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GOODWILL - Summary of Goodwill by Reportable Segment (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Oct. 03, 2022 | Dec. 31, 2023 | Dec. 31, 2022
Goodwill [Roll Forward] |  |  |
Beginning Balance |  | $ 4,522,632 | $ 4,477,300
Ending Balance |  | 4,532,100 | 4,522,632
New England Service Company (NESC) |  |  |
Goodwill [Roll Forward] |  |  |
Measurement Period Adjustments |  |  | 500
The Torrington Water Company (TWC) |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  |  | 44,800
Water Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  | 9,500 |
Electric Distribution |  |  |
Goodwill [Roll Forward] |  |  |
Beginning Balance |  | 2,543,600 | 2,543,600
Ending Balance |  | 2,543,600 | 2,543,600
Electric Distribution | New England Service Company (NESC) |  |  |
Goodwill [Roll Forward] |  |  |
Measurement Period Adjustments |  |  | 0
Electric Distribution | The Torrington Water Company (TWC) |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  |  | 0
Electric Distribution | Water Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  | 0 |
Electric Transmission |  |  |
Goodwill [Roll Forward] |  |  |
Beginning Balance |  | 576,800 | 576,800
Ending Balance |  | 576,800 | 576,800
Electric Transmission | New England Service Company (NESC) |  |  |
Goodwill [Roll Forward] |  |  |
Measurement Period Adjustments |  |  | 0
Electric Transmission | The Torrington Water Company (TWC) |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  |  | 0
Electric Transmission | Water Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  | 0 |
Natural Gas Distribution |  |  |
Goodwill [Roll Forward] |  |  |
Beginning Balance |  | 451,000 | 451,000
Ending Balance |  | 451,000 | 451,000
Natural Gas Distribution | New England Service Company (NESC) |  |  |
Goodwill [Roll Forward] |  |  |
Measurement Period Adjustments |  |  | 0
Natural Gas Distribution | The Torrington Water Company (TWC) |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  |  | 0
Natural Gas Distribution | Water Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  | 0 |
Water Distribution |  |  |
Goodwill [Roll Forward] |  |  |
Beginning Balance |  | 951,200 | 905,900
Ending Balance |  | 960,700 | 951,200
Water Distribution | New England Service Company (NESC) |  |  |
Goodwill [Roll Forward] |  |  |
Measurement Period Adjustments |  | 500 | 500
Goodwill acquired |  | 22,200 |
Water Distribution | The Torrington Water Company (TWC) |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired | $ 44,800 |  | $ 44,800
Water Distribution | Water Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill acquired |  | $ 9,500 |

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