| Document and Entity Information | Jan. 13, 2021 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | AMERICAN TOWER CORP /MA/ |
| Amendment Flag | false |
| Entity Central Index Key | 0001053507 |
| Document Type | 8-K |
| Document Period End Date | Jan. 13, 2021 |
| Entity Incorporation State 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 |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, $0.01 par value |
| Trading Symbol | AMT |
| Security Exchange Name | NYSE |
| One Point Three Seventy Five Percent Senior Notesdue 2025 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.375% Senior Notes due 2025 |
| Trading Symbol | AMT 25A |
| Security Exchange Name | NYSE |
| One Point Nine Five Zero Percent Senior Notes Due 2026 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.950% Senior Notes due 2026 |
| Trading Symbol | AMT 26B |
| Security Exchange Name | NYSE |
| Zero Point Five Percent Senior Notes Due 2028 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 0.500% Senior Notes due 2028 |
| Trading Symbol | AMT 28A |
| Security Exchange Name | NYSE |
| One Point Zero Percent Senior Notes Due 2032 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.000% Senior Notes due 2032 |
| Trading Symbol | AMT 32 |
| Security Exchange Name | NYSE |
