Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Feb. 18, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-14195
Entity Registrant Name	American Tower Corporation
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	65-0723837
Entity Address, Address Line One	116 Huntington Avenue
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02116
City Area Code	617
Local Phone Number	375-7500
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 114.3
Entity Common Stock, Shares Outstanding		444,384,437
Documents Incorporated by Reference	Portions of the definitive proxy statement (the “Definitive Proxy Statement”) to be filed with the Securities and Exchange Commission relative to the registrant’s 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this Report.
Entity Central Index Key	0001053507
Document Period End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	AMT
Security Exchange Name	NYSE
1.375% Senior Notes due 2025
Document Information [Line Items]
Title of 12(b) Security	1.375% Senior Notes due 2025
Trading Symbol	AMT 25A
Security Exchange Name	NYSE
1.950% Senior Notes due 2026
Document Information [Line Items]
Title of 12(b) Security	1.950% Senior Notes due 2026
Trading Symbol	AMT 26B
Security Exchange Name	NYSE
0.500% Notes
Document Information [Line Items]
Title of 12(b) Security	0.500% Senior Notes due 2028
Trading Symbol	AMT 28A
Security Exchange Name	NYSE
1.000% Senior Notes due 2032
Document Information [Line Items]
Title of 12(b) Security	1.000% Senior Notes due 2032
Trading Symbol	AMT 32
Security Exchange Name	NYSE