| Document and Entity Information | Sep. 29, 2021 |
| Cover [Abstract] | |
| Amendment Flag | true |
| Entity Central Index Key | 0001806952 |
| Document Type | 8-K/A |
| Document Period End Date | Sep. 29, 2021 |
| Entity Registrant Name | LYELL IMMUNOPHARMA, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-40502 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | LYEL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Amendment Description | This Current Report on Form 8-K/A of Lyell Immunopharma, Inc. (the “Company”) amends the Company’s Current Report on Form 8-K dated September 29, 2021 and filed with the Securities and Exchange Commission on September 30, 2021 (the “Original Filing”) to correct a typo referring to the date on which Dr. Richard Klausner will no longer be an employee of the Company. On September 29, 2021, Dr. Klausner informed the Company that he will be resigning from his position as Executive Chairman of the Company and will no longer be an employee, effective October 1, 2021. Except as described herein, no other changes have been made to the Original Filing. |
