Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	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	0001053507
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	2018
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 - 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	0.0	1.0
Accounts receivable, net	459.0	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	11,101.0
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	1,499.0
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	1,210.0	1,175.3
DEFERRED TAX LIABILITY	535.9	898.1
OTHER NON-CURRENT LIABILITIES	1,265.1	1,244.2
Total liabilities	26,106.0	25,260.0
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)	(974.0)
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	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	$ 0.0

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	$ 0.0	$ 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 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	2,022.0	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	637.0	543.4
Other operating expenses	513.3	256.0	73.3
Total operating expenses	5,535.1	4,665.5	3,932.7
OPERATING INCOME	1,905.0	1,998.4	1,853.0
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	(14.0)
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
NET INCOME PER COMMON SHARE AMOUNTS:
Basic net income attributable to American Tower Corporation common stockholders (in dollars per share)	$ 2.79	$ 2.69	$ 2.00
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	$ 98.0	$ 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 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 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	0.0
Purchase of noncontrolling interest	0.5	0.0	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	$ 785.0

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	$ 0.0	$ 0.0
Reclassification of unrealized losses on cash flow hedges to net income, tax	0.0	0.0	0.0
Foreign currency translation adjustments, tax	$ (2.6)	$ 1.0	$ 3.8

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	South Africa	Preferred Stock Series A Preferred Stock Convertible Preferred Stock Subject to Mandatory Redemption	Preferred Stock Series B Preferred Stock Convertible Preferred Stock Subject to Mandatory Redemption	Common Stock	Treasury Stock	Additional Paid-in Capital	Additional Paid-in Capital South Africa	Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income South Africa	Earnings (Distributions) in Excess of Distributions (Earnings)	Noncontrolling Interest	Noncontrolling Interest South 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	$ 0.0	$ 4.3	$ (207.7)	$ 9,690.6		$ (1,837.0)		$ (998.5)	$ 61.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation related activity (shares)					1,959,000
Stock-based compensation related activity	155.1				$ 0.0		155.1
Issuance of common stock - stock purchase plan (shares)					88,000
Issuance of common stock—stock purchase plan	7.5				$ 0.0		7.5
Issuance of stock (shares)					1,171,000
Issuance of stock	120.8				$ 0.0		120.8
Changes in fair value of cash flow hedges, net of tax	(0.4)								(0.4)			0.0
Reclassification of unrealized gains on cash flow hedges to net income, net of tax	(0.3)								(0.3)			0.0
Foreign currency translation adjustment, net of tax	(179.4)								(170.7)		0.0	(8.7)
Contributions from noncontrolling interest	239.5						69.5		9.1			160.9
Adjustment to/purchase of noncontrolling interest	0.0
Distributions to noncontrolling interest	(1.0)											(1.0)
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	$ 0.0	$ 4.3	$ (207.7)	10,043.5		(1,999.3)		(1,077.0)	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				$ 0.0		195.0
Issuance of common stock - stock purchase plan (shares)					93,000
Issuance of common stock—stock purchase plan	9.0				$ 0.0		9.0
Conversion of preferred stock (shares)			(6,000,000)	0	5,602,000
Conversion of preferred stock	0.0		$ (0.1)	$ 0.0	$ 0.1		0.0
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		0.0			314.1
Adjustment to/purchase of noncontrolling interest	0.0
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	$ 0.0	$ 4.4	$ (974.0)	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				$ 0.0		190.4
Issuance of common stock - stock purchase plan (shares)					86,000
Issuance of common stock—stock purchase plan	10.2				$ 0.0		10.2
Conversion of preferred stock (shares)			0	(1,375,000)	12,020,000
Conversion of preferred stock	0.0		$ 0.0	$ 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	(15.0)											(15.0)
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	$ 0.0	$ 4.5	$ (1,206.8)	$ 10,380.8		$ (2,642.9)		$ (1,199.5)	$ 563.5

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	(18.0)	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	20.0	17.7
Deferred income taxes	(303.0)	(86.6)	27.0
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	(32.1)	(191.1)	11.4
Prepaid and other assets	(101.7)	(179.9)	(80.0)
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	(14.0)	(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)	(2,007.0)	(1,411.3)
Payment for Verizon transaction	0.0	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	(0.8)
Deposits and other	(52.8)	(5.0)	(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	2,674.0	3,236.4
Proceeds from term loan	1,500.0	0.0	0.0
Proceeds from issuance of securities in securitization transaction	500.0	0.0	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)	0.0
Proceeds from stock options and stock purchase plan	98.9	119.7	92.5
Distributions paid on common stock	(1,323.5)	(1,073.0)	(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)	(40.0)	(26.5)
Purchase of noncontrolling interest	(20.5)	0.0	0.0
Cash used for financing activities	(607.7)	(113.0)	(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	350.0	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 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—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 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.

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

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.

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 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 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. As of December 31, 2018, the Company has withheld from issuance an aggregate of 1.7 million shares, including 0.3 million shares related to the vesting of restricted stock units during the year ended December 31, 2018.

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—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—The Company has a 401(k) plan covering substantially all employees who meet certain age and employment requirements. For the years ended December 31, 2018 and 2017, the Company matched 100% of the first 5% of a participant's contributions. For the year ended December 31, 2016, the Company matched 75% of the first 6% of a participant’s contributions. For the years ended December 31, 2018, 2017 and 2016, the Company contributed $11.2 million, $11.0 million and $9.1 million to the plan, respectively.

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.

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 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			Services		Total
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-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

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—