| Document And Entity Information | Oct. 26, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 26, 2021 |
| Entity Registrant Name | SQZ BIOTECHNOLOGIES COMPANY |
| Entity Central Index Key | 0001604477 |
| Entity Emerging Growth Company | true |
| Entity File Number | 001-39662 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 46-2431115 |
| Entity Address, Address Line One | 200 Arsenal Yards Blvd |
| Entity Address, Address Line Two | Suite 210 |
| Entity Address, City or Town | Watertown |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02472 |
| City Area Code | 617 |
| Local Phone Number | 758-8672 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Ex Transition Period | false |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | SQZ |
| Security Exchange Name | NYSE |
