PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 20,766,100	$ 19,656,500
Distribution - Natural Gas	8,569,300	8,155,300
Transmission - Electric	15,679,100	14,666,800
Distribution - Water	2,319,200	2,280,100
Solar	201,100	201,100
Utility	47,534,800	44,959,800
Other	2,233,900	2,006,800
Property, Plant and Equipment, Gross	49,768,700	46,966,600
Less:  Accumulated Depreciation
Utility	(10,137,900)	(9,670,100)
Other	(1,003,500)	(869,600)
Total Accumulated Depreciation	(11,141,400)	(10,539,700)
Property, Plant and Equipment, Net	38,627,300	36,426,900
Construction Work in Progress	3,284,200	3,071,700
Total Property, Plant and Equipment, Net	41,911,467	39,498,607
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	8,336,400	7,897,100
Transmission - Electric	6,804,100	6,548,200
Solar	0	0
Property, Plant and Equipment, Gross	15,140,500	14,445,300
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,874,100)	(2,670,500)
Property, Plant and Equipment, Net	12,266,400	11,774,800
Construction Work in Progress	563,400	565,400
Total Property, Plant and Equipment, Net	12,829,760	12,340,192
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	9,558,100	9,000,500
Transmission - Electric	6,183,700	5,630,800
Solar	201,100	201,100
Property, Plant and Equipment, Gross	15,942,900	14,832,400
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,719,700)	(3,585,900)
Property, Plant and Equipment, Net	12,223,200	11,246,500
Construction Work in Progress	1,404,000	1,507,300
Total Property, Plant and Equipment, Net	13,627,246	12,753,787
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,911,900	2,799,200
Transmission - Electric	2,692,900	2,489,500
Solar	0	0
Property, Plant and Equipment, Gross	5,604,800	5,288,700
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(1,014,200)	(984,000)
Property, Plant and Equipment, Net	4,590,600	4,304,700
Construction Work in Progress	368,300	270,000
Total Property, Plant and Equipment, Net	$ 4,958,890	$ 4,574,652