v3.25.1
Cover - shares
3 Months Ended
Mar. 31, 2025
May 08, 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 001-40502  
Entity Registrant Name Lyell Immunopharma, Inc.  
Entity Incorporation State Country Code DE  
Entity Tax Identification Number 83-1300510  
Entity Address Line 201 Haskins Way  
Entity Address City Or Town South San Francisco  
Entity Address State Or Province CA  
Entity Address Postal Zip Code 94080  
City Area Code 650  
Local Phone Number 695-0677  
Title12(b) Security Common Stock, $0.0001 par value per share  
Trading Symbol LYEL  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   295,337,557
Entity Central Index Key 0001806952  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q1  
Amendment Flag false