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Cover - shares
 3 Months Ended
Mar. 31, 2025
May 02, 2025
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2025  
Document Transition Report false  
Entity File Number 000-20859  
Entity Registrant Name GERON CORP  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 75-2287752  
Entity Address, Address Line One 919 EAST HILLSDALE BOULEVARD  
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  
Title of 12(b) Security Common Stock, $0.001 par value  
Trading Symbol GERN  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   636,917,758
Entity Central Index Key 0000886744  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Document Fiscal Year Focus 2025