| Cover Page | Aug. 31, 2020 | Aug. 07, 2020 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Aug. 31, 2020 | |
| 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 |
