Organization	12 Months Ended
	Dec. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	OrganizationLyell Immunopharma, Inc. (the “Company”) was incorporated in Delaware in June 2018. The Company is a clinical-stage cell therapy company advancing a pipeline of proprietary next-generation chimeric antigen receptor (“CAR”) T-cell product candidates for patients with hematologic malignancies and solid tumors. The Company’s primary activities since incorporation have been to develop T‑cell therapies, conduct research and development, acquire technology and product candidates, enter into strategic collaboration and license arrangements, enable and execute manufacturing activities in support of its product candidate development efforts, organize and staff the Company, conduct business planning, establish its intellectual property portfolio, submit regulatory submissions, execute clinical trials, raise capital and provide general and administrative support for these activities.