PSNH GENERATION ASSET SALE - PSNH Generation Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Gross Plant	$ 27,060,500	$ 25,226,600
Accumulated Depreciation	(6,722,400)	(6,396,700)
Total Property, Plant and Equipment, Net	21,350,510	19,892,441
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	4,197,300	3,891,100
Accumulated Depreciation	(1,254,700)	(1,171,000)
Total Property, Plant and Equipment, Net	3,039,313	$ 2,855,363
Electricity Generation Plant, Non-Nuclear [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	1,192,100
Accumulated Depreciation	(556,000)
Total Property, Plant and Equipment, Net	636,100
Fuel	99,900
Materials and Supplies	42,700
Emission Allowances	19,900
Total Generation Assets	$ 798,600