| Cover Page | Nov. 03, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0000749251 |
| Document Type | 8-K |
| Document Period End Date | Nov. 3, 2020 |
| Entity Registrant Name | GARTNER, INC. |
| Entity File Number | 1-14443 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 04-3099750 |
| Entity Address, Address Line One | P.O. Box 10212 |
| Entity Address, Address Line Two | 56 Top Gallant Road |
| Entity Address, City or Town | Stamford |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06902-7747 |
| City Area Code | 203 |
| Local Phone Number | 316-1111 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock, $0.0005 par value per share |
| Trading Symbol | IT |
| Security Exchange Name | NYSE |
