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Cover - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Mar. 06, 2025
Jun. 28, 2024
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-40502    
Entity Registrant Name Lyell Immunopharma, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 83-1300510    
Entity Address, Address Line One 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    
Title of 12(b) Security Common Stock, $0.0001 par value per share    
Trading Symbol LYEL    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
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    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction Flag false    
Entity Shell Company false    
Entity Public Float     $ 306
Entity Common Stock, Shares Outstanding   295,228,868  
Documents Incorporated by Reference
Portions of the registrant’s Proxy Statement for the 2025 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K to the extent stated herein. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the registrant’s fiscal year ended December 31, 2024.
    
Entity Central Index Key 0001806952    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY    
Amendment Flag false