INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Contingency [Line Items]
(Loss)/Income Before Income Tax Benefit	$ (275,037)	$ 1,865,968	$ 1,572,269
Statutory Federal Income Tax Expense at 21%	(57,700)	391,900	330,200
Tax Effect of Differences:
Depreciation	(25,800)	(17,100)	(18,100)
Investment Tax Credit Amortization	(2,100)	(2,600)	(2,800)
State Income Taxes, Net of Federal Impact	(11,400)	75,900	54,400
Dividends on ESOP	(5,300)	(5,100)	(5,100)
Tax Asset Valuation   Allowance/Reserve Adjustments	295,800	51,600	44,600
Tax Deficiency/(Excess Stock Benefit)	500	(2,100)	(4,000)
EDIT Amortization	(51,500)	(49,100)	(69,100)
Other, Net	17,200	10,200	14,100
Income Tax Expense	$ 159,684	$ 453,574	$ 344,223
Effective Tax Rate	(58.10%)	24.30%	21.90%
CL&P
Income Tax Contingency [Line Items]
(Loss)/Income Before Income Tax Benefit	$ 689,642	$ 704,118	$ 532,998
Statutory Federal Income Tax Expense at 21%	144,900	147,900	111,900
Tax Effect of Differences:
Depreciation	(5,600)	(3,700)	(6,400)
Investment Tax Credit Amortization	0	(500)	(600)
State Income Taxes, Net of Federal Impact	(10,700)	(6,600)	(4,600)
Tax Asset Valuation   Allowance/Reserve Adjustments	51,300	44,700	36,700
Tax Deficiency/(Excess Stock Benefit)	200	(700)	(1,500)
EDIT Amortization	(10,500)	(9,200)	(9,800)
Other, Net	1,300	(700)	5,600
Income Tax Expense	$ 170,909	$ 171,198	$ 131,273
Effective Tax Rate	24.80%	24.30%	24.60%
NSTAR Electric
Income Tax Contingency [Line Items]
(Loss)/Income Before Income Tax Benefit	$ 697,524	$ 632,405	$ 590,904
Statutory Federal Income Tax Expense at 21%	146,500	132,800	124,100
Tax Effect of Differences:
Depreciation	(8,800)	(4,200)	(3,400)
Investment Tax Credit Amortization	(1,700)	(1,700)	(1,700)
State Income Taxes, Net of Federal Impact	42,500	40,300	37,500
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Tax Deficiency/(Excess Stock Benefit)	200	(800)	(1,400)
EDIT Amortization	(28,400)	(29,200)	(43,200)
Other, Net	2,700	2,800	2,400
Income Tax Expense	$ 152,996	$ 139,977	$ 114,335
Effective Tax Rate	21.90%	22.10%	19.30%
PSNH
Income Tax Contingency [Line Items]
(Loss)/Income Before Income Tax Benefit	$ 254,673	$ 222,884	$ 189,771
Statutory Federal Income Tax Expense at 21%	53,500	46,800	39,900
Tax Effect of Differences:
Depreciation	(1,000)	900	(200)
Investment Tax Credit Amortization	0	0	0
State Income Taxes, Net of Federal Impact	14,100	12,500	8,900
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Tax Deficiency/(Excess Stock Benefit)	100	(300)	(500)
EDIT Amortization	(6,800)	(7,700)	(10,500)
Other, Net	(900)	(900)	1,800
Income Tax Expense	$ 59,014	$ 51,314	$ 39,433
Effective Tax Rate	23.20%	23.00%	20.80%