicable spreads and to receive fixed interest at a rate of 3.000% through June 15, 2023. The Company entered into three interest rate swap agreements with an aggregate notional value of $600.0 million related to the 2.250% senior unsecured notes due 2022 (the “ 2.250% Notes”). These interest rate swaps, which were designated as fair value hedges at inception, were entered into to hedge against changes in fair value of the 2.250% Notes resulting from changes in interest rates. The interest rate swap agreements require the Company to pay interest at a variable interest rate of one-month LIBOR plus applicable spreads and to receive fixed interest at a rate of 2.250% through January 15, 2022. The fair value of the interest rate swap agreements in the U.S. at December 31, 2018 and 2017 was $33.5 million and $28.5 million , respectively, and were included in Other non-current liabilities on the consolidated balance sheets. During the year ended December 31, 2018, the Company recorded net fair value adjustments of $1.7 million related to interest rate swaps and the change in fair value of debt due to interest rate swaps in Other expense in the consolidated statement of operations. One of the Company’s Colombian subsidiaries is party to an interest rate swap agreement with an aggregate notional value of 55.0 billion COP ( $16.9 million ) with certain of the lenders under the Colombian Credit Facility. The interest rate swap agreement, which was designated as a cash flow hedge at inception, was entered into to manage exposure to variability in interest rates on debt. The interest rate swap agreement requires the payment of a fixed interest rate of 5.74% and pays variable interest at the three-month Inter-bank Rate (IBR) through the earlier of termination of the underlying debt or April 24, 2021. The notional value is reduced in accordance with the repayment schedule under the Colombian Credit Facility. The fair value of the interest rate swap agreements in Colombia at December 31, 2018 and 2017 was $0.3 million and $0.5 million , respectively, and were included in Other non-current liabilities on the consolidated balance sheets. Embedded Derivative in Lease Agreement In connection with the acquisition of communications sites in Nigeria, the Company entered into a site lease agreement where a portion of the monthly rent to be received is escalated based on an index outside the lessor’s economic environment. The fair value of the portion of the lease tied to the U.S. consumer price index was $14.6 million at the date of acquisition and was recorded in Notes receivable and other non-current assets on the consolidated balance sheets. The fair value of the Company’s embedded derivative is determined using a discounted cash flow approach, which takes into consideration Level 3 unobservable inputs, including expected future cash flows over the period in which the associated payment is expected to be received and applies a discount factor that captures uncertainties in the future periods associated with the expected payment. During the year ended December 31, 2018, the Company recorded $0.9 million of fair value adjustments, which were recorded in Other expense in the consolidated statement of operations. Acquisition-Related Contingent Consideration Acquisition-related contingent consideration is initially measured and recorded at fair value as an element of consideration paid in connection with an acquisition with subsequent adjustments recognized in Other operating expenses in the consolidated statements of operations. The fair value of acquisition-related contingent consideration, and any subsequent changes in fair value, is determined by using a discounted probability-weighted approach, which takes into consideration Level 3 unobservable inputs, including assessments of expected future cash flows over the period in which the obligation is expected to be settled, and applies a discount factor that captures the uncertainties associated with the obligation. Changes in the unobservable inputs of Level 3 assets or liabilities could significantly impact the fair value of these assets or liabilities recorded in the accompanying consolidated balance sheets, with the adjustments being recorded in the consolidated statements of operations. As of December 31, 2018 , the Company estimates that the value of all potential acquisition-related contingent consideration required payments to be between $0.0 million and $0.9 million . The changes in fair value of the contingent consideration were as follows during the years ended December 31,: 2018 2017 Balance as of January 1 $ 10.1 $ 15.4 Additions — — Settlements (8.7 ) — Change in fair value (0.9 ) (6.3 ) Foreign currency translation adjustment 0.4 1.0 Balance as of December 31 $ 0.9 $ 10.1 Redeemable Noncontrolling Interests The Company records the carrying amount of the redeemable noncontrolling interests as described in note 14. The fair value of redeemable noncontrolling interests is determined using a discounted cash flow approach, which takes into consideration Level 3 unobservable inputs, including expected future cash flows and applies a discount factor that captures uncertainties in the future periods. If required, the Company adjusts the redeemable noncontrolling interests to redemption value on each balance sheet date with changes in redemption value recognized as an adjustment to net income (loss) attributable to noncontrolling interests. The recurring Level 3 fair value measurements of the Company’s embedded derivative in lease agreement, acquisition-related contingent consideration and redeemable noncontrolling interests include the following significant unobservable inputs as of December 31, 2018: Significant Unobservable Input Range Embedded derivative in lease agreement Discount rate 10.93% - 13.96% Acquisition-related contingent consideration Probability of payout 0.00% - 100.00% Redeemable noncontrolling interests Revenue growth 3.16% - 12.87% Long-term growth rate 4.00 % Items Measured at Fair Value on a Nonrecurring Basis Assets Held and Used —The Company’s long-lived assets are recorded at amortized cost and, if impaired, are adjusted to fair value using Level 3 inputs. During the year ended December 31, 2018 , certain long-lived assets held and used with a carrying value of $22.4 billion were written down to their net realizable value as a result of an asset impairment charge of $ 394.0 million . During the year ended December 31, 2017 , certain long-lived assets held and used with a carrying value of $21.7 billion were written down to their net realizable value as a result of an asset impairment charge of $211.4 million . The asset impairment charges are recorded in Other operating expenses in the accompanying consolidated statements of operations. These adjustments were determined by comparing the estimated fair value utilizing projected future discounted cash flows to be provided from the long-lived assets to the asset’s carrying value. There were no other items measured at fair value on a nonrecurring basis during the year ended December 31, 2018 . Fair Value of Financial Instruments —The Company’s financial instruments for which the carrying value reasonably approximates fair value at December 31, 2018 and 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 December 31, 2018 , the carrying value and fair value of long-term obligations, including the current portion, were $21.2 billion and $21.1 billion , respectively, of which $13.4 billion was measured using Level 1 inputs and $7.7 billion was measured using Level 2 inputs. As of December 31, 2017 , the carrying value and fair value of long-term obligations, including the current portion, were $20.2 billion and $20.6 billion , respectively, 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	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Beginning in the taxable year ended December 31, 2012, the Company has filed, and intends to continue to file, U.S. federal income tax returns as a REIT, and its domestic TRSs filed, and intend to continue to file, separate tax returns as required. The Company also files tax returns in various states and countries. The Company’s state tax returns reflect different combinations of the Company’s subsidiaries and are dependent on the connection each subsidiary has with a particular state and form of organization. The following information pertains to the Company’s income taxes on a consolidated basis. The income tax provision from continuing operations consisted of the following for the years ended December 31,: 2018 2017 2016 Current: Federal $ (1.4 ) $ (0.1 ) $ (26.5 ) State (1.8 ) (3.8 ) (2.0 ) Foreign (189.7 ) (113.4 ) (100.1 ) Deferred: Federal 4.0 0.2 (0.6 ) State 0.7 1.0 (0.3 ) Foreign 298.3 85.4 (26.0 ) Income tax benefit (provision) $ 110.1 $ (30.7 ) $ (155.5 ) The effective tax rate (“ETR”) on income from continuing operations for the years ended December 31, 2018, 2017 and 2016 differs from the federal statutory rate primarily due to the Company’s qualification for taxation as a REIT, as well as adjustments for state and foreign items. As a REIT, the Company may deduct earnings distributed to stockholders against the income generated by its REIT operations. In addition, the Company is able to offset certain income by utilizing its NOLs, subject to specified limitations. The Tax Act significantly changed how the U.S. taxes corporations. The Tax Act contained several key provisions including, among other things, a reduction in the corporate income rate from 35% to 21% for tax years beginning after December 31, 2017. As a result of this change in tax rate, the rate at which the Company’s deferred tax assets of the Company’s TRSs decreased, resulting in additional tax expense of $2.4 million , which did not significantly impact the Company's effective tax rate. As of December 31, 2017, the analysis of the full impact of the Tax Act on the Company was considered provisional and subject to further analysis. As of December 31, 2018 the Company has completed its analysis and all amounts are considered final. There were no material changes to the provisional impact. In 2015, there was an income tax law change in Ghana that disallowed unused capital allowances to be carried into 2016, which resulted in a charge to income tax expense for the year ended December 31, 2015. In 2017, the Ghana Revenue Authority issued Practice Note Number DT/2016/010 (the “Practice Note”), which clarified the Capital Allowance section of the Income Tax Act of 2015. The Practice Note allowed for unused Capital Allowance from 2015 to be treated as a deduction in 2016. As a result, the Company recorded a tax benefit of $17.8 million for the year ended December 31, 2017. The change in the income tax (benefit) provision for the year ended December 31, 2018 was primarily attributable to receipt of the payment associated with the Tata settlement and the deferred benefit resulting from impairment charges and accelerated amortization taken in the same foreign jurisdiction. The net impact from restructuring was primarily due to a benefit of $85.7 million which resulted from the restructuring of foreign operations in certain jurisdictions. Reconciliation between the U.S. statutory rate and the effective rate from continuing operations is as follows for the years ended December 31,: 2018 2017 2016 Statutory tax rate 21% 35 % 35 % Adjustment to reflect REIT status (1) (21 ) (35 ) (35 ) Foreign taxes (8 ) 1 5 Foreign withholding taxes 4 3 4 Uncertain tax positions — — 5 Changes in tax laws — (2 ) — Impact from restructuring (6 ) — — Effective tax rate (10 )% 2 % 14 % _______________ (1) As a result of the ability to utilize the dividends paid deduction to offset the Company’s REIT income and gains. The domestic and foreign components of income from continuing operations before income taxes are as follows for the years ended December 31,: 2018 2017 2016 United States $ 1,212.7 $ 971.2 $ 882.6 Foreign (58.1 ) 284.9 243.3 Total $ 1,154.6 $ 1,256.1 $ 1,125.9 The components of the net deferred tax asset and liability and related valuation allowance were as follows as of December 31,: 2018 2017 Assets: Net operating loss carryforwards $ 264.9 $ 287.0 Accrued asset retirement obligations 165.7 157.0 Stock-based compensation 6.3 3.9 Unearned revenue 28.3 19.3 Unrealized loss on foreign currency 12.9 27.4 Other accruals and allowances 78.6 50.2 Items not currently deductible and other 26.2 28.0 Liabilities: Depreciation and amortization (757.0 ) (1,073.9 ) Deferred rent (36.9 ) (35.9 ) Other (15.3 ) (14.7 ) Subtotal (226.3 ) (551.7 ) Valuation allowance (151.9 ) (142.0 ) Net deferred tax liabilities $ (378.2 ) $ (693.7 ) At December 31, 2018 and 2017, the Company has provided a valuation allowance of $151.9 million and $142.0 million , respectively, which primarily relates to foreign items. The increase in the valuation allowance for the year ending December 31, 2018 is due to uncertainty as to the timing of, and the Company’s ability to recover, net deferred tax assets in certain foreign operations in the foreseeable future, offset by fluctuations in foreign currency exchange rates. The amount of deferred tax assets considered realizable, however, could be adjusted if objective evidence in the form of cumulative losses is no longer present and additional weight may be given to subjective evidence such as the Company’s projections for growth. A summary of the activity in the valuation allowance is as follows: 2018 2017 2016 Balance as of January 1, $ 142.0 $ 144.4 $ 137.0 Additions (1) 15.7 11.6 14.1 Reversals — (9.1 ) — Foreign currency translation (5.8 ) (4.9 ) (6.7 ) Balance as of December 31, $ 151.9 $ 142.0 $ 144.4 _______________ (1) Includes net charges to expense and allowances established through goodwill at acquisition. The recoverability of the Company’s deferred tax assets has been assessed utilizing projections based on its current operations. Accordingly, the recoverability of the deferred tax assets is not dependent on material asset sales or other non-routine transactions. Based on its current outlook of future taxable income during the carryforward period, the Company believes that deferred tax assets, other than those for which a valuation allowance has been recorded, will be realized. Despite a mandatory one-time inclusion in U.S. taxable income of accumulated earnings of foreign subsidiaries under the Tax Act for the year ended December 31, 2017, the Company intends to continue to reinvest foreign earnings indefinitely outside of the U.S. and does not expect to incur any significant additional taxes, including withholding taxes, related to such amounts. At December 31, 2018 , the Company had net federal, state and foreign operating loss carryforwards available to reduce future taxable income. If not utilized, the Company’s NOLs expire as follows: Years ended December 31, Federal State Foreign 2019 to 2023 $ — $ 142.9 $ 46.0 2024 to 2028 141.7 378.4 142.7 2029 to 2033 — 13.9 4.5 2034 to 2038 10.6 135.4 — Indefinite carryforward 9.6 — 746.5 Total $ 161.9 $ 670.6 $ 939.7 As of December 31, 2018 and 2017 , the total amount of unrecognized tax benefits that would impact the ETR, if recognized, is $93.7 million and $105.8 million , respectively. The amount of unrecognized tax benefits for the year ended December 31, 2018 includes additions to the Company’s existing tax positions of $8.4 million . The Company expects the unrecognized tax benefits to change over the next 12 months if certain tax matters ultimately settle with the applicable taxing jurisdiction during this timeframe, or if the applicable statute of limitations lapses. The impact of the amount of such changes to previously recorded uncertain tax positions could range from zero to $2.7 million . A reconciliation of the beginning and ending amount of unrecognized tax benefits are as follows for the years ended December 31,: 2018 2017 2016 Balance at January 1 $ 116.7 $ 107.6 $ 28.1 Additions based on tax positions related to the current year 8.1 7.6 82.9 Additions and reductions for tax positions of prior years 0.3 — — Foreign currency (8.1 ) 1.9 (0.2 ) Reduction as a result of the lapse of statute of limitations (2.6 ) (0.4 ) (3.2 ) Reduction as a result of effective settlements (6.7 ) — — Balance at December 31 $ 107.7 $ 116.7 $ 107.6 During the years ended December 31, 2018 , 2017 and 2016 , the statute of limitations on certain unrecognized tax benefits lapsed and certain positions were effectively settled, which resulted in a decrease of $9.3 million , $0.4 million and $3.2 million , respectively, in the liability for uncertain tax benefits. The Company recorded penalties and tax-related interest expense to the tax provision of $8.0 million , $5.0 million and $9.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. In addition, due to the expiration of the statute of limitations in certain jurisdictions and certain positions that were effectively settled, the Company reduced its liability for penalties and income tax-related interest expense related to uncertain tax positions during the years ended December 31, 2018 , 2017 and 2016 by $16.2 million , $0.6 million and $3.4 million , respectively. As of December 31, 2018 and 2017 , the total amount of accrued income tax-related interest and penalties included in the consolidated balance sheets were $19.1 million and $29.0 million , respectively. The Company has filed for prior taxable years, and for its taxable year ended December 31, 2018 will file, numerous consolidated and separate income tax returns, including U.S. federal and state tax returns and foreign tax returns. The Company is subject to examination in the U.S. and various state and foreign jurisdictions for certain tax years. As a result of the Company’s ability to carryforward federal, state and foreign NOLs, the applicable tax years generally remain open to examination several years after the applicable loss carryforwards have been used or have expired. The Company regularly assesses the likelihood of additional assessments in each of the tax jurisdictions resulting from these examinations. The Company believes that adequate provisions have been made for income taxes for all periods through December 31, 2018 .

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 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 RSUs and stock options and three years for PSUs. Stock options generally expire 10 years from the date of grant. As of December 31, 2018 , the Company had the ability to grant stock-based awards with respect to an aggregate of 7.7 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 years ended December 31, 2018 , 2017 and 2016 , the Company recorded and capitalized the following stock-based compensation expenses: 2018 2017 2016 Stock-based compensation expense $ 137.5 $ 108.5 $ 89.9 Stock-based compensation expense capitalized as property and equipment 2.0 1.6 1.4 Stock Options —The fair value of each option granted during the period was estimated on the date of grant using the Black-Scholes option pricing model based on the assumptions noted in the table below. The expected life of stock options (estimated period of time outstanding) was estimated using the vesting term and historical exercise behavior of the Company’s employees. The risk-free interest rate was based on the U.S. Treasury yield with a term that approximated the estimated life in effect at the accounting measurement date. The expected volatility of the underlying stock price was based on historical volatility for a period equal to the expected life of the stock options. The expected annual dividend yield was the Company’s best estimate of expected future dividend yield. There were no options granted during the year ended December 31, 2018. Key assumptions used to apply the Black-Scholes option pricing model were as follows (percentages and years disclosed in full amounts): 2017 2016 Range of risk-free interest rate 1.88%-1.94% 1.00%-1.73% Weighted average risk-free interest rate 1.89% 1.44% Range of expected life of stock options 5.2 years 4.5 - 5.2 years Range of expected volatility of the underlying stock price 18.95% - 19.45% 20.59% - 21.45% Weighted average expected volatility of underlying stock price 19.05% 21.43% Range of expected annual dividend yield 2.40% 1.85% - 2.40% The weighted average grant date fair value per share during the years ended December 31, 2017 and 2016 was $16.84 and $14.60 , respectively. The intrinsic value of stock options exercised during the years ended December 31, 2018 , 2017 and 2016 was $98.8 million , $100.3 million and $77.6 million , respectively. As of December 31, 2018 , total unrecognized compensation expense related to unvested stock options was $4.5 million and is expected to be recognized over a weighted average period of approximately one year. The amount of cash received from the exercise of stock options was $88.7 million during the year ended December 31, 2018 . The Company’s option activity for the year ended December 31, 2018 was as follows (share and per share data disclosed in full amounts): Options Weighted Average Exercise Price Per Share Weighted Average Remaining Life (Years) Aggregate Intrinsic Value Outstanding as of January 1, 2018 5,557,561 $81.32 Granted — — Exercised (1,242,536 ) 71.41 Forfeited (57,555 ) 94.66 Expired — — Outstanding as of December 31, 2018 4,257,470 $84.03 5.18 $315.7 Exercisable as of December 31, 2018 3,360,226 $81.10 4.76 $259.0 Vested or expected to vest as of December 31, 2018 4,257,470 $84.03 5.18 $315.7 The following table sets forth information regarding options outstanding at December 31, 2018 (share and per share data disclosed in full amounts): Options Outstanding Options Exercisable Range of Exercise Price Per Share Outstanding Number of Options Weighted Average Exercise Price Per Share Weighted Average Remaining Life (Years) Options Exercisable Weighted Average Exercise Price Per Share $28.39 - $62.00 594,690 $ 56.69 2.67 594,690 $ 56.69 $71.07 - $74.06 14,717 73.26 4.48 14,717 73.26 $76.90 - $77.75 559,293 76.91 4.00 559,293 76.91 $81.18 - $94.23 983,105 81.55 4.98 967,146 81.43 $94.57 - $94.71 2,070,809 94.62 6.28 1,213,187 94.60 $96.46 - $121.15 34,856 109.92 7.38 11,193 107.20 $28.39 - $121.15 4,257,470 $ 84.03 5.18 3,360,226 $ 81.10 Restricted Stock Units and Performance-Based Restricted Stock Units —The Company’s RSU and PSU activity for the year ended December 31, 2018 was as follows (share and per share data disclosed in full amounts): RSUs Weighted Average Grant Date Fair Value PSUs Weighted Average Grant Date Fair Value Outstanding as of January 1, 2018 (1) 1,742,725 $ 102.60 444,031 $ 102.81 Granted (2) 686,789 144.96 300,651 116.71 Vested and Released (3) (682,311 ) 98.24 (120,171 ) 100.35 Forfeited (97,230 ) 116.37 — — Outstanding as of December 31, 2018 1,649,973 $ 121.23 624,511 $ 109.97 Expected to vest as of December 31, 2018 1,649,973 $ 121.23 624,511 $ 109.97 Vested and deferred as of December 31, 2018 (4) 32,596 $ 119.14 — $ — _______________ (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 (each defined below), 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 first, second and third year’s performance periods, or 120,171 shares. (2) PSUs represent the shares above target that are issuable for the 2016 PSUs at the end of the three -year performance cycle based on exceeding the performance metric for the three-year performance period, or 169,340 shares, and 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. RSUs exclude 32,596 shares that are vested and deferred. (4) Vested and deferred RSUs are related to deferred compensation for certain former employees. The total fair value of RSUs and PSUs that vested during the year ended December 31, 2018 was $115.1 million . Restricted Stock Units— As of December 31, 2018 , total unrecognized compensation expense related to unvested RSUs granted under the 2007 Plan was $111.8 million and is expected to be recognized over a weighted average period of approximately two years . Performance-Based Restricted Stock Units— During the years ended December 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 each of 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 or death, disability or qualified retirement (each as defined in the applicable PSU award agreement). PSUs will accrue dividend equivalents prior to vesting, which will be paid out only in respect of shares that actually vest. On July 26, 2018, the Company changed the vesting terms of the PSU award agreements in the event of a participant’s death, disability or qualified retirement (each as defined in the applicable award agreement) for all plan participants with the exception of its Chief Executive Officer. During the year ended December 31, 2018 , the Company recorded $52.2 million in stock-based compensation expense for equity awards in which the performance goals have been established and were probable of being achieved. This amount included $19.1 million of incremental compensation that was accelerated in the third quarter due to the changes in vesting terms. The remaining unrecognized compensation expense related to these awards at December 31, 2018 , was $8.6 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	12 Months Ended
	Dec. 31, 2018
Temporary Equity Disclosure [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 Sons”), Tata Teleservices, IDFC Private Equity Fund III (“IDFC”), Macquarie SBI Infrastructure Investments Pte Limited and SBI Macquarie Infrastructure Trust (collectively, the “Remaining Shareholders”). During the year ended December 31, 2018, pursuant to the terms of the Shareholders Agreement, the Company merged 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 year ended December 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 Net income attributable to noncontrolling interests. Due primarily to the impact of impairment charges on net income and, as a result, on the carrying value of the noncontrolling interests, the Company adjusted noncontrolling interests by $86.7 million for the year ended December 31, 2018. The put options may be exercised, requiring the Company to purchase the Remaining Shareholders’ equity interests, on specified dates through March 31, 2021. The price of the put options will be based on the fair market value of the exercising Remaining Shareholders’ interest in the Company’s India operations at the time the option is exercised. Put options held by certain of the Remaining Shareholders are subject to a floor price of 216 INR. In the fourth quarter of 2018, Tata Teleservices delivered to the Company notice of exercise of their put options under the Shareholders Agreement with respect to 50% of their combined holdings with Tata Sons of ATC TIPL. Also in the fourth quarter of 2018, IDFC delivered notice to the Company of exercise of its put option under the Shareholders Agreement with respect of 100% of its holdings of ATC TIPL. The Company expects to complete the redemption of the put shares, subject to regulatory approval, for total consideration of INR 29.4 billion (approximately $420.0 million ) in the first half of 2019. As a result of the redemption, the Company’s controlling interest in ATC TIPL would increase to approximately 79% . The changes in Redeemable noncontrolling interests for the year ended December 31, 2018, 2017 and 2016 were as follows: Year Ended December 31, 2018 2017 2016 Balance as of January 1, $ 1,126.2 $ 1,091.3 $ — Fair value at acquisition — — 1,100.9 Net (loss) income attributable to noncontrolling interests (87.9 ) (33.4 ) 13.9 Adjustment to noncontrolling interest redemption value 86.7 — — Adjustment to noncontrolling interest due to merger (28.1 ) — — Foreign currency translation adjustment attributable to noncontrolling interests (92.1 ) 68.3 (23.5 ) Balance as of December 31, $ 1,004.8 $ 1,126.2 $ 1,091.3

EQUITY

EQUITY	12 Months Ended
	Dec. 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”). As of December 31, 2017, the Company had 13,749,860 depositary shares, each representing a 1/10th interest in a share of its Series B Preferred Stock outstanding, after giving effect to the early conversion of 140 depositary shares at the option of the holder at a conversion rate of 0.8687 per depositary share in May 2017. 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. Unless converted or redeemed earlier, each share of the Series B Preferred Stock converted automatically on February 15, 2018 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 shares of the Company’s common stock pursuant to the provisions of the Certificate of Designations governing the Series B Preferred Stock. As a result of the conversions of the Series B Preferred Stock in 2018, the Company issued an aggregate of 12,020,064 shares of its common 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. Dividends —The Company may pay dividends in cash or, subject to certain limitations, in shares of common stock or any combination of cash and shares of common stock. Sales of Equity Securities —The Company receives proceeds from sales of its equity securities pursuant to the ESPP and upon exercise of stock options granted under its equity incentive plan. During the year ended December 31, 2018, the Company received an aggregate of $98.9 million in proceeds upon exercises of stock options and sales pursuant to the ESPP. Stock Repurchase Programs —In March 2011, the Company’s Board of Directors approved a stock repurchase program, pursuant to which the Company is authorized to repurchase up to $1.5 billion of its common stock (the “2011 Buyback”). In December 2017, the Board of Directors approved an additional stock repurchase program, pursuant to which the Company is authorized to repurchase up to $2.0 billion of its common stock (the “2017 Buyback” and, together with the 2011 Buyback, the “Buyback Programs”). During the year ended December 31, 2018 , the Company repurchased 1,647,489 shares of its common stock under the 2011 Buyback for an aggregate of $232.8 million , including commissions and fees. As of December 31, 2018 , the Company had repurchased a total of 14,003,543 shares of its common stock under the 2011 Buyback for an aggregate of $1.4 billion , including commissions and fees. There were no repurchases under the 2017 Buyback. Under the Buyback Programs, the Company is authorized to purchase shares from time to time through open market purchases, in privately negotiated transactions not to exceed market prices, and (with respect to such open market purchases) pursuant to plans adopted in accordance with Rule 10b5-1 under the Securities Exchange Act of 1934 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 years ended December 31, 2018 , 2017 and 2016 , the Company declared the following cash distributions: For the year ended December 31, 2018 2017 2016 Distribution Aggregate Distribution Aggregate Distribution Aggregate Common Stock $ 3.15 $ 1,389.8 $ 2.62 $ 1,122.5 $ 2.17 $ 923.7 Series A Preferred Stock (1) $ — $ — $ 2.63 $ 15.8 $ 5.25 $ 31.5 Series B Preferred Stock $ 13.75 $ 18.9 $ 55.00 $ 75.6 $ 55.00 $ 75.6 _______________ (1) 5.25% Mandatory Convertible Preferred Stock, Series A, par value $0.01 per share (the “Series A Preferred Stock”), which converted into shares of the Company’s common stock pursuant to the provisions of the Certificate of Designations governing the Series A Preferred Stock in 2017. The following table characterizes the tax treatment of distributions declared per share of common stock and Mandatory Convertible Preferred Stock. For the year ended December 31, 2018 2017 2016 Per Share % Per Share % Per Share % Common Stock Ordinary dividend $ 3.1500 (1) 100.00 % $ 2.6200 100.00 % $ 2.1700 100.00 % Capital gains distribution — — — — — — Total $ 3.1500 100.00 % $ 2.6200 100.00 % $ 2.1700 100.00 % Series A Preferred Stock Ordinary dividend $ — — % $ 3.3643 (2) 100.00 % $ 6.4578 (3) 100.00 % Capital gains distribution — — — — — — Total $ — — % $ 3.3643 100.00 % $ 6.4578 100.00 % Series B Preferred Stock (4) Ordinary dividend $ 2.1314 (5) 100.00 % $ 6.5233 (6) 100.00 % $ 5.5000 100.00 % Capital gains distribution — — — — — — Total $ 2.1314 100.00 % $ 6.5233 100.00 % $ 5.5000 100.00 % _______________ (1) Includes dividend declared on December 4, 2018 of $0.84 per share, which was paid on January 14, 2019 to common stockholders of record at the close of business on December 27, 2018. (2) Includes a deemed distribution as a result of a conversion rate adjustment triggered on April 27, 2017. (3) Includes a deemed distribution as a result of a conversion rate adjustment triggered on June 17, 2016. (4) Represents the tax treatment on dividends per depositary share, each of which represents a 1/10th interest in a share of Series B Preferred Stock. (5) Includes a deemed distribution as a result of a conversion rate adjustment triggered on January 18, 2018. (6) Includes a deemed distribution as a result of a conversion rate adjustment triggered on April 12, 2017. The Company accrues distributions on unvested restricted stock units, which are payable upon vesting. The amount accrued for distributions payable related to unvested restricted stock units was $13.7 million and $10.1 million as of December 31, 2018 and 2017, respectively. During the year ended December 31, 2018 , the Company paid $4.3 million of distributions payable 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.

