SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) customer in Millions			3 Months Ended			6 Months Ended
	May 26, 2023 USD ($)	May 25, 2023 USD ($) a mile project	Jun. 30, 2023 USD ($) mi² project mile	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) mi² customer project mile regulatedUtility	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	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			$ 532,400,000	$ 535,100,000	$ 457,800,000	$ 532,400,000	$ 457,800,000	$ 486,300,000	$ 432,200,000	$ 417,400,000
Number of offshore wind projects | project		3	3			3
Payments for investment						$ 390,002,000	277,001,000
Impairment charge			$ 401,000,000		0	401,000,000	0
After-tax impairment			331,000,000
Valuation allowance			40,000,000			40,000,000
Energy Relief Fund - Merrimack Valley Programs
Summary of Accounting Policies [Line Items]
Restricted cash, current			20,000,000			20,000,000		20,000,000
Restricted cash, noncurrent			14,400,000			14,400,000		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		50,900,000
CL&P
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			262,800,000	253,400,000	192,700,000	$ 262,800,000	192,700,000	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		16,000,000
NSTAR Electric
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			97,800,000	94,600,000	100,500,000	97,800,000	100,500,000	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		4,100,000
PSNH
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			12,700,000	33,500,000	$ 27,300,000	12,700,000	$ 27,300,000	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		$ 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%	50.00%			50.00%
Lease area off coasts of Massachusetts and Rhode Island (in square miles) | mi²			257			257
Adjacent lease area (in square miles) | mi²			300			300
Number of miles off south coast of Massachusetts | mile			25			25
North East Offshore
Summary of Accounting Policies [Line Items]
Ownership interest (percent)			50.00%			50.00%
Renewable Energy Investment Fund
Summary of Accounting Policies [Line Items]
Ownership interest (percent)			90.00%			90.00%
Proceeds from sale of equity method investments			$ 23,600,000	$ 123,400,000		$ 147,000,000
Renewable Energy Investment Fund | Equity Method Investee
Summary of Accounting Policies [Line Items]
Charitable contributions			$ 20,000,000
Uncommitted Lease Area
Summary of Accounting Policies [Line Items]
Ownership interest (percent)		50.00%
Uncommitted area of developable acres (in acres) | a		175,000
Number of miles off south coast of Massachusetts | mile		25
Payments for investment		$ 625,000,000
Uncommitted Lease Area | Orsted
Summary of Accounting Policies [Line Items]
Ownership interest (percent)		50.00%
South Fork Wind, LLC
Summary of Accounting Policies [Line Items]
Ownership interest (percent)		50.00%	50.00%			50.00%
Payments for investment	$ 575,000,000
Payments For Equity Method Investments, Percentage Returned		0.5