| Cover | Sep. 25, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 25, 2023 |
| Entity File Number | 1-02301 |
| Entity Registrant Name | NSTAR ELECTRIC COMPANY |
| Entity Central Index Key | 0000013372 |
| Entity Tax Identification Number | 04-1278810 |
| Entity Incorporation, State or Country Code | MA |
| Entity Address, Address Line One | 800 Boylston Street |
| Entity Address, City or Town | Boston |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02199 |
| City Area Code | 800 |
| Local Phone Number | 286-5000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
