| Document and Entity Information | Sep. 15, 2021 |
| Cover [Abstract] | |
| Security Exchange Name | NASDAQ |
| Amendment Flag | false |
| Entity Central Index Key | 0001095981 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Sep. 15, 2021 |
| Entity Registrant Name | PLUS THERAPEUTICS, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-34375 |
| Entity Tax Identification Number | 33-0827593 |
| Entity Address, Address Line One | 4200 Marathon Blvd. |
| Entity Address, Address Line Two | Suite 200 |
| Entity Address, City or Town | Austin |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 78756 |
| City Area Code | (737) |
| Local Phone Number | 255-7194 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.001 |
| Trading Symbol | PSTV |
| Entity Emerging Growth Company | false |
