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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Public Utility, Property, Plant and Equipment [Line Items] |  |
Distribution - Electric | $ 17,257,300 | $ 16,703,200
Distribution - Natural Gas | 6,334,900 | 6,111,200
Transmission - Electric | 12,396,200 | 11,954,000
Distribution - Water | 1,771,100 | 1,743,100
Solar | 200,400 | 201,500
Utility | 37,959,900 | 36,713,000
Other | 1,430,500 | 1,269,000
Property, Plant and Equipment, Gross | 39,390,400 | 37,982,000
Less: Accumulated Depreciation |  |
Utility | (8,830,200) | (8,476,300)
Other | (550,000) | (477,600)
Total Accumulated Depreciation | (9,380,200) | (8,953,900)
Property, Plant and Equipment, Net | 30,010,200 | 29,028,100
Construction Work in Progress | 2,456,900 | 1,854,400
Total Property, Plant and Equipment, Net | 32,467,069 | 30,882,523
CL&P |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Distribution - Electric | 7,028,900 | 6,820,700
Transmission - Electric | 5,707,900 | 5,512,000
Solar | 0 | 0
Property, Plant and Equipment, Gross | 12,736,800 | 12,332,700
Less: Accumulated Depreciation |  |
Total Accumulated Depreciation | (2,574,600) | (2,475,400)
Property, Plant and Equipment, Net | 10,162,200 | 9,857,300
Construction Work in Progress | 436,600 | 377,300
Total Property, Plant and Equipment, Net | 10,598,836 | 10,234,556
NSTAR Electric |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Distribution - Electric | 7,798,800 | 7,544,400
Transmission - Electric | 4,884,000 | 4,701,300
Solar | 200,400 | 201,500
Property, Plant and Equipment, Gross | 12,883,200 | 12,447,200
Less: Accumulated Depreciation |  |
Total Accumulated Depreciation | (3,220,700) | (3,074,100)
Property, Plant and Equipment, Net | 9,662,500 | 9,373,100
Construction Work in Progress | 949,200 | 750,000
Total Property, Plant and Equipment, Net | 10,611,728 | 10,123,062
PSNH |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Distribution - Electric | 2,469,900 | 2,378,400
Transmission - Electric | 1,805,900 | 1,742,400
Solar | 0 | 0
Property, Plant and Equipment, Gross | 4,275,800 | 4,120,800
Less: Accumulated Depreciation |  |
Total Accumulated Depreciation | (895,400) | (848,900)
Property, Plant and Equipment, Net | 3,380,400 | 3,271,900
Construction Work in Progress | 148,700 | 102,400
Total Property, Plant and Equipment, Net | $ 3,529,050 | $ 3,374,270

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