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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 | 6 Months Ended
--- | --- | ---
Jul. 31, 2025 | Jun. 30, 2025 | May 31, 2025 | Feb. 28, 2025 | Jan. 31, 2025 | Jun. 30, 2025 | Jun. 30, 2024
Debt Instrument [Line Items] |  |  |  |  |  |  |
Retirement of Long-Term Debt |  |  |  |  |  | $ 375,122 | $ 900,000
CL&P | First Mortgage | CL&P Series A First Mortgage Bonds |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  |  |  |  | 4.95% |  |
Issuances |  |  |  |  | $ 400,000 |  |
NSTAR Electric | Unsecured Debt | NSTAR Electric Debentures |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  |  |  | 4.85% |  |  |
Issuances |  |  |  | $ 400,000 |  |  |
Short-term debt, paid |  |  |  | 3.25% |  |  |
NSTAR Electric | Unsecured Debt | NSTAR Electric Debentures |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  |  |  | 5.20% |  |  |
Issuances |  |  |  | $ 400,000 |  |  |
Short-term debt, paid |  |  |  | 3.25% |  |  |
PSNH | First Mortgage | PSNH Series Y First Mortgage Bonds |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  | 4.40% |  |  |  | 4.40% |
Issuances |  | $ 300,000 |  |  |  |  |
Eversource Parent Series H Senior Notes | Senior Notes | Eversource Parent Series H Senior Notes | Eversource Parent |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  |  |  |  | 3.15% |  |
Retirement of Long-Term Debt |  |  |  |  | $ 300,000 |  |
NSTAR Gas Series R First Mortgage Bonds | First Mortgage | NSTAR Gas Series Y First Mortgage Bonds |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  | 4.86% |  |  |  | 4.86% |
Issuances |  | $ 205,000 |  |  |  |  |
NSTAR Gas Series R First Mortgage Bonds | First Mortgage | NSTAR Gas Series Z First Mortgage Bonds |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  | 5.30% |  |  |  | 5.30% |
Issuances |  | $ 20,000 |  |  |  |  |
NSTAR Gas Series R First Mortgage Bonds | First Mortgage | NSTAR Gas Series R First Mortgage Bonds |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) |  |  | 2.33% |  |  |  |
Retirement of Long-Term Debt |  |  | $ 75,000 |  |  |  |
Yankee Gas | First Mortgage | Yankee Gas Series Y First Mortgage Bonds | Subsequent Event |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) | 5.02% |  |  |  |  |  |
Issuances | $ 148,000 |  |  |  |  |  |
Yankee Gas | First Mortgage | Yankee Gas Series Z First Mortgage Bonds | Subsequent Event |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate, stated percentage (in percent) | 5.55% |  |  |  |  |  |
Issuances | $ 37,000 |  |  |  |  |  |

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