Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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GOODWILL - Summary of Goodwill by Reportable Segment (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 03, 2022	Dec. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Beginning Balance		$ 4,477,269	$ 4,446,000
Ending Balance		4,522,632	4,477,269
The Torrington Water Company (TWC)
Goodwill [Roll Forward]
Goodwill acquired		44,800
New England Service Company (NESC)
Goodwill [Roll Forward]
Measurement Period Adjustments		500
Goodwill acquired			21,700
CMA
Goodwill [Roll Forward]
Measurement Period Adjustments			9,600
Goodwill acquired		51,900
Electric Distribution
Goodwill [Roll Forward]
Beginning Balance		2,543,600	2,543,600
Ending Balance		2,543,600	2,543,600
Electric Distribution \| The Torrington Water Company (TWC)
Goodwill [Roll Forward]
Goodwill acquired		0
Electric Distribution \| New England Service Company (NESC)
Goodwill [Roll Forward]
Measurement Period Adjustments		0
Goodwill acquired			0
Electric Distribution \| CMA
Goodwill [Roll Forward]
Measurement Period Adjustments			0
Electric Transmission
Goodwill [Roll Forward]
Beginning Balance		576,800	576,800
Ending Balance		576,800	576,800
Electric Transmission \| The Torrington Water Company (TWC)
Goodwill [Roll Forward]
Goodwill acquired		0
Electric Transmission \| New England Service Company (NESC)
Goodwill [Roll Forward]
Measurement Period Adjustments		0
Goodwill acquired			0
Electric Transmission \| CMA
Goodwill [Roll Forward]
Measurement Period Adjustments			0
Natural Gas Distribution
Goodwill [Roll Forward]
Beginning Balance		451,000	441,400
Ending Balance		451,000	451,000
Natural Gas Distribution \| The Torrington Water Company (TWC)
Goodwill [Roll Forward]
Goodwill acquired		0
Natural Gas Distribution \| New England Service Company (NESC)
Goodwill [Roll Forward]
Measurement Period Adjustments		0
Goodwill acquired			0
Natural Gas Distribution \| CMA
Goodwill [Roll Forward]
Measurement Period Adjustments			9,600
Water Distribution
Goodwill [Roll Forward]
Beginning Balance		905,900	884,200
Ending Balance		951,200	905,900
Water Distribution \| The Torrington Water Company (TWC)
Goodwill [Roll Forward]
Goodwill acquired	$ 44,800	44,800
Water Distribution \| New England Service Company (NESC)
Goodwill [Roll Forward]
Measurement Period Adjustments		500
Goodwill acquired		22,200	21,700
Water Distribution \| CMA
Goodwill [Roll Forward]
Measurement Period Adjustments		$ 9,600	$ 0