INCOME TAXES - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current Income Taxes:
Federal	$ 75,800	$ 95,800	$ 21,500
State	600	13,600	(21,600)
Total Current	76,400	109,400	(100)
Deferred Income Taxes, Net:
Federal	(900)	198,800	199,700
State	86,300	148,000	147,400
Total Deferred	85,405	346,779	347,056
Investment Tax Credits, Net	(2,100)	(2,600)	(2,800)
Income Tax Expense	159,684	453,574	344,223
CL&P
Current Income Taxes:
Federal	(10,800)	106,200	15,000
State	(2,300)	20,100	(7,000)
Total Current	(13,100)	126,300	8,000
Deferred Income Taxes, Net:
Federal	130,300	17,200	76,300
State	53,700	28,200	47,600
Total Deferred	184,037	45,381	123,889
Investment Tax Credits, Net	0	(500)	(600)
Income Tax Expense	170,909	171,198	131,273
NSTAR Electric
Current Income Taxes:
Federal	50,700	55,000	52,300
State	7,800	8,700	6,200
Total Current	58,500	63,700	58,500
Deferred Income Taxes, Net:
Federal	50,100	35,600	16,300
State	46,100	42,400	41,200
Total Deferred	96,224	78,039	57,507
Investment Tax Credits, Net	(1,700)	(1,700)	(1,700)
Income Tax Expense	152,996	139,977	114,335
PSNH
Current Income Taxes:
Federal	(40,000)	29,600	43,100
State	(20,000)	5,900	10,800
Total Current	(60,000)	35,500	53,900
Deferred Income Taxes, Net:
Federal	81,200	5,900	(14,900)
State	37,800	9,900	400
Total Deferred	118,970	15,765	(14,530)
Investment Tax Credits, Net	0	0	0
Income Tax Expense	$ 59,014	$ 51,314	$ 39,433