COMMITMENTS AND CONTINGENCIES - CL&P Regulatory Matters (Details) $ / shares in Units, $ in Thousands		9 Months Ended
	Oct. 01, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($) $ / shares	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 01, 2021 USD ($)	Jul. 14, 2021 USD ($) $ / shares	May 07, 2021	May 06, 2021 USD ($)	Apr. 28, 2021	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Loss contingency, allowed rate of ROE (in percent)										9.25%
Loss contingency, allowed rate of ROE, downward adjustment (in basis points)										0.0090
Cash, cash equivalents, restricted cash and restricted cash equivalents		$ 602,256	$ 218,129		$ 221,008						$ 264,950
Regulatory Liabilities		988,714			602,432
Loss related to litigation settlement		(72,041)	103,583
Basis points reduction to return on equity, scenario 1	0.90%
Basis points reduction to return on equity, scenario 2	0.45%
CL&P
Loss Contingencies [Line Items]
Cash, cash equivalents, restricted cash and restricted cash equivalents		23,120	71,762		74,788						$ 99,809
Regulatory Liabilities		434,465			266,489
Loss related to litigation settlement		(72,041)	$ 103,583
Customer Assistance Fund | CL&P
Loss Contingencies [Line Items]
Cash, cash equivalents, restricted cash and restricted cash equivalents				$ 10,000	$ 10,000
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact									$ 30,000
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards									28,400
Loss contingency, estimate of possible earnings impact, accident reporting violation fines									$ 1,600
Non-compliance fine							$ 28,600
Loss contingency, accident reporting violation fines							$ 200
Loss contingency, penalty rate as a percent of distribution revenues								2.50%
Loss contingency, after-tax earnings impact per share (in dollars per share) | $ / shares			$ 0.25				$ 0.07
Loss related to litigation settlement			$ 103,600
Loss Contingency, Settlement Agreement, Customer Credits And Assistance	$ 75,000
Gain ​(Loss) Related To Litigation Settlement, Net Of Tax			(85,800)
Unfavorable Regulatory Action | Sales
Loss Contingencies [Line Items]
Loss related to litigation settlement			65,000
Unfavorable Regulatory Action | Oil and Gas, Operation and Maintenance
Loss Contingencies [Line Items]
Loss related to litigation settlement			10,000
Unfavorable Regulatory Action | CL&P
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards						$ 28,400
Loss contingency, settlement agreement, customer credits	65,000
Loss contingency, settlement agreement, customer assistance initiatives	$ 10,000
Regulatory Liabilities			$ 75,000
Unfavorable Regulatory Action | CL&P | Sales
Loss Contingencies [Line Items]
Loss related to litigation settlement		$ 65,000