PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 17,809,000	$ 17,679,100
Distribution - Natural Gas	6,713,700	6,694,800
Transmission - Electric	13,011,000	12,882,400
Distribution - Water	1,924,900	1,900,900
Solar	200,900	200,900
Utility	39,659,500	39,358,100
Other	1,509,600	1,469,500
Property, Plant and Equipment, Gross	41,169,100	40,827,600
Less:  Accumulated Depreciation
Utility	(8,976,200)	(8,885,200)
Other	(609,800)	(580,100)
Total Accumulated Depreciation	(9,586,000)	(9,465,300)
Property, Plant and Equipment, Net	31,583,100	31,362,300
Construction Work in Progress	2,269,500	2,015,400
Total Property, Plant and Equipment, Net	33,852,596	33,377,650
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	7,188,900	7,117,600
Transmission - Electric	5,912,500	5,859,000
Solar	0	0
Property, Plant and Equipment, Gross	13,101,400	12,976,600
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,592,600)	(2,572,100)
Property, Plant and Equipment, Net	10,508,800	10,404,500
Construction Work in Progress	432,200	399,000
Total Property, Plant and Equipment, Net	10,941,005	10,803,543
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	8,151,100	8,105,500
Transmission - Electric	5,137,100	5,090,500
Solar	200,900	200,900
Property, Plant and Equipment, Gross	13,489,100	13,396,900
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,271,800)	(3,227,300)
Property, Plant and Equipment, Net	10,217,300	10,169,600
Construction Work in Progress	791,600	707,000
Total Property, Plant and Equipment, Net	11,008,899	10,876,614
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,509,300	2,496,200
Transmission - Electric	1,963,100	1,934,600
Solar	0	0
Property, Plant and Equipment, Gross	4,472,400	4,430,800
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(912,800)	(908,400)
Property, Plant and Equipment, Net	3,559,600	3,522,400
Construction Work in Progress	163,000	134,100
Total Property, Plant and Equipment, Net	$ 3,722,618	$ 3,656,462