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REVENUES - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Loss Contingencies [Line Items] |  |  |  |
Revenue | $ 11,801,800 | $ 11,890,600 | $ 12,270,200 |
Loss related to litigation settlement | 0 | 0 | (72,041) |
Lease revenue | $ 2,500 | $ 4,600 | $ 4,000 |
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Income, Net | Other Income, Net | Other Income, Net |
CL&P |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Loss related to litigation settlement | $ 0 | $ 0 | $ (72,041) |
Lease revenue | 500 | 700 | 800 |
NSTAR Electric |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Lease revenue | 1,200 | 2,500 | 2,500 |
Reserve for Revenues Subject to Refund |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Revenue | (1,900) | 4,300 | 72,000 |
Operating Segments | CL&P |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Revenue | 5,222,100 | 5,077,600 | 5,343,200 |
Operating Segments | NSTAR Electric |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Revenue | 4,332,000 | 4,129,400 | 4,127,300 |
Operating Segments | Reserve for Revenues Subject to Refund | CL&P |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Revenue | 0 | 4,300 | 72,700 |
Operating Segments | Reserve for Revenues Subject to Refund | NSTAR Electric |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Revenue | $ 0 | $ 0 | $ 0 |
Unfavorable Regulatory Action | Operating Segments | Reserve for Revenues Subject to Refund | CL&P |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Revenue |  |  |  | $ 93,400

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