(Notes)

(Notes)	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Other Operating Expenses	OTHER OPERATING EXPENSE Other operating expense consists primarily of impairment charges, net losses on sales or disposals of assets and other operating expense items. The Company records impairment charges to write down certain assets to their net realizable value after an indicator of impairment is identified and subsequent analysis determines that the asset is either partially recoverable or not recoverable. These assets consisted primarily of towers, which are typically assessed on an individual basis, network location intangibles, which relate directly to towers, and tenant-related intangibles, which are assessed on a tenant basis. For the years ended December 31, 2018, 2017 and 2016, impairment charges included amounts related to land easements. Net losses on sales or disposals of assets primarily relate to certain non-core towers, other assets and miscellaneous items. Other operating expenses includes acquisition-related costs and integration costs. Other operating expenses included the following for the years ended December 31,: 2018 2017 2016 Impairment charges $ 394.0 $ 211.4 $ 28.5 Net losses on sales or disposals of assets 85.6 32.8 25.1 Other operating expenses (1) 33.7 11.8 19.7 Total Other operating expenses $ 513.3 $ 256.0 $ 73.3 _______________ (1) For the year ended December 31, 2017, the amount also includes refunds of acquisition costs and a charitable contribution. Impairment charges included the following for the years ended December 31,: 2018 2017 2016 Tower and network location intangible assets $ 284.9 $ 108.7 $ 18.0 Tenant relationships 107.3 100.1 — Other 1.8 2.6 10.5 Total impairment charges $ 394.0 $ 211.4 $ 28.5 On February 28, 2018, one of the Company’s tenants in Asia, Aircel Ltd.’s (“Aircel”), filed for bankruptcy protection with the National Company Law Tribunal of India. The bankruptcy process is ongoing 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 primarily consisted of towers, network location intangibles and tenant-related intangibles. As a result, an impairment of $40.1 million was recorded on the tower and network location intangible assets. The Company also fully impaired the tenant relationship for Aircel, which resulted in an impairment of $107.3 million during the year ended December 31, 2018. In October 2017, one of the Company’s tenants in Asia, 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. In October 2018, the Company entered into agreements with Tata for a settlement and release of certain contractual lease obligations of Tata. The Company performed an impairment test based on current expectations of the impact of the settlement on projected cash flows for assets related to Tata. These assets consisted primarily of towers, network location intangibles and tenant-related intangibles. As a result, an impairment of $164.2 million was recorded on the tower and network location intangible assets. During the year ended December 31, 2018, the Company recorded an additional $54.0 million of impairments on tower and network location intangible assets related to other carrier consolidation-driven churn in India. During the year ended December 31, 2017, $81.0 million of impairment charges on tower and network location intangible assets and all impairment charges on tenant relationships related to carrier consolidation-driven churn in India.

EARNINGS PER COMMON SHARE

EARNINGS PER COMMON SHARE	12 Months Ended
	Dec. 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 for the years ended December 31, (shares in thousands, except per share data): 2018 2017 2016 Net income attributable to American Tower Corporation stockholders $ 1,236.4 $ 1,238.9 $ 956.4 Dividends on preferred stock (9.4 ) (87.4 ) (107.1 ) Net income attributable to American Tower Corporation common stockholders 1,227.0 1,151.5 849.3 Basic weighted average common shares outstanding 439,606 428,181 425,143 Dilutive securities 3,354 3,507 4,140 Diluted weighted average common shares outstanding 442,960 431,688 429,283 Basic net income attributable to American Tower Corporation common stockholders per common share $ 2.79 $ 2.69 $ 2.00 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 2.77 $ 2.67 $ 1.98 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 for the years ended December 31, (in thousands, on a weighted average basis): 2018 2017 2016 Restricted stock awards — 3 6 Stock options — 4 817 Preferred stock 1,456 14,040 17,509

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 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 2,280 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 December 31, 2018 , the Company has purchased an aggregate of 149 of the subleased towers upon expiration of the applicable agreement, including 61 towers purchased during the year ended December 31, 2018 for an aggregate purchase price of $22.2 million . The aggregate purchase option price for the remaining towers leased and subleased is $891.5 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 December 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 December 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. Taxing authorities may issue preliminary notices or assessments while audits are being conducted. In certain jurisdictions, taxing authorities may issue assessments with minimal examination. These notices and assessments do not represent amounts that the Company is obligated to pay and are often not reflective of the actual tax liability for which the Company will ultimately be liable. 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 has appealed this ruling at a higher appellate authority. The Company estimates that there is a more likely than not probability that the Company’s position will be sustained upon appeal. Accordingly, no liability has been recorded. Additionally, the assessment was made with respect to transactions that took place in the tax year commencing in 2007, prior to the Company’s acquisition of ETIPL. Under the Company’s definitive acquisition agreement 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. 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 applicable 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 December 31, 2018 are as follows: Year Ending December 31, 2019 $ 926.0 2020 904.2 2021 879.8 2022 834.2 2023 792.6 Thereafter 6,173.1 Total $ 10,509.9 Aggregate rent expense (including the effect of straight-line rent expense) under operating leases for the years ended December 31, 2018 , 2017 and 2016 approximated $1,128.0 million , $1,088.0 million and $986.2 million , respectively. Future minimum payments under capital leases in effect at December 31, 2018 were as follows: Year Ending December 31, 2019 $ 40.7 2020 32.7 2021 27.8 2022 23.7 2023 19.2 Thereafter 117.5 Total minimum lease payments 261.6 Less amounts representing interest (82.1 ) Present value of capital lease obligations $ 179.5 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. Historically, the Company has been able to successfully renew its ground leases as needed to ensure its tower revenue. Accordingly, the Company assumes that it will have access to the land underneath its tower sites when calculating future minimum rental receipts. Future minimum rental receipts expected from tenants under non-cancellable operating lease agreements in effect at December 31, 2018 were as follows: Year Ending December 31, 2019 $ 5,251.2 2020 5,062.2 2021 4,676.1 2022 3,754.6 2023 3,457.3 Thereafter 12,641.1 Total $ 34,842.5 Guaranties and Indemnifications —The Company enters into agreements from time to time in the ordinary course of business pursuant to which it agrees to guarantee or indemnify third parties for certain claims. The Company has also entered into purchase and sale agreements relating to the sale or acquisition of assets containing customary indemnification provisions. The Company’s indemnification obligations under these agreements generally are limited solely to damages resulting from breaches of representations and warranties or covenants under the applicable agreements. In addition, payments under such indemnification clauses are generally conditioned on the other party making a claim that is subject to whatever defenses the Company may have and are governed by dispute resolution procedures specified in the particular agreement. Further, the Company’s obligations under these agreements may be limited in duration and amount, and in some instances, the Company may have recourse against third parties for payments made by the Company. The Company has not historically made any material payments under these agreements and, as of December 31, 2018 , is not aware of any agreements that could result in a material payment.

SUPPLEMENTAL CASH FLOW INFORMAT

SUPPLEMENTAL CASH FLOW INFORMATION	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	SUPPLEMENTAL CASH FLOW INFORMATION Supplemental cash flow information and non-cash investing and financing activities are as follows for the years ended December 31,: 2018 2017 2016 Supplemental cash flow information: Cash paid for interest $ 789.7 $ 712.1 $ 645.1 Cash paid for income taxes (net of refunds of $25.0, $20.7 and $19.6, respectively) 163.9 136.5 96.2 Non-cash investing and financing activities: Increase (decrease) in accounts payable and accrued expenses for purchases of property and equipment and construction activities 8.3 34.0 (19.0 ) Purchases of property and equipment under capital leases 57.8 54.8 55.6 Fair value of debt assumed through acquisitions — — 786.9 Exercise of purchase option for property and equipment for common shares issued — — 120.8 Acquisition of Commercialization Rights 24.8 — — Conversion of third-party debt to equity — 48.2 — Debt financed acquisition of communication sites 54.2 — —

BUSINESS SEGMENTS

BUSINESS SEGMENTS	12 Months Ended
	Dec. 31, 2018
Segment Reporting, Measurement Disclosures [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 December 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, Kenya, Nigeria, South Africa and Uganda; and • Latin America: property operations in Argentina, Brazil, Chile, Colombia, Costa Rica, Mexico, Paraguay and Peru. The Company’s services segment offers tower-related services in the United States, including AZP and structural analysis, which primarily support its site leasing business, including the addition of new tenants and equipment on its sites. The services segment is a strategic business unit that offers different services from, and requires different resources, skill sets and marketing strategies than, the property operating segments. The accounting policies applied in compiling segment information below are similar to those described in note 1. 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, for periods through September 30, 2018, the Latin America property segment gross margin and segment operating profit also include Interest income (expense), 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 years ended December 31, 2018 , 2017 and 2016 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 Year ended December 31, 2018 U.S. Asia EMEA Latin America Segment revenues (1) $ 3,822.1 $ 1,540.5 $ 687.3 $ 1,264.8 $ 7,314.7 $ 125.4 $ 7,440.1 Segment operating expenses (2) 771.0 710.9 238.1 406.3 2,126.3 48.2 2,174.5 Interest expense, TV Azteca, net — — — (0.1 ) (0.1 ) — (0.1 ) Segment gross margin 3,051.1 829.6 449.2 858.4 5,188.3 77.2 5,265.5 Segment selling, general, administrative and development expense (2) 165.2 110.7 69.1 83.5 428.5 14.4 442.9 Segment operating profit $ 2,885.9 $ 718.9 $ 380.1 $ 774.9 $ 4,759.8 $ 62.8 $ 4,822.6 Stock-based compensation expense $ 137.5 137.5 Other selling, general, administrative and development expense 156.1 156.1 Depreciation, amortization and accretion 2,110.8 2,110.8 Other expense (3) 1,263.6 1,263.6 Income from continuing operations before income taxes $ 1,154.6 Capital expenditures (4) $ 376.9 $ 101.0 $ 232.7 $ 220.7 $ 931.3 $ — $ 13.9 $ 945.2 _______________ (1) Asia segment revenues include a net impact of $333.7 million as a result of the settlement payment received from Tata in the fourth quarter of 2018. (2) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $3.3 million and $134.2 million , respectively. (3) Primarily includes interest expense and $394.0 million in impairment charges. (4) Includes $32.0 million of capital lease payments included in Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases in the cash flow from financing activities in the Company’s consolidated statement of cash flows. Property Total Property Services Other Total Year ended December 31, 2017 U.S. Asia EMEA Latin America Segment revenues $ 3,605.7 $ 1,164.4 $ 626.2 $ 1,169.6 $ 6,565.9 $ 98.0 $ 6,663.9 Segment operating expenses (1) 746.5 649.0 238.3 386.1 2,019.9 33.8 2,053.7 Interest income, TV Azteca, net — — — 10.8 10.8 — 10.8 Segment gross margin 2,859.2 515.4 387.9 794.3 4,556.8 64.2 4,621.0 Segment selling, general, administrative and development expense (1) 151.4 82.4 67.9 77.5 379.2 13.7 392.9 Segment operating profit $ 2,707.8 $ 433.0 $ 320.0 $ 716.8 $ 4,177.6 $ 50.5 $ 4,228.1 Stock-based compensation expense $ 108.5 108.5 Other selling, general, administrative and development expense 138.5 138.5 Depreciation, amortization and accretion 1,715.9 1,715.9 Other expense (2) 1,009.1 1,009.1 Income from continuing operations before income taxes $ 1,256.1 Capital expenditures (3) $ 360.6 $ 118.0 $ 141.7 $ 197.4 $ 817.7 $ — $ 17.7 $ 835.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $2.9 million and $105.6 million , respectively. (2) Primarily includes interest expense. (3) Includes $31.8 million of capital lease payments included in Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases in the cash flow from financing activities in the Company’s consolidated statement of cash flows. Property Total Property Other Total Year ended December 31, 2016 U.S. Asia EMEA Latin America Segment revenues $ 3,370.1 $ 827.6 $ 529.5 $ 985.9 $ 5,713.1 $ 72.6 $ 5,785.7 Segment operating expenses (1) 733.4 465.9 223.7 338.0 1,761.0 27.0 1,788.0 Interest income, TV Azteca, net — — — 10.9 10.9 — 10.9 Segment gross margin 2,636.7 361.7 305.8 658.8 3,963.0 45.6 4,008.6 Segment selling, general, administrative and development expense (1) 147.6 48.2 60.9 60.7 317.4 12.5 329.9 Segment operating profit $ 2,489.1 $ 313.5 $ 244.9 $ 598.1 $ 3,645.6 $ 33.1 $ 3,678.7 Stock-based compensation expense $ 89.9 89.9 Other selling, general, administrative and development expense 126.0 126.0 Depreciation, amortization and accretion 1,525.6 1,525.6 Other expense (2) 811.3 811.3 Income from continuing operations before income taxes $ 1,125.9 Capital expenditures (3) $ 310.7 $ 115.5 $ 86.1 $ 172.6 $ 684.9 $ — $ 16.5 $ 701.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $2.4 million and $87.5 million , respectively. (2) Primarily includes interest expense. (3) Includes $18.9 million of capital lease payments included in Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases in the cash flow from financing activities in the Company’s consolidated statement of cash flows. Additional information relating to the total assets of the Company’s operating segments is as follows for the years ended December 31,: 2018 2017 2016 U.S. property $ 18,782.0 $ 19,032.6 $ 18,846.9 Asia property (1) 4,938.8 4,770.8 4,535.3 EMEA property (1) 3,367.8 3,213.6 2,062.4 Latin America property (1) 5,594.7 5,868.4 4,938.1 Services 46.3 42.3 48.3 Other (2) 280.8 286.6 448.2 Total assets $ 33,010.4 $ 33,214.3 $ 30,879.2 _______________ (1) Balances are translated at the applicable period end exchange rate, which may impact comparability between periods. (2) Balances include corporate assets such as cash and cash equivalents, certain tangible and intangible assets and income tax accounts that have not been allocated to specific segments. Summarized geographic information related to the Company’s operating revenues for the years ended December 31, 2018 , 2017 and 2016 and long-lived assets as of December 31, 2018 and 2017 is as follows: 2018 2017 2016 Operating Revenues: United States $ 3,947.5 $ 3,703.7 $ 3,442.7 Asia (1): India 1,540.5 1,164.4 827.6 EMEA (1): France 72.7 59.5 — Germany 69.1 63.1 60.2 Ghana 125.4 122.9 116.2 Kenya 7.0 — — Nigeria 220.7 213.9 215.4 South Africa 125.3 106.5 80.0 Uganda 67.1 60.3 57.7 Latin America (1): Argentina 16.0 15.9 1.0 Brazil 595.5 620.1 506.2 Chile 44.2 40.4 33.8 Colombia 103.8 89.3 79.7 Costa Rica 18.4 19.4 19.0 Mexico 456.5 364.3 331.2 Paraguay 10.4 2.7 — Peru 20.0 17.5 15.0 Total International 3,492.6 2,960.2 2,343.0 Total operating revenues $ 7,440.1 $ 6,663.9 $ 5,785.7 _______________ (1) Balances are translated at the applicable exchange rate, which may impact comparability between periods. 2018 2017 Long-Lived Assets (1): United States $ 16,543.7 $ 16,930.2 Asia (2): India 3,947.8 4,052.6 EMEA (2): France 963.8 1,009.6 Germany 388.5 428.0 Ghana 159.2 171.4 Kenya 190.0 — Nigeria 606.5 587.2 South Africa 342.5 330.4 Uganda 138.7 136.9 Latin America (2): Argentina 81.6 117.9 Brazil 2,288.1 2,557.4 Chile 129.7 151.2 Colombia 381.6 369.0 Costa Rica 119.1 112.9 Mexico 1,421.3 1,396.8 Paraguay 107.4 77.5 Peru 113.8 93.7 Total International 11,379.6 11,592.5 Total long-lived assets $ 27,923.3 $ 28,522.7 _______________ (1) Includes Property and equipment, net, Goodwill and Other intangible assets, net. (2) Balances are translated at the applicable period end exchange rate, which may impact comparability between periods. The following tenants within the property and services segments individually accounted for 10% or more of the Company’s consolidated operating revenues for the years ended December 31,: 2018 2017 2016 AT&T 19 % 19 % 21 % Verizon Wireless 15 % 16 % 15 % Sprint 8 % 9 % 11 %

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2018
Related Party Transaction, Due from (to) Related Party [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS During the years ended December 31, 2018 , 2017 and 2016 , the Company had no significant related party transactions.

SELECTED QUARTERLY FINANCIAL DA

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Information [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) Selected quarterly financial data for the years ended December 31, 2018 and 2017 is as follows (in millions, except per share data): Three Months Ended Year Ended December 31, March 31, June 30, September 30, December 31, 2018: Operating revenues $ 1,741.8 $ 1,780.9 $ 1,785.5 $ 2,131.9 $ 7,440.1 Costs of operations (1) 519.9 560.3 556.7 540.9 2,177.8 Operating income 402.9 546.0 567.2 388.9 1,905.0 Net income 280.3 314.4 377.3 292.7 1,264.7 Net income attributable to American Tower Corporation stockholders 285.2 306.7 366.9 277.6 1,236.4 Dividends on preferred stock (9.4 ) — — — (9.4 ) Net income attributable to American Tower Corporation common stockholders 275.8 306.7 366.9 277.6 1,227.0 Basic net income per share attributable to American Tower Corporation common stockholders 0.63 0.69 0.83 0.63 2.79 Diluted net income per share attributable to American Tower Corporation common stockholders 0.63 0.69 0.83 0.62 2.77 Three Months Ended Year Ended December 31, March 31, June 30, September 30, December 31, 2017: Operating revenues $ 1,616.2 $ 1,662.5 $ 1,680.7 $ 1,704.5 $ 6,663.9 Costs of operations (1) 492.7 517.2 519.8 526.9 2,056.6 Operating income 531.4 576.9 561.1 329.0 1,998.4 Net income 307.4 388.5 334.7 194.8 1,225.4 Net income attributable to American Tower Corporation stockholders 316.1 367.0 317.3 238.5 1,238.9 Dividends on preferred stock (26.8 ) (22.8 ) (18.9 ) (18.9 ) (87.4 ) Net income attributable to American Tower Corporation common stockholders 289.3 344.2 298.4 219.6 1,151.5 Basic net income per share attributable to American Tower Corporation common stockholders 0.68 0.81 0.70 0.51 2.69 Diluted net income per share attributable to American Tower Corporation common stockholders 0.67 0.80 0.69 0.51 2.67 _______________ (1) Represents Operating expenses, exclusive of Depreciation, amortization and accretion, Selling, general, administrative and development expense, and Other operating expenses.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS 2019 Term Loan— On February 14, 2019, the Company entered into a $1.3 billion unsecured term loan (the “2019 Term Loan”), the net proceeds of which were used, together with cash on hand, to repay all outstanding indebtedness under the 2018 Term Loan. The 2019 Term Loan matures on February 13, 2020. The Company has the option of choosing either a defined base rate or LIBOR as the applicable base rate for borrowings under the 2019 Term Loan. The interest rate on the 2019 Term Loan ranges between 0.550% and 1.375% above LIBOR for LIBOR based borrowings or up to 0.375% above the defined base rate for base rate borrowings, in each case based upon the Company’s debt ratings. The current margin over LIBOR for the 2019 Term Loan is 0.800% . Any outstanding principal and accrued but unpaid interest will be due and payable in full at maturity. The 2019 Term Loan does not require amortization of principal and may be paid prior to maturity in whole or in part at the Company’s option without penalty or premium. The agreement for the 2019 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.

Schedule III - SCHEDULE OF REAL

Schedule III - SCHEDULE OF REAL ESTATE AND ACCUMULATED DEPRECIATION	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Real Estate and Accumulated Depreciation Disclosure	AMERICAN TOWER CORPORATION AND SUBSIDIARIES SCHEDULE III—SCHEDULE OF REAL ESTATE AND ACCUMULATED DEPRECIATION (dollars in millions) Description Encumbrances Initial cost to company Cost capitalized subsequent to acquisition Gross amount carried at close of current period Accumulated depreciation at close of current period Date of construction Date acquired Life on which depreciation in latest income statements is computed 168,985 sites (1) $ 3,014.2 (2) (3) (3) $ 15,960.1 (4) $ (5,724.7 ) Various Various Up to 20 years _______________ (1) No single site exceeds 5% of the total amounts indicated in the table above. (2) Certain assets secure debt of $3.0 billion . (3) The Company has omitted this information, as it would be impracticable to compile such information on a site-by-site basis. (4) Does not include those sites under construction. 2018 2017 2016 Gross amount at beginning $ 15,349.0 $ 14,277.0 $ 13,046.3 Additions during period: Acquisitions 721.4 499.7 787.2 Discretionary capital projects (1) 173.5 120.7 105.3 Discretionary ground lease purchases (2) 180.4 150.4 168.1 Redevelopment capital expenditures (3) 177.3 138.8 136.8 Capital improvements (4) 94.0 65.6 81.8 Start-up capital expenditures (5) 113.1 158.1 128.7 Other (6) (3.0 ) 106.4 139.4 Total additions 1,456.7 1,239.7 1,547.3 Deductions during period: Cost of real estate sold or disposed (395.7 ) (246.5 ) (85.8 ) Other (7) (449.9 ) 78.8 (230.8 ) Total deductions: (845.6 ) (167.7 ) (316.6 ) Balance at end $ 15,960.1 $ 15,349.0 $ 14,277.0 2018 2017 2016 Gross amount of accumulated depreciation at beginning $ (5,181.2 ) $ (4,548.1 ) $ (3,994.9 ) Additions during period: Depreciation (751.4 ) (718.7 ) (647.9 ) Other — — Total additions (751.4 ) (718.7 ) (647.9 ) Deductions during period: Amount of accumulated depreciation for assets sold or disposed 129.3 100.7 24.9 Other (7) 78.6 (15.1 ) 69.8 Total deductions 207.9 85.6 94.7 Balance at end $ (5,724.7 ) $ (5,181.2 ) $ (4,548.1 ) _______________ (1) Includes amounts incurred primarily for the construction of new sites. (2) Includes amounts incurred to purchase or otherwise secure the land under communications sites. (3) Includes amounts incurred to increase the capacity of existing sites, which results in new incremental tenant revenue. (4) Includes amounts incurred to enhance existing sites by adding additional functionality, capacity or general asset improvements. (5) Includes amounts incurred in connection with acquisitions or new market launches. Start-up capital expenditures includes non-recurring expenditures contemplated in acquisitions, new market launch business cases or initial deployment of new technologies or innovation solutions that lead to an increase in site-level cash flow generation. (6) Primarily includes regional improvements and other additions. (7) Primarily includes foreign currency exchange rate fluctuations and other deductions.

