ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Narrative (Details) mi in Thousands						3 Months Ended	12 Months Ended
	Nov. 01, 2022 USD ($)	Nov. 01, 2021 USD ($)	Oct. 09, 2020 USD ($) customer mi	Oct. 07, 2020 USD ($) reset rateIncrease	Oct. 01, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2020 USD ($)
Business Acquisition [Line Items]
Number of customers | customer			303,000
Operating revenues										$ 154,800,000
Pre-tax income										$ 13,900,000
Impairment loss					$ 0
Cash outflows for the acquisition of CMA							$ 1,113,252,000	$ 0	$ 0
TSA
Business Acquisition [Line Items]
TSA and pre-TSA costs						$ 15,900,000
Energy Efficiency expense						$ 2,000,000.0
DPU
Business Acquisition [Line Items]
Authorized regulatory ROE				9.70%
Authorized common equity ratio				53.25%
Approved rate base				$ 995,000,000
Number of rate base resets in agreement | reset				2
Term of agreement				8 years
Number of distribution rate increases | rateIncrease				2
DPU | Forecast [Member]
Business Acquisition [Line Items]
Rate increase approved	$ 10,000,000	$ 13,000,000
CMA
Business Acquisition [Line Items]
Consideration transferred			$ 1,100,000,000
Number of customers | customer			332,000
Number of communities served | customer			60
Length of natural gas pipeline | mi			5
Operating revenues							9,273,000,000	$ 9,103,000,000
Contingent liability for future refund to customers			$ 6,700,000
Energy relief fund liability			$ 56,800,000
Arrearage Forgiveness Fund											$ 15,400,000
Cash outflows for the acquisition of CMA							$ 1,110,000,000