INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 1,865,968	$ 1,572,269	$ 1,558,872
Statutory Federal Income Tax Expense at 21%	391,900	330,200	327,400
Tax Effect of Differences:
Depreciation	(17,100)	(18,100)	(11,100)
Investment Tax Credit Amortization	(2,600)	(2,800)	(3,700)
State Income Taxes, Net of Federal Impact	75,900	54,400	44,900
Dividends on ESOP	(5,100)	(5,100)	(5,100)
Tax Asset Valuation   Allowance/Reserve Adjustments	51,600	44,600	33,400
Excess Stock Benefit	(2,100)	(4,000)	(6,600)
EDIT Amortization	(49,100)	(69,100)	(48,700)
Other, Net	10,200	14,100	15,700
Income Tax Expense	$ 453,574	$ 344,223	$ 346,186
Effective Tax Rate	24.30%	21.90%	22.20%
CL&P
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 704,118	$ 532,998	$ 607,636
Statutory Federal Income Tax Expense at 21%	147,900	111,900	127,600
Tax Effect of Differences:
Depreciation	(3,700)	(6,400)	400
Investment Tax Credit Amortization	(500)	(600)	(700)
State Income Taxes, Net of Federal Impact	(6,600)	(4,600)	(1,200)
Tax Asset Valuation   Allowance/Reserve Adjustments	44,700	36,700	30,700
Excess Stock Benefit	(700)	(1,500)	(2,300)
EDIT Amortization	(9,200)	(9,800)	(9,000)
Other, Net	(700)	5,600	4,200
Income Tax Expense	$ 171,198	$ 131,273	$ 149,702
Effective Tax Rate	24.30%	24.60%	24.60%
NSTAR Electric
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 632,405	$ 590,904	$ 575,829
Statutory Federal Income Tax Expense at 21%	132,800	124,100	120,900
Tax Effect of Differences:
Depreciation	(4,200)	(3,400)	(3,700)
Investment Tax Credit Amortization	(1,700)	(1,700)	(2,600)
State Income Taxes, Net of Federal Impact	40,300	37,500	36,000
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit	(800)	(1,400)	(2,300)
EDIT Amortization	(29,200)	(43,200)	(20,400)
Other, Net	2,800	2,400	2,900
Income Tax Expense	$ 139,977	$ 114,335	$ 130,828
Effective Tax Rate	22.10%	19.30%	22.70%
PSNH
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 222,884	$ 189,771	$ 178,992
Statutory Federal Income Tax Expense at 21%	46,800	39,900	37,600
Tax Effect of Differences:
Depreciation	900	(200)	(1,400)
Investment Tax Credit Amortization	0	0	0
State Income Taxes, Net of Federal Impact	12,500	8,900	9,800
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit	(300)	(500)	(800)
EDIT Amortization	(7,700)	(10,500)	(15,400)
Other, Net	(900)	1,800	1,900
Income Tax Expense	$ 51,314	$ 39,433	$ 31,680
Effective Tax Rate	23.00%	20.80%	17.70%