PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 23,108,600	$ 22,695,300
Distribution - Natural Gas	9,899,000	9,888,000
Transmission - Electric	17,181,800	17,082,400
Distribution - Water	2,608,300	2,577,300
Solar	206,800	206,800
Utility	53,004,500	52,449,800
Other	2,532,600	2,476,300
Property, Plant and Equipment, Gross	55,537,100	54,926,100
Less:  Accumulated Depreciation
Utility	(11,114,000)	(10,911,700)
Other	(1,303,900)	(1,246,100)
Total Accumulated Depreciation	(12,417,900)	(12,157,800)
Property, Plant and Equipment, Net	43,119,200	42,768,300
Construction Work in Progress	3,351,000	3,162,700
Total Property, Plant and Equipment, Net	46,470,244	45,930,959
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	9,038,700	8,906,000
Transmission - Electric	7,263,700	7,222,500
Solar	0	0
Property, Plant and Equipment, Gross	16,302,400	16,128,500
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,140,800)	(3,081,300)
Property, Plant and Equipment, Net	13,161,600	13,047,200
Construction Work in Progress	606,400	576,100
Total Property, Plant and Equipment, Net	13,768,014	13,623,296
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	10,870,200	10,635,700
Transmission - Electric	6,749,200	6,722,900
Solar	206,800	206,800
Property, Plant and Equipment, Gross	17,826,200	17,565,400
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(4,088,000)	(4,014,200)
Property, Plant and Equipment, Net	13,738,200	13,551,200
Construction Work in Progress	1,831,200	1,757,700
Total Property, Plant and Equipment, Net	15,569,419	15,308,896
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	3,239,900	3,193,800
Transmission - Electric	3,170,600	3,138,700
Solar	0	0
Property, Plant and Equipment, Gross	6,410,500	6,332,500
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(1,105,200)	(1,085,400)
Property, Plant and Equipment, Net	5,305,300	5,247,100
Construction Work in Progress	264,400	260,600
Total Property, Plant and Equipment, Net	$ 5,569,694	$ 5,507,663