SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2024 USD ($) project	Dec. 31, 2025 USD ($) customer regulatedUtility	Dec. 31, 2024 USD ($) project	Dec. 31, 2023 USD ($)
Summary of Accounting Policies [Line Items]
Number of electric and natural gas customers | customer		4,600,000
Number of offshore wind projects | project	3		3
Goodwill	$ 3,571,333,000	$ 4,233,767,000	$ 3,571,333,000	$ 4,532,100,000
Charitable contributions		7,000,000	0	$ 20,000,000.0
Energy Relief Fund
Summary of Accounting Policies [Line Items]
Restricted cash, current	20,000,000	$ 21,400,000	20,000,000
Restricted cash, noncurrent	5,900,000		5,900,000
CL&P
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress		180 days
Maximum loans receivable outstanding	70,000,000	$ 50,000,000	70,000,000
Loans transferred receivable current	9,400,000	8,900,000	9,400,000
Loans transferred receivable non-current	$ 17,300,000	$ 21,800,000	17,300,000
Yankee Gas Services Company
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress		90 days
Disposal Group, Held-for-Sale, Not Discontinued Operations | Aquarion
Summary of Accounting Policies [Line Items]
Goodwill Impairment Loss Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag	goodwill impairment charge
Goodwill impairment charge	$ 297,000,000
Remaining goodwill	$ 662,500,000	$ 662,500,000	$ 662,500,000
Tax Equity
Summary of Accounting Policies [Line Items]
Ownership interest (in percent)	50.00%		50.00%
Tax Equity Investment in South Fork Wind
Summary of Accounting Policies [Line Items]
Ownership interest (in percent)	50.00%		50.00%
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | regulatedUtility		12