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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($)
$ in Thousands
Jun. 30, 2025
Dec. 31, 2024
Public Utility, Property, Plant and Equipment [Line Items]    
Distribution - Electric $ 21,785,500 $ 21,144,100
Distribution - Natural Gas 9,210,400 8,922,200
Transmission - Electric 16,569,500 16,130,900
Solar 206,300 201,000
Utility 47,771,700 46,398,200
Other 2,390,500 2,254,100
Property, Plant and Equipment, Gross 50,162,200 48,652,300
Less:  Accumulated Depreciation    
Utility (9,926,900) (9,636,500)
Other (1,144,200) (1,044,100)
Total Accumulated Depreciation (11,071,100) (10,680,600)
Property, Plant and Equipment, Net 39,091,100 37,971,700
Construction Work in Progress 3,212,300 3,014,900
Total Property, Plant and Equipment, Net 42,303,414 40,986,578
CL&P    
Public Utility, Property, Plant and Equipment [Line Items]    
Distribution - Electric 8,653,100 8,437,900
Transmission - Electric 7,062,700 6,937,700
Solar 0 0
Property, Plant and Equipment, Gross 15,715,800 15,375,600
Less:  Accumulated Depreciation    
Total Accumulated Depreciation (3,011,700) (2,928,000)
Property, Plant and Equipment, Net 12,704,100 12,447,600
Construction Work in Progress 561,900 554,600
Total Property, Plant and Equipment, Net 13,265,994 13,002,193
NSTAR Electric    
Public Utility, Property, Plant and Equipment [Line Items]    
Distribution - Electric 10,104,500 9,782,300
Transmission - Electric 6,536,500 6,375,200
Solar 206,300 201,000
Property, Plant and Equipment, Gross 16,847,300 16,358,500
Less:  Accumulated Depreciation    
Total Accumulated Depreciation (3,891,000) (3,782,000)
Property, Plant and Equipment, Net 12,956,300 12,576,500
Construction Work in Progress 1,682,500 1,461,300
Total Property, Plant and Equipment, Net 14,638,823 14,037,828
PSNH    
Public Utility, Property, Plant and Equipment [Line Items]    
Distribution - Electric 3,068,200 2,964,200
Transmission - Electric 2,971,900 2,819,600
Solar 0 0
Property, Plant and Equipment, Gross 6,040,100 5,783,800
Less:  Accumulated Depreciation    
Total Accumulated Depreciation (1,054,900) (1,032,300)
Property, Plant and Equipment, Net 4,985,200 4,751,500
Construction Work in Progress 321,800 338,400
Total Property, Plant and Equipment, Net $ 5,307,012 $ 5,089,943