BUSINESS AND SUMMARY OF SIGNI_2

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business	Business —American Tower Corporation (together with its subsidiaries, “ATC” or the “Company”) is one of the largest global real estate investment trusts and a leading independent owner, operator and developer of multitenant communications real estate. The Company’s primary business is the leasing of space on communications sites to wireless service providers, radio and television broadcast companies, wireless data providers, government agencies and municipalities and tenants in a number of other industries. The Company refers to this business as its property operations. Additionally, the Company offers tower-related services in the United States, which the Company refers to as its services operations. These services include site acquisition, zoning and permitting (“AZP”) and structural analysis, which primarily support the Company’s site leasing business, including the addition of new tenants and equipment on its sites. The Company’s portfolio primarily consists of towers that it owns and towers that it operates pursuant to long-term lease arrangements, as well as distributed antenna system (“DAS”) networks, which provide seamless coverage solutions in certain in-building and certain outdoor wireless environments. In addition to the communications sites in its portfolio, the Company manages rooftop and tower sites for property owners under various contractual arrangements. The Company also holds other telecommunications infrastructure, fiber and property interests that it leases primarily to communications service providers and third-party tower operators. American Tower Corporation is a holding company that conducts its operations through its directly and indirectly owned subsidiaries and joint ventures. ATC’s principal domestic operating subsidiaries are American Towers LLC and SpectraSite Communications, LLC. ATC conducts its international operations primarily through its subsidiary, American Tower International, Inc., which in turn conducts operations through its various international holding and operating subsidiaries and joint ventures. The Company operates as a real estate investment trust for U.S. federal income tax purposes (“REIT”). Accordingly, the Company generally is not required to pay U.S. federal income taxes on income generated by its REIT operations, including the income derived from leasing space on its towers, as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on earnings from its domestic taxable REIT subsidiaries (“TRSs”). In addition, the Company’s international assets and operations, regardless of their classification for U.S. tax purposes, continue to be subject to taxation in the jurisdictions where those assets are held or those operations are conducted. The use of TRSs enables the Company to continue to engage in certain businesses while complying with REIT qualification requirements. The Company may, from time to time, change the election of previously designated TRSs to be included as part of the REIT. As of December 31, 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.
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation —The accompanying consolidated financial statements include the accounts of the Company and those entities in which it has a controlling interest. Investments in entities that the Company does not control are accounted for using the equity 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.
Significant Accounting Policies and Use of Estimates	Significant Accounting Policies and Use of Estimates —The preparation of financial statements in conformity with accounting principles generally accepted in the United States (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results may differ from those estimates, and such differences could be material to the accompanying consolidated financial statements. The significant estimates in the accompanying consolidated financial statements include impairment of long-lived assets (including goodwill), asset retirement obligations, revenue recognition, rent expense, income taxes and accounting for business combinations and acquisitions of assets. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued as additional evidence for certain estimates or to identify matters that require additional disclosure.
Accounts Receivable and Deferred Rent Asset	Accounts Receivable and Deferred Rent Asset —The Company derives the largest portion of its revenues, corresponding accounts receivable and the related deferred rent asset from a relatively small number of tenants in the telecommunications industry, and 51% of its current-year revenues are derived from four tenants. The Company’s deferred rent asset is associated with non-cancellable tenant leases that contain fixed escalation clauses over the terms of the applicable lease in which revenue is recognized on a straight-line basis over the lease term. The Company mitigates its concentrations of credit risk with respect to notes and trade receivables and the related deferred rent assets by actively monitoring the creditworthiness of its borrowers and tenants. In recognizing tenant revenue, the Company assesses the collectibility of both the amounts billed and the portion recognized in advance of billing on a straight-line basis. This assessment takes tenant credit risk and business and industry conditions into consideration to ultimately determine the collectibility of the amounts billed. To the extent the amounts, based on management’s estimates, may not be collectible, recognition is deferred until such point as collectibility is determined to be reasonably assured. Any amounts that were previously recognized as revenue and subsequently determined to be uncollectible are charged to bad debt expense included in Selling, general, administrative and development expense in the accompanying consolidated statements of operations. Accounts receivable is reported net of allowances for doubtful accounts related to estimated losses resulting from a tenant’s inability to make required payments and allowances for amounts invoiced whose collectibility is not reasonably assured. These allowances are generally estimated based on payment patterns, days past due and collection history, and incorporate changes in economic conditions that may not be reflected in historical trends, such as tenants in bankruptcy, liquidation or reorganization. Receivables are written-off against the allowances when they are determined to be uncollectible. Such determination includes analysis and consideration of the particular conditions of the account.
Functional Currency	Functional Currency —The functional currency of each of the Company’s foreign operating subsidiaries is normally the respective local currency, except for Costa Rica, where the functional currency is the U.S. Dollar. All foreign currency assets and liabilities held by the subsidiaries are translated into U.S. Dollars at the exchange rate in effect at the end of the applicable fiscal reporting period and all foreign currency revenues and expenses are translated at the average monthly exchange rates. Translation adjustments are reflected in equity as a component of Accumulated other comprehensive loss (“AOCL”) in the consolidated balance sheets and included as a component of Comprehensive income in the consolidated statements of comprehensive income. Gains and losses on foreign currency transactions are reflected in Other expense in the consolidated statements of operations. However, the effect from fluctuations in foreign currency exchange rates on intercompany debt for which repayment is not anticipated in the foreseeable future is reflected in AOCL in the consolidated balance sheets and included as a component of comprehensive income.
Cash and Cash Equivalents	Cash and Cash Equivalents —Cash and cash equivalents include cash on hand, demand deposits and short-term investments with original maturities of three months or less. The Company maintains its deposits at high quality financial institutions and monitors the credit ratings of those institutions.
Restricted Cash	Restricted Cash— Restricted cash includes cash pledged as collateral to secure obligations and all cash whose use is otherwise limited by contractual provisions.
Short-Term Investments	Short-Term Investments— Short-term investments consists of highly liquid investments with original maturities in excess of three months.
Property and Equipment	Property and Equipment —Property and equipment is recorded at cost or, in the case of acquired properties, at estimated fair value on the date acquired. Cost for self-constructed towers includes direct materials and labor, capitalized interest and certain indirect costs associated with construction of the tower, such as transportation costs, employee benefits and payroll taxes. The Company begins the capitalization of costs during the pre-construction period, which is the period during which costs are incurred to evaluate the site, and continues to capitalize costs until the tower is substantially completed and ready for occupancy by a tenant. Labor and related costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were $55.0 million , $50.9 million and $47.7 million , respectively. Capitalized interest costs were not material for the years ended December 31, 2018 , 2017 and 2016 . Expenditures for repairs and maintenance are expensed as incurred. Augmentation and improvements that extend an asset’s useful life or enhance capacity are capitalized. Depreciation expense is recorded using the straight-line method over the assets’ estimated useful lives. Towers and related assets on leased land are depreciated over the shorter of the estimated useful life of the asset or the term of the corresponding ground lease, taking into consideration lease renewal options and residual value. Towers or assets acquired through capital leases are recorded net at the present value of future minimum lease payments or the fair value of the leased asset at the inception of the lease. Property and equipment and assets held under capital leases are amortized over the shorter of the applicable lease term or the estimated useful life of the respective assets for periods generally not exceeding twenty years. The Company reviews its tower portfolio for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company reviews other long-lived assets for impairment whenever events, changes in circumstances or other evidence indicate that the carrying amount of the Company’s assets may not be recoverable. The Company records impairment charges in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets —The Company reviews goodwill for impairment at least annually (as of December 31) or whenever events or circumstances indicate the carrying value of an asset may not be recoverable. Goodwill is recorded in the applicable segment and assessed for impairment at the reporting unit level. The Company utilizes the two-step impairment test and employs a discounted cash flow analysis when testing goodwill for impairment. The key assumptions utilized in the discounted cash flow analysis include current operating performance, terminal sales growth rate, management’s expectations of future operating results and cash requirements, the current weighted average cost of capital and an expected tax rate. Under the first step of the test, the Company compares the fair value of the reporting unit, as calculated under an income approach using future discounted cash flows, to the carrying amount of the applicable reporting unit. If the carrying amount exceeds the fair value, the Company conducts the second step of this test, in which the implied fair value of the applicable reporting unit’s goodwill is compared to the carrying amount of that goodwill. If the carrying amount of goodwill exceeds its implied fair value, an impairment loss would be recognized for the amount of the excess. During the years ended December 31, 2018 , 2017 and 2016 , no potential impairment was identified under the first step of the test, as the fair value of each of the reporting units was in excess of its carrying amount. Intangible assets that are separable from goodwill and are deemed to have a definite life are amortized over their useful lives, generally ranging from three to twenty years and are evaluated separately for impairment at least annually or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. The Company reviews its network location intangible assets for indicators of impairment on an individual tower basis. Impairments primarily result from a tower not having current tenant leases or from having expenses in excess of revenues. The Company monitors its tenant-related intangible assets on a tenant by tenant basis for indicators of impairment, such as high levels of turnover or attrition, non-renewal of a significant number of contracts or the cancellation or termination of a relationship. The Company assesses recoverability by determining whether the carrying amount of the related assets will be recovered primarily through projected undiscounted future cash flows. If the Company determines that the carrying amount of an asset may not be recoverable, the Company measures any impairment loss based on the projected future discounted cash flows to be provided from the asset or available market information relative to the asset’s fair value, as compared to the asset’s carrying amount. The Company records impairment charges, which are discussed in note 16, in Other operating expenses in the consolidated statements of operations in the period in which the Company identifies such impairment.
Derivatives Financial Instruments	Derivative Financial Instruments —Derivatives are recorded on the consolidated balance sheet at fair value. If a derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in AOCL, as well as a component of comprehensive income, and are recognized in the results of operations when the hedged item affects earnings. Changes in fair value of the ineffective portions of cash flow hedges are recognized in the results of operations. For derivative instruments that are designated and qualify as fair value hedges, changes in value of the derivatives are recorded in Other expense in the consolidated statements of operations in the current period, along with the offsetting gain or loss on the hedged item attributable to the hedged risk. For derivative instruments not designated as hedging instruments, changes in fair value are recognized in the results of operations in the period that the change occurs. The primary risks managed through the use of derivative instruments is interest rate risk, exposure to changes in the fair value of debt attributable to interest rate risk and currency risk. From time to time, the Company enters into interest rate swap agreements or foreign currency contracts to manage exposure to these risks. Under these agreements, the Company is exposed to counterparty credit risk to the extent that a counterparty fails to meet the terms of a contract. The Company’s exposure is limited to the current value of the contract at the time the counterparty fails to perform. The Company assesses, both at the inception of the hedge and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in cash flows or fair values of hedged items. The Company does not hold derivatives for trading purposes.
Fair Value Measurements	Fair Value Measurements —The Company determines the fair value of its financial instruments based on the fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value.
Asset Retirement Obligations	Asset Retirement Obligations —When required, the Company recognizes the fair value of obligations to remove its tower assets and remediate the leased land upon which certain of its tower assets are located. Generally, the associated retirement costs are capitalized as part of the carrying amount of the related tower assets and depreciated over their estimated useful lives and the liability is accreted through the obligation’s estimated settlement date. Fair value estimates of asset retirement obligations generally involve discounting of estimated future cash flows associated with takedown costs. Periodic accretion of such liabilities due to the passage of time is included in Depreciation, amortization and accretion expense in the consolidated statements of operations. Adjustments are also made to the asset retirement obligation liability to reflect changes in the estimates of timing and amount of expected cash flows, with an offsetting adjustment made to the related long-lived tangible asset. The significant assumptions used in estimating the Company’s aggregate asset retirement obligation are: timing of tower removals; cost of tower removals; timing and number of land lease renewals; expected inflation rates; and credit-adjusted, risk-free interest rates that approximate the Company’s incremental borrowing rate.
Income Taxes	Income Taxes —As a REIT, the Company generally is not subject to U.S. federal income taxes on income generated by its REIT operations as it receives a dividends paid deduction for distributions to stockholders that generally offsets its REIT income and gains. However, the Company remains obligated to pay U.S. federal income taxes on certain earnings and continues to be subject to taxation in its foreign jurisdictions. Accordingly, the consolidated financial statements reflect provisions for federal, state, local and foreign income taxes. The Company recognizes deferred tax assets and liabilities for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, as well as operating loss and tax credit carryforwards. The Company measures deferred tax assets and liabilities using enacted tax rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities as a result of a change in tax rates is recognized in income in the period that includes the enactment date. The Company periodically reviews its deferred tax assets, and provides valuation allowances if, based on the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Valuation allowances would be reversed as a reduction to the provision for income taxes if related deferred tax assets are deemed realizable based on changes in facts and circumstances relevant to the assets’ recoverability. The Company classifies uncertain tax positions as non-current income tax liabilities in Other non-current liabilities in the consolidated balance sheet, unless expected to be paid within one year. The Company reports penalties and tax-related interest expense as a component of the income tax provision and interest income from tax refunds as a component of Other expense in the consolidated statements of operations.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) —Other comprehensive income (loss) refers to items excluded from net income that are recorded as an adjustment to equity, net of tax. The Company’s other comprehensive income (loss) primarily consisted of changes in fair value of effective derivative cash flow hedges, foreign currency translation adjustments and reclassification of unrealized losses on effective derivative cash flow hedges.
Distributions	Distributions —As a REIT, the Company must annually distribute to its stockholders an amount equal to at least 90% of its REIT taxable income (determined before the deduction for distributed earnings and excluding any net capital gain). Generally, the Company has distributed, and expects to continue to distribute, all or substantially all of its REIT taxable income after taking into consideration its utilization of net operating losses (“NOLs”). The amount, timing and frequency of future distributions will be at the sole discretion of the Board of Directors and will depend upon various factors, a number of which may be beyond the Company’s control, including the Company’s financial condition and operating cash flows, the amount required to maintain its qualification for taxation as a REIT and reduce any income and excise taxes that the Company otherwise would be required to pay, limitations on distributions in the Company’s existing and future debt and preferred equity instruments, the Company’s ability to utilize NOLs to offset the Company’s distribution requirements, limitations on its ability to fund distributions using cash generated through its TRSs and other factors that the Board of Directors may deem relevant.
Acquisitions	Acquisitions —For acquisitions that meet the definition of a business combination, the Company applies the acquisition method of accounting where assets acquired and liabilities assumed are recorded at fair value at the date of each acquisition, and the results of operations are included with those of the Company from the dates of the respective acquisitions. Any excess of the purchase price paid by the Company over the amounts recognized for assets acquired and liabilities assumed is recorded as goodwill. The Company continues to evaluate acquisitions for a period not to exceed one year after the applicable acquisition date of each transaction to determine whether any additional adjustments are needed to the allocation of the purchase price paid for the assets acquired and liabilities assumed. All other acquisitions are accounted for as asset acquisitions and the purchase price is allocated to the net assets acquired with no recognition of goodwill. The purchase price is not subsequently adjusted. The fair value of the assets acquired and liabilities assumed is typically determined by using either estimates of replacement costs or discounted cash flow valuation methods. When determining the fair value of tangible assets acquired, the Company must estimate the cost to replace the asset with a new asset taking into consideration such factors as age, condition and the economic useful life of the asset. When determining the fair value of intangible assets acquired and liabilities assumed, the Company must estimate the applicable discount rate and the timing and amount of future cash flows, including rate and terms of renewal and attrition.
Revenue Recognition	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 year ended December 31, 2018 is due to payments received, offset by $79.5 million of revenue recognized during the year ended December 31, 2018, that was included in the Unearned revenue balance as of January 1, 2018. There was $0.5 million of revenue recognized from Other non-current liabilities during the year ended December 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 attributable to revenue recognized during the year ended December 31, 2018 was $1.0 million . The change in contract assets attributable to revenue recognized during the year ended December 31, 2018 was $0.4 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. Revenue —The Company’s revenue from leasing arrangements, including fixed escalation clauses present in non-cancellable lease arrangements, is reported on a straight-line basis over the term of the respective leases when collectibility is probable. Escalation clauses tied to the Consumer Price Index or other inflation-based indices, and other incentives present in lease agreements with the Company’s tenants are excluded from the straight-line calculation. Total property straight-line revenues for the years ended December 31, 2018, 2017 and 2016 were $87.6 million , $194.4 million and $131.7 million , respectively. During the year ended December 31, 2018 the Company entered into agreements with one of its tenants in India, Tata Teleservices Limited (“Tata Teleservices”) and related entities (collectively, “Tata”), for a settlement and release of certain contractual lease obligations of Tata Teleservices for which the Company received a cash settlement payment of $345.5 million . The new revenue recognition accounting standard, which applies to revenue not recorded under the lease 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. For the year ended December 31, 2018, the impact of applying the new standard was an increase to revenue of $4.9 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 to enter into lease arrangements are capitalized under the applicable lease accounting guidance. Costs incurred to obtain non-lease contracts that are capitalized primarily relate to DAS networks and are not material to the consolidated financial statements. The Company has excluded sales tax, value-added tax and similar taxes from non-lease revenue. 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, or otherwise charge for, these services. 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 networks, fiber and other property related revenue. DAS networks and fiber arrangements require that the Company provide the tenant the right to use the applicable communications infrastructure. Performance obligations are satisfied over time for the duration of the arrangements. Other property related revenue streams, which include site inspections, are not material on either an individual or consolidated basis. Services revenue —The Company offers tower-related services in the United States. These services include AZP and structural analysis. There is a single performance obligation related to AZP, and revenue is recognized over time based on milestones achieved, which are determined based on costs expected to be incurred. Structural analysis services may have more than one performance obligation, contingent upon the number of contracted services. Revenue is recognized at the point in time the services are completed. Some of the Company’s contracts with tenants contain multiple performance obligations. For these arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price, which is typically based on the price charged to tenants.
Rent Expense	Rent Expense —Many of the leases underlying the Company’s tower sites have fixed rent escalations, which provide for periodic increases in the amount of ground rent payable by the Company over time. In addition, certain of the Company’s tenant leases require the Company to exercise available renewal options pursuant to the underlying ground lease if the tenant exercises its renewal option. The Company calculates straight-line ground rent expense for these leases based on the fixed non-cancellable term of the underlying ground lease plus all periods, if any, for which failure to renew the lease imposes an economic penalty to the Company such that renewal appears to be reasonably assured. Total property straight-line ground rent expense for the years ended December 31, 2018 , 2017 and 2016 was $57.9 million , $62.3 million and $67.8 million , respectively. The Company records a liability for straight-line ground rent expense in Other non-current liabilities. The Company records prepaid ground rent in Prepaid and other current assets and Notes receivable and other non-current assets in the accompanying consolidated balance sheets according to the anticipated period of benefit.
Selling, General, Administrative and Development Expense	Selling, General, Administrative and Development Expense —Selling, general and administrative expense consists of overhead expenses related to the Company’s property and services operations and corporate overhead costs not specifically allocable to any of the Company’s individual business operations. Development expense consists of costs related to the Company’s acquisition efforts, costs associated with new business initiatives and project cancellation costs.
Stock-Based Compensation	Stock-Based Compensation —Stock-based compensation expense is measured at the accounting measurement date based on the fair value of the award and is generally recognized as an expense over the service period, which typically represents the vesting period. The Company provides for accelerated vesting and extended exercise periods of stock options and restricted stock units upon an employee’s death or permanent disability, or upon an employee’s qualified retirement, provided certain eligibility criteria are met. Accordingly, the Company recognizes compensation expense for stock options and time-based restricted stock units (“RSUs”) over the shorter of (i) the four -year vesting period or (ii) the period from the date of grant to the date the employee becomes eligible for such retirement benefits, which may occur upon grant. The expense recognized includes the impact of forfeitures as they occur. The Company grants performance-based restricted stock units (“PSUs”) to its executive officers. Threshold, target and maximum parameters are established for a three -year performance period at the time of grant. The metrics are used to calculate the number of shares that will be issuable when the awards vest, which may range from zero to 200% of the target amounts. The Company recognizes compensation expense for PSUs over the three -year vesting period, subject to adjustment based on the date the employee becomes eligible for retirement benefits as well as performance relative to grant parameters. The fair value of stock options is determined using the Black-Scholes option-pricing model and the fair value of RSUs and PSUs is based on the fair value of the Company’s common stock on the date of grant. The Company recognizes all stock-based compensation expense in either Selling, general, administrative and development expense, costs of operations or as part of the costs associated with the construction of the tower assets. In connection with the vesting of restricted stock units, the Company withholds from issuance a number of shares of common stock to satisfy certain employee tax withholding obligations arising from such vesting. The shares withheld are considered constructively retired. The Company recognizes the fair value of the shares withheld in Additional paid-in capital on the consolidated balance sheets
Litigation Costs	Litigation Costs —The Company periodically becomes involved in various claims and lawsuits that are incidental to its business. The Company regularly monitors the status of pending legal actions to evaluate both the magnitude and likelihood of any potential loss. The Company accrues for these potential losses when it is probable that a liability has been incurred and the amount of loss, or possible range of loss, can be reasonably estimated. Should the ultimate losses on contingencies or litigation vary from estimates, adjustments to those liabilities may be required. The Company also incurs legal costs in connection with these matters and records estimates of these expenses, which are reflected in Selling, general, administrative and development expense in the accompanying consolidated statements of operations.
Earnings Per Common Share-Basic and Diluted	Earnings Per Common Share — Basic and Diluted —Basic net income per common share represents net income attributable to American Tower Corporation common stockholders divided by the weighted average number of common shares outstanding during the period. Diluted net income per common share represents net income attributable to American Tower Corporation common stockholders divided by the weighted average number of common shares outstanding during the period and any dilutive common share equivalents, including (A) shares issuable upon (i) the vesting of RSUs, (ii) exercise of stock options, and (iii) conversion of the Company’s mandatory convertible preferred stock and (B) shares expected to be earned upon the achievement of the parameters established for PSUs, each to the extent not anti-dilutive. Dilutive common share equivalents also include the dilutive impact of the shares issuable in the Alltel transaction, which is described in note 18. The Company uses the treasury stock method to calculate the effect of its outstanding RSUs, PSUs and stock options and uses the if-converted method to calculate the effect of its outstanding mandatory convertible preferred stock.
Retirement Plan	Retirement Plan —The Company has a 401(k) plan covering substantially all employees who meet certain age and employment requirements.
Accounting Standards Updates	Accounting Standards Updates Lease Accounting —In February 2016, the Financial Accounting Standards Board (the “FASB”) issued 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. In January 2018, the FASB issued 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 July 2018, the FASB issued additional guidance on the accounting for leases. The guidance provides companies with another transition method by allowing entities to recognize a cumulative-effect adjustment to the opening balance of retained earnings as of the date of adoption. Under this method, previously presented years’ financial positions and results would not be adjusted. The new guidance also provides lessors with a practical expedient, by class of underlying asset, to not separate non-lease components from the associated lease component if the non-lease components would otherwise be accounted for under the new revenue recognition standard and both the timing and pattern of transfer are the same for the non-lease components and associated lease component and, if accounted for separately, the lease component would be classified as an operating lease. In December 2018, the FASB issued additional guidance with narrow-scope improvements for lessors. The guidance permits lessors, as an accounting policy election, to exclude sales and related taxes from the evaluation of lessor costs, requires lessors to exclude from revenue and expense lessor costs paid directly to a third party by lessees and clarifies the lessors’ accounting for variable payments related to both lease and non-lease components. The lease accounting guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018. The Company plans to adopt the standard using the modified retrospective method applied to lease arrangements that were in place on the transition date. Results for reporting periods beginning January 1, 2019 will be presented under the new standard, while prior-period amounts will not be adjusted and will continue to be reported in accordance with accounting under the previously applicable guidance. The Company will elect certain available practical expedients that permit the adopter to not reassess certain items upon adoption, including: (i) whether any existing contracts are or contain leases, (ii) the classification of existing leases and (iii) initial directs costs for existing leases. As a result, the vast majority of the Company’s ground leases will continue to be accounted for as operating leases under the standard and have recognition patterns similar to those under prior guidance. The Company will also elect the practical expedient related to land easements, which permits carryforward accounting treatment of capitalizing long-term easements that have a specified term. The Company will elect to not separate non-lease components from the related lease components and will account for the components together as a single lease component on the transition date. The Company estimates adoption of the standard will result in recognition of operating lease right of use assets and operating lease liabilities of approximately $7.1 billion and $6.8 billion , respectively, as of January 1, 2019. The right of use assets recorded include, among other items, amounts previously classified as prepaid rent, deferred lease acquisition costs and long-term deferred rent obligations. The Company also expects to record approximately $24.7 million as an adjustment to retained earnings related to right of use assets assets recorded on previously impaired sites. The Company’s capital lease assets, which are disclosed in note 3, and liabilities, which are disclosed in note 8, remain largely unchanged under the lease accounting standard. Although adoption of the standard will require the Company to provide additional disclosures in the financial statements and notes, the Company does not expect the standard will have a material impact on its results of operations or liquidity. The Company does not expect the guidance to have a material impact on its debt covenant compliance. Other Updates —In January 2017, the FASB issued guidance on accounting for goodwill impairments. The guidance eliminates Step 2 from the goodwill impairment test and requires, among other things, recognition of an impairment loss when the carrying value of a reporting unit exceeds its fair value. The loss recognized is limited to the total amount of goodwill allocated to that reporting unit. The guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a material impact on the Company’s financial statements. In August 2017, the FASB issued 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 early adopted this guidance during the fourth quarter of 2018. The adoption of this guidance did not have a material impact on the Company’s 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 “Tax 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 the Company’s financial statements. In August 2018, the FASB issued guidance on fair value measurements. The guidance modifies the disclosure requirements on fair value measurements and is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company early adopted this guidance during the fourth quarter of 2018. The adoption of this guidance did not have a material impact on the Company’s financial statements. Other Disclosure Requirement Updates In August 2018, the Securities and Exchange Commission issued a final rule that amends certain of its disclosure requirements. Among other amendments, the final rule extends to interim periods the annual disclosure requirement of presenting changes in stockholders’ equity and the amount of dividends per share for each class of shares and deletes the provisions of the rules that require the presentation of dividends per share on the face of the income statement for interim periods, moving the required disclosure to the analysis of changes in stockholders’ equity. The final rule was effective as of November 5, 2018. The adoption of these disclosure requirements did not have a material impact on the Company’s financial statements.

BUSINESS AND SUMMARY OF SIGNI_3

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Changes in Allowances	Changes in the allowances were as follows: Year Ended December 31, 2018 2017 2016 Balance as of January 1, $ 131.0 $ 45.9 $ 23.1 Current year increases 157.8 87.2 50.0 Write-offs, recoveries and other (1) (6.4 ) (2.1 ) (27.2 ) Balance as of December 31, $ 282.4 $ 131.0 $ 45.9 _______________ (1) Recoveries includes recognition of revenue resulting from collections of previously reserved amounts.
Net Foreign Currency Losses	The Company recorded the following net foreign currency losses: Year Ended December 31, 2018 2017 2016 Foreign currency losses recorded in AOCL $ 385.8 $ 51.6 $ 105.0 Foreign currency losses (gains) recorded in Other expense 4.5 (26.4 ) 48.9 Net foreign currency losses $ 390.3 $ 25.2 $ 153.9
Schedule of Cash, cash Equivalents, and Restricted Cash	The reconciliation of cash and cash equivalents and restricted cash reported within the applicable balance sheet that sum to the total of the same such amounts shown in the statement of cash flows is as follows: Year Ended December 31, 2018 2017 2016 Cash and cash equivalents $ 1,208.7 $ 802.1 $ 787.2 Restricted cash 96.2 152.8 149.3 Total cash, cash equivalents and restricted cash $ 1,304.9 $ 954.9 $ 936.5
Summary of Non-lease Disaggregated Revenue by Source and Geography	Non-lease revenue is disaggregated by geography in a manner consistent with the Company’s business segments, which are discussed further in note 20. A summary of non-lease revenue disaggregated by source and geography is as follows: Year Ended December 31, 2018 U.S. Asia EMEA Latin America Total Power and fuel pass-through revenue $ — $ 450.0 $ 140.3 $ 16.8 $ 607.1 Other non-lease revenue 273.2 7.0 1.3 102.1 383.6 Total non-lease property revenue $ 273.2 $ 457.0 $ 141.6 $ 118.9 $ 990.7 Services revenue 125.4 — — — 125.4 Total non-lease revenue $ 398.6 $ 457.0 $ 141.6 $ 118.9 $ 1,116.1 Property lease revenue 3,548.9 1,083.5 545.7 1,145.9 6,324.0 Total revenue $ 3,947.5 $ 1,540.5 $ 687.3 $ 1,264.8 $ 7,440.1
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 December 31, 2018 Accounts receivable $ 222.2 $ 260.7 Prepaids and other current assets 79.7 103.2 Notes receivable and other non-current assets 24.2 22.2 Unearned revenue 26.6 37.6 Other non-current liabilities 68.5 54.9

PREPAID AND OTHER CURRENT ASS_2

PREPAID AND OTHER CURRENT ASSETS (Tables)	12 Months Ended
	Dec. 31, 2018
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid and other current assets	Prepaid and other current assets consisted of the following as of December 31,: 2018 2017 Prepaid operating ground leases $ 165.0 $ 148.6 Unbilled receivables 126.1 107.9 Prepaid income tax 125.1 136.5 Value added tax and other consumption tax receivables 86.3 64.2 Prepaid assets 40.5 39.6 Other miscellaneous current assets 78.2 71.8 Prepaids and other current assets $ 621.2 $ 568.6

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and equipment (including assets held under capital leases) consisted of the following as of December 31,: Estimated Useful Lives (years) (1) 2018 2017 Towers Up to 20 $ 12,777.9 $ 12,500.5 Equipment (2) 2 - 20 1,667.3 1,423.0 Buildings and improvements 3 - 32 628.5 631.4 Land and improvements (3) Up to 20 2,285.4 2,112.9 Construction-in-progress 358.1 282.1 Total 17,717.2 16,949.9 Less accumulated depreciation (6,470.1 ) (5,848.9 ) Property and equipment, net $ 11,247.1 $ 11,101.0 _______________ (1) Assets on leased land are depreciated over the shorter of the estimated useful life of the asset or the term of the corresponding ground lease taking into consideration lease renewal options and residual value. (2) Includes fiber and DAS assets. (3) Estimated useful lives apply to improvements only.

GOODWILL AND OTHER INTANGIBLE_2

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying Value of Goodwill	The changes in the carrying value of goodwill for the Company’s business segments were as follows: Property Services Total U.S. Asia EMEA Latin America Balance as of January 1, 2017 $ 3,379.2 $ 1,029.3 $ 150.5 $ 509.7 $ 2.0 $ 5,070.7 Additions (1) — 0.4 220.9 264.8 — 486.1 Effect of foreign currency translation — 65.3 33.5 (17.2 ) — 81.6 Balance as of January 1, 2018 $ 3,379.2 $ 1,095.0 $ 404.9 $ 757.3 $ 2.0 $ 5,638.4 Additions (2) 3.3 44.5 — 0.4 — 48.2 Effect of foreign currency translation — (94.0 ) (23.6 ) (67.1 ) — (184.7 ) Balance as of December 31, 2018 $ 3,382.5 $ 1,045.5 $ 381.3 $ 690.6 $ 2.0 $ 5,501.9 _______________ (1) Additions consist of $485.1 million resulting from 2017 acquisitions and $1.0 million from revisions to prior-year acquisitions due to measurement period adjustments. (2) Additions consist of $47.8 million resulting from 2018 acquisitions and $0.4 million from revisions to prior-year acquisitions due to measurement period adjustments.
Finite Intangible Assets	The Company’s other intangible assets subject to amortization consisted of the following: As of December 31, 2018 As of December 31, 2017 Estimated Useful Lives 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 $ 4,780.3 $ (1,704.9 ) $ 3,075.4 $ 4,858.8 $ (1,525.3 ) $ 3,333.5 Acquired tenant-related intangibles 15-20 11,156.5 (3,147.2 ) 8,009.3 11,150.9 (2,754.7 ) 8,396.2 Acquired licenses and other intangibles 3-20 104.1 (14.5 ) 89.6 58.8 (8.1 ) 50.7 Economic Rights, TV Azteca (2) 70 — — — 14.5 (11.6 ) 2.9 Total other intangible assets $ 16,040.9 $ (4,866.6 ) $ 11,174.3 $ 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. (2) As discussed in note 5, in conjunction with the extinguishment of a note from TV Azteca (as defined in note 5), the Company restructured the Economic Rights Agreement (as defined in note 5) and wrote off the corresponding asset. The intangible asset related to the Commercialization Rights (as defined in note 5) agreement with TV Azteca is included in Acquired licenses and other intangibles.
Expected future amortization expenses	Based on current exchange rates, the Company expects to record amortization expense as follows over the next five years: Year Ending December 31, 2019 $ 786.0 2020 765.8 2021 749.6 2022 745.1 2023 740.6

NOTES RECEIVABLE AND OTHER NO_2

NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS (Tables)	12 Months Ended
	Dec. 31, 2018
Notes Receivable And Other Long Term Assets [Abstract]
Notes Receivable and Other Non-current Assets	Notes receivable and other non-current assets consisted of the following as of December 31,: 2018 2017 Long-term prepaid ground rent $ 607.5 $ 552.8 Notes receivable 1.0 83.7 Other miscellaneous assets 354.1 313.6 Notes receivable and other non-current assets $ 962.6 $ 950.1

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of merger and acquisition related costs	During the years ended December 31, 2018 , 2017 and 2016 , the Company recorded the following acquisition and merger related expenses for business combinations and integration costs: Year Ended December 31, 2018 2017 2016 Acquisition and merger related expenses $ 14.1 $ 16.3 $ 15.9 Integration costs $ 16.1 $ 11.5 $ 9.9
Schedule of recognized identified assets acquired and liabilities assumed	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 EMEA Idea Vodafone (1) Kenya (2) Other (3) Preliminary Allocation Updated Allocation Current assets $ 100.7 $ 82.9 $ 15.1 $ 0.1 $ 3.6 Non-current assets 2.6 11.6 5.8 24.7 5.1 Property and equipment 161.2 161.2 194.6 51.2 271.5 Intangible assets (4): Tenant-related intangible assets 321.2 323.4 309.5 106.2 191.5 Network location intangible assets 82.9 83.5 88.5 25.6 91.5 Other intangible assets — — — — 28.7 Current liabilities (52.5 ) (47.4 ) (13.1 ) — (3.6 ) Deferred tax liability (20.7 ) (17.7 ) — (32.2 ) — Other non-current liabilities (10.5 ) (16.1 ) (12.5 ) (1.5 ) (21.3 ) Net assets acquired 584.9 581.4 587.9 174.1 567.0 Goodwill (5) 50.6 44.5 — — 3.3 Fair value of net assets acquired 635.5 625.9 587.9 174.1 570.3 Debt assumed — — — — — Purchase price $ 635.5 $ 625.9 $ 587.9 $ 174.1 $ 570.3 _______________ (1) Includes $1.3 million in acquisition and merger related expenses that were capitalized as part of the purchase price. (2) Includes $1.7 million in acquisition and merger related expenses that were capitalized as part of the purchase price. (3) Other includes 145 sites in Peru held pursuant to long-term capital leases. (4) Tenant-related intangible assets, network location intangible assets and other intangible assets are amortized on a straight-line basis over periods of up to 20 years. (5) The Company expects the majority of goodwill to be deductible for tax purposes. The following table summarizes the preliminary and final allocation of the purchase price paid and the amounts of assets acquired and liabilities assumed for the acquisition based upon its estimated fair value at the date of acquisition. Balances are reflected in the accompanying consolidated balance sheet as of December 31, 2018. Latin America Mexico Preliminary Allocation (1) Final Allocation (2) Current assets $ 44.4 $ 42.5 Non-current assets — — Property and equipment 94.0 102.2 Intangible assets: Tenant-related intangible assets 153.3 138.0 Network location intangible assets — — Other intangible assets 22.0 20.3 Current liabilities (28.8 ) (27.2 ) Deferred tax liability (38.8 ) (36.2 ) Other non-current liabilities (4.5 ) (4.5 ) Net assets acquired 241.6 235.1 Goodwill (3) 264.2 264.6 Fair value of net assets acquired 505.8 499.7 Debt assumed — — Purchase price $ 505.8 $ 499.7 _______________ (1) As reported for the year ended December 31, 2017. (2) The allocation of the purchase price for the Mexico acquisition was finalized during the year ended December 31, 2018. (3) Primarily results from purchase accounting adjustments, which are not deductible for tax purposes.
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 the 2017 acquisitions 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 dates indicated, nor are they indicative of the future operating results of the Company. Year Ended December 31, 2018 2017 Pro forma revenues $ 7,610.6 $ 7,161.0 Pro forma net income attributable to American Tower Corporation common stockholders $ 1,218.2 $ 1,127.6 Pro forma net income per common share amounts: Basic net income attributable to American Tower Corporation common stockholders $ 2.77 $ 2.63 Diluted net income attributable to American Tower Corporation common stockholders $ 2.75 $ 2.61
Schedule of Contingent Consideration Changes	A summary of the value of the Company’s acquisition-related contingent consideration obligations are as follows: Year Ended December 31, 2018 Maximum potential value (1) Estimated value at December 31, 2018 Additions Settlements Change in Fair Value Ghana 0.6 0.6 — — 0.0 South Africa — — — (8.6 ) (0.5 ) United States 0.3 0.3 — (0.1 ) — Total $ 0.9 $ 0.9 $ — $ (8.7 ) $ (0.5 ) _______________ (1) The maximum potential value is based on exchange rates at December 31, 2018 . The minimum value could be zero . The changes in fair value of the contingent consideration were as follows during the years ended December 31,: 2018 2017 Balance as of January 1 $ 10.1 $ 15.4 Additions — — Settlements (8.7 ) — Change in fair value (0.9 ) (6.3 ) Foreign currency translation adjustment 0.4 1.0 Balance as of December 31 $ 0.9 $ 10.1

