| Cover | Aug. 16, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 16, 2021 |
| Entity File Number | 000-20859 |
| Entity Registrant Name | GERON CORPORATION |
| Entity Central Index Key | 0000886744 |
| Entity Tax Identification Number | 75-2287752 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 919 E. HILLSDALE BLVD. |
| Entity Address, Address Line Two | SUITE 250 |
| Entity Address, City or Town | FOSTER CITY |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94404 |
| City Area Code | (650) |
| Local Phone Number | 473-7700 |
| 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 |
| Trading Symbol | GERN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
