PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 19,929,500	$ 19,656,500
Distribution - Natural Gas	8,234,700	8,155,300
Transmission - Electric	15,182,600	14,666,800
Distribution - Water	2,294,900	2,280,100
Solar	201,100	201,100
Utility	45,842,800	44,959,800
Other	2,069,300	2,006,800
Property, Plant and Equipment, Gross	47,912,100	46,966,600
Less:  Accumulated Depreciation
Utility	(9,835,700)	(9,670,100)
Other	(916,200)	(869,600)
Total Accumulated Depreciation	(10,751,900)	(10,539,700)
Property, Plant and Equipment, Net	37,160,200	36,426,900
Construction Work in Progress	3,129,200	3,071,700
Total Property, Plant and Equipment, Net	40,289,378	39,498,607
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	8,003,900	7,897,100
Transmission - Electric	6,609,200	6,548,200
Solar	0	0
Property, Plant and Equipment, Gross	14,613,100	14,445,300
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,707,900)	(2,670,500)
Property, Plant and Equipment, Net	11,905,200	11,774,800
Construction Work in Progress	627,300	565,400
Total Property, Plant and Equipment, Net	12,532,477	12,340,192
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	9,138,500	9,000,500
Transmission - Electric	6,014,500	5,630,800
Solar	201,100	201,100
Property, Plant and Equipment, Gross	15,354,100	14,832,400
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,648,700)	(3,585,900)
Property, Plant and Equipment, Net	11,705,400	11,246,500
Construction Work in Progress	1,334,900	1,507,300
Total Property, Plant and Equipment, Net	13,040,321	12,753,787
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,827,400	2,799,200
Transmission - Electric	2,560,500	2,489,500
Solar	0	0
Property, Plant and Equipment, Gross	5,387,900	5,288,700
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(1,004,700)	(984,000)
Property, Plant and Equipment, Net	4,383,200	4,304,700
Construction Work in Progress	324,400	270,000
Total Property, Plant and Equipment, Net	$ 4,707,625	$ 4,574,652