PSNH GENERATION ASSET SALE - PSNH Generation Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Gross Plant	$ 28,189,300	$ 27,060,500
Accumulated Depreciation	(7,112,900)	(6,722,400)
Net Plant	22,537,304	21,350,510
Emission Allowances	305,035	328,721
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Gross Plant	4,344,300	4,197,300
Accumulated Depreciation	(1,315,700)	(1,254,700)
Net Plant	3,167,905	3,039,313
Emission Allowances	158,091	$ 162,354
Electricity Generation Plant, Non-Nuclear | Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Gross Plant	1,184,100
Accumulated Depreciation	(573,300)
Net Plant	610,800
Fuel	92,900
Materials and Supplies	44,000
Emission Allowances	19,400
Total Generation Assets	$ 767,100