| Cover Cover | Jul. 31, 2019 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 31, 2019 |
| Entity Registrant Name | AMERICAN TOWER CORP /MA/ |
| Entity Central Index Key | 0001053507 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-14195 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| NEW YORK STOCK EXCHANGE, INC. | Common Stock | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | AMT |
| Security Exchange Name | NYSE |
| NEW YORK STOCK EXCHANGE, INC. | 1.375% Senior Notes due 2025 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 1.375% Senior Notes due 2025 |
| Trading Symbol | AMT 25A |
| Security Exchange Name | NYSE |
| NEW YORK STOCK EXCHANGE, INC. | 1.950% Senior Notes due 2026 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 1.950% Senior Notes due 2026 |
| Trading Symbol | AMT 26B |
| Security Exchange Name | NYSE |
