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LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($) $ in Thousands | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jan. 31, 2024 | Dec. 31, 2023 | Nov. 30, 2023 | Sep. 30, 2023 | Aug. 31, 2023 | Jul. 31, 2023 | May 31, 2023 | Mar. 31, 2023 | Jan. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  |  | $ (2,008,470) | $ (1,175,000) | $ (1,142,500)
NSTAR Electric |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  |  | (80,000) | (400,000) | (250,000)
CL&P |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  |  | (400,000) | 0 | (120,500)
PSNH |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  |  | (325,000) | 0 | (282,000)
CL&P 2023 Series A First Mortgage Bonds | First Mortgage Bonds | CL&P |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  | 5.25% |  |  |
Issuance |  |  |  |  |  |  |  |  | $ 500,000 |  |  |
CL&P 2013 Series A First Mortgage Bonds | First Mortgage Bonds | CL&P |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  | 2.50% |  |  |
Repayments of debt |  |  |  |  |  |  |  |  | $ (400,000) |  |  |
CL&P 2023 Series B First Mortgage Bonds | First Mortgage Bonds | CL&P |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  | 4.90% |  |  |  |  |  |
Issuance |  |  |  |  |  | $ 300,000 |  |  |  |  |  |
CL&P 2024 Series A First Mortgage Bonds | First Mortgage Bonds | CL&P | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate | 4.65% |  |  |  |  |  |  |  |  |  |  |
Issuance | $ 350,000 |  |  |  |  |  |  |  |  |  |  |
NSTAR Electric 2023 Debentures | Debentures | NSTAR Electric |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  | 5.60% |  |  |  |  |  |  |  |
Issuance |  |  |  | $ 150,000 |  |  |  |  |  |  |  |
NSTAR Electric 2013 Series G Senior Notes | Senior Notes | NSTAR Electric |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  | 3.88% |  |  |  |  |  |  |  |  |
Repayments of debt |  |  | $ (80,000) |  |  |  |  |  |  |  |  |
PSNH Series W First Mortgage Bonds | First Mortgage Bonds | PSNH |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  | 5.15% |  |  |
Issuance |  |  |  |  |  |  |  |  | $ 300,000 |  |  |
PSNH Series X First Mortgage Bonds | First Mortgage Bonds | PSNH |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  | 5.35% |  |  |  |  |  |  |  |
Issuance |  |  |  | $ 300,000 |  |  |  |  |  |  |  |
PSNH Series S First Mortgage Bonds | First Mortgage Bonds | PSNH |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  | 3.50% |  |  |  |  |  |  |  |  |
Repayments of debt |  |  | $ (325,000) |  |  |  |  |  |  |  |  |
Yankee Gas Series V First Mortgage Bonds | First Mortgage Bonds | Yankee Gas Services Company |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  | 5.51% |  |  |  |  |  |  |
Issuance |  |  |  |  | $ 170,000 |  |  |  |  |  |  |
EGMA Series D First Mortgage Bonds | First Mortgage Bonds | EGMA |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  | 5.73% |  |  |  |  |  |  |  |  |
Issuance |  |  | $ 58,000 |  |  |  |  |  |  |  |  |
Aquarion Water Company of Connecticut Senior Notes | Senior Notes | Aquarion Water Company Of Connecticut |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  | 5.89% |  |  |  |  |  |  |  |
Issuance |  |  |  | $ 50,000 |  |  |  |  |  |  |  |
Eversource |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  |  | $ (1,200,000) | $ (750,000) | $ (450,000)
Eversource | Eversource Parent Series Z Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  | 5.45% | 5.45% |  |  |  |
Issuance |  |  |  |  |  |  | $ 550,000 | $ 750,000 |  |  |  |
Eversource | Eversource Parent Series F Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  | 2.80% |  |  |  |  |
Repayments of debt |  |  |  |  |  |  | $ (450,000) |  |  |  |  |
Eversource | Eversource Parent Series AA Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  | 4.75% |  |  |  |  |
Issuance |  |  |  |  |  |  | $ 450,000 |  |  |  |  |
Eversource | Eversource Parent Series BB Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  | 5.125% |  |  |  |  |
Issuance |  |  |  |  |  |  | $ 800,000 |  |  |  |  |
Eversource | Eversource Parent Variable Rate Series T Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  | $ (350,000) |  |  |  |  |  |  |
Eversource | Eversource Parent Variable Rate Series T Senior Notes | Senior Notes | Secured Overnight Financing Rate (SOFR) |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on compounded SOFR |  |  |  |  | 0.25% |  |  |  |  |  |  |
Eversource | Eversource Parent Series CC Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  | 5.95% |  |  |  |  |  |  |  |  |
Issuance |  |  | $ 800,000 |  |  |  |  |  |  |  |  |
Eversource | Eversource Parent Series N Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  | 3.80% |  |  |  |  |  |  |  | 3.80% |  |
Repayments of debt |  | $ (400,000) |  |  |  |  |  |  |  |  |  |
Eversource | Eversource Parent Series DD Senior Notes | Senior Notes | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate | 5.00% |  |  |  |  |  |  |  |  |  |  |
Issuance | $ 350,000 |  |  |  |  |  |  |  |  |  |  |
Eversource | Eversource Parent Series EE Senior Notes | Senior Notes | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Interest rate | 5.50% |  |  |  |  |  |  |  |  |  |  |
Issuance | $ 650,000 |  |  |  |  |  |  |  |  |  |  |

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