PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, Plant and Equipment By Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 19,656,500	$ 18,326,200
Distribution - Natural Gas	8,155,300	7,443,800
Transmission - Electric	14,666,800	13,709,300
Distribution - Water	2,280,100	2,112,600
Solar	201,100	200,800
Utility	44,959,800	41,792,700
Other	2,006,800	1,738,100
Property, Plant and Equipment, Gross	46,966,600	43,530,800
Less:  Accumulated Depreciation
Utility	(9,670,100)	(9,167,400)
Other	(869,600)	(706,100)
Total Accumulated Depreciation	(10,539,700)	(9,873,500)
Property, Plant and Equipment, Net	36,426,900	33,657,300
Construction Work in Progress	3,071,700	2,455,500
Total Property, Plant and Equipment, Net	39,498,607	36,112,820
CL&P
Property, Plant and Equipment [Line Items]
Distribution - Electric	7,897,100	7,370,100
Transmission - Electric	6,548,200	6,165,100
Solar	0	0
Property, Plant and Equipment, Gross	14,445,300	13,535,200
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,670,500)	(2,567,100)
Property, Plant and Equipment, Net	11,774,800	10,968,100
Construction Work in Progress	565,400	498,900
Total Property, Plant and Equipment, Net	12,340,192	11,467,024
NSTAR Electric
Property, Plant and Equipment [Line Items]
Distribution - Electric	9,000,500	8,410,000
Transmission - Electric	5,630,800	5,333,800
Solar	201,100	200,800
Property, Plant and Equipment, Gross	14,832,400	13,944,600
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,585,900)	(3,381,200)
Property, Plant and Equipment, Net	11,246,500	10,563,400
Construction Work in Progress	1,507,300	1,063,600
Total Property, Plant and Equipment, Net	12,753,787	11,626,968
PSNH
Property, Plant and Equipment [Line Items]
Distribution - Electric	2,799,200	2,586,400
Transmission - Electric	2,489,500	2,212,000
Solar	0	0
Property, Plant and Equipment, Gross	5,288,700	4,798,400
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(984,000)	(912,300)
Property, Plant and Equipment, Net	4,304,700	3,886,100
Construction Work in Progress	270,000	174,100
Total Property, Plant and Equipment, Net	$ 4,574,652	$ 4,060,224