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	12 Months Ended
	Dec. 31, 2018
Accrued Liabilities, Current [Abstract]
Schedule of accrued expenses	Accrued expenses consisted of the following as of December 31,: 2018 2017 Accrued property and real estate taxes $ 169.7 $ 154.4 Amounts payable to tenants 93.5 60.8 Payroll and related withholdings 90.4 82.2 Accrued pass-through costs 71.2 59.7 Accrued rent 61.4 54.0 Accrued income tax payable 57.9 15.3 Accrued construction costs 41.5 31.9 Accrued pass-through taxes 2.2 25.3 Other accrued expenses 360.5 370.7 Accrued expenses $ 948.3 $ 854.3

LONG-TERM OBLIGATIONS (Tables)

LONG-TERM OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	Amounts outstanding and key terms of other subsidiary debt consisted of the following as of December 31, (in millions, except percentages): Carrying Value (Denominated Currency) (1) Carrying Value (USD) (1) Interest Rate Maturity Date 2018 2017 2018 2017 South African Credit Facility (2) 577.4 866.0 $ 40.2 $ 69.9 9.10 % December 17, 2020 Colombian Credit Facility (3) 109,193.8 138,740.3 $ 33.6 $ 46.5 8.14 % April 24, 2021 Brazil Credit Facility (4) 94.7 122.4 $ 24.4 $ 37.0 Various January 15, 2022 Kenya Debt (5) 51.8 $ — $ 51.8 $ — 8.00 % October 1, 2021 U.S. Subsidiary Debt (6) 2.5 — $ 2.5 $ — — % January 1, 2022 BR Towers Debentures (7) — 306.8 $ — $ 92.7 N/A N/A _______________ (1) Includes applicable deferred financing costs. (2) Denominated in ZAR, with an original principal amount of 830.0 million ZAR. On December 23, 2016, the borrower borrowed an additional 500.0 million ZAR. Debt accrues interest at a variable rate. The borrower no longer maintains the ability to draw on the South African Credit Facility. (3) Denominated in COP, with an original principal amount of 200.0 billion COP. Debt accrues interest at a variable rate. The loan agreement for the Colombian Credit Facility requires that the borrower manage exposure to variability in interest rates on certain of the amounts outstanding under the Colombian Credit Facility. The borrower no longer maintains the ability to draw on the Colombian Credit Facility. (4) Denominated in BRL, with an original principal amount of 271.0 million BRL. Debt accrues interest at a variable rate. The borrower no longer maintains the ability to draw on the Brazil Credit Facility. (5) Denominated in USD, with an original principal amount of $51.8 million . The loan agreement for the Kenya Debt requires that the debt be paid either (i) in future installments subject to the satisfaction of specified conditions or (ii) three years from the note origination date. (6) Related to a seller-financed acquisition. Denominated in USD with an original principal amount of $2.5 million . (7) Denominated in BRL, with an original principal amount of 300.0 million BRL. Debt accrued interest at a variable rate. In October 2018, the BR Towers Debentures were repaid in full. 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 December 31,: 2018 2017 Contractual Interest Rate (1) Maturity Date (1) 2018 Term Loan (2)(3) $ 1,499.8 $ — 3.405 % March 29, 2019 2013 Credit Facility (2) 1,875.0 2,075.6 3.616 % June 28, 2022 2013 Term Loan (2) 994.8 994.5 3.655 % January 31, 2024 2014 Credit Facility (2) — 495.0 3.655 % January 31, 2024 3.40% senior notes (4) 1,000.0 999.8 3.400 % February 15, 2019 2.800% senior notes 747.8 746.3 2.800 % June 1, 2020 5.050% senior notes 698.7 698.0 5.050 % September 1, 2020 3.300% senior notes 747.2 746.0 3.300 % February 15, 2021 3.450% senior notes 646.3 645.1 3.450 % September 15, 2021 5.900% senior notes 498.4 497.8 5.900 % November 1, 2021 2.250% senior notes 572.7 572.4 2.250 % January 15, 2022 4.70% senior notes 697.4 696.7 4.700 % March 15, 2022 3.50% senior notes 992.6 990.9 3.500 % January 31, 2023 3.000% senior notes 687.5 692.5 3.000 % June 15, 2023 5.00% senior notes 1,002.1 1,002.4 5.000 % February 15, 2024 1.375% senior notes 564.0 589.1 1.375 % April 4, 2025 4.000% senior notes 742.1 741.0 4.000 % June 1, 2025 4.400% senior notes 496.1 495.6 4.400 % February 15, 2026 1.950% senior notes 566.0 — 1.950 % May 22, 2026 3.375% senior notes 986.3 984.8 3.375 % October 15, 2026 3.125% senior notes 397.3 397.1 3.125 % January 15, 2027 3.55% senior notes 743.5 742.8 3.550 % July 15, 2027 3.600% senior notes 691.9 691.1 3.600 % January 15, 2028 Total American Tower Corporation debt 17,847.5 16,494.5 Series 2013-1A Securities (5) — 499.8 N/A N/A Series 2013-2A Securities (6) 1,293.4 1,291.8 3.070 % March 15, 2023 Series 2018-1A Securities (6) 493.5 — 3.652 % March 15, 2028 Series 2015-1 Notes (7) 348.8 348.0 2.350 % June 15, 2020 Series 2015-2 Notes (8) 520.8 520.1 3.482 % June 16, 2025 India indebtedness (9) 240.1 512.6 8.40% - 8.95% Various India preference shares (10) 23.9 26.1 10.250 % March 2, 2020 Shareholder loans (11) 59.9 100.6 Various Various Other subsidiary debt (12) 152.5 246.1 Various Various Total American Tower subsidiary debt 3,132.9 3,545.1 Other debt, including capital lease obligations 179.5 165.5 Total 21,159.9 20,205.1 Less current portion long-term obligations (2,754.8 ) (774.8 ) Long-term obligations $ 18,405.1 $ 19,430.3 _______________ (1) Represents the interest rate or maturity date as of December 31, 2018; interest rate does not reflect the impact of interest rate swap agreements. (2) Accrues interest at a variable rate. Interest rates on outstanding balances are calculated using a weighted average. (3) Repaid in full subsequent to December 31, 2018. For more information see note 23. (4) Repaid in full on the maturity date in February 2019 with borrowings from the 2013 Credit Facility and the 2014 Credit Facility (each defined below). (5) Repaid in full on the March 2018 payment date. (6) Maturity date reflects the anticipated repayment date; final legal maturity is March 15, 2048. (7) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2045. (8) Maturity date reflects the anticipated repayment date; final legal maturity is June 15, 2050. (9) Denominated in INR. Includes India working capital facilities, remaining debt assumed by the Company in connection with the Viom Acquisition (as defined in note 14) and debt that has been entered into by ATC TIPL. (10) Mandatorily redeemable preference shares (the “Preference Shares”) denominated in INR and classified as debt. The Company intends to redeem these shares on March 2, 2019. (11) Reflects balances owed to the Company’s joint venture partners in Ghana and Uganda. The Ghana loan is denominated in Ghanaian Cedi (“GHS”) and the Uganda loan is denominated in Ugandan Shillings (“UGX”). On August 30, 2018, the Company repaid the remaining 127.2 billion UGX ( $33.8 million ) under the Uganda loan, including principal and accrued unpaid interest. As a result, no amounts were outstanding under the Uganda loan as of December 31, 2018. (12) Includes the BR Towers Debentures (as defined below) and the Brazil Credit Facility (as defined below), which are denominated in BRL and have an original amortization through October 15, 2023 and January 15, 2022, respectively, the South African Credit Facility (as defined below), which is denominated in South African Rand (“ZAR”) and amortizes through December 17, 2020, the Colombian Credit Facility (as defined below), which is denominated in Colombian Pesos (“COP”) and amortizes through April 24, 2021, the Kenya Debt (as defined below), which is denominated in U.S. Dollars (“USD”) and is payable either (i) in future installments subject to the satisfaction of specified conditions or (ii) three years from the note origination date, and U.S. subsidiary debt related to a seller-financed acquisition. In October 2018, the Company repaid the BR Towers Debentures in full, including any accrued and unpaid interest.
Schedule of Line of Credit Facilities	As of December 31, 2018 , the key terms under the 2013 Credit Facility, the 2014 Credit Facility, the 2013 Term Loan and 2018 Term loan were as follows: Outstanding Principal Balance Undrawn letters of credit Maturity Date Current margin over LIBOR Current commitment fee (1) 2013 Credit Facility $ 1,875.0 (2) $ 3.8 June 28, 2022 (3) 1.125 % 0.125 % 2014 Credit Facility $ — $ 6.2 January 31, 2024 (3) 1.125 % 0.125 % 2013 Term Loan $ 1,000.0 (2) N/A January 31, 2024 1.125 % N/A 2018 Term Loan $ 1,500.0 (2) N/A March 29, 2019 0.875 % N/A _______________ (1) Fee on undrawn portion of each credit facility. (2) Borrowed at LIBOR. (3) Subject to two optional renewal periods.
Schedule of Debt Discounts	The following table outlines key terms related to the Company ’ s outstanding senior notes as of December 31, 2018 : Adjustments to Principal Amount (1) Aggregate Principal Amount 2018 2017 Interest payments due (2) Issue Date Par Call Date (3) 3.40% Notes (4) 1,000.0 — (0.2 ) February 15 and August 15 August 19, 2013 N/A 2.800% Notes 750.0 (2.2 ) (3.7 ) June 1 and December 1 May 7, 2015 May 1, 2020 5.050% Notes 700.0 (1.3 ) (2.0 ) March 1 and September 1 August 16, 2010 N/A 3.300% Notes 750.0 (2.8 ) (4.0 ) February 15 and August 15 January 12, 2016 January 15, 2021 3.450% Notes 650.0 (3.7 ) (4.9 ) March 15 and September 15 August 7, 2014 N/A 5.900% Notes 500.0 (1.6 ) (2.2 ) May 1 and November 1 October 6, 2011 N/A 2.250% Notes (5) 600.0 (27.3 ) (27.6 ) January 15 and July 15 September 30, 2016 N/A 4.70% Notes 700.0 (2.6 ) (3.3 ) March 15 and September 15 March 12, 2012 N/A 3.50% Notes 1,000.0 (7.4 ) (9.1 ) January 31 and July 31 January 8, 2013 N/A 3.000% Notes (6) 700.0 (12.5 ) (7.5 ) June 15 and December 15 December 8, 2017 N/A 5.00% Notes (4) 1,000.0 2.1 2.4 February 15 and August 15 August 19, 2013 N/A 1.375% Notes (7) 573.3 (9.3 ) (11.1 ) April 4 April 6, 2017 January 4, 2025 4.000% Notes 750.0 (7.9 ) (9.0 ) June 1 and December 1 May 7, 2015 March 1, 2025 4.400% Notes 500.0 (3.9 ) (4.4 ) February 15 and August 15 January 12, 2016 November 15, 2025 1.950% Notes (7) 573.3 (7.3 ) — May 22 May 22, 2018 February 22, 2026 3.375% Notes 1,000.0 (13.7 ) (15.2 ) April 15 and October 15 May 13, 2016 July 15, 2026 3.125% Notes 400.0 (2.7 ) (2.9 ) January 15 and July 15 September 30, 2016 October 15, 2026 3.55% Notes 750.0 (6.5 ) (7.2 ) January 15 and July 15 June 30, 2017 April 15, 2027 3.600% Notes 700.0 (8.1 ) (8.9 ) January 15 and July 15 December 8, 2017 October 15, 2027 _______________ (1) Includes unamortized discounts, premiums and debt issuance costs and fair value adjustments due to interest rate swaps. (2) Interest payments are due semi-annually for each series of senior notes, except for the 1.375% Notes and the 1.950% Notes, for which interest payments are due annually. (3) The Company will not be required to pay a make-whole premium if redeemed on or after the par call date. (4) The original issue date for the 3.40% Notes and the 5.00% Notes was August 19, 2013. The issue date for the reopened 3.40% Notes and the reopened 5.00% Notes was January 10, 2014. The 3.40% Notes were repaid on February 15, 2019. (5) Includes $24.3 million and $23.7 million fair value adjustment due to interest rate swaps in 2018 and 2017, respectively. (6) Includes $7.0 million and $0.8 million fair value adjustment due to interest rate swaps in 2018 and 2017, respectively. (7) Notes are denominated in EUR.
Schedule of India Indebtedness	Amounts outstanding and key terms of the India indebtedness consisted of the following as of December 31, 2018 (in millions, except percentages): Amount Outstanding (INR) Amount Outstanding (USD) Interest Rate (Range) Maturity Date (Range) Term loans (1) 16,751 $ 240.1 8.75% - 8.95% January 1, 2019 - November 30, 2024 Working capital facilities (2) — $ — 8.40% - 8.75% March 18, 2019 - October 23, 2019 _______________ (1) In January 2019, the Company repaid approximately 5.0 billion INR ($ 72.0 million ) of India indebtedness. (2) 5.7 billion INR ( $81.8 million ) of borrowing capacity as of December 31, 2018.
Schedule of Shareholder Loans	The portions of the loans made by the Company’s wholly owned subsidiaries are eliminated in consolidation and the portions of the loans made by each of the Company’s joint venture partner’s wholly owned subsidiaries are reported as outstanding debt of the Company. Outstanding amounts under each of the Company’s shareholder loans consisted of the following as of December 31, : 2018 2017 Contractual Interest Rate Maturity Date Ghana loan (1) $ 59.9 $ 66.5 21.87 % December 31, 2019 Uganda loan (2) $ — 34.1 N/A N/A _______________ (1) Denominated in GHS. As of December 31, 2018, the aggregate principal amount outstanding under the Ghana loan was 294.4 million GHS. (2) Denominated in UGX. On August 30, 2018, the Company repaid the remaining 127.2 billion UGX ($ 33.8 million ) under the Uganda loan, including principal and accrued unpaid interest. As a result, no amounts were outstanding under the Uganda loan as of December 31, 2018
Schedule of Maturities of Long-term Debt	Aggregate principal maturities of long-term debt, including capital leases, for the next five years and thereafter are expected to be: Year Ending December 31, 2019 $ 2,754.8 2020 1,884.4 2021 2,014.2 2022 3,238.8 2023 3,043.1 Thereafter 8,367.9 Total cash obligations 21,303.2 Unamortized discounts, premiums and debt issuance costs and fair value adjustments, net (143.3 ) Balance as of December 31, 2018 $ 21,159.9

OTHER NON-CURRENT LIABILITIES (

OTHER NON-CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2018
Other Liabilities, Noncurrent [Abstract]
Other non-current liabilities	Other non-current liabilities consisted of the following as of December 31,: 2018 2017 Deferred rent liability $ 506.7 $ 467.0 Unearned revenue 504.6 509.2 Other miscellaneous liabilities 253.8 268.0 Other non-current liabilities $ 1,265.1 $ 1,244.2

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation [Abstract]
Carrying value of asset retirement obligations	The changes in the carrying amount of the Company’s asset retirement obligations were as follows: 2018 2017 Beginning balance as of January 1, $ 1,175.3 $ 965.5 Additions 39.6 33.4 Accretion expense 83.6 94.5 Revisions in estimates (1) (81.5 ) 86.6 Settlements (7.0 ) (4.7 ) Balance as of December 31, $ 1,210.0 $ 1,175.3 _______________ (1) Revisions in estimates include a decrease to the liability of $49.4 million and an increase to the liability of $13.0 million related to foreign currency translation for the years ended December 31, 2018 and 2017, respectively

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Assets and Liabilities Measured on a Recurring Basis	The fair value of the Company’s financial assets and liabilities that are required to be measured on a recurring basis at fair value was as follows: December 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) $ — — — $ 1.0 — — Embedded derivative in lease agreement — — $ 11.5 — — $ 12.4 Liabilities: Interest rate swap agreements — $ 33.8 — — $ 29.0 — Acquisition-related contingent consideration — — $ 0.9 — — $ 10.1 Fair value of debt related to interest rate swap agreements $ (31.3 ) — — $ (24.5 ) — — Redeemable noncontrolling interests — — $ 1,004.8 — — $ 1,126.2 _______________ (1) Consists of highly liquid investments with original maturities in excess of three months.
Schedule of Contingent Consideration Changes	A summary of the value of the Company’s acquisition-related contingent consideration obligations are as follows: Year Ended December 31, 2018 Maximum potential value (1) Estimated value at December 31, 2018 Additions Settlements Change in Fair Value Ghana 0.6 0.6 — — 0.0 South Africa — — — (8.6 ) (0.5 ) United States 0.3 0.3 — (0.1 ) — Total $ 0.9 $ 0.9 $ — $ (8.7 ) $ (0.5 ) _______________ (1) The maximum potential value is based on exchange rates at December 31, 2018 . The minimum value could be zero . The changes in fair value of the contingent consideration were as follows during the years ended December 31,: 2018 2017 Balance as of January 1 $ 10.1 $ 15.4 Additions — — Settlements (8.7 ) — Change in fair value (0.9 ) (6.3 ) Foreign currency translation adjustment 0.4 1.0 Balance as of December 31 $ 0.9 $ 10.1
Recurring Level 3 Fair Value Measurements	The recurring Level 3 fair value measurements of the Company’s embedded derivative in lease agreement, acquisition-related contingent consideration and redeemable noncontrolling interests include the following significant unobservable inputs as of December 31, 2018: Significant Unobservable Input Range Embedded derivative in lease agreement Discount rate 10.93% - 13.96% Acquisition-related contingent consideration Probability of payout 0.00% - 100.00% Redeemable noncontrolling interests Revenue growth 3.16% - 12.87% Long-term growth rate 4.00 %

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax provision from continuing operations	The income tax provision from continuing operations consisted of the following for the years ended December 31,: 2018 2017 2016 Current: Federal $ (1.4 ) $ (0.1 ) $ (26.5 ) State (1.8 ) (3.8 ) (2.0 ) Foreign (189.7 ) (113.4 ) (100.1 ) Deferred: Federal 4.0 0.2 (0.6 ) State 0.7 1.0 (0.3 ) Foreign 298.3 85.4 (26.0 ) Income tax benefit (provision) $ 110.1 $ (30.7 ) $ (155.5 )
Reconciliation between the U.S. statutory rate and the effective rate from continuing operations	Reconciliation between the U.S. statutory rate and the effective rate from continuing operations is as follows for the years ended December 31,: 2018 2017 2016 Statutory tax rate 21% 35 % 35 % Adjustment to reflect REIT status (1) (21 ) (35 ) (35 ) Foreign taxes (8 ) 1 5 Foreign withholding taxes 4 3 4 Uncertain tax positions — — 5 Changes in tax laws — (2 ) — Impact from restructuring (6 ) — — Effective tax rate (10 )% 2 % 14 % _______________ (1) As a result of the ability to utilize the dividends paid deduction to offset the Company’s REIT income and gains.
Components of income from continuing operations before income taxes and income on equity method investments	The domestic and foreign components of income from continuing operations before income taxes are as follows for the years ended December 31,: 2018 2017 2016 United States $ 1,212.7 $ 971.2 $ 882.6 Foreign (58.1 ) 284.9 243.3 Total $ 1,154.6 $ 1,256.1 $ 1,125.9
Components of the net deferred tax asset and related valuation allowance	The components of the net deferred tax asset and liability and related valuation allowance were as follows as of December 31,: 2018 2017 Assets: Net operating loss carryforwards $ 264.9 $ 287.0 Accrued asset retirement obligations 165.7 157.0 Stock-based compensation 6.3 3.9 Unearned revenue 28.3 19.3 Unrealized loss on foreign currency 12.9 27.4 Other accruals and allowances 78.6 50.2 Items not currently deductible and other 26.2 28.0 Liabilities: Depreciation and amortization (757.0 ) (1,073.9 ) Deferred rent (36.9 ) (35.9 ) Other (15.3 ) (14.7 ) Subtotal (226.3 ) (551.7 ) Valuation allowance (151.9 ) (142.0 ) Net deferred tax liabilities $ (378.2 ) $ (693.7 )
Summary of valuation allowance	A summary of the activity in the valuation allowance is as follows: 2018 2017 2016 Balance as of January 1, $ 142.0 $ 144.4 $ 137.0 Additions (1) 15.7 11.6 14.1 Reversals — (9.1 ) — Foreign currency translation (5.8 ) (4.9 ) (6.7 ) Balance as of December 31, $ 151.9 $ 142.0 $ 144.4 _______________ (1) Includes net charges to expense and allowances established through goodwill at acquisition.
Net operating loss carryforwards expire	At December 31, 2018 , the Company had net federal, state and foreign operating loss carryforwards available to reduce future taxable income. If not utilized, the Company’s NOLs expire as follows: Years ended December 31, Federal State Foreign 2019 to 2023 $ — $ 142.9 $ 46.0 2024 to 2028 141.7 378.4 142.7 2029 to 2033 — 13.9 4.5 2034 to 2038 10.6 135.4 — Indefinite carryforward 9.6 — 746.5 Total $ 161.9 $ 670.6 $ 939.7
Change in unrecognized tax benefit	A reconciliation of the beginning and ending amount of unrecognized tax benefits are as follows for the years ended December 31,: 2018 2017 2016 Balance at January 1 $ 116.7 $ 107.6 $ 28.1 Additions based on tax positions related to the current year 8.1 7.6 82.9 Additions and reductions for tax positions of prior years 0.3 — — Foreign currency (8.1 ) 1.9 (0.2 ) Reduction as a result of the lapse of statute of limitations (2.6 ) (0.4 ) (3.2 ) Reduction as a result of effective settlements (6.7 ) — — Balance at December 31 $ 107.7 $ 116.7 $ 107.6

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of stock-based compensation expenses	During the years ended December 31, 2018 , 2017 and 2016 , the Company recorded and capitalized the following stock-based compensation expenses: 2018 2017 2016 Stock-based compensation expense $ 137.5 $ 108.5 $ 89.9 Stock-based compensation expense capitalized as property and equipment 2.0 1.6 1.4
Assumptions used to determine the grant date fair value for options granted	Key assumptions used to apply the Black-Scholes option pricing model were as follows (percentages and years disclosed in full amounts): 2017 2016 Range of risk-free interest rate 1.88%-1.94% 1.00%-1.73% Weighted average risk-free interest rate 1.89% 1.44% Range of expected life of stock options 5.2 years 4.5 - 5.2 years Range of expected volatility of the underlying stock price 18.95% - 19.45% 20.59% - 21.45% Weighted average expected volatility of underlying stock price 19.05% 21.43% Range of expected annual dividend yield 2.40% 1.85% - 2.40%
Summary of the company's option activity	The Company’s option activity for the year ended December 31, 2018 was as follows (share and per share data disclosed in full amounts): Options Weighted Average Exercise Price Per Share Weighted Average Remaining Life (Years) Aggregate Intrinsic Value Outstanding as of January 1, 2018 5,557,561 $81.32 Granted — — Exercised (1,242,536 ) 71.41 Forfeited (57,555 ) 94.66 Expired — — Outstanding as of December 31, 2018 4,257,470 $84.03 5.18 $315.7 Exercisable as of December 31, 2018 3,360,226 $81.10 4.76 $259.0 Vested or expected to vest as of December 31, 2018 4,257,470 $84.03 5.18 $315.7
Schedule of options outstanding	The following table sets forth information regarding options outstanding at December 31, 2018 (share and per share data disclosed in full amounts): Options Outstanding Options Exercisable Range of Exercise Price Per Share Outstanding Number of Options Weighted Average Exercise Price Per Share Weighted Average Remaining Life (Years) Options Exercisable Weighted Average Exercise Price Per Share $28.39 - $62.00 594,690 $ 56.69 2.67 594,690 $ 56.69 $71.07 - $74.06 14,717 73.26 4.48 14,717 73.26 $76.90 - $77.75 559,293 76.91 4.00 559,293 76.91 $81.18 - $94.23 983,105 81.55 4.98 967,146 81.43 $94.57 - $94.71 2,070,809 94.62 6.28 1,213,187 94.60 $96.46 - $121.15 34,856 109.92 7.38 11,193 107.20 $28.39 - $121.15 4,257,470 $ 84.03 5.18 3,360,226 $ 81.10
Summary of the company's restricted stock unit activity	The Company’s RSU and PSU activity for the year ended December 31, 2018 was as follows (share and per share data disclosed in full amounts): RSUs Weighted Average Grant Date Fair Value PSUs Weighted Average Grant Date Fair Value Outstanding as of January 1, 2018 (1) 1,742,725 $ 102.60 444,031 $ 102.81 Granted (2) 686,789 144.96 300,651 116.71 Vested and Released (3) (682,311 ) 98.24 (120,171 ) 100.35 Forfeited (97,230 ) 116.37 — — Outstanding as of December 31, 2018 1,649,973 $ 121.23 624,511 $ 109.97 Expected to vest as of December 31, 2018 1,649,973 $ 121.23 624,511 $ 109.97 Vested and deferred as of December 31, 2018 (4) 32,596 $ 119.14 — $ — _______________ (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 (each defined below), 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 first, second and third year’s performance periods, or 120,171 shares. (2) PSUs represent the shares above target that are issuable for the 2016 PSUs at the end of the three -year performance cycle based on exceeding the performance metric for the three-year performance period, or 169,340 shares, and 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. RSUs exclude 32,596 shares that are vested and deferred. (4) Vested and deferred RSUs are related to deferred compensation for certain former employees.

REDEEMABLE NONCONTROLLING INT_2

REDEEMABLE NONCONTROLLING INTERESTS (Tables)	12 Months Ended
	Dec. 31, 2018
Temporary Equity Disclosure [Abstract]
Schedule of Redeemable Noncontrolling Interests	The changes in Redeemable noncontrolling interests for the year ended December 31, 2018, 2017 and 2016 were as follows: Year Ended December 31, 2018 2017 2016 Balance as of January 1, $ 1,126.2 $ 1,091.3 $ — Fair value at acquisition — — 1,100.9 Net (loss) income attributable to noncontrolling interests (87.9 ) (33.4 ) 13.9 Adjustment to noncontrolling interest redemption value 86.7 — — Adjustment to noncontrolling interest due to merger (28.1 ) — — Foreign currency translation adjustment attributable to noncontrolling interests (92.1 ) 68.3 (23.5 ) Balance as of December 31, $ 1,004.8 $ 1,126.2 $ 1,091.3

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Dividends Declared	During the years ended December 31, 2018 , 2017 and 2016 , the Company declared the following cash distributions: For the year ended December 31, 2018 2017 2016 Distribution Aggregate Distribution Aggregate Distribution Aggregate Common Stock $ 3.15 $ 1,389.8 $ 2.62 $ 1,122.5 $ 2.17 $ 923.7 Series A Preferred Stock (1) $ — $ — $ 2.63 $ 15.8 $ 5.25 $ 31.5 Series B Preferred Stock $ 13.75 $ 18.9 $ 55.00 $ 75.6 $ 55.00 $ 75.6 _______________ (1) 5.25% Mandatory Convertible Preferred Stock, Series A, par value $0.01 per share (the “Series A Preferred Stock”), which converted into shares of the Company’s common stock pursuant to the provisions of the Certificate of Designations governing the Series A Preferred Stock in 2017.
Schedule of Stock by Class	The following table characterizes the tax treatment of distributions declared per share of common stock and Mandatory Convertible Preferred Stock. For the year ended December 31, 2018 2017 2016 Per Share % Per Share % Per Share % Common Stock Ordinary dividend $ 3.1500 (1) 100.00 % $ 2.6200 100.00 % $ 2.1700 100.00 % Capital gains distribution — — — — — — Total $ 3.1500 100.00 % $ 2.6200 100.00 % $ 2.1700 100.00 % Series A Preferred Stock Ordinary dividend $ — — % $ 3.3643 (2) 100.00 % $ 6.4578 (3) 100.00 % Capital gains distribution — — — — — — Total $ — — % $ 3.3643 100.00 % $ 6.4578 100.00 % Series B Preferred Stock (4) Ordinary dividend $ 2.1314 (5) 100.00 % $ 6.5233 (6) 100.00 % $ 5.5000 100.00 % Capital gains distribution — — — — — — Total $ 2.1314 100.00 % $ 6.5233 100.00 % $ 5.5000 100.00 % _______________ (1) Includes dividend declared on December 4, 2018 of $0.84 per share, which was paid on January 14, 2019 to common stockholders of record at the close of business on December 27, 2018. (2) Includes a deemed distribution as a result of a conversion rate adjustment triggered on April 27, 2017. (3) Includes a deemed distribution as a result of a conversion rate adjustment triggered on June 17, 2016. (4) Represents the tax treatment on dividends per depositary share, each of which represents a 1/10th interest in a share of Series B Preferred Stock. (5) Includes a deemed distribution as a result of a conversion rate adjustment triggered on January 18, 2018. (6) Includes a deemed distribution as a result of a conversion rate adjustment triggered on April 12, 2017.

