| Document and Entity Information | Dec. 02, 2021 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Dec. 2, 2021 |
| Entity File Number | 001-40925 |
| Entity Registrant Name | Xilio Therapeutics, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 85-1623397 |
| Entity Address State Or Province | MA |
| Entity Address, Address Line One | 828 Winter Street, Suite 300 |
| Entity Address, City or Town | Waltham |
| Entity Address, Postal Zip Code | 02451 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| City Area Code | 617 |
| Local Phone Number | 430-4680 |
| Title of 12(b) Security | Common stock, par value $0.0001 per share |
| Trading Symbol | XLO |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001840233 |
| Amendment Flag | false |
