| Cover Page | Aug. 07, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 9, 2021 |
| Entity Registrant Name | JOUNCE THERAPEUTICS, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-37998 |
| Entity Tax Identification Number | 45-4870634 |
| Entity Address, Address Line One | 780 Memorial Drive |
| Entity Address, City or Town | Cambridge, |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02139 |
| City Area Code | (857) |
| Local Phone Number | 259-3840 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | JNCE |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Entity Central Index Key | 0001640455 |
| Amendment Flag | false |
