SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands, customer in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) project regulatedUtility customer	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Summary of Accounting Policies [Line Items]
Number of electric and natural gas customers | customer	4.4
Number of offshore wind projects | project	3
Number of tax equity projects | project	1
Goodwill	$ 4,532,100	$ 4,522,632	$ 4,477,300
Charitable contributions	$ 20,000	8,000
Offshore Wind Business
Summary of Accounting Policies [Line Items]
Ownership interest (in percent)	50.00%
Number of offshore wind projects | project	2
Tax Equity
Summary of Accounting Policies [Line Items]
Ownership interest (in percent)	50.00%
Energy Relief Fund
Summary of Accounting Policies [Line Items]
Restricted cash, current	$ 20,000	20,000
Restricted cash, noncurrent	$ 14,100	15,900
CL&P
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress	180 days
Maximum loans receivable outstanding	$ 55,000
Loans transferred receivable current	8,500	9,100
Loans transferred receivable non-current	$ 14,500	13,000
Long term receivable		25,000
Yankee Gas Services Company
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress	90 days
NSTAR Electric
Summary of Accounting Policies [Line Items]
Long term receivable		5,500
PSNH
Summary of Accounting Policies [Line Items]
Long term receivable		$ 3,800
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | regulatedUtility	12