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REVENUES - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Sep. 01, 2021 | May 06, 2021
Loss Contingencies [Line Items] |  |  |  |  |
Loss related to litigation settlement | $ 81,274 | $ 0 | $ 0 |  |
Revenues from Contracts with Customers | 9,815,000 | 8,766,500 | 8,450,000 |  |
Lease revenue | 4,800 | 4,300 | 4,400 |  |
The Connecticut Light and Power Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Loss related to litigation settlement | 81,274 | 0 | 0 |  |
Lease revenue | 800 | 800 | 1,000 |  |
NSTAR Electric Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Lease revenue | 3,100 | 2,700 | 2,700 |  |
Reserve for Revenues Subject to Refund |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Revenues from Contracts with Customers | (78,700) |  |  |  |
Operating Segments | The Connecticut Light and Power Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Revenues from Contracts with Customers | 4,238,900 | 4,044,700 | 3,626,900 |  |
Operating Segments | NSTAR Electric Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Revenues from Contracts with Customers | 3,541,600 | 3,327,500 | 3,396,400 |  |
Operating Segments | Reserve for Revenues Subject to Refund | The Connecticut Light and Power Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Revenues from Contracts with Customers | (76,100) | 0 | 0 |  |
Operating Segments | Reserve for Revenues Subject to Refund | NSTAR Electric Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Revenues from Contracts with Customers | 0 | $ 0 | $ 0 |  |
Unfavorable Regulatory Action |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Loss related to litigation settlement | 103,600 |  |  |  |
Unfavorable Regulatory Action | The Connecticut Light and Power Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards |  |  |  | $ 28,400 | $ 28,400
Unfavorable Regulatory Action | Operating Segments | Reserve for Revenues Subject to Refund | The Connecticut Light and Power Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Revenues from Contracts with Customers | 93,400 |  |  |  |
Sales | Unfavorable Regulatory Action |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Loss related to litigation settlement | 65,000 |  |  |  |
Sales | Unfavorable Regulatory Action | The Connecticut Light and Power Company |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Loss related to litigation settlement | $ 65,000 |  |  |  |

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