OTHER OPERATING EXPENSES (Table

OTHER OPERATING EXPENSES (Tables)	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Schedule of Other Operating Expenses	Other operating expenses included the following for the years ended December 31,: 2018 2017 2016 Impairment charges $ 394.0 $ 211.4 $ 28.5 Net losses on sales or disposals of assets 85.6 32.8 25.1 Other operating expenses (1) 33.7 11.8 19.7 Total Other operating expenses $ 513.3 $ 256.0 $ 73.3 _______________ (1) For the year ended December 31, 2017, the amount also includes refunds of acquisition costs and a charitable contribution.
Schedule of Impairment Charges	Impairment charges included the following for the years ended December 31,: 2018 2017 2016 Tower and network location intangible assets $ 284.9 $ 108.7 $ 18.0 Tenant relationships 107.3 100.1 — Other 1.8 2.6 10.5 Total impairment charges $ 394.0 $ 211.4 $ 28.5

EARNINGS PER COMMON SHARE (Tabl

EARNINGS PER COMMON SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of earnings per basic and diluted by common class	The following table sets forth basic and diluted net income per common share computational data for the years ended December 31, (shares in thousands, except per share data): 2018 2017 2016 Net income attributable to American Tower Corporation stockholders $ 1,236.4 $ 1,238.9 $ 956.4 Dividends on preferred stock (9.4 ) (87.4 ) (107.1 ) Net income attributable to American Tower Corporation common stockholders 1,227.0 1,151.5 849.3 Basic weighted average common shares outstanding 439,606 428,181 425,143 Dilutive securities 3,354 3,507 4,140 Diluted weighted average common shares outstanding 442,960 431,688 429,283 Basic net income attributable to American Tower Corporation common stockholders per common share $ 2.79 $ 2.69 $ 2.00 Diluted net income attributable to American Tower Corporation common stockholders per common share $ 2.77 $ 2.67 $ 1.98
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 for the years ended December 31, (in thousands, on a weighted average basis): 2018 2017 2016 Restricted stock awards — 3 6 Stock options — 4 817 Preferred stock 1,456 14,040 17,509

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
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 December 31, 2018 are as follows: Year Ending December 31, 2019 $ 926.0 2020 904.2 2021 879.8 2022 834.2 2023 792.6 Thereafter 6,173.1 Total $ 10,509.9
Future minimum payments under capital leases	Future minimum payments under capital leases in effect at December 31, 2018 were as follows: Year Ending December 31, 2019 $ 40.7 2020 32.7 2021 27.8 2022 23.7 2023 19.2 Thereafter 117.5 Total minimum lease payments 261.6 Less amounts representing interest (82.1 ) Present value of capital lease obligations $ 179.5
Future minimum rental receipts under operating lease agreements	Future minimum rental receipts expected from tenants under non-cancellable operating lease agreements in effect at December 31, 2018 were as follows: Year Ending December 31, 2019 $ 5,251.2 2020 5,062.2 2021 4,676.1 2022 3,754.6 2023 3,457.3 Thereafter 12,641.1 Total $ 34,842.5

SUPPLEMENTAL CASH FLOW INFORM_2

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information and Non-Cash Investing and Financing Activities	Supplemental cash flow information and non-cash investing and financing activities are as follows for the years ended December 31,: 2018 2017 2016 Supplemental cash flow information: Cash paid for interest $ 789.7 $ 712.1 $ 645.1 Cash paid for income taxes (net of refunds of $25.0, $20.7 and $19.6, respectively) 163.9 136.5 96.2 Non-cash investing and financing activities: Increase (decrease) in accounts payable and accrued expenses for purchases of property and equipment and construction activities 8.3 34.0 (19.0 ) Purchases of property and equipment under capital leases 57.8 54.8 55.6 Fair value of debt assumed through acquisitions — — 786.9 Exercise of purchase option for property and equipment for common shares issued — — 120.8 Acquisition of Commercialization Rights 24.8 — — Conversion of third-party debt to equity — 48.2 — Debt financed acquisition of communication sites 54.2 — —

BUSINESS SEGMENTS (Tables)

BUSINESS SEGMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting, Measurement Disclosures [Abstract]
Summarized financial information concerning the company's reportable segments	Summarized financial information concerning the Company’s reportable segments for the years ended December 31, 2018 , 2017 and 2016 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 Year ended December 31, 2018 U.S. Asia EMEA Latin America Segment revenues (1) $ 3,822.1 $ 1,540.5 $ 687.3 $ 1,264.8 $ 7,314.7 $ 125.4 $ 7,440.1 Segment operating expenses (2) 771.0 710.9 238.1 406.3 2,126.3 48.2 2,174.5 Interest expense, TV Azteca, net — — — (0.1 ) (0.1 ) — (0.1 ) Segment gross margin 3,051.1 829.6 449.2 858.4 5,188.3 77.2 5,265.5 Segment selling, general, administrative and development expense (2) 165.2 110.7 69.1 83.5 428.5 14.4 442.9 Segment operating profit $ 2,885.9 $ 718.9 $ 380.1 $ 774.9 $ 4,759.8 $ 62.8 $ 4,822.6 Stock-based compensation expense $ 137.5 137.5 Other selling, general, administrative and development expense 156.1 156.1 Depreciation, amortization and accretion 2,110.8 2,110.8 Other expense (3) 1,263.6 1,263.6 Income from continuing operations before income taxes $ 1,154.6 Capital expenditures (4) $ 376.9 $ 101.0 $ 232.7 $ 220.7 $ 931.3 $ — $ 13.9 $ 945.2 _______________ (1) Asia segment revenues include a net impact of $333.7 million as a result of the settlement payment received from Tata in the fourth quarter of 2018. (2) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $3.3 million and $134.2 million , respectively. (3) Primarily includes interest expense and $394.0 million in impairment charges. (4) Includes $32.0 million of capital lease payments included in Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases in the cash flow from financing activities in the Company’s consolidated statement of cash flows. Property Total Property Services Other Total Year ended December 31, 2017 U.S. Asia EMEA Latin America Segment revenues $ 3,605.7 $ 1,164.4 $ 626.2 $ 1,169.6 $ 6,565.9 $ 98.0 $ 6,663.9 Segment operating expenses (1) 746.5 649.0 238.3 386.1 2,019.9 33.8 2,053.7 Interest income, TV Azteca, net — — — 10.8 10.8 — 10.8 Segment gross margin 2,859.2 515.4 387.9 794.3 4,556.8 64.2 4,621.0 Segment selling, general, administrative and development expense (1) 151.4 82.4 67.9 77.5 379.2 13.7 392.9 Segment operating profit $ 2,707.8 $ 433.0 $ 320.0 $ 716.8 $ 4,177.6 $ 50.5 $ 4,228.1 Stock-based compensation expense $ 108.5 108.5 Other selling, general, administrative and development expense 138.5 138.5 Depreciation, amortization and accretion 1,715.9 1,715.9 Other expense (2) 1,009.1 1,009.1 Income from continuing operations before income taxes $ 1,256.1 Capital expenditures (3) $ 360.6 $ 118.0 $ 141.7 $ 197.4 $ 817.7 $ — $ 17.7 $ 835.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $2.9 million and $105.6 million , respectively. (2) Primarily includes interest expense. (3) Includes $31.8 million of capital lease payments included in Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases in the cash flow from financing activities in the Company’s consolidated statement of cash flows. Property Total Property Other Total Year ended December 31, 2016 U.S. Asia EMEA Latin America Segment revenues $ 3,370.1 $ 827.6 $ 529.5 $ 985.9 $ 5,713.1 $ 72.6 $ 5,785.7 Segment operating expenses (1) 733.4 465.9 223.7 338.0 1,761.0 27.0 1,788.0 Interest income, TV Azteca, net — — — 10.9 10.9 — 10.9 Segment gross margin 2,636.7 361.7 305.8 658.8 3,963.0 45.6 4,008.6 Segment selling, general, administrative and development expense (1) 147.6 48.2 60.9 60.7 317.4 12.5 329.9 Segment operating profit $ 2,489.1 $ 313.5 $ 244.9 $ 598.1 $ 3,645.6 $ 33.1 $ 3,678.7 Stock-based compensation expense $ 89.9 89.9 Other selling, general, administrative and development expense 126.0 126.0 Depreciation, amortization and accretion 1,525.6 1,525.6 Other expense (2) 811.3 811.3 Income from continuing operations before income taxes $ 1,125.9 Capital expenditures (3) $ 310.7 $ 115.5 $ 86.1 $ 172.6 $ 684.9 $ — $ 16.5 $ 701.4 _______________ (1) Segment operating expenses and segment selling, general, administrative and development expenses exclude stock-based compensation expense of $2.4 million and $87.5 million , respectively. (2) Primarily includes interest expense. (3) Includes $18.9 million of capital lease payments included in Repayments of notes payable, credit facilities, term loan, senior notes, secured debt and capital leases in the cash flow from financing activities in the Company’s consolidated statement of cash flows.
Reconciliation of assets from segments to consolidated	Additional information relating to the total assets of the Company’s operating segments is as follows for the years ended December 31,: 2018 2017 2016 U.S. property $ 18,782.0 $ 19,032.6 $ 18,846.9 Asia property (1) 4,938.8 4,770.8 4,535.3 EMEA property (1) 3,367.8 3,213.6 2,062.4 Latin America property (1) 5,594.7 5,868.4 4,938.1 Services 46.3 42.3 48.3 Other (2) 280.8 286.6 448.2 Total assets $ 33,010.4 $ 33,214.3 $ 30,879.2 _______________ (1) Balances are translated at the applicable period end exchange rate, which may impact comparability between periods. (2) Balances include corporate assets such as cash and cash equivalents, certain tangible and intangible assets and income tax accounts that have not been allocated to specific segments.
Schedule of disclosure on geographic areas, long-lived assets	Summarized geographic information related to the Company’s operating revenues for the years ended December 31, 2018 , 2017 and 2016 and long-lived assets as of December 31, 2018 and 2017 is as follows: 2018 2017 2016 Operating Revenues: United States $ 3,947.5 $ 3,703.7 $ 3,442.7 Asia (1): India 1,540.5 1,164.4 827.6 EMEA (1): France 72.7 59.5 — Germany 69.1 63.1 60.2 Ghana 125.4 122.9 116.2 Kenya 7.0 — — Nigeria 220.7 213.9 215.4 South Africa 125.3 106.5 80.0 Uganda 67.1 60.3 57.7 Latin America (1): Argentina 16.0 15.9 1.0 Brazil 595.5 620.1 506.2 Chile 44.2 40.4 33.8 Colombia 103.8 89.3 79.7 Costa Rica 18.4 19.4 19.0 Mexico 456.5 364.3 331.2 Paraguay 10.4 2.7 — Peru 20.0 17.5 15.0 Total International 3,492.6 2,960.2 2,343.0 Total operating revenues $ 7,440.1 $ 6,663.9 $ 5,785.7 _______________ (1) Balances are translated at the applicable exchange rate, which may impact comparability between periods. 2018 2017 Long-Lived Assets (1): United States $ 16,543.7 $ 16,930.2 Asia (2): India 3,947.8 4,052.6 EMEA (2): France 963.8 1,009.6 Germany 388.5 428.0 Ghana 159.2 171.4 Kenya 190.0 — Nigeria 606.5 587.2 South Africa 342.5 330.4 Uganda 138.7 136.9 Latin America (2): Argentina 81.6 117.9 Brazil 2,288.1 2,557.4 Chile 129.7 151.2 Colombia 381.6 369.0 Costa Rica 119.1 112.9 Mexico 1,421.3 1,396.8 Paraguay 107.4 77.5 Peru 113.8 93.7 Total International 11,379.6 11,592.5 Total long-lived assets $ 27,923.3 $ 28,522.7 _______________ (1) Includes Property and equipment, net, Goodwill and Other intangible assets, net. (2) Balances are translated at the applicable period end exchange rate, which may impact comparability between periods.
Schedule of revenue by major customers	The following tenants within the property and services segments individually accounted for 10% or more of the Company’s consolidated operating revenues for the years ended December 31,: 2018 2017 2016 AT&T 19 % 19 % 21 % Verizon Wireless 15 % 16 % 15 % Sprint 8 % 9 % 11 %

SELECTED QUARTERLY FINANCIAL _2

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Information [Abstract]
Schedule of quarterly financial information	Selected quarterly financial data for the years ended December 31, 2018 and 2017 is as follows (in millions, except per share data): Three Months Ended Year Ended December 31, March 31, June 30, September 30, December 31, 2018: Operating revenues $ 1,741.8 $ 1,780.9 $ 1,785.5 $ 2,131.9 $ 7,440.1 Costs of operations (1) 519.9 560.3 556.7 540.9 2,177.8 Operating income 402.9 546.0 567.2 388.9 1,905.0 Net income 280.3 314.4 377.3 292.7 1,264.7 Net income attributable to American Tower Corporation stockholders 285.2 306.7 366.9 277.6 1,236.4 Dividends on preferred stock (9.4 ) — — — (9.4 ) Net income attributable to American Tower Corporation common stockholders 275.8 306.7 366.9 277.6 1,227.0 Basic net income per share attributable to American Tower Corporation common stockholders 0.63 0.69 0.83 0.63 2.79 Diluted net income per share attributable to American Tower Corporation common stockholders 0.63 0.69 0.83 0.62 2.77 Three Months Ended Year Ended December 31, March 31, June 30, September 30, December 31, 2017: Operating revenues $ 1,616.2 $ 1,662.5 $ 1,680.7 $ 1,704.5 $ 6,663.9 Costs of operations (1) 492.7 517.2 519.8 526.9 2,056.6 Operating income 531.4 576.9 561.1 329.0 1,998.4 Net income 307.4 388.5 334.7 194.8 1,225.4 Net income attributable to American Tower Corporation stockholders 316.1 367.0 317.3 238.5 1,238.9 Dividends on preferred stock (26.8 ) (22.8 ) (18.9 ) (18.9 ) (87.4 ) Net income attributable to American Tower Corporation common stockholders 289.3 344.2 298.4 219.6 1,151.5 Basic net income per share attributable to American Tower Corporation common stockholders 0.68 0.81 0.70 0.51 2.69 Diluted net income per share attributable to American Tower Corporation common stockholders 0.67 0.80 0.69 0.51 2.67 _______________ (1) Represents Operating expenses, exclusive of Depreciation, amortization and accretion, Selling, general, administrative and development expense, and Other operating expenses.

BUSINESS AND SUMMARY OF SIGNI_4

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)customersjoint_ventureshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2018	Jan. 01, 2018USD ($)
Principles of Consolidation and Basis of Presentation:
Number of joint ventures with controlling interests | joint_venture	2
Adjustment to noncontrolling interest due to merger	$ (28.1)	$ 0	$ 0
Accounts Receivable and Deferred Rent Asset:
Number of customers, concentration of credit risk | customers	4
Property and Equipment:
Labor costs capitalized	$ 55	50.9	47.7
Other Comprehensive Income (Loss):
Accumulated other comprehensive loss	(2,642.9)	(1,978.3)
Revenue Recognition:
Straight Line Revenue	87.6	194.4	131.7
Cash payment for settlement and release of contractual lease obligations	345.5
Distributions in excess of earnings	1,199.5	1,058.1
Revenue from contracts with customers	7,440.1
Revenue recognized	79.5
Rent Expense:
Straight-line ground rent expense	$ 57.9	$ 62.3	$ 67.8
Share-based Compensation:
Shares paid for tax withholding for share based compensation | shares	1,700,000
Retirement Plan:
Employers percentage of employees first 6 percent	100.00%	100.00%	75.00%
Employee maximum annual contribution eligible for match	5.00%	5.00%	6.00%
Company's contribution	$ 11.2	$ 11	$ 9.1
RSUs
Share-based Compensation:
Shares paid for tax withholding for share based compensation | shares	300,000
RSUs | 2007 Plan
Share-based Compensation:
Vesting period	4 years
PSUs
Share-based Compensation:
Vesting period	3 years
PSUs | 2007 Plan
Share-based Compensation:
Vesting period	3 years
Other Noncurrent Liabilities
Revenue Recognition:
Revenue recognized	$ 0.5
Prepaid Expenses and Other Current Assets
Revenue Recognition:
Decrease in unbilled receivables due to revenue recognized	1
Other Noncurrent Assets
Revenue Recognition:
Change in contract asset, revenue recognized	(0.4)
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenue Recognition:
Distributions in excess of earnings					$ 38.4
Revenue from contracts with customers	$ (4.9)
Maximum
Goodwill and Other Intangible Assets:
Estimated useful life of respective assets	20 years
Maximum | PSUs
Share-based Compensation:
Percentage of potential target shares	200.00%
Minimum
Goodwill and Other Intangible Assets:
Estimated useful life of respective assets	3 years
Minimum | PSUs
Share-based Compensation:
Percentage of potential target shares	0.00%
Sales Revenue, Net | Customer Concentration Risk | Four Customers
Accounts Receivable and Deferred Rent Asset:
Concentration risk, percentage	51.00%
Additional Paid-in Capital
Principles of Consolidation and Basis of Presentation:
Adjustment to noncontrolling interest due to merger	$ 50.7
Accumulated Foreign Currency Adjustment
Other Comprehensive Income (Loss):
Accumulated other comprehensive loss	2,600	$ 2,000	$ 2,000
Accumulated Other Comprehensive Loss
Principles of Consolidation and Basis of Presentation:
Adjustment to noncontrolling interest due to merger	$ (78.8)
ATC Europe
Principles of Consolidation and Basis of Presentation:
Company's ownership percentage	51.00%
Noncontrolling owners, ownership percentage	49.00%
ATC, TIPL
Principles of Consolidation and Basis of Presentation:
Company's ownership percentage	63.00%
Ghana
Principles of Consolidation and Basis of Presentation:
Number of joint ventures with controlling interests | joint_venture	1
Uganda
Principles of Consolidation and Basis of Presentation:
Number of joint ventures with controlling interests | joint_venture	1
South Africa
Principles of Consolidation and Basis of Presentation:
Purchase of interest in subsidiary	$ 20.5
Adjustment to noncontrolling interest due to merger	20.5
South Africa | Additional Paid-in Capital
Principles of Consolidation and Basis of Presentation:
Adjustment to noncontrolling interest due to merger	16.5
South Africa | Accumulated Other Comprehensive Loss
Principles of Consolidation and Basis of Presentation:
Adjustment to noncontrolling interest due to merger	(0.5)
South Africa | Noncontrolling Interest
Principles of Consolidation and Basis of Presentation:
Adjustment to noncontrolling interest due to merger	$ 4.5
South Africa | South African Subsidiary
Principles of Consolidation and Basis of Presentation:
Noncontrolling Interest, purchase of interest in subsidiary, percent	6.00%
Noncontrolling interest, ownership percentage by Parent	75.00%
Argentina
Functional Currency:
Exchange rate, remeasurement U.S. Dollar to Argentinean Peso				29.4
Corporate Joint Venture | Ghana
Principles of Consolidation and Basis of Presentation:
Company's ownership percentage	51.00%
Noncontrolling owners, ownership percentage	49.00%
Corporate Joint Venture | Uganda
Principles of Consolidation and Basis of Presentation:
Company's ownership percentage	51.00%
Noncontrolling owners, ownership percentage	49.00%
Corporate Joint Venture | South Africa
Principles of Consolidation and Basis of Presentation:
Company's ownership percentage	81.00%
Noncontrolling owners, ownership percentage	19.00%

BUSINESS AND SUMMARY OF SIGNI_5

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Changes in Allowances) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance as of January 1	$ 131	$ 45.9	$ 23.1
Current year increases	157.8	87.2	50
Write-offs, recoveries and other	(6.4)	(2.1)	(27.2)
Balance as of December 31	$ 282.4	$ 131	$ 45.9

BUSINESS AND SUMMARY OF SIGNI_6

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Net Foreign Currency Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Foreign currency losses recorded in AOCL	$ 385.8	$ 51.6	$ 105
Foreign currency losses (gains) recorded in Other expense	4.5	(26.4)	48.9
Net foreign currency losses	$ 390.3	$ 25.2	$ 153.9

BUSINESS AND SUMMARY OF SIGNI_7

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Cash, Cash Equivalents, And Restricted Cash) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 1,208.7	$ 802.1	$ 787.2
Restricted cash	96.2	152.8	149.3
Total cash, cash equivalents and restricted cash	$ 1,304.9	$ 954.9	$ 936.5	$ 462.9

BUSINESS AND SUMMARY OF SIGNI_8

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Disaggregation of Revenue) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 7,440.1
United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,947.5
Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,540.5
EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	687.3
Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,264.8
Power And Fuel Pass-Through Revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	607.1
Power And Fuel Pass-Through Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Power And Fuel Pass-Through Revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	450
Power And Fuel Pass-Through Revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	140.3
Power And Fuel Pass-Through Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16.8
Other Non-Lease Revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	383.6
Other Non-Lease Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	273.2
Other Non-Lease Revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7
Other Non-Lease Revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.3
Other Non-Lease Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	102.1
Non-Lease Property Revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	990.7
Non-Lease Property Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	273.2
Non-Lease Property Revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	457
Non-Lease Property Revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	141.6
Non-Lease Property Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118.9
Services Revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	125.4
Services Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	125.4
Services Revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Services Revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Services Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Non-Lease Revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,116.1
Non-Lease Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	398.6
Non-Lease Revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	457
Non-Lease Revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	141.6
Non-Lease Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118.9
Property Lease Revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,324
Property Lease Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,548.9
Property Lease Revenue | Asia
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,083.5
Property Lease Revenue | EMEA
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	545.7
Property Lease Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,145.9

BUSINESS AND SUMMARY OF SIGNI_9

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Schedule of Contract Assets and Liabilities From Contracts with Tenants) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Contract Assets And Liabilities From Contracts With Customers [Line Items]
Prepaids and other current assets	$ 621.2		$ 568.6
Notes receivable and other non-current assets	962.6		950.1
Other non-current liabilities	1,265.1		$ 1,244.2
Non-Lease Revenue
Schedule of Contract Assets And Liabilities From Contracts With Customers [Line Items]
Accounts receivable	260.7	$ 222.2
Prepaids and other current assets	103.2	79.7
Notes receivable and other non-current assets	22.2	24.2
Unearned revenue	37.6	26.6
Other non-current liabilities	$ 54.9	$ 68.5

BUSINESS AND SUMMARY OF SIGN_10

BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Accounting Standards Updates) (Details) - USD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		$ (1,199.5)	$ (1,058.1)
Scenario, Forecast | Subsequent Event | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease, right-of-use asset	$ 7,100
Lease liabilities	6,800
Retained earnings	$ 24.7

PREPAID AND OTHER CURRENT ASS_3

PREPAID AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid operating ground leases	$ 165	$ 148.6
Unbilled receivables	126.1	107.9
Prepaid income tax	125.1	136.5
Value added tax and other consumption tax receivables	86.3	64.2
Prepaid assets	40.5	39.6
Other miscellaneous current assets	78.2	71.8
Prepaids and other current assets	$ 621.2	$ 568.6

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Towers	$ 12,777.9	$ 12,500.5
Equipment	1,667.3	1,423
Buildings and improvements	628.5	631.4
Land and improvements	2,285.4	2,112.9
Construction-in-progress	358.1	282.1
Total	17,717.2	16,949.9
Less accumulated depreciation	(6,470.1)	(5,848.9)
Property and equipment, net	$ 11,247.1	$ 11,101
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	20 years
Tower | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	20 years
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Buildings and Improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Buildings and Improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	32 years
Land and Improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	20 years

PROPERTY AND EQUIPMENT (Narrati

PROPERTY AND EQUIPMENT (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 883.1	$ 835.5	$ 758.9
Assets Held under Capital Leases
Property, Plant and Equipment [Line Items]
Capital leases, which are primarily classified as towers or land and improvements	4,369.5	4,944.2
Capital leases, accumulated depreciation	$ 1,016.2	$ 1,370.4

GOODWILL AND OTHER INTANGIBLE_3

GOODWILL AND OTHER INTANGIBLE ASSETS (Changes in the Carrying Value of Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 5,638.4	$ 5,070.7
Additions	48.2	486.1
Effect of foreign currency translation	(184.7)	81.6
Goodwill, ending balance	5,501.9	5,638.4
Services
Goodwill [Roll Forward]
Goodwill, beginning balance	2	2
Additions	0	0
Effect of foreign currency translation	0	0
Goodwill, ending balance	2	2
U.S. | Property
Goodwill [Roll Forward]
Goodwill, beginning balance	3,379.2	3,379.2
Additions	3.3	0
Effect of foreign currency translation	0	0
Goodwill, ending balance	3,382.5	3,379.2
Asia | Property
Goodwill [Roll Forward]
Goodwill, beginning balance	1,095	1,029.3
Additions	44.5	0.4
Effect of foreign currency translation	(94)	65.3
Goodwill, ending balance	1,045.5	1,095
EMEA | Property
Goodwill [Roll Forward]
Goodwill, beginning balance	404.9	150.5
Additions	0	220.9
Effect of foreign currency translation	(23.6)	33.5
Goodwill, ending balance	381.3	404.9
Latin America | Property
Goodwill [Roll Forward]
Goodwill, beginning balance	757.3	509.7
Additions	0.4	264.8
Effect of foreign currency translation	(67.1)	(17.2)
Goodwill, ending balance	690.6	757.3
2017 Acquisitions
Goodwill [Roll Forward]
Additions		485.1
Goodwill, measurement period adjustments		$ 1
2018 Acquisitions [Member]
Goodwill [Roll Forward]
Additions	47.8
Goodwill, measurement period adjustments	$ 0.4

GOODWILL AND OTHER INTANGIBLE_4

GOODWILL AND OTHER INTANGIBLE ASSETS (Other Intangible Assets Subject to Amortization) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 25, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets		$ 1,144.1	$ 785.9	$ 699.8
Gross Carrying Value		16,040.9	16,083
Accumulated Amortization		(4,866.6)	(4,299.7)
Net Book Value		11,174.3	11,783.3
Acquired network location intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value		4,780.3	4,858.8
Accumulated Amortization		(1,704.9)	(1,525.3)
Net Book Value		$ 3,075.4	3,333.5
Acquired network location intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life		20 years
Acquired tenant-related intangibles
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 327.5
Gross Carrying Value		$ 11,156.5	11,150.9
Accumulated Amortization		(3,147.2)	(2,754.7)
Net Book Value		$ 8,009.3	8,396.2
Acquired tenant-related intangibles | Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life		15 years
Acquired tenant-related intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life		20 years
Acquired licenses and other intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value		$ 104.1	58.8
Accumulated Amortization		(14.5)	(8.1)
Net Book Value		$ 89.6	50.7
Acquired licenses and other intangibles | Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life		3 years
Acquired licenses and other intangibles | Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life		20 years
Economic Rights, TV Azteca
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value		$ 0	14.5
Accumulated Amortization		0	(11.6)
Net Book Value		$ 0	$ 2.9		$ 3
Intangible assets, useful life		70 years

GOODWILL AND OTHER INTANGIBLE_5

GOODWILL AND OTHER INTANGIBLE ASSETS (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets		$ 1,144.1	$ 785.9	$ 699.8
Weighted Average
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, remaining amortization period		15 years
Acquired tenant-related intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 327.5

GOODWILL AND OTHER INTANGIBLE_6

GOODWILL AND OTHER INTANGIBLE ASSETS (Expected Future Amortization Expenses) (Details) $ in Millions	Dec. 31, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,019	$ 786
2,020	765.8
2,021	749.6
2,022	745.1
2,023	$ 740.6

NOTES RECEIVABLE AND OTHER NO_3

NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS (Notes Receivable and Other Non-Current Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Notes Receivable And Other Long Term Assets [Abstract]
Long-term prepaid ground rent	$ 607.5	$ 552.8
Notes receivable	1	83.7
Other miscellaneous assets	354.1	313.6
Notes receivable and other non-current assets	$ 962.6	$ 950.1

NOTES RECEIVABLE AND OTHER NO_4

NOTES RECEIVABLE AND OTHER NON-CURRENT ASSETS (Narrative) (Details) $ in Millions	Sep. 25, 2018USD ($)communications_site	Dec. 31, 2000USD ($)communications_site	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Notes Receivable And Other NonCurrent Assets [Line Items]
TV Azteca paid to extinguish loan	$ 59.5
Fair value of agreement	24.8
Capital lease, liability	$ 14.1		$ 179.5	$ 165.5
Required to pay quarterly percentage of gross revenue associated with the Commercialization Rights	25.00%
Net carrying value			11,174.3	11,783.3
Economic Rights, TV Azteca
Notes Receivable And Other NonCurrent Assets [Line Items]
Term of the loan, years		70 years
Number of broadcast towers | communications_site		190
Commercial rights, annual payment		$ 1.5
Percentage of the revenues from leasing of towers		100.00%
Capital lease, asset		$ 18.6
Capital lease, liability		18.6
Capital lease asset and discount on note		30.2
Write-off of deferred financing costs	$ 1.5
Net carrying value	3		$ 0	2.9
Gain recorded	$ 9.7
Commercialization Rights, TV Azteca
Notes Receivable And Other NonCurrent Assets [Line Items]
Number of broadcast towers | communications_site	190
TV Azteca
Notes Receivable And Other NonCurrent Assets [Line Items]
Loans receivable		$ 119.8		91.8
Loan interest rate		13.11%
Term of the loan, years		70 years
Loans receivable, net of discount				$ 82.9

