PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, Plant and Equipment By Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 22,695,300	$ 21,144,100
Distribution - Natural Gas	9,888,000	8,922,200
Transmission - Electric	17,082,400	16,130,900
Distribution - Water	2,577,300	0
Solar	206,800	201,000
Utility	52,449,800	46,398,200
Other	2,476,300	2,254,100
Property, Plant and Equipment, Gross	54,926,100	48,652,300
Less:  Accumulated Depreciation
Utility	(10,911,700)	(9,636,500)
Other	(1,246,100)	(1,044,100)
Total Accumulated Depreciation	(12,157,800)	(10,680,600)
Property, Plant and Equipment, Net	42,768,300	37,971,700
Construction Work in Progress	3,162,700	3,014,900
Total Property, Plant and Equipment, Net	45,930,959	40,986,578
CL&P
Property, Plant and Equipment [Line Items]
Distribution - Electric	8,906,000	8,437,900
Transmission - Electric	7,222,500	6,937,700
Solar	0	0
Property, Plant and Equipment, Gross	16,128,500	15,375,600
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,081,300)	(2,928,000)
Property, Plant and Equipment, Net	13,047,200	12,447,600
Construction Work in Progress	576,100	554,600
Total Property, Plant and Equipment, Net	13,623,296	13,002,193
NSTAR Electric
Property, Plant and Equipment [Line Items]
Distribution - Electric	10,635,700	9,782,300
Transmission - Electric	6,722,900	6,375,200
Solar	206,800	201,000
Property, Plant and Equipment, Gross	17,565,400	16,358,500
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(4,014,200)	(3,782,000)
Property, Plant and Equipment, Net	13,551,200	12,576,500
Construction Work in Progress	1,757,700	1,461,300
Total Property, Plant and Equipment, Net	15,308,896	14,037,828
PSNH
Property, Plant and Equipment [Line Items]
Distribution - Electric	3,193,800	2,964,200
Transmission - Electric	3,138,700	2,819,600
Solar	0	0
Property, Plant and Equipment, Gross	6,332,500	5,783,800
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(1,085,400)	(1,032,300)
Property, Plant and Equipment, Net	5,247,100	4,751,500
Construction Work in Progress	260,600	338,400
Total Property, Plant and Equipment, Net	$ 5,507,663	$ 5,089,943