PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 22,182,300	$ 21,144,100
Distribution - Natural Gas	9,452,800	8,922,200
Transmission - Electric	16,705,200	16,130,900
Solar	206,800	201,000
Utility	48,547,100	46,398,200
Other	2,455,500	2,254,100
Property, Plant and Equipment, Gross	51,002,600	48,652,300
Less:  Accumulated Depreciation
Utility	(10,055,000)	(9,636,500)
Other	(1,195,900)	(1,044,100)
Total Accumulated Depreciation	(11,250,900)	(10,680,600)
Property, Plant and Equipment, Net	39,751,700	37,971,700
Construction Work in Progress	3,292,400	3,014,900
Total Property, Plant and Equipment, Net	43,044,113	40,986,578
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	8,777,300	8,437,900
Transmission - Electric	7,097,500	6,937,700
Solar	0	0
Property, Plant and Equipment, Gross	15,874,800	15,375,600
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,046,000)	(2,928,000)
Property, Plant and Equipment, Net	12,828,800	12,447,600
Construction Work in Progress	594,300	554,600
Total Property, Plant and Equipment, Net	13,423,071	13,002,193
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	10,304,700	9,782,300
Transmission - Electric	6,558,600	6,375,200
Solar	206,800	201,000
Property, Plant and Equipment, Gross	17,070,100	16,358,500
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,948,000)	(3,782,000)
Property, Plant and Equipment, Net	13,122,100	12,576,500
Construction Work in Progress	1,788,300	1,461,300
Total Property, Plant and Equipment, Net	14,910,449	14,037,828
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	3,140,600	2,964,200
Transmission - Electric	3,050,700	2,819,600
Solar	0	0
Property, Plant and Equipment, Gross	6,191,300	5,783,800
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(1,069,000)	(1,032,300)
Property, Plant and Equipment, Net	5,122,300	4,751,500
Construction Work in Progress	278,900	338,400
Total Property, Plant and Equipment, Net	$ 5,401,185	$ 5,089,943