ACQUISITIONS (Merger and Integr

ACQUISITIONS (Merger and Integration Expenses) (Details) - USD ($) $ in Millions	Oct. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Combinations [Abstract]
Acquisition and merger related expenses	$ 1.7	$ 14.1	$ 16.3	$ 15.9
Integration costs		$ 16.1	$ 11.5	$ 9.9

ACQUISITIONS (Narrative) (Detai

ACQUISITIONS (Narrative) (Details) R$ in Millions, $ in Millions, ₨ in Billions

Nov. 01, 2018USD ($)

Nov. 01, 2018BRL (R$)

Oct. 01, 2018USD ($)site

May 31, 2018USD ($)site

May 31, 2018INR (₨)site

Mar. 31, 2018USD ($)site

Mar. 31, 2018INR (₨)

Nov. 17, 2017USD ($)

Nov. 17, 2017concrete_pole

Nov. 17, 2017route_miles_of_fiber

Dec. 31, 2018USD ($)site

Dec. 31, 2018USD ($)site

Dec. 31, 2018INR (₨)

Dec. 31, 2017USD ($)

Business Acquisition [Line Items]

Proceeds from previous acquisition

$ 22.2

Business combination, pro forma information, revenue of acquiree since acquisition date, actual

232.2

Business combination pro forma information gross margin of acquiree since acquisition date actual

83

Accounts payable

$ 130.8

130.8

$ 142.9

Contingent consideration

0.9

0.9

Vodafone

Business Acquisition [Line Items]

Asset acquisition, consideration transferred

$ 587.9

Vodafone | Communication Sites

Business Acquisition [Line Items]

Number of communications sites acquired | site

10,200

Asset acquisition, consideration transferred

$ 587.9

₨ 38.3

Accounts payable

$ 1.1

Kenya Acquisition

Business Acquisition [Line Items]

Asset acquisition, consideration transferred

$ 174.1

Contingent consideration

$ 51.8

Contingent consideration liability, installment payment period

3 years

Kenya Acquisition | Kenya | Communication Sites

Business Acquisition [Line Items]

Number of communications sites acquired | site

700

Other Acquisitions 2018

Business Acquisition [Line Items]

Asset acquisition, consideration transferred

570.3

Accounts payable

$ 11.8

$ 11.8

Other Acquisitions 2018 | Communication Sites

Business Acquisition [Line Items]

Number of communications sites acquired | site

1,335

1,335

Asset acquisition, consideration transferred

$ 414.5

Cia Energetica De Minas Gerais SA | Telecommunication Poles

Business Acquisition [Line Items]

Asset acquisition, consideration transferred

$ 155.8

R$ 576.9

Idea Cellular Limited

Business Acquisition [Line Items]

Percentage of voting interest acquired

100.00%

100.00%

Number of communications sites acquired | site

9,700

9,700

Consideration, purchase price

$ 635.5

$ 625.9

Idea Cellular Limited | Communication Sites

Business Acquisition [Line Items]

Consideration, purchase price

$ 635.5

₨ 42.8

625.9

₨ 42.2

Entities With Urban Telecommunications Assets In Mexico

Business Acquisition [Line Items]

Percentage of voting interest acquired

100.00%

100.00%

100.00%

Consideration, purchase price

$ 505.8

$ 499.7

Number of assets acquired

50,000

2,100

ACQUISITIONS (Schedule of Aggre

ACQUISITIONS (Schedule of Aggregate Purchase Consideration Paid and the Amount of Assets Acquired) (Details) $ in Millions, ₨ in Billions	Oct. 01, 2018USD ($)	May 31, 2018USD ($)site	May 31, 2018INR (₨)	Mar. 31, 2018USD ($)site	Mar. 31, 2018INR (₨)	Nov. 17, 2017USD ($)	Mar. 31, 2018USD ($)site	Dec. 31, 2018USD ($)sitecommunications_site	Dec. 31, 2018USD ($)sitecommunications_site	Dec. 31, 2018INR (₨)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Business Combination
Goodwill								$ 5,501.9	$ 5,501.9		$ 5,638.4	$ 5,070.7
Asset Acquisition [Abstract]
Current assets								2,385.1	2,385.1		2,038.1
PROPERTY AND EQUIPMENT, net								11,247.1	11,247.1		11,101
Intangible assets								11,174.3	11,174.3		11,783.3
Current liabilities								(4,689.9)	(4,689.9)		(2,512.1)
Deferred tax liability								(535.9)	(535.9)		(898.1)
Other non-current liabilities								(1,265.1)	(1,265.1)		(1,244.2)
Acquisition and merger related expenses	$ 1.7								14.1		16.3	$ 15.9
Tenant-related intangible assets
Asset Acquisition [Abstract]
Intangible assets								8,009.3	$ 8,009.3		8,396.2
Tenant-related intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life									20 years	20 years
Network location intangible assets
Asset Acquisition [Abstract]
Intangible assets								3,075.4	$ 3,075.4		$ 3,333.5
Network location intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life									20 years	20 years
Vodafone
Business Combination
Goodwill				$ 0			$ 0
Asset Acquisition [Abstract]
Current assets				15.1			15.1
Non-current assets				5.8			5.8
PROPERTY AND EQUIPMENT, net				194.6			194.6
Current liabilities				(13.1)			(13.1)
Deferred tax liability				0			0
Other non-current liabilities				(12.5)			(12.5)
Net assets acquired				587.9			587.9
Fair value of net assets acquired				587.9			$ 587.9
Debt assumed				0
Purchase price				587.9
Acquisition and merger related expenses				1.3
Vodafone | Communication Sites
Asset Acquisition [Abstract]
Purchase price				$ 587.9	₨ 38.3
Number of communications sites acquired | site				10,200			10,200
Vodafone | Tenant-related intangible assets
Asset Acquisition [Abstract]
Intangible assets				$ 309.5			$ 309.5
Vodafone | Tenant-related intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life							20 years
Vodafone | Network location intangible assets
Asset Acquisition [Abstract]
Intangible assets				88.5			$ 88.5
Vodafone | Network location intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life							20 years
Vodafone | Other intangible assets
Asset Acquisition [Abstract]
Intangible assets				$ 0			$ 0
Vodafone | Other intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life							20 years
Kenya
Business Combination
Goodwill	0
Asset Acquisition [Abstract]
Current assets	0.1
Non-current assets	24.7
PROPERTY AND EQUIPMENT, net	51.2
Current liabilities	0
Deferred tax liability	(32.2)
Other non-current liabilities	(1.5)
Net assets acquired	174.1
Fair value of net assets acquired	174.1
Debt assumed	0
Purchase price	174.1
Kenya | Tenant-related intangible assets
Asset Acquisition [Abstract]
Intangible assets	$ 106.2
Kenya | Tenant-related intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life	20 years
Kenya | Network location intangible assets
Asset Acquisition [Abstract]
Intangible assets	$ 25.6
Kenya | Network location intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life	20 years
Kenya | Other intangible assets
Asset Acquisition [Abstract]
Intangible assets	$ 0
Kenya | Other intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life	20 years
Other Acquisitions 2018
Business Combination
Goodwill								3.3	$ 3.3
Asset Acquisition [Abstract]
Current assets								3.6	3.6
Non-current assets								5.1	5.1
PROPERTY AND EQUIPMENT, net								271.5	271.5
Current liabilities								(3.6)	(3.6)
Deferred tax liability								0	0
Other non-current liabilities								(21.3)	(21.3)
Net assets acquired								567	567
Fair value of net assets acquired								$ 570.3	570.3
Debt assumed									0
Purchase price									570.3
Other Acquisitions 2018 | Communication Sites
Asset Acquisition [Abstract]
Purchase price									$ 414.5
Number of communications sites acquired | site								1,335	1,335
Other Acquisitions 2018 | Communication Sites | Peru
Asset Acquisition [Abstract]
Number of communications sites acquired | communications_site								145	145
Other Acquisitions 2018 | Tenant-related intangible assets
Asset Acquisition [Abstract]
Intangible assets								$ 191.5	$ 191.5
Other Acquisitions 2018 | Tenant-related intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life									20 years	20 years
Other Acquisitions 2018 | Network location intangible assets
Asset Acquisition [Abstract]
Intangible assets								91.5	$ 91.5
Other Acquisitions 2018 | Network location intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life									20 years	20 years
Other Acquisitions 2018 | Other intangible assets
Asset Acquisition [Abstract]
Intangible assets								28.7	$ 28.7
Other Acquisitions 2018 | Other intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life									20 years	20 years
Idea Cellular Limited
Business Combination
Current assets		$ 100.7						82.9	$ 82.9
Non-current assets		2.6						11.6	11.6
Property and equipment		161.2						161.2	161.2
Current liabilities		(52.5)						(47.4)	(47.4)
Deferred tax liability		(20.7)						(17.7)	(17.7)
Other non-current liabilities		(10.5)						(16.1)	(16.1)
Net assets acquired		584.9						581.4	581.4
Goodwill		50.6						44.5	44.5
Fair value of net assets acquired		635.5						625.9	625.9
Debt assumed		0						0
Purchase price		$ 635.5						625.9
Asset Acquisition [Abstract]
Number of communications sites acquired | site		9,700
Idea Cellular Limited | Communication Sites
Business Combination
Purchase price		$ 635.5	₨ 42.8						625.9	₨ 42.2
Idea Cellular Limited | Tenant-related intangible assets
Business Combination
Intangible assets		$ 321.2						323.4	$ 323.4
Idea Cellular Limited | Tenant-related intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life		20 years	20 years						20 years	20 years
Idea Cellular Limited | Network location intangible assets
Business Combination
Intangible assets		$ 82.9						83.5	$ 83.5
Idea Cellular Limited | Network location intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life		20 years	20 years						20 years	20 years
Idea Cellular Limited | Other intangible assets
Business Combination
Intangible assets		$ 0						0	$ 0
Idea Cellular Limited | Other intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life		20 years	20 years						20 years	20 years
Entities With Urban Telecommunications Assets In Mexico
Business Combination
Current assets						$ 44.4		42.5	$ 42.5
Non-current assets						0		0	0
Property and equipment						94		102.2	102.2
Current liabilities						(28.8)		(27.2)	(27.2)
Deferred tax liability						(38.8)		(36.2)	(36.2)
Other non-current liabilities						(4.5)		(4.5)	(4.5)
Net assets acquired						241.6		235.1	235.1
Goodwill						264.2		264.6	264.6
Fair value of net assets acquired						505.8		499.7	499.7
Debt assumed						0			0
Purchase price						505.8			499.7
Entities With Urban Telecommunications Assets In Mexico | Tenant-related intangible assets
Business Combination
Intangible assets						$ 153.3		138	$ 138
Entities With Urban Telecommunications Assets In Mexico | Tenant-related intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life						20 years			20 years	20 years
Entities With Urban Telecommunications Assets In Mexico | Network location intangible assets
Business Combination
Intangible assets						$ 0		0	$ 0
Entities With Urban Telecommunications Assets In Mexico | Network location intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life						20 years			20 years	20 years
Entities With Urban Telecommunications Assets In Mexico | Other intangible assets
Business Combination
Intangible assets						$ 22		$ 20.3	$ 20.3
Entities With Urban Telecommunications Assets In Mexico | Other intangible assets | Maximum
Asset Acquisition [Abstract]
Intangible assets, useful life						20 years			20 years	20 years

ACQUISITIONS (Pro Forma Informa

ACQUISITIONS (Pro Forma Information) (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Combinations [Abstract]
Pro forma revenues	$ 7,610.6	$ 7,161
Pro forma net income attributable to American Tower Corporation common stockholders	$ 1,218.2	$ 1,127.6
Pro forma net income per common share amounts:
Basic net income attributable to American Tower Corporation (in dollars per share)	$ 2.77	$ 2.63
Diluted net income attributable to American Tower Corporation (in dollars per share)	$ 2.75	$ 2.61

ACQUISITIONS (Summary Of Acquis

ACQUISITIONS (Summary Of Acquisition-related Contingent Consideration Obligations) (Details)	12 Months Ended
	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Contingent consideration, Maximum potential value	$ 900,000
Contingent consideration	900,000
Contingent consideration, additions	0
Contingent consideration, settlements	(8,700,000)
Change in fair value	(500,000)
Contingent consideration arrangements, range of outcomes, value, low	0
Ghana
Business Acquisition [Line Items]
Contingent consideration, Maximum potential value	600,000
Contingent consideration	600,000
Contingent consideration, additions	0
Contingent consideration, settlements	0
Change in fair value	0
South Africa
Business Acquisition [Line Items]
Contingent consideration, Maximum potential value	0
Contingent consideration	0
Contingent consideration, additions	0
Contingent consideration, settlements	(8,600,000)
Change in fair value	(500,000)
United States
Business Acquisition [Line Items]
Contingent consideration, Maximum potential value	300,000
Contingent consideration	300,000
Contingent consideration, additions	0
Contingent consideration, settlements	(100,000)
Change in fair value	$ 0

ACCRUED EXPENSES (Details)

ACCRUED EXPENSES (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities, Current [Abstract]
Accrued property and real estate taxes	$ 169.7	$ 154.4
Amounts payable to tenants	93.5	60.8
Payroll and related withholdings	90.4	82.2
Accrued pass-through taxes	71.2	59.7
Accrued rent	61.4	54
Accrued income tax payable	57.9	15.3
Accrued construction costs	41.5	31.9
Accrued pass-through taxes	2.2	25.3
Other accrued expenses	360.5	370.7
Accrued expenses	$ 948.3	$ 854.3

LONG-TERM OBLIGATIONS (Outstand

LONG-TERM OBLIGATIONS (Outstanding Amounts) (Details) ₨ in Millions, GH₵ in Millions, USh in Billions	Aug. 30, 2018USD ($)	Aug. 30, 2018UGX (USh)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018INR (₨)	Dec. 31, 2018GHS (GH₵)	Nov. 30, 2018USD ($)	May 22, 2018	Dec. 31, 2017USD ($)	Dec. 08, 2017	May 29, 2015USD ($)	Jan. 10, 2014	Aug. 19, 2013
Debt Instrument [Line Items]
Long-term debt				$ 21,159,900,000
Other long-term debt				179,500,000					$ 165,500,000
Debt, long-term and short-term, combined amount				21,159,900,000					20,205,100,000
Less current portion long-term obligations				(2,754,800,000)					(774,800,000)
Long-term debt, excluding current maturities				$ 18,405,100,000					19,430,300,000
Payment terms, repayment period				12 months
Parent
Debt Instrument [Line Items]
Long-term debt				$ 17,847,500,000					16,494,500,000
Subsidiaries
Debt Instrument [Line Items]
Long-term debt				3,132,900,000					3,545,100,000
Revolving Credit Facility | Credit Facility 2013
Debt Instrument [Line Items]
Long-term debt							$ 2,850,000,000
Long-term line of credit				$ 1,875,000,000					2,075,600,000
Debt interest rate, effective percentage				3.6162%	3.6162%	3.6162%
Revolving Credit Facility | Credit Facility 2014
Debt Instrument [Line Items]
Long-term debt							$ 2,100,000,000
Long-term line of credit				$ 0					495,000,000
Debt interest rate, effective percentage				3.655%	3.655%	3.655%
Unsecured Debt
Debt Instrument [Line Items]
Long-term debt				$ 152,500,000					246,100,000
Payment terms, repayment period				3 years
Unsecured Debt | Term Loan 2018
Debt Instrument [Line Items]
Long-term debt				$ 1,499,800,000					0
Less current portion long-term obligations				$ (1,500,000,000)
Debt interest rate, effective percentage				3.405%	3.405%	3.405%
Unsecured Debt | Term Loan 2013
Debt Instrument [Line Items]
Long-term debt				$ 994,800,000					994,500,000
Debt interest rate, effective percentage				3.655%	3.655%	3.655%
Unsecured Debt | India Indebtedness
Debt Instrument [Line Items]
Long-term debt				$ 240,100,000					512,600,000
Less current portion long-term obligations				(101,900,000)	₨ (7,100)
Unsecured Debt | Shareholder loans
Debt Instrument [Line Items]
Long-term debt				59,900,000					100,600,000
Less current portion long-term obligations				(59,900,000)		GH₵ (294.4)
Repayments of long-term debt	$ 33,800,000	USh 127.2
Senior Notes | 3.40% senior notes
Debt Instrument [Line Items]
Long-term debt				1,000,000,000					999,800,000
Less current portion long-term obligations				$ (1,000,000,000)
Long-term debt, stated interest rate				3.40%	3.40%	3.40%						3.40%	3.40%
Senior Notes | 2.800% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 747,800,000					746,300,000
Long-term debt, stated interest rate				2.80%	2.80%	2.80%
Senior Notes | 5.050% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 698,700,000					698,000,000
Long-term debt, stated interest rate				5.05%	5.05%	5.05%
Senior Notes | 3.300% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 747,200,000					746,000,000
Long-term debt, stated interest rate				3.30%	3.30%	3.30%
Senior Notes | 3.450% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 646,300,000					645,100,000
Long-term debt, stated interest rate				3.45%	3.45%	3.45%
Senior Notes | 5.900% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 498,400,000					497,800,000
Long-term debt, stated interest rate				5.90%	5.90%	5.90%
Senior Notes | 2.250% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 572,700,000					$ 572,400,000
Long-term debt, stated interest rate				2.25%	2.25%	2.25%			2.25%
Senior Notes | 4.70% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 697,400,000					$ 696,700,000
Long-term debt, stated interest rate				4.70%	4.70%	4.70%
Senior Notes | 3.50% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 992,600,000					990,900,000
Long-term debt, stated interest rate				3.50%	3.50%	3.50%
Senior Notes | 3.000% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 687,500,000					$ 692,500,000
Long-term debt, stated interest rate				3.00%	3.00%	3.00%			3.00%	3.00%
Senior Notes | 5.00% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 1,002,100,000					$ 1,002,400,000
Long-term debt, stated interest rate				5.00%	5.00%	5.00%						5.00%	5.00%
Senior Notes | 1.375% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 564,000,000					589,100,000
Long-term debt, stated interest rate				1.375%	1.375%	1.375%
Senior Notes | 4.000% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 742,100,000					741,000,000
Long-term debt, stated interest rate				4.00%	4.00%	4.00%
Senior Notes | 4.400% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 496,100,000					495,600,000
Long-term debt, stated interest rate				4.40%	4.40%	4.40%
Senior Notes | 1.950% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 566,000,000					0
Long-term debt, stated interest rate				1.95%	1.95%	1.95%		1.95%
Senior Notes | 3.375% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 986,300,000					984,800,000
Long-term debt, stated interest rate				3.375%	3.375%	3.375%
Senior Notes | 3.125% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 397,300,000					397,100,000
Long-term debt, stated interest rate				3.125%	3.125%	3.125%
Senior Notes | 3.55% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 743,500,000					742,800,000
Long-term debt, stated interest rate				3.55%	3.55%	3.55%
Senior Notes | 3.600% senior notes
Debt Instrument [Line Items]
Long-term debt				$ 691,900,000					691,100,000
Long-term debt, stated interest rate				3.60%	3.60%	3.60%
Secured Debt | Series 2013-1A Securities | Series 2013-1A and Series 2013-2A Securities
Debt Instrument [Line Items]
Long-term debt				$ 0					499,800,000
Secured Debt | Series 2013-2A Securities | Series 2013-1A and Series 2013-2A Securities
Debt Instrument [Line Items]
Long-term debt				$ 1,293,400,000					1,291,800,000
Long-term debt, stated interest rate				3.07%	3.07%	3.07%
Secured Debt | Series 2018-1A Securities | Secured Tower Revenue Securities, Series 2018-1A
Debt Instrument [Line Items]
Long-term debt				$ 493,500,000					0
Long-term debt, stated interest rate				3.652%	3.652%	3.652%
Repayments of long-term debt			$ 500,000,000
Secured Debt | Series 2015-1 Class A
Debt Instrument [Line Items]
Long-term debt				$ 348,800,000					348,000,000		$ 350,000,000
Long-term debt, stated interest rate				2.35%	2.35%	2.35%
Secured Debt | Series 2015-2 Class A
Debt Instrument [Line Items]
Long-term debt				$ 520,800,000					520,100,000		$ 525,000,000
Long-term debt, stated interest rate				3.482%	3.482%	3.482%
Secured Debt | India Indebtedness | Minimum
Debt Instrument [Line Items]
Long-term debt, stated interest rate				8.40%	8.40%	8.40%
Secured Debt | India Indebtedness | Maximum
Debt Instrument [Line Items]
Long-term debt, stated interest rate				8.95%	8.95%	8.95%
Mandatorily Redeemable Preferred Stock | India preference shares
Debt Instrument [Line Items]
Long-term debt				$ 23,900,000					$ 26,100,000
Less current portion long-term obligations				$ (23,900,000)	₨ (1,670)
Long-term debt, stated interest rate				10.25%	10.25%	10.25%

LONG-TERM OBLIGATIONS (Current

LONG-TERM OBLIGATIONS (Current Portion) (Details) ₨ in Millions, GH₵ in Millions, $ in Millions	Dec. 31, 2018USD ($)	Dec. 31, 2018INR (₨)	Dec. 31, 2018GHS (GH₵)	Dec. 31, 2017USD ($)	Jan. 10, 2014	Aug. 19, 2013
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 2,754.8			$ 774.8
Term Loan 2018 | Unsecured Debt
Debt Instrument [Line Items]
Current portion of long-term obligations	1,500
3.40% senior notes | Senior Notes
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 1,000
Long-term debt, stated interest rate	3.40%	3.40%	3.40%		3.40%	3.40%
India Indebtedness | Unsecured Debt
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 101.9	₨ 7,100
Shareholder loans | Unsecured Debt
Debt Instrument [Line Items]
Current portion of long-term obligations	59.9		GH₵ 294.4
India preference shares | Mandatorily Redeemable Preferred Stock
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 23.9	₨ 1,670
Long-term debt, stated interest rate	10.25%	10.25%	10.25%

LONG-TERM OBLIGATIONS (Bank Fac

LONG-TERM OBLIGATIONS (Bank Facilities) (Details)	1 Months Ended
	Nov. 30, 2018USD ($)	Oct. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Long-term debt			$ 21,159,900,000
Revolving Credit Facility | Credit Facility 2013
Debt Instrument [Line Items]
Increase commitments under Credit Facility	$ 100,000,000
Long-term debt	2,850,000,000
Line of credit facility, maximum borrowing capacity	4,500,000,000
Limit on indebtedness of, guaranteed by subsidiaries to the greater of	$ 2,500,000,000
Limit on indebtedness of, guaranteed by subsidiaries, consolidated adjustment EBITDA, percent	0.5
Threshold for certain defaults, attachments or acceleration of indebtedness	$ 400,000,000	$ 300,000,000
Revolving Credit Facility | Credit Facility 2014
Debt Instrument [Line Items]
Increase commitments under Credit Facility	100,000,000
Long-term debt	2,100,000,000
Line of credit facility, maximum borrowing capacity	3,250,000,000
Limit on indebtedness of, guaranteed by subsidiaries to the greater of	$ 2,500,000,000
Limit on indebtedness of, guaranteed by subsidiaries, consolidated adjustment EBITDA, percent	0.50

LONG-TERM OBLIGATIONS (Narrativ

LONG-TERM OBLIGATIONS (Narrative) (Details) ₨ in Millions, R$ in Millions	May 22, 2018USD ($)	May 22, 2018EUR (€)	Mar. 29, 2018USD ($)	May 29, 2015USD ($)tower	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)siteshares	Dec. 31, 2017USD ($)quarter	Dec. 31, 2016USD ($)	Dec. 31, 2018INR (₨)siteshares	Dec. 31, 2018BRL (R$)siteshares	Nov. 30, 2018USD ($)	Sep. 25, 2018USD ($)	May 22, 2018EUR (€)	Dec. 31, 2017BRL (R$)quarter	Dec. 08, 2017	Mar. 02, 2017shares	Nov. 30, 2014BRL (R$)
Debt Instrument [Line Items]
Borrowings under credit facilities						$ 3,263,300,000	$ 5,359,400,000	$ 2,446,800,000
Proceeds from term loan						$ 1,500,000,000	0	$ 0
Number Of Trust Sites Assets | site						5,116			5,116	5,116
Long-term debt						$ 21,159,900,000
Payment terms, repayment period						12 months
Capital lease obligations						$ 179,500,000	165,500,000					$ 14,100,000
Capital lease obligation and notes payable interest rates ranging minimum						3.36%			3.36%	3.36%
Capital lease obligation and notes payable interest rates ranging maximum						9.25%			9.25%	9.25%
Capital lease obligation and notes payable interest mature in periods minimum (less than)						1 year
Capital lease obligation and notes payable interest mature in periods maximum						75 years
Credit Facility 2013 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, remaining borrowing capacity						$ 2,850,000,000
Borrowings under credit facilities						2,100,000,000
Repayments of lines of credit						$ 2,300,000,000
Repayments of credit facility			$ 1,100,000,000
Long-term debt											$ 2,850,000,000
Credit Facility 2013 | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						1.125%
Credit Facility 2013 | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						0.75%
Credit Facility 2013 | Minimum | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						0.875%
Credit Facility 2013 | Maximum | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						1.75%
Credit Facility 2014 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, remaining borrowing capacity						$ 2,100,000,000
Borrowings under credit facilities						1,100,000,000
Repayments of lines of credit						1,500,000,000
Repayments of credit facility			445,000,000
Long-term debt											$ 2,100,000,000
Credit Facility 2014 | Swingline Loan
Debt Instrument [Line Items]
Line of credit facility, remaining borrowing capacity						$ 50,000,000
Credit Facility 2014 | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						1.125%
Credit Facility 2014 | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						0.75%
Credit Facility 2014 | Minimum | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						0.875%
Credit Facility 2014 | Maximum | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate						0.175%
Term Loan 2013 | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate						0.75%
Term Loan 2013 | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						0.875%
Term Loan 2013 | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						0.175%
Term Loan 2018 | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						0.875%
Term Loan 2018 | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate						0.50%
Term Loan 2018 | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						0.625%
Term Loan 2018 | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						1.50%
Unsecured Debt
Debt Instrument [Line Items]
Long-term debt						$ 152,500,000	246,100,000
Payment terms, repayment period						3 years
Unsecured Debt | Term Loan 2013
Debt Instrument [Line Items]
Principal amount						$ 1,000,000,000
Long-term debt						$ 994,800,000	994,500,000
Unsecured Debt | Term Loan 2013 | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						1.125%
Unsecured Debt | BR Towers Debentures
Debt Instrument [Line Items]
Long-term debt | R$																	R$ 300.0
Unsecured Debt | Term Loan 2018
Debt Instrument [Line Items]
Principal amount						$ 1,500,000,000
Long-term debt						$ 1,499,800,000	$ 0
Senior Notes
Debt Instrument [Line Items]
Redemption price percentage						100.00%
Repurchase price as percentage of principal							101.00%							101.00%
Maximum adjusted EBITDA							3.5							3.5
Senior Notes | 1.375% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate						1.375%			1.375%	1.375%
Principal amount						$ 573,263,013
Long-term debt						$ 564,000,000	$ 589,100,000
Senior Notes | 3.55% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate						3.55%			3.55%	3.55%
Principal amount						$ 750,000,000
Long-term debt						$ 743,500,000	$ 742,800,000
Senior Notes | 3.000% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate						3.00%	3.00%		3.00%	3.00%				3.00%	3.00%
Principal amount						$ 700,000,000
Long-term debt						687,500,000	$ 692,500,000
Senior Notes | 3.000% senior notes | Interest Rate Swap
Debt Instrument [Line Items]
Derivative, notional amount						$ 6,997,660	800,000
Senior Notes | 3.600% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate						3.60%			3.60%	3.60%
Principal amount						$ 700,000,000
Long-term debt						$ 691,900,000	691,100,000
Senior Notes | 1.950% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	1.95%					1.95%			1.95%	1.95%			1.95%
Proceeds from term loan	$ 581,000,000	€ 493,200,000
Debt Instrument, face amount	$ 589,000,000												€ 500,000,000
Principal amount						$ 573,263,013
Long-term debt						$ 566,000,000	0
Secured Debt | Series 2018-1A Securities
Debt Instrument [Line Items]
Period during which no prepayment consideration is due						36 months
Secured Debt | Series 2018-1A Securities | Secured Tower Revenue Securities, Series 2018-1R
Debt Instrument [Line Items]
Long-term debt, stated interest rate						4.459%			4.459%	4.459%
Secured Debt | Series 2018-1A Securities | Secured Tower Revenue Securities, Series 2018-1A
Debt Instrument [Line Items]
Long-term debt, stated interest rate						3.652%			3.652%	3.652%
Principal amount			500,000,000
Long-term debt						$ 493,500,000	$ 0
Repayments of long-term debt					$ 500,000,000
Secured Debt | Series 2013-1A and Series 2013-2A Securities
Debt Instrument [Line Items]
Cash trap debt service credit ratio							1.30							1.30
Debt covenant, number of consecutive quarters required for release of funds | quarter							2							2
Minimum debt service credit ratio							1.15							1.15
Debt covenant, threshold for majority of holders in event of default						50.00%
Restricted cash and cash equivalents						$ 63,300,000
Secured Debt | Series 2015-1 Class A
Debt Instrument [Line Items]
Long-term debt, stated interest rate						2.35%			2.35%	2.35%
Long-term debt				$ 350,000,000		$ 348,800,000	$ 348,000,000
Period during which no prepayment consideration is due						12 months
Secured Debt | Series 2015-2 Class A
Debt Instrument [Line Items]
Long-term debt, stated interest rate						3.482%			3.482%	3.482%
Long-term debt				$ 525,000,000		$ 520,800,000	520,100,000
Secured Debt | Commercial Mortgage Pass Through Certificates Series 2015
Debt Instrument [Line Items]
Number of broadcast and wireless communications towers | tower				3,556
Weighted average life				8 years 1 month 6 days
Weighted average interest rate				3.029%
Restricted cash and cash equivalents						$ 16,800,000
Secured Debt | Series 2013-1A Securities
Debt Instrument [Line Items]
Period during which no prepayment consideration is due						18 months
Secured Debt | Viom Term Loan
Debt Instrument [Line Items]
Long-term debt						$ 240,100,000			₨ 16,751
Secured Debt | Viom Term Loan | Minimum
Debt Instrument [Line Items]
Debt Instrument, Term						1 year
Long-term debt, stated interest rate						8.75%			8.75%	8.75%
Prepayment penalty, percent of principal						1.00%
Payment terms, repayment period						6 months
Secured Debt | Viom Term Loan | Maximum
Debt Instrument [Line Items]
Debt Instrument, Term						10 years
Long-term debt, stated interest rate						8.95%			8.95%	8.95%
Prepayment penalty, percent of principal						2.00%
Payment terms, repayment period						36 months
Secured Debt | BR Towers Debentures
Debt Instrument [Line Items]
Long-term debt						$ 0	92,700,000			R$ 0.0				R$ 306.8
Mandatorily Redeemable Preferred Stock | Viom preferred shares
Debt Instrument [Line Items]
Long-term debt, stated interest rate						10.25%			10.25%	10.25%
Long-term debt						$ 23,900,000	$ 26,100,000
Preferred stock, shares issued | shares																166,666,666
Preferred stock, shares outstanding | shares						166,666,666			166,666,666	166,666,666
Financial instruments subject to mandatory redemption, settlement terms, maximum amount						$ 23,900,000			₨ 1,670
Affiliated Entity | Secured Debt | Series 2018-1A Securities | Secured Tower Revenue Securities, Series 2018-1R
Debt Instrument [Line Items]
Principal amount			$ 26,400,000
Multicurrency Borrowings | Credit Facility 2013 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, capacity available for specific purpose other than for trade purchases						1,000,000,000
Letter of Credit | Credit Facility 2013 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, capacity available for specific purpose other than for trade purchases						200,000,000
Letter of Credit | Credit Facility 2014 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, capacity available for specific purpose other than for trade purchases						200,000,000
Swingline Loan | Credit Facility 2013 | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, capacity available for specific purpose other than for trade purchases						$ 50,000,000

