PSNH GENERATION ASSET SALE - PSNH Generation Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Gross Plant	$ 27,733,900	$ 27,060,500
Accumulated Depreciation	(6,969,400)	(6,722,400)
Net Plant	22,071,496	21,350,510
Emission Allowances	286,296	328,721
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	4,301,100	4,197,300
Accumulated Depreciation	(1,290,100)	(1,254,700)
Net Plant	3,118,456	3,039,313
Emission Allowances	150,066	$ 162,354
Electricity Generation Plant, Non-Nuclear [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	1,183,300
Accumulated Depreciation	(564,100)
Net Plant	619,200
Fuel	94,600
Materials and Supplies	36,300
Emission Allowances	19,500
Total Generation Assets	$ 769,600