GENERATION ASSET SALE - Schedule of Assets-Held-for-Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Thermal Gross Plant	$ 31,353,700	$ 29,213,900
Accumulated Depreciation	(7,462,900)	(7,133,800)
Total Property, Plant and Equipment, Net	25,610,428	23,617,463
Other Assets	778,600	693,700
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Thermal Gross Plant	3,517,300	3,244,700
Accumulated Depreciation	(772,900)	(751,800)
Total Property, Plant and Equipment, Net	2,880,073	$ 2,642,274
Electricity Generation Plant, Non-Nuclear | Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Thermal Gross Plant	1,091,400
Hydroelectric Gross Plant	83,000
Accumulated Depreciation	(575,400)
Total Property, Plant and Equipment, Net	599,000
Fuel and Inventory	87,700
Materials and Supplies	27,300
Emission Allowances	19,100
Other Assets	2,600
Deferred Costs from Thermal Generation Asset Sale	(516,100)
Total Generation Assets Held for Sale	$ 219,600