LONG-TERM OBLIGATIONS (Schedule

LONG-TERM OBLIGATIONS (Schedule of Line of Credit Facilities) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)renewal_period	Dec. 31, 2017USD ($)
Line of Credit Facility [Line Items]
Annual renewal periods, number | renewal_period	2
Credit Facility 2013 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term line of credit	$ 1,875	$ 2,075.6
Letters of credit, amount outstanding	$ 3.8
Line of credit facility, commitment fee percentage	0.125%
Credit Facility 2014 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term line of credit	$ 0	$ 495
Letters of credit, amount outstanding	$ 6.2
Line of credit facility, commitment fee percentage	0.125%
Term Loan 2013 | Unsecured Debt
Line of Credit Facility [Line Items]
Principal amount	$ 1,000
Term Loan 2018 | Unsecured Debt
Line of Credit Facility [Line Items]
Principal amount	$ 1,500
LIBOR | Credit Facility 2013 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.125%
LIBOR | Credit Facility 2014 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.125%
LIBOR | Term Loan 2013 | Unsecured Debt
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.125%
LIBOR | Term Loan 2018
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.875%

LONG-TERM OBLIGATIONS (Outline

LONG-TERM OBLIGATIONS (Outline of Key Terms Related to Outstanding Senior Notes) (Details) - Senior Notes - USD ($)	Dec. 31, 2018	May 22, 2018	Dec. 31, 2017	Dec. 08, 2017	Jan. 10, 2014	Aug. 19, 2013
3.40% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.40%				3.40%	3.40%
Principal amount	$ 1,000,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ 0		$ (200,000)
2.800% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	2.80%
Principal amount	$ 750,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (2,200,000)		(3,700,000)
5.050% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	5.05%
Principal amount	$ 700,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (1,300,000)		(2,000,000)
3.300% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.30%
Principal amount	$ 750,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (2,800,000)		(4,000,000)
3.450% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.45%
Principal amount	$ 650,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (3,700,000)		(4,900,000)
5.900% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	5.90%
Principal amount	$ 500,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (1,600,000)		$ (2,200,000)
2.250% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	2.25%		2.25%
Principal amount	$ 600,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	(27,300,000)		$ (27,600,000)
Interest rate swap agreements	$ 24,300,000		23,700,000
4.70% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	4.70%
Principal amount	$ 700,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (2,600,000)		(3,300,000)
3.50% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.50%
Principal amount	$ 1,000,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (7,400,000)		$ (9,100,000)
3.000% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.00%		3.00%	3.00%
Principal amount	$ 700,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	(12,500,000)		$ (7,500,000)
3.000% senior notes | Interest Rate Swap
Debt Instrument [Line Items]
Derivative, notional amount	$ 6,997,660		800,000
5.00% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	5.00%				5.00%	5.00%
Principal amount	$ 1,000,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ 2,100,000		2,400,000
1.375% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	1.375%
Principal amount	$ 573,263,013
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (9,300,000)		(11,100,000)
4.000% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	4.00%
Principal amount	$ 750,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (7,900,000)		(9,000,000)
4.400% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	4.40%
Principal amount	$ 500,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (3,900,000)		(4,400,000)
1.950% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	1.95%	1.95%
Principal amount	$ 573,263,013
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ 0		(7,300,000)
3.375% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.375%
Principal amount	$ 1,000,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (13,700,000)		(15,200,000)
3.125% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.125%
Principal amount	$ 400,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (2,700,000)		(2,900,000)
3.55% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.55%
Principal amount	$ 750,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (6,500,000)		(7,200,000)
3.600% senior notes
Debt Instrument [Line Items]
Long-term debt, stated interest rate	3.60%
Principal amount	$ 700,000,000
Debt Instrument, unamortized discount (premium) and debt issuance costs, net	$ (8,100,000)		$ (8,900,000)

Long-Term Obligations (India In

Long-Term Obligations (India Indebtedness) (Details) ₨ in Millions, $ in Millions	1 Months Ended
	Jan. 31, 2019USD ($)	Jan. 31, 2019INR (₨)	Dec. 31, 2018USD ($)	Dec. 31, 2018INR (₨)
Debt Instrument [Line Items]
Long-term debt			$ 21,159.9
Viom Term Loan | Secured Debt
Debt Instrument [Line Items]
Long-term debt			$ 240.1	₨ 16,751
Viom Term Loan | Secured Debt | Minimum
Debt Instrument [Line Items]
Long-term debt, stated interest rate			8.75%	8.75%
Viom Term Loan | Secured Debt | Maximum
Debt Instrument [Line Items]
Long-term debt, stated interest rate			8.95%	8.95%
Viom Term Loan | Secured Debt | Subsequent Event
Debt Instrument [Line Items]
Repayments of long-term debt	$ 72	₨ 5,000
Viom Working Capital Facilities | Line of Credit
Debt Instrument [Line Items]
Long-term debt			$ 0	₨ 0
Line of credit facility, remaining borrowing capacity			$ 81.8	₨ 5,700
Viom Working Capital Facilities | Line of Credit | Minimum
Debt Instrument [Line Items]
Long-term debt, stated interest rate			8.40%	8.40%
Viom Working Capital Facilities | Line of Credit | Maximum
Debt Instrument [Line Items]
Long-term debt, stated interest rate			8.65%	8.65%

Long-Term Obligations (Other Su

Long-Term Obligations (Other Subsidiary Debt) (Details) R$ in Millions, R in Millions, $ in Millions, $ in Millions

Dec. 23, 2016ZAR (R)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2018COP ($)

Dec. 31, 2018BRL (R$)

Dec. 31, 2018ZAR (R)

Dec. 31, 2017COP ($)

Dec. 31, 2017BRL (R$)

Dec. 31, 2017ZAR (R)

Dec. 31, 2016BRL (R$)

Jan. 23, 2015ZAR (R)

Nov. 30, 2014BRL (R$)

Debt Instrument [Line Items]

Long-term debt

$ 21,159.9

Borrowings under credit facilities

3,263.3

$ 5,359.4

$ 2,446.8

Kenya Debt

Debt Instrument [Line Items]

Long-term debt

$ 51.8

R$ 51.8

R$ 0.0

Long-term debt, stated interest rate

8.00%

8.00%

8.00%

8.00%

US Subsidiary Debt

Debt Instrument [Line Items]

Long-term debt | R$

R$ 2.5

0

Secured Debt | BR Towers Debentures

Debt Instrument [Line Items]

Long-term debt

$ 0

92.7

R$ 0.0

306.8

Revolving Credit Facility | South African Facility

Debt Instrument [Line Items]

Borrowings under credit facilities | R

R 500

Revolving Credit Facility | Colombian Credit Facility

Debt Instrument [Line Items]

Long-term debt

$ 200,000

Unsecured Debt

Debt Instrument [Line Items]

Long-term debt

152.5

246.1

Unsecured Debt | BR Towers Debentures

Debt Instrument [Line Items]

Long-term debt | R$

R$ 300.0

Unsecured Debt | Brazil Credit Facility

Debt Instrument [Line Items]

Original borrowing | R$

R$ 271.0

Revolving Credit Facility | South African Facility

Debt Instrument [Line Items]

Long-term line of credit

$ 40.2

69.9

R 577.4

R 866

Long-term debt | R

R 830

Long-term debt, stated interest rate

9.10%

9.10%

9.10%

9.10%

Revolving Credit Facility | Colombian Credit Facility

Debt Instrument [Line Items]

Long-term line of credit

$ 33.6

46.5

$ 109,193.8

$ 138,740.3

Long-term debt, stated interest rate

8.143%

8.143%

8.143%

8.143%

Revolving Credit Facility | Brazil Credit Facility

Debt Instrument [Line Items]

Long-term line of credit

$ 24.4

$ 37

R$ 94.7

R$ 122.4

Long-Term Obligations (Schedu_2

Long-Term Obligations (Schedule of Shareholder Loans) (Details) GH₵ in Millions, $ in Millions, USh in Billions	Aug. 30, 2018USD ($)	Aug. 30, 2018UGX (USh)	Dec. 31, 2018USD ($)	Dec. 31, 2018GHS (GH₵)	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Long-term debt			$ 21,159.9
Unsecured Debt
Debt Instrument [Line Items]
Long-term debt			152.5		$ 246.1
Unsecured Debt | Ghana Loan
Debt Instrument [Line Items]
Long-term debt			$ 59.9	GH₵ 294.4	66.5
Long-term debt, stated interest rate			21.87%	21.87%
Unsecured Debt | Uganda Loan
Debt Instrument [Line Items]
Long-term debt			$ 0		34.1
Unsecured Debt | Shareholder loans
Debt Instrument [Line Items]
Long-term debt			$ 59.9		$ 100.6
Repayments of long-term debt	$ 33.8	USh 127.2
Unsecured Debt | Shareholder loans | Uganda
Debt Instrument [Line Items]
Repayments of long-term debt	$ 33.8	USh 127.2

Long-Term Obligations (Maturiti

Long-Term Obligations (Maturities of Long Term Debt) (Details) $ in Millions	Dec. 31, 2018USD ($)
Debt Disclosure [Abstract]
2,019	$ 2,754.8
2,020	1,884.4
2,021	2,014.2
2,022	3,238.8
2,023	3,043.1
Thereafter	8,367.9
Total cash obligations	21,303.2
Unamortized discounts, premiums and debt issuance costs and fair value adjustments, net	(143.3)
Balance as of December 31, 2018	$ 21,159.9

OTHER NON-CURRENT LIABILITIES_2

OTHER NON-CURRENT LIABILITIES (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities, Noncurrent [Abstract]
Deferred rent liability	$ 506.7	$ 467
Unearned revenue	504.6	509.2
Other miscellaneous liabilities	253.8	268
Other non-current liabilities	$ 1,265.1	$ 1,244.2

ASSET RETIREMENT OBLIGATIONS (C

ASSET RETIREMENT OBLIGATIONS (Changes in Carrying Value of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance as of January 1,	$ 1,175.3	$ 965.5
Additions	39.6	33.4
Accretion expense	83.6	94.5
Revisions in estimates	(81.5)	86.6
Settlements	(7)	(4.7)
Balance as of December 31,	1,210	1,175.3
Asset retirement obligation, foreign currency translation loss	$ 49.4	$ 13

ASSET RETIREMENT OBLIGATIONS (N

ASSET RETIREMENT OBLIGATIONS (Narrative) (Details) $ in Billions	Dec. 31, 2018USD ($)
Asset Retirement Obligation [Abstract]
Estimated undiscounted future cash outlay for asset retirement obligations	$ 2.7

FAIR VALUE MEASUREMENTS (Assets

FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 01, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 0	$ 1
Fair value of embedded derivative asset				$ 14.6
Acquisition-related contingent consideration	0.9
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	1
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt related to interest rate swap agreements	(31.3)	(24.5)
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements	33.8	29
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of embedded derivative asset	11.5	12.4
Acquisition-related contingent consideration	0.9	10.1	$ 15.4
Redeemable noncontrolling interests	$ 1,004.8	$ 1,126.2

FAIR VALUE MEASUREMENTS (Narrat

FAIR VALUE MEASUREMENTS (Narrative) (Details) $ in Billions	12 Months Ended
	Dec. 31, 2018USD ($)interest_rate_swap	Dec. 31, 2017USD ($)interest_rate_swap	Dec. 31, 2016USD ($)	Dec. 31, 2018COP ($)interest_rate_swap	Dec. 08, 2017	Jul. 01, 2015USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of embedded derivative asset						$ 14,600,000
Business combination, contingent consideration arrangements, range of outcomes, value, low	$ 0
Business combination, contingent consideration arrangements, range of outcomes, value, high	900,000
Assets held and used, original carrying value	22,400,000,000	$ 21,700,000,000
Impairment charges	394,000,000	211,400,000	$ 28,500,000
Impairment of long-lived assets held for use		211,400,000
Debt, long-term and short-term, combined amount	21,159,900,000	20,205,100,000
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments recognized in other expense	900,000
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	21,100,000,000	20,600,000,000
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	13,400,000,000	13,300,000,000
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	7,700,000,000	7,300,000,000
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, fair value	33,500,000	28,500,000
Interest Rate Swap | Colombia
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, fair value	300,000	500,000
Senior Notes | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments recognized in other expense	$ 1,700,000
3.000% senior notes | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount		$ 500,000,000
3.000% senior notes | Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, stated interest rate	3.00%	3.00%		3.00%	3.00%
3.000% senior notes | Senior Notes | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps entered into | interest_rate_swap		3
2.250% senior notes | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount		$ 600,000,000
2.250% senior notes | Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, stated interest rate	2.25%	2.25%		2.25%
2.250% senior notes | Senior Notes | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps entered into | interest_rate_swap	3			3
Colombian Credit Facility | Revolving Credit Facility | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, notional amount	$ 16,900,000			$ 55
Derivative, fixed interest rate	5.74%			5.74%

FAIR VALUE MEASUREMENTS (Contin

FAIR VALUE MEASUREMENTS (Contingent Consideration) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	$ (0.5)
Balance as of December 31	0.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of January 1	10.1	$ 15.4
Additions	0	0
Settlements	(8.7)	0
Change in fair value	(0.9)	(6.3)
Foreign currency translation adjustment	0.4	1
Balance as of December 31	$ 0.9	$ 10.1

FAIR VALUE MEASUREMENTS (Recurr

FAIR VALUE MEASUREMENTS (Recurring Level 3 Fair Value Measurements Unobservable Inputs) (Details) - Fair Value, Inputs, Level 3	Dec. 31, 2018
Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Redeemable noncontrolling interests	0.1159
Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded derivative in lease agreement	0.1093
Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded derivative in lease agreement	0.1396
Probability of payout | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquisition-related contingent consideration	0
Probability of payout | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquisition-related contingent consideration	1
Revenue growth | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Redeemable noncontrolling interests	0.0316
Revenue growth | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Redeemable noncontrolling interests	0.1287
Long-term growth rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Redeemable noncontrolling interests	0.0400

INCOME TAXES (Income Tax Provis

INCOME TAXES (Income Tax Provision from Continuing Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ (1.4)	$ (0.1)	$ (26.5)
State	(1.8)	(3.8)	(2)
Foreign	(189.7)	(113.4)	(100.1)
Deferred:
Federal	4	0.2	(0.6)
State	0.7	1	(0.3)
Foreign	298.3	85.4	(26)
Income tax benefit (provision)	$ 110.1	$ (30.7)	$ (155.5)

INCOME TAXES (Narrative) (Detai

INCOME TAXES (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statue of Limitations and Effective Settlements	$ 9,300,000
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax asset, income tax expense	2,400,000
One-time tax benefit	85,700,000
Valuation allowance	151,900,000	$ 142,000,000	$ 144,400,000	$ 137,000,000
Unrecognized tax benefits that would impact the ETR	93,700,000	105,800,000
Unrecognized Tax Benefits, Period Increase (Decrease)	8,400,000
Additions based on tax positions related to the current year	8,100,000	7,600,000	82,900,000
Decrease in unrecognized tax benefits, lapse of applicable statute of limitations	2,600,000	400,000	3,200,000
Unrecognized tax benefits, income tax penalties and interest	8,000,000	5,000,000	9,200,000
Decrease in income tax penalties and interest expense	16,200,000	600,000	$ 3,400,000
Unrecognized tax benefits, income tax penalties and interest accrued	19,100,000	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	$ 2,700,000
Ghana Revenue Authority | Foreign
Income Tax Contingency [Line Items]
Tax benefit		$ 17,800,000

INCOME TAXES (Reconciliation Be

INCOME TAXES (Reconciliation Between the U.S. Statutory Rate and the Effective Rate from Continuing Operations) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	21.00%	35.00%	35.00%
Tax adjustment related to REIT	(21.00%)	(35.00%)	(35.00%)
Foreign taxes	(8.00%)	1.00%	5.00%
Foreign withholding taxes	4.00%	3.00%	4.00%
Uncertain tax positions	0.00%	0.00%	5.00%
Changes in tax laws	0.00%	(2.00%)	0.00%
MIPT tax election	(6.00%)	0.00%	0.00%
Effective tax rate	(10.00%)	2.00%	14.00%

INCOME TAXES (Components of Inc

INCOME TAXES (Components of Income from Continuing Operations Before Income Taxes and Income on Equity Method Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States	$ 1,212.7	$ 971.2	$ 882.6
Foreign	(58.1)	284.9	243.3
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	$ 1,154.6	$ 1,256.1	$ 1,125.9

INCOME TAXES (Components of the

INCOME TAXES (Components of the Net Deferred Tax Asset and Related Valuation Allowance) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 264.9	$ 287
Accrued asset retirement obligations	165.7	157
Stock-based compensation	6.3	3.9
Unearned revenue	28.3	19.3
Unrealized loss on foreign currency	12.9	27.4
Other accruals and allowances	78.6	50.2
Items not currently deductible and other	26.2	28
Depreciation and amortization	(757)	(1,073.9)
Deferred rent	(36.9)	(35.9)
Other	(15.3)	(14.7)
Subtotal	(226.3)	(551.7)
Valuation allowance	(151.9)	(142)	$ (144.4)	$ (137)
Net deferred tax liabilities	$ (378.2)	$ (693.7)

INCOME TAXES (Valuation Allowan

INCOME TAXES (Valuation Allowance Activity) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of January 1,	$ 142	$ 144.4	$ 137
Additions	15.7	11.6	14.1
Reversals	0	(9.1)	0
Foreign currency translation	(5.8)	(4.9)	(6.7)
Balance as of December 31,	$ 151.9	$ 142	$ 144.4

INCOME TAXES (Net Operating Los

INCOME TAXES (Net Operating Loss Carryforwards Expire) (Details) $ in Millions	Dec. 31, 2018USD ($)
Federal
Operating Loss Carryforwards [Line Items]
2019 to 2023	$ 0
2024 to 2028	141.7
2029 to 2033	0
2034 to 2038	10.6
Indefinite carryforward	9.6
Total	161.9
State
Operating Loss Carryforwards [Line Items]
2019 to 2023	142.9
2024 to 2028	378.4
2029 to 2033	13.9
2034 to 2038	135.4
Indefinite carryforward	0
Total	670.6
Foreign
Operating Loss Carryforwards [Line Items]
2019 to 2023	46
2024 to 2028	142.7
2029 to 2033	4.5
2034 to 2038	0
Indefinite carryforward	746.5
Total	$ 939.7

INCOME TAXES (Reconciliation of

INCOME TAXES (Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1	$ 116.7	$ 107.6	$ 28.1
Additions based on tax positions related to the current year	8.1	7.6	82.9
Additions and reductions for tax positions of prior years	0.3	0	0
Foreign currency	(8.1)		(0.2)
Foreign currency		1.9
Reduction as a result of the lapse of statute of limitations	(2.6)	(0.4)	(3.2)
Reduction as a result of effective settlements	(6.7)	0	0
Balance at December 31	$ 107.7	$ 116.7	$ 107.6

STOCK-BASED COMPENSATION (Narra

STOCK-BASED COMPENSATION (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount from market price		15.00%
Total unrecognized compensation expense		$ 4.5
Stock-based compensation expense		137.5	$ 108.5	$ 89.9
Compensation accelerated due to changes in vesting terms	$ 19.1
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense		$ 111.8
Expected recognition of stock award compensation expense weighted average period in years		2 years
Total fair value of restricted stock units vested during period		$ 115.1
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Total unrecognized compensation expense		$ 8.6
Expected recognition of stock award compensation expense weighted average period in years		2 years
Three year performance grant, shares granted (in shares)		131,311	154,520	169,340
Stock-based compensation expense		$ 52.2
PSUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential target shares		0.00%
PSUs | 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]
Options granted (in shares)		0
Weighted average grant date fair value (in dollars per share)			$ 16.84	$ 14.60
Intrinsic value of stock options exercised		$ 98.8	$ 100.3	$ 77.6
Expected recognition of stock award compensation expense weighted average period in years		1 year
Cash received from exercise of stock options		$ 88.7
2007 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issuable under stock incentive plan (in shares)		7,700,000
2007 Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2007 Plan | PSUs
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 (Summa

STOCK-BASED COMPENSATION (Summary of Stock-Based Compensation Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense	$ 137.5	$ 108.5	$ 89.9
Stock-based compensation expense capitalized as property and equipment	$ 2	$ 1.6	$ 1.4

STOCK-BASED COMPENSATION (Assum

STOCK-BASED COMPENSATION (Assumptions Used to Determine the Grant Date Fair Value for Options Granted) (Details) - Employee Stock Option	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Minimum range of risk-free interest rate	1.88%	1.00%
Maximum range of risk-free interest rate	1.94%	1.73%
Weighted average risk-free interest rate	1.89%	1.44%
Expected life of stock options	5 years 2 months 5 days
Minimum range of expected volatility of underlying stock price	18.95%	20.59%
Maximum range of expected volatility of underlying stock price	19.45%	21.45%
Weighted average expected volatility of underlying stock price	19.05%	21.43%
Range of expected annual dividend yield	2.40%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of stock options		4 years 6 months
Range of expected annual dividend yield		1.85%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of stock options		5 years 2 months 12 days
Range of expected annual dividend yield		2.40%

STOCK-BASED COMPENSATION (Sum_2

STOCK-BASED COMPENSATION (Summary of the Company's Option Activity) (Details) - Employee Stock Option $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)$ / sharesshares
Options
Outstanding (in shares) | shares	5,557,561
Granted (in shares) | shares	0
Exercised (in shares) | shares	(1,242,536)
Forfeited (in shares) | shares	(57,555)
Expired (in shares) | shares	0
Outstanding (in shares) | shares	4,257,470
Exercisable (in shares) | shares	3,360,226
Vested or expected to vest (in shares) | shares	4,257,470
Weighted Average Exercise Price Per Share
Outstanding (in dollars per share) | $ / shares	$ 81.32
Granted (in dollars per share) | $ / shares	0
Exercised (in dollars per share) | $ / shares	71.41
Forfeited (in dollars per share) | $ / shares	94.66
Expired (in dollars per share) | $ / shares	0
Outstanding (in dollars per share) | $ / shares	84.03
Exercisable (in dollars per share) | $ / shares	81.10
Vested or expected to vest (in dollars per share) | $ / shares	$ 84.03
Weighted Average Remaining Life, Outstanding	5 years 2 months 5 days
Weighted Average Remaining Life, Exercisable	4 years 9 months 4 days
Weighted Average Remaining Life, Vested or expected to vest	5 years 2 months 5 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Aggregate intrinsic value, outstanding | $	$ 315.7
Aggregate intrinsic value, exercisable | $	259
Aggregate intrinsic value, vested or expected to vest | $	$ 315.7

STOCK-BASED COMPENSATION (Sched

STOCK-BASED COMPENSATION (Schedule of Options Outstanding) (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
$28.39 - $62.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	594,690
Exercise price per share, minimum	$ 28.39
Exercise price per share, maximum	62
Weighted Average Exercise Price Per Share (in dollars per share)	$ 56.69
Weighted Average Remaining Life	2 years 8 months 1 day
Options Exercisable (in shares) | shares	594,690
Weighted Average Exercise Price Per Share (in dollars per share)	$ 56.69
$71.07 - $74.06
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	14,717
Exercise price per share, minimum	$ 71.07
Exercise price per share, maximum	74.06
Weighted Average Exercise Price Per Share (in dollars per share)	$ 73.26
Weighted Average Remaining Life	4 years 5 months 22 days
Options Exercisable (in shares) | shares	14,717
Weighted Average Exercise Price Per Share (in dollars per share)	$ 73.26
$76.90 - $77.75
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	559,293
Exercise price per share, minimum	$ 76.90
Exercise price per share, maximum	77.75
Weighted Average Exercise Price Per Share (in dollars per share)	$ 76.91
Weighted Average Remaining Life	4 years
Options Exercisable (in shares) | shares	559,293
Weighted Average Exercise Price Per Share (in dollars per share)	$ 76.91
$81.18 - $94.23
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	983,105
Exercise price per share, minimum	$ 81.18
Exercise price per share, maximum	94.23
Weighted Average Exercise Price Per Share (in dollars per share)	$ 81.55
Weighted Average Remaining Life	4 years 11 months 24 days
Options Exercisable (in shares) | shares	967,146
Weighted Average Exercise Price Per Share (in dollars per share)	$ 81.43
$94.57 - $94.71
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	2,070,809
Exercise price per share, minimum	$ 94.57
Exercise price per share, maximum	94.71
Weighted Average Exercise Price Per Share (in dollars per share)	$ 94.62
Weighted Average Remaining Life	6 years 3 months 12 days
Options Exercisable (in shares) | shares	1,213,187
Weighted Average Exercise Price Per Share (in dollars per share)	$ 94.60
$96.46 - $121.15
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	34,856
Exercise price per share, minimum	$ 96.46
Exercise price per share, maximum	121.15
Weighted Average Exercise Price Per Share (in dollars per share)	$ 109.92
Weighted Average Remaining Life	7 years 4 months 18 days
Options Exercisable (in shares) | shares	11,193
Weighted Average Exercise Price Per Share (in dollars per share)	$ 107.20
$28.39 - $121.15
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Number of Options (in shares) | shares	4,257,470
Exercise price per share, minimum	$ 28.39
Exercise price per share, maximum	121.15
Weighted Average Exercise Price Per Share (in dollars per share)	$ 84.03
Weighted Average Remaining Life	5 years 2 months 6 days
Options Exercisable (in shares) | shares	3,360,226
Weighted Average Exercise Price Per Share (in dollars per share)	$ 81.10

