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SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Thousands |  | 1 Months Ended | 9 Months Ended
--- | --- | --- | ---
Oct. 15, 2022 | Oct. 31, 2022 | Sep. 30, 2022 | Aug. 31, 2022 | Jul. 31, 2022 | Jun. 30, 2022 | May 31, 2022 | Mar. 31, 2022 | Feb. 28, 2022 | Sep. 30, 2022 | Sep. 30, 2021
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Retirement of Long-Term Debt |  |  |  |  |  |  |  |  |  | $ (775,000) | $ (1,142,500)
NSTAR Electric |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Retirement of Long-Term Debt |  |  |  |  |  |  |  |  |  | $ 0 | $ (250,000)
NSTAR Electric | Subsequent Event |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Retirement of Long-Term Debt | $ (400,000) |  |  |  |  |  |  |  |  |  |
NSTAR Electric | Debentures | NSTAR Electric 4.55% 2022 Debentures |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  |  | 4.55% |  |  |  |
Issuances |  |  |  |  |  |  | $ 450,000 |  |  |  |
NSTAR Electric | Debentures | NSTAR Electric 4.95% 2022 Debentures |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  | 4.95% |  |  |  |  |  |  | 4.95% |
Issuances |  |  | $ 400,000 |  |  |  |  |  |  |  |
NSTAR Electric | Debentures | NSTAR Electric 2.375% 2012 Debentures | Subsequent Event |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  | 2.375% |  |  |  |  |  |  |  |  |
Retirement of Long-Term Debt |  | $ (400,000) |  |  |  |  |  |  |  |  |
Yankee Gas | First Mortgage | Yankee Gas 8.48% Series B First Mortgage Bonds |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  |  |  | 8.48% |  |  |
Retirement of Long-Term Debt |  |  |  |  |  |  |  | $ (20,000) |  |  |
Yankee Gas | First Mortgage | Yankee Gas 4.31% Series U First Mortgage Bonds |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  | 4.31% |  |  |  |  |  |  | 4.31% |
Issuances |  |  | $ 100,000 |  |  |  |  |  |  |  |
EGMA | First Mortgage | EGMA 4.70% Series C First Mortgage Bonds |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  | 4.70% |  |  |  |  |
Issuances |  |  |  |  |  | $ 100,000 |  |  |  |  |
NSTAR Gas | First Mortgage | NSTAR Gas 4.40% Series V First Mortgage Bonds |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  | 4.40% |  |  |  |  |  |
Issuances |  |  |  |  | $ 125,000 |  |  |  |  |  |
Aquarian Water Company | Senior Notes | Aquarion Water Company of Connecticut 4.69% Senior Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 4.69% |  |  |  |  |  |  |
Issuances |  |  |  | $ 70,000 |  |  |  |  |  |  |
Aquarian Water Company | General Mortgage Bonds | Aquarion Water Company of New Hampshire 4.45% General Mortgage Bonds |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  | 4.45% |  |  |  |  |  |
Retirement of Long-Term Debt |  |  |  |  | $ (5,000) |  |  |  |  |  |
Eversource Parent | Senior Notes | Eversource Parent 2.90% Series V Senior Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  |  |  |  | 2.90% |  |
Issuances |  |  |  |  |  |  |  |  | $ 650,000 |  |
Eversource Parent | Senior Notes | Eversource Parent 3.375% Series W Senior Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  |  |  |  | 3.375% |  |
Issuances |  |  |  |  |  |  |  |  | $ 650,000 |  |
Eversource Parent | Senior Notes | Eversource Parent 4.20% Series X Senior Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  | 4.20% |  |  |  |  |
Issuances |  |  |  |  |  | $ 900,000 |  |  |  |  |
Eversource Parent | Senior Notes | Eversource Parent 4.60% Series Y Senior Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  | 4.60% |  |  |  |  |
Issuances |  |  |  |  |  | $ 600,000 |  |  |  |  |
Eversource Parent | Senior Notes | Eversource Parent 2.75% Series K Senior Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  |  |  |  |  | 2.75% |  |  |
Retirement of Long-Term Debt |  |  |  |  |  |  |  | $ (750,000) |  |  |

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