| Document and Entity Information | Nov. 17, 2021 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001758766 |
| Document Type | 8-K |
| Document Period End Date | Nov. 17, 2021 |
| Entity Registrant Name | STEM, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39455 |
| Entity Tax Identification Number | 85-1972187 |
| Entity Address, Address Line One | 100 California St. |
| Entity Address, Address Line Two | 14th Fl |
| Entity Address, City or Town | San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94111 |
| City Area Code | 877 |
| Local Phone Number | 374-7836 |
| 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 |
| Trading Symbol | STEM |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