STOCK-BASED COMPENSATION (Sum_3

STOCK-BASED COMPENSATION (Summary of the Company's Restricted Stock Unit Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
RSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Outstanding (in shares)	1,742,725
Granted (in shares)	686,789
Vested (in shares)	(682,311)
Forfeited (in shares)	(97,230)
Outstanding (in shares)	1,742,725	1,742,725		1,649,973
Expected to vest, net of estimated forfeitures (in shares)				1,649,973
Vested And deferred at end of period (in shares)	32,596
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding (in dollars per share)	$ 102.60
Granted (in dollars per share)	144.96
Vested (in dollars per share)	98.24
Forfeitures (in dollars per share)	116.37
Outstanding (in dollars per share)	$ 121.23	$ 102.60
Expected to vest, (in dollars per share)				$ 121.23
Vested and deferred (in dollars per share)				$ 119.14
PSUs
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Outstanding (in shares)	444,031
Granted (in shares)	300,651
Vested (in shares)	(120,171)
Forfeited (in shares)	0
Outstanding (in shares)	444,031	444,031		624,511
Expected to vest, net of estimated forfeitures (in shares)				624,511
Vested And deferred at end of period (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding (in dollars per share)	$ 102.81
Granted (in dollars per share)	116.71
Vested (in dollars per share)	100.35
Forfeitures (in dollars per share)	0
Outstanding (in dollars per share)	$ 109.97	$ 102.81
Expected to vest, (in dollars per share)				$ 109.97
Vested and deferred (in dollars per share)				$ 0
Vesting period	3 years
Three year performance grant, shares granted (in shares)	131,311	154,520	169,340
Three year performance grant, shares issuable based on first, second and third years	120,171

REDEEMABLE NONCONTROLLING INT_3

REDEEMABLE NONCONTROLLING INTERESTS Narrative (Details) ₨ / shares in Units, $ in Millions, ₨ in Billions	3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)	Jun. 30, 2019	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018INR (₨)₨ / shares	Apr. 21, 2016
Redeemable Noncontrolling Interest [Line Items]
Adjustment to noncontrolling interest due to merger			$ (28.1)	$ 0	$ 0
Adjustment to noncontrolling interest redemption value			86.7	$ 0	$ 0
Temporary equity redemption price per share (in INR per share) | ₨ / shares						₨ 216
Consideration paid for redemption	$ 420		$ 420			₨ 29.4
Tata Teleservices
Redeemable Noncontrolling Interest [Line Items]
Percentage of ownership	50.00%
IDFC
Redeemable Noncontrolling Interest [Line Items]
Percentage of ownership	100.00%
India Transaction
Redeemable Noncontrolling Interest [Line Items]
Percentage of voting interest acquired	63.00%		63.00%			63.00%	51.00%
Increase in additional paid in capital			$ 28.1
Noncontrolling owners, ownership percentage	37.00%		37.00%	49.00%		37.00%
Adjustment to noncontrolling interest due to merger			$ 28.1
Reclass of previously recorded accumulated other comprehensive loss to additional paid in capital			78.8
Adjustment to noncontrolling interest redemption value			$ 86.7
Scenario, Forecast | Tata Teleservices
Redeemable Noncontrolling Interest [Line Items]
Ownership percentage		79.00%

REDEEMABLE NONCONTROLLING INT_4

REDEEMABLE NONCONTROLLING INTERESTS (Changes in Redeemable Noncontrolling Interest) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in redeemable noncontrolling interest [Roll Forward]
Balance as of January 1,	$ 1,126.2	$ 1,091.3	$ 0
Fair value at acquisition		314.1	239.5
Net income attributable to noncontrolling interests	(87.9)	(33.4)	13.9
Adjustment to noncontrolling interest redemption value	86.7	0	0
Adjustment to noncontrolling interest due to merger	(28.1)	0	0
Foreign currency translation adjustment attributable to noncontrolling interests	(92.1)	68.3	(23.5)
Ending balance	1,004.8	1,126.2	1,091.3
India Transaction
Changes in redeemable noncontrolling interest [Roll Forward]
Fair value at acquisition	0	$ 0	$ 1,100.9
Adjustment to noncontrolling interest redemption value	86.7
Adjustment to noncontrolling interest due to merger	$ 28.1

Equity (Narrative) (Details)

Equity (Narrative) (Details) - USD ($)	Feb. 15, 2018	May 31, 2017	Mar. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2011
Class of Stock [Line Items]
Proceeds from stock options and stock purchase plan				$ 98,900,000	$ 119,700,000	$ 92,500,000
Treasury stock activity				$ 232,800,000	$ 766,300,000
Treasury stock, shares				10,557,000	8,909,000
Treasury stock				$ 1,206,800,000	$ 974,000,000
Accrued dividend RSU				$ 13,700,000	$ 10,100,000
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, depositary shares, percentage of preferred shares				0.1
Convertible Preferred Stock Subject to Mandatory Redemption | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage				5.50%	5.50%
Dividends Declared and Paid
Class of Stock [Line Items]
Paid dividend RSU				$ 4,300,000
Preferred stock
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share)				$ 0.01
Preferred stock | Convertible Preferred Stock Subject to Mandatory Redemption | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage				5.25%
Preferred stock, par value (in dollars per share)				$ 0.01	$ 0.01
Conversion of preferred stock (shares)				0	(6,000,000)
Preferred stock | Convertible Preferred Stock Subject to Mandatory Redemption | Series B Preferred Stock
Class of Stock [Line Items]
Issuance of stock (shares)			1,375,000
Preferred stock, dividend rate, percentage			5.50%
Preferred stock, par value (in dollars per share)			$ 0.01
Preferred stock, depositary shares (shares)					13,749,860
Shares converted (shares)		140
Conversion factor, depository shares, preferred stock	0.8742	0.8687
Dividends	$ 18,900,000
Conversion factor, preferred stock (shares)	8.7420
Conversion of preferred stock (shares)	12,020,064			(1,375,000)	0
2011 Buyback
Class of Stock [Line Items]
Authorized repurchase of common stock							$ 1,500,000,000
Treasury stock activity (in shares)				1,647,489
Treasury stock activity				$ 232,800,000
Treasury stock, shares				14,003,543
Treasury stock				$ 1,400,000,000
2017 Buyback
Class of Stock [Line Items]
Authorized repurchase of common stock					$ 2,000,000,000
Treasury stock activity				$ 0

Equity (Distributions) (Detail)

Equity (Distributions) (Detail) - USD ($) $ / shares in Units, $ in Millions	Dec. 04, 2018	Mar. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends Payable [Line Items]
Payments of ordinary dividends, common stock			$ 1,323.5	$ 1,073	$ 886.1
Preferred stock dividends declared			$ 18.9	$ 91.4	$ 107.1
Common Stock
Dividends Payable [Line Items]
Common stock, dividends declared per share (in dollars per share)	$ 0.84		$ 3.15	$ 2.62	$ 2.17
Dividends declared, common stock, percent of total			100.00%	100.00%	100.00%
Common Stock | Ordinary Income
Dividends Payable [Line Items]
Common stock, dividends declared per share (in dollars per share)			$ 3.15	$ 2.62	$ 2.17
Dividends declared, common stock, percent of total			100.00%	100.00%	100.00%
Common Stock | Capital Gain
Dividends Payable [Line Items]
Common stock, dividends declared per share (in dollars per share)			$ 0	$ 0	$ 0
Dividends declared, common stock, percent of total			0.00%	0.00%	0.00%
Common Stock | Dividends Declared and Paid
Dividends Payable [Line Items]
Common stock, dividends declared per share (in dollars per share)			$ 3.15	$ 2.62	$ 2.17
Payments of ordinary dividends, common stock			$ 1,389.8	$ 1,122.5	$ 923.7
Series A Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 0	$ 3.3643	$ 6.4578
Dividends declared, preferred stock, declared			0.00%	100.00%	100.00%
Series A Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption | Ordinary Income
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 0	$ 3.36433	$ 6.4578
Dividends declared, preferred stock, declared			0.00%	100.00%	100.00%
Series A Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption | Capital Gain
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 0	$ 0	$ 0
Dividends declared, preferred stock, declared			0.00%	0.00%	0.00%
Series A Preferred Stock | Dividends Declared and Paid | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 0	$ 2.63	$ 5.25
Preferred stock dividends declared			$ 0	$ 15.8	$ 31.5
Series B Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 2.1314	$ 6.5233	$ 5.5
Preferred stock, dividend rate, percentage			5.50%	5.50%
Dividends declared, preferred stock, declared			100.00%	100.00%	100.00%
Series B Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption | Ordinary Income
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 2.13144	$ 6.523315	$ 5.5
Dividends declared, preferred stock, declared			100.00%	100.00%	100.00%
Series B Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption | Capital Gain
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 0	$ 0	$ 0
Dividends declared, preferred stock, declared			0.00%	0.00%	0.00%
Series B Preferred Stock | Dividends Declared and Paid | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Preferred stock, dividends per share, declared (in dollars per share)			$ 13.75	$ 55	$ 55
Preferred stock dividends declared			$ 18.9	$ 75.6	$ 75.6
Preferred stock
Dividends Payable [Line Items]
Preferred stock, par value (in dollars per share)			$ 0.01
Preferred stock | Series A Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Preferred stock, dividend rate, percentage			5.25%
Preferred stock, par value (in dollars per share)			$ 0.01	$ 0.01
Preferred stock | Series B Preferred Stock | Convertible Preferred Stock Subject to Mandatory Redemption
Dividends Payable [Line Items]
Preferred stock, dividend rate, percentage		5.50%
Preferred stock, par value (in dollars per share)		$ 0.01

OTHER OPERATING EXPENSES Other

OTHER OPERATING EXPENSES Other Operating Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Impairment charges	$ 394	$ 211.4	$ 28.5
Net losses on sales or disposals of assets	85.6	32.8	25.1
Other operating expenses	33.7	11.8	19.7
Total Other operating expenses	$ 513.3	$ 256	$ 73.3

OTHER OPERATING EXPENSES Impair

OTHER OPERATING EXPENSES Impairment Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of intangible asset impairment [Line Items]
Impairment charges	$ 394	$ 211.4	$ 28.5
Tower and network location intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges	284.9	108.7	18
Tenant relationships
Schedule of intangible asset impairment [Line Items]
Impairment charges	107.3	100.1	0
Other
Schedule of intangible asset impairment [Line Items]
Impairment charges	$ 1.8	$ 2.6	$ 10.5

OTHER OPERATING EXPENSES Narrat

OTHER OPERATING EXPENSES Narrative (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of intangible asset impairment [Line Items]
Impairment charges		$ 394	$ 211.4	$ 28.5
Tower and network location intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges		284.9	108.7	18
Tenant-related intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges		107.3	100.1	$ 0
Aircel, Asia | Tower and network location intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges		40.1
Aircel, Asia | Tenant-related intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges		107.3
Tata Teleservices Limited | Tower and network location intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges	$ 164.2
Asia | Property | Tower and network location intangible assets
Schedule of intangible asset impairment [Line Items]
Impairment charges		$ 54	$ 81

EARNINGS PER COMMON SHARE (Sche

EARNINGS PER COMMON SHARE (Schedule of Earnings Per Basic And Diluted by Common Class) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income attributable to American Tower Corporation stockholders	$ 277.6	$ 366.9	$ 306.7	$ 285.2	$ 238.5	$ 317.3	$ 367	$ 316.1	$ 1,236.4	$ 1,238.9	$ 956.4
Dividends on preferred stock	0	0	0	(9.4)	(18.9)	(18.9)	(22.8)	(26.8)	(9.4)	(87.4)	(107.1)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 277.6	$ 366.9	$ 306.7	$ 275.8	$ 219.6	$ 298.4	$ 344.2	$ 289.3	$ 1,227	$ 1,151.5	$ 849.3
Basic weighted average common shares outstanding									439,606	428,181	425,143
Dilutive securities (shares)									3,354	3,507	4,140
Diluted weighted average common shares outstanding									442,960	431,688	429,283
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 0.63	$ 0.83	$ 0.69	$ 0.63	$ 0.51	$ 0.70	$ 0.81	$ 0.68	$ 2.79	$ 2.69	$ 2
Diluted net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 0.62	$ 0.83	$ 0.69	$ 0.63	$ 0.51	$ 0.69	$ 0.80	$ 0.67	$ 2.77	$ 2.67	$ 1.98

EARNINGS PER COMMON SHARE (Sc_2

EARNINGS PER COMMON SHARE (Schedule of Shares Excluded From Computation of Earnings Per Share) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares issuable upon conversion of the stock-based awards and convertible notes	0	3	6
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares issuable upon conversion of the stock-based awards and convertible notes	0	4	817
Preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares issuable upon conversion of the stock-based awards and convertible notes	1,456	14,040	17,509

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES (Narrative) (Details) ₨ in Millions	Dec. 05, 2016USD ($)	Dec. 05, 2016INR (₨)	Mar. 27, 2015USD ($)communications_siterenewal_period	Dec. 31, 2000tower	Dec. 31, 2018USD ($)towerrenewal_periodshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)tower
Loss Contingencies [Line Items]
Loss contingency, foreign income tax assessment	$ 69,800,000	₨ 4,750
Aggregate rent expense | $					$ 1,128,000,000	$ 1,088,000,000	$ 986,200,000
Initial lease term					10 years
Verizon Transaction
Loss Contingencies [Line Items]
Capital leased assets, number of units | communications_site			11,300
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 | renewal_period			8
Renewal term			5 years
At T Transaction
Loss Contingencies [Line Items]
Capital leased assets, number of units | tower					2,280
Aggregate purchase option price for towers | $					$ 891,500,000
Successive terms to renew lease | renewal_period					4
Renewal term					5 years
Operating lease, term of contract					27 years
Number of sites acquired life to date | tower					149
Number of communications sites acquired | tower					61
Purchase Price of Towers Acquired Through Purchase Option | $					$ 22,200,000
Purchase price accretion rate (per year)					10.00%
ALLTEL Transaction
Loss Contingencies [Line Items]
Capital leased assets, number of units | tower				1,800
Aggregate purchase option price for towers | $					$ 10,400,000
Average lease term (in years)				15 years
Number of units acquired through purchase option | tower							1,523
Number of unit with intent to exercise purchase option | tower							243
Cash purchase price per tower | $					$ 42,844
Purchase price of tower in shares of common stock | shares					769

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES (Future Minimum Rental Payments Under Non-Cancelable Operating Leases) (Details) $ in Billions	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	$ 926
2,020	904.2
2,021	879.8
2,022	834.2
2,023	792.6
Thereafter	6,173.1
Total	$ 10,509.9

COMMITMENTS AND CONTINGENCIES_4

COMMITMENTS AND CONTINGENCIES (Future Minimum Payments Under Capital Leases) (Details) $ in Millions	Dec. 31, 2018USD ($)
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	$ 40.7
2,020	32.7
2,021	27.8
2,022	23.7
2,023	19.2
Thereafter	117.5
Total minimum lease payments	261.6
Less amounts representing interest	(82.1)
Present value of capital lease obligations	$ 179.5

COMMITMENTS AND CONTINGENCIES_5

COMMITMENTS AND CONTINGENCIES (Future Minimum Rental Receipts Under Operating Lease Agreements) (Details) $ in Millions	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Receivable [Abstract]
2,019	$ 5,251.2
2,020	5,062.2
2,021	4,676.1
2,022	3,754.6
2,023	3,457.3
Thereafter	12,641.1
Total	$ 34,842.5

SUPPLEMENTAL CASH FLOW INFORM_3

SUPPLEMENTAL CASH FLOW INFORMATION (Supplemental Cash Flow Information and Non-Cash Investing and Financing Activities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental cash flow information:
Cash paid for interest	$ 789.7	$ 712.1	$ 645.1
Cash paid for income taxes (net of refunds of $25.0, $20.7 and $19.6, respectively)	163.9	136.5	96.2
Tax refunds	25	20.7	19.6
Non-cash investing and financing activities:
Increase (decrease) in accounts payable and accrued expenses for purchases of property and equipment and construction activities	8.3	34	(19)
Purchases of property and equipment under capital leases	57.8	54.8	55.6
Fair value of debt assumed through acquisitions	0	0	786.9
Exercise of purchase option for property and equipment for common shares issued	0	0	120.8
Acquisition of Commercialization Rights	24.8	0	0
Conversion of third-party debt to equity	0	48.2	0
Debt financed acquisition of communication sites	$ 54.2	$ 0	$ 0

BUSINESS SEGMENTS (Summarized F

BUSINESS SEGMENTS (Summarized Financial Information Concerning the Company's Reportable Segments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Segment revenues	$ 2,131.9	$ 1,785.5	$ 1,780.9	$ 1,741.8	$ 1,704.5	$ 1,680.7	$ 1,662.5	$ 1,616.2	$ 7,440.1	$ 6,663.9	$ 5,785.7
Segment operating expenses									2,174.5	2,053.7	1,788
Segment gross margin									5,265.5	4,621	4,008.6
Segment selling, general, administrative and development expense									442.9	392.9	329.9
Segment operating profit									4,822.6	4,228.1	3,678.7
Stock-based compensation expense									137.5	108.5	89.9
Other selling, general, administrative and development expense									156.1	138.5	126
Depreciation, amortization and accretion									2,110.8	1,715.9	1,525.6
Other expense									1,263.6	1,009.1	811.3
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									1,154.6	1,256.1	1,125.9
Capital expenditures									945.2	835.4	701.4
Repayment of capital lease for capital expenditures									32	31.8	18.9
Operating Expense
Segment Reporting Information [Line Items]
Stock-based compensation expense									3.3	2.9	2.4
Selling General Administrative And Development Expense
Segment Reporting Information [Line Items]
Stock-based compensation expense									134.2	105.6	87.5
TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									(0.1)	10.8	10.9
U.S.
Segment Reporting Information [Line Items]
Segment revenues									3,947.5	3,703.7	3,442.7
Other
Segment Reporting Information [Line Items]
Stock-based compensation expense									137.5	108.5
Other selling, general, administrative and development expense									156.1	138.5
Depreciation, amortization and accretion									2,110.8	1,715.9
Other expense									1,263.6	1,009.1
Capital expenditures									13.9
Property | Operating Segments
Segment Reporting Information [Line Items]
Segment revenues									7,314.7	6,565.9	5,713.1
Segment operating expenses									2,126.3	2,019.9	1,761
Segment gross margin									5,188.3	4,556.8	3,963
Segment selling, general, administrative and development expense									428.5	379.2	317.4
Segment operating profit									4,759.8	4,177.6	3,645.6
Capital expenditures									931.3	817.7	684.9
Property | Operating Segments | TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									(0.1)	10.8	10.9
Property | Operating Segments | U.S.
Segment Reporting Information [Line Items]
Segment revenues									3,822.1	3,605.7	3,370.1
Segment operating expenses									771	746.5	733.4
Segment gross margin									3,051.1	2,859.2	2,636.7
Segment selling, general, administrative and development expense									165.2	151.4	147.6
Segment operating profit									2,885.9	2,707.8	2,489.1
Capital expenditures									376.9	360.6	310.7
Property | Operating Segments | U.S. | TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									0	0	0
Property | Operating Segments | Asia
Segment Reporting Information [Line Items]
Segment revenues									1,540.5	1,164.4	827.6
Segment operating expenses									710.9	649	465.9
Segment gross margin									829.6	515.4	361.7
Segment selling, general, administrative and development expense									110.7	82.4	48.2
Segment operating profit									718.9	433	313.5
Capital expenditures									101	118	115.5
Revenue net of settlement payment received	$ 333.7
Property | Operating Segments | Asia | TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									0	0	0
Property | Operating Segments | EMEA
Segment Reporting Information [Line Items]
Segment revenues									687.3	626.2	529.5
Segment operating expenses									238.1	238.3	223.7
Segment gross margin									449.2	387.9	305.8
Segment selling, general, administrative and development expense									69.1	67.9	60.9
Segment operating profit									380.1	320	244.9
Capital expenditures									232.7	141.7	86.1
Property | Operating Segments | EMEA | TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									0	0	0
Property | Operating Segments | Latin America
Segment Reporting Information [Line Items]
Segment revenues									1,264.8	1,169.6	985.9
Segment operating expenses									406.3	386.1	338
Segment gross margin									858.4	794.3	658.8
Segment selling, general, administrative and development expense									83.5	77.5	60.7
Segment operating profit									774.9	716.8	598.1
Capital expenditures									220.7	197.4	172.6
Property | Operating Segments | Latin America | TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									(0.1)	10.8	10.9
Services | Operating Segments
Segment Reporting Information [Line Items]
Segment revenues									125.4	98	72.6
Segment operating expenses									48.2	33.8	27
Segment gross margin									77.2	64.2	45.6
Segment selling, general, administrative and development expense									14.4	13.7	12.5
Segment operating profit									62.8	50.5	33.1
Capital expenditures									0	0	0
Services | Operating Segments | TV Azteca
Segment Reporting Information [Line Items]
Interest (expense) income, TV Azteca, each net of interest expense of $1.2									$ 0	0	0
Other
Segment Reporting Information [Line Items]
Stock-based compensation expense											89.9
Other selling, general, administrative and development expense											126
Depreciation, amortization and accretion											1,525.6
Other expense											811.3
Capital expenditures										$ 17.7	$ 16.5

BUSINESS SEGMENTS (Additional I

BUSINESS SEGMENTS (Additional Information Relating to the Company's Operating Segments) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 33,010.4	$ 33,214.3	$ 30,879.2
Operating Segments | Property | U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	18,782	19,032.6	18,846.9
Operating Segments | Property | Asia
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,938.8	4,770.8	4,535.3
Operating Segments | Property | EMEA
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,367.8	3,213.6	2,062.4
Operating Segments | Property | Latin America
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	5,594.7	5,868.4	4,938.1
Operating Segments | Services
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	46.3	42.3	48.3
Corporate, Non-Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 280.8	$ 286.6	$ 448.2

BUSINESS SEGMENTS (Summarized G

BUSINESS SEGMENTS (Summarized Geographic Information Related to the Company's Operating Revenues and Long-Lived Assets) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 2,131.9	$ 1,785.5	$ 1,780.9	$ 1,741.8	$ 1,704.5	$ 1,680.7	$ 1,662.5	$ 1,616.2	$ 7,440.1	$ 6,663.9	$ 5,785.7
Long-Lived Assets	27,923.3				28,522.7				27,923.3	28,522.7
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									3,947.5	3,703.7	3,442.7
Long-Lived Assets	16,543.7				16,930.2				16,543.7	16,930.2
India
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									1,540.5	1,164.4	827.6
Long-Lived Assets	3,947.8				4,052.6				3,947.8	4,052.6
France
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									72.7	59.5	0
Long-Lived Assets	963.8				1,009.6				963.8	1,009.6
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									69.1	63.1	60.2
Long-Lived Assets	388.5				428				388.5	428
Ghana
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									125.4	122.9	116.2
Long-Lived Assets	159.2				171.4				159.2	171.4
Kenya
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									7	0	0
Long-Lived Assets	190				0				190	0
Nigeria
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									220.7	213.9	215.4
Long-Lived Assets	606.5				587.2				606.5	587.2
South Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									125.3	106.5	80
Long-Lived Assets	342.5				330.4				342.5	330.4
Uganda
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									67.1	60.3	57.7
Long-Lived Assets	138.7				136.9				138.7	136.9
Argentina
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									16	15.9	1
Long-Lived Assets	81.6				117.9				81.6	117.9
Brazil
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									595.5	620.1	506.2
Long-Lived Assets	2,288.1				2,557.4				2,288.1	2,557.4
Chile
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									44.2	40.4	33.8
Long-Lived Assets	129.7				151.2				129.7	151.2
Colombia
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									103.8	89.3	79.7
Long-Lived Assets	381.6				369				381.6	369
Costa Rica
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									18.4	19.4	19
Long-Lived Assets	119.1				112.9				119.1	112.9
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									456.5	364.3	331.2
Long-Lived Assets	1,421.3				1,396.8				1,421.3	1,396.8
Paraguay
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									10.4	2.7	0
Long-Lived Assets	107.4				77.5				107.4	77.5
Peru
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									20	17.5	15
Long-Lived Assets	113.8				93.7				113.8	93.7
Total International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									3,492.6	2,960.2	$ 2,343
Long-Lived Assets	$ 11,379.6				$ 11,592.5				$ 11,379.6	$ 11,592.5

BUSINESS SEGMENTS (Major Custom

BUSINESS SEGMENTS (Major Customers) (Details) - Customer Concentration Risk - Sales Revenue, Net	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AT&T
Revenue, Major Customer [Line Items]
Concentration risk, percentage	19.00%	19.00%	21.00%
Verizon Wireless
Revenue, Major Customer [Line Items]
Concentration risk, percentage	15.00%	16.00%	15.00%
Sprint
Revenue, Major Customer [Line Items]
Concentration risk, percentage	8.00%	9.00%	11.00%

SELECTED QUARTERLY FINANCIAL _3

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Revenues	$ 2,131.9	$ 1,785.5	$ 1,780.9	$ 1,741.8	$ 1,704.5	$ 1,680.7	$ 1,662.5	$ 1,616.2	$ 7,440.1	$ 6,663.9	$ 5,785.7
Cost of operations	540.9	556.7	560.3	519.9	526.9	519.8	517.2	492.7	2,177.8	2,056.6
Operating income	388.9	567.2	546	402.9	329	561.1	576.9	531.4	1,905	1,998.4	1,853
Net income	292.7	377.3	314.4	280.3	194.8	334.7	388.5	307.4	1,264.7	1,225.4	970.4
Net income attributable to American Tower Corporation stockholders	277.6	366.9	306.7	285.2	238.5	317.3	367	316.1	1,236.4	1,238.9	956.4
Dividends on preferred stock	0	0	0	(9.4)	(18.9)	(18.9)	(22.8)	(26.8)	(9.4)	(87.4)	(107.1)
NET INCOME ATTRIBUTABLE TO AMERICAN TOWER CORPORATION COMMON STOCKHOLDERS	$ 277.6	$ 366.9	$ 306.7	$ 275.8	$ 219.6	$ 298.4	$ 344.2	$ 289.3	$ 1,227	$ 1,151.5	$ 849.3
Basic net income per common share (in dollars per share)	$ 0.63	$ 0.83	$ 0.69	$ 0.63	$ 0.51	$ 0.70	$ 0.81	$ 0.68	$ 2.79	$ 2.69	$ 2
Diluted net income per common share (in dollars per share)	$ 0.62	$ 0.83	$ 0.69	$ 0.63	$ 0.51	$ 0.69	$ 0.80	$ 0.67	$ 2.77	$ 2.67	$ 1.98

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($) $ in Millions	Feb. 14, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Term loan		$ 21,159.9
Unsecured Debt
Subsequent Event [Line Items]
Term loan		$ 152.5	$ 246.1
Subsequent Event | Term Loan 2019 | Unsecured Debt
Subsequent Event [Line Items]
Term loan	$ 1,300
Subsequent Event | Term Loan 2019 | Unsecured Debt | LIBOR
Subsequent Event [Line Items]
Basis spread on variable rate	0.80%
Subsequent Event | Term Loan 2019 | Unsecured Debt | Base Rate
Subsequent Event [Line Items]
Basis spread on variable rate	0.375%
Subsequent Event | Term Loan 2019 | Unsecured Debt | Minimum | LIBOR
Subsequent Event [Line Items]
Basis spread on variable rate	0.55%
Subsequent Event | Term Loan 2019 | Unsecured Debt | Maximum | LIBOR
Subsequent Event [Line Items]
Basis spread on variable rate	1.375%

Schedule III - SCHEDULE OF RE_2

Schedule III - SCHEDULE OF REAL ESTATE AND ACCUMULATED DEPRECIATION (Schedule Of Real Estate And Accumulated Depreciation) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)communication_site	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Number of units | communication_site	168,985
Encumbrances	$ 3,014.2
Gross amount carried at close of current period	15,960.1	$ 15,349	$ 14,277	$ 13,046.3
Accumulated depreciation at close of current period	$ (5,724.7)	$ (5,181.2)	$ (4,548.1)	$ (3,994.9)
Date of construction	Various
Date acquired	Various
Percentage exceeds total amounts	5.00%
Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statements is computed	20 years

Schedule III - SCHEDULE OF RE_3

Schedule III - SCHEDULE OF REAL ESTATE AND ACCUMULATED DEPRECIATION (Activity Of Real Estate And Accumulated Depreciation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Gross amount at beginning	$ 15,349	$ 14,277	$ 13,046.3
Acquisitions	721.4	499.7	787.2
Discretionary capital projects	173.5	120.7	105.3
Discretionary ground lease purchases	180.4	150.4	168.1
Redevelopment capital expenditures	177.3	138.8	136.8
Capital improvements	94	65.6	81.8
Start-up capital expenditures	113.1	158.1	128.7
Other additions	(3)	106.4	139.4
Total additions	1,456.7	1,239.7	1,547.3
Cost of real estate sold or disposed	(395.7)	(246.5)	(85.8)
Other deductions	(449.9)	78.8	(230.8)
Total deductions	(845.6)	(167.7)	(316.6)
Balance at end	15,960.1	15,349	14,277
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Gross amount of accumulated depreciation at beginning	(5,181.2)	(4,548.1)	(3,994.9)
Depreciation	(751.4)	(718.7)	(647.9)
Other additions		0	0
Total additions	(751.4)	(718.7)	(647.9)
Amount of accumulated depreciation for assets sold or disposed	129.3	100.7	24.9
Other deductions	78.6	(15.1)	69.8
Total deductions	207.9	85.6	94.7
Balance at end	$ (5,724.7)	$ (5,181.2)	$ (4,548.1)

Uncategorized Items - amt-20181

Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 38,400,000
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 38,400,000