PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 19,238,300	$ 18,326,200
Distribution - Natural Gas	7,754,400	7,443,800
Transmission - Electric	14,233,100	13,709,300
Distribution - Water	2,203,600	2,112,600
Solar	200,800	200,800
Utility	43,630,200	41,792,700
Other	1,959,200	1,738,100
Property, Plant and Equipment, Gross	45,589,400	43,530,800
Less:  Accumulated Depreciation
Utility	(9,518,600)	(9,167,400)
Other	(823,000)	(706,100)
Total Accumulated Depreciation	(10,341,600)	(9,873,500)
Property, Plant and Equipment, Net	35,247,800	33,657,300
Construction Work in Progress	3,270,500	2,455,500
Total Property, Plant and Equipment, Net	38,518,294	36,112,820
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	7,717,000	7,370,100
Transmission - Electric	6,345,800	6,165,100
Solar	0	0
Property, Plant and Equipment, Gross	14,062,800	13,535,200
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,659,000)	(2,567,100)
Property, Plant and Equipment, Net	11,403,800	10,968,100
Construction Work in Progress	632,200	498,900
Total Property, Plant and Equipment, Net	12,035,967	11,467,024
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	8,816,500	8,410,000
Transmission - Electric	5,536,600	5,333,800
Solar	200,800	200,800
Property, Plant and Equipment, Gross	14,553,900	13,944,600
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,535,500)	(3,381,200)
Property, Plant and Equipment, Net	11,018,400	10,563,400
Construction Work in Progress	1,390,800	1,063,600
Total Property, Plant and Equipment, Net	12,409,156	11,626,968
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,745,100	2,586,400
Transmission - Electric	2,352,400	2,212,000
Solar	0	0
Property, Plant and Equipment, Gross	5,097,500	4,798,400
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(974,200)	(912,300)
Property, Plant and Equipment, Net	4,123,300	3,886,100
Construction Work in Progress	309,700	174,100
Total Property, Plant and Equipment, Net	$ 4,433,033	$ 4,060,224