SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) customer in Millions		3 Months Ended
	Mar. 21, 2023 USD ($)	Mar. 31, 2023 USD ($) regulatedUtility project customer	Dec. 31, 2022 USD ($)	May 04, 2022	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Summary of Accounting Policies [Line Items]
Number of electric, natural gas and water customers | customer		4.4
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 535,100,000	$ 486,300,000		$ 432,200,000	$ 417,400,000
Number of offshore wind projects | project		3
Energy Relief Fund - Merrimack Valley Programs
Summary of Accounting Policies [Line Items]
Restricted cash, current		$ 20,000,000	20,000,000
Restricted cash, noncurrent		16,700,000	15,900,000
COVID-19
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		50,900,000	50,900,000
CL&P
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 253,400,000	225,300,000		180,500,000	181,300,000
Period of accounts receivable recoverable under financial or medical duress		180 days
CL&P | COVID-19
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 16,000,000	16,000,000
NSTAR Electric
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		94,600,000	95,000,000.0		94,800,000	97,000,000.0
NSTAR Electric | COVID-19
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		4,100,000	4,100,000
PSNH
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		33,500,000	29,200,000		$ 26,200,000	$ 24,300,000
PSNH | COVID-19
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 0	$ 0
Yankee Gas
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress		90 days
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | regulatedUtility		12
Offshore Wind Business
Summary of Accounting Policies [Line Items]
Ownership interest (percent)				50.00%
North East Offshore LLC
Summary of Accounting Policies [Line Items]
Ownership interest (percent)		50.00%
Renewable Energy Investment Fund
Summary of Accounting Policies [Line Items]
Ownership interest (percent)		90.00%
Proceeds from sale of equity method investments	$ 123,400,000
Renewable Energy Investment Fund | Equity Method Investee
Summary of Accounting Policies [Line Items]
Charitable contributions		$ 20,000,000