| Cover | Apr. 07, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 7, 2021 |
| Entity File Number | 001-05324 |
| Entity Registrant Name | EVERSOURCE ENERGY |
| Entity Central Index Key | 0000072741 |
| Entity Tax Identification Number | 04-2147929 |
| Entity Incorporation, State or Country Code | MA |
| Entity Address, Address Line One | 300 Cadwell Drive |
| Entity Address, City or Town | Springfield |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 01104 |
| 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 |
| Title of 12(b) Security | Common Shares, $5.00 par value per share |
| Trading Symbol | ES |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
