PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 16,117,400	$ 15,880,000
Distribution - Natural Gas	3,984,200	3,931,100
Transmission - Electric	11,059,400	10,958,400
Distribution - Water	1,730,200	1,726,500
Solar	200,500	200,200
Utility	33,091,700	32,696,200
Other	1,073,200	1,025,600
Property, Plant and Equipment, Gross	34,164,900	33,721,800
Less: Accumulated Depreciation
Utility	(7,572,400)	(7,483,500)
Other	(408,000)	(387,400)
Total Accumulated Depreciation	(7,980,400)	(7,870,900)
Property, Plant and Equipment, Net	26,184,500	25,850,900
Construction Work in Progress	1,856,900	1,734,600
Total Property, Plant and Equipment, Net	28,041,356	27,585,470
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	6,607,800	6,485,500
Transmission - Electric	5,094,100	5,043,000
Solar	0	0
Property, Plant and Equipment, Gross	11,701,900	11,528,500
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,413,600)	(2,385,700)
Property, Plant and Equipment, Net	9,288,300	9,142,800
Construction Work in Progress	472,600	483,000
Total Property, Plant and Equipment, Net	9,760,890	9,625,765
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	7,250,800	7,163,700
Transmission - Electric	4,444,700	4,411,900
Solar	200,500	200,200
Property, Plant and Equipment, Gross	11,896,000	11,775,800
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,925,200)	(2,895,300)
Property, Plant and Equipment, Net	8,970,800	8,880,500
Construction Work in Progress	643,800	592,300
Total Property, Plant and Equipment, Net	9,614,555	9,472,770
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,299,100	2,271,100
Transmission - Electric	1,515,800	1,498,700
Solar	0	0
Property, Plant and Equipment, Gross	3,814,900	3,769,800
Less: Accumulated Depreciation
Total Accumulated Depreciation	(810,100)	(799,900)
Property, Plant and Equipment, Net	3,004,800	2,969,900
Construction Work in Progress	182,500	159,600
Total Property, Plant and Equipment, Net	$ 3,187,282	$ 3,129,506