PSNH GENERATION ASSET SALE - PSNH Generation Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Gross Plant	$ 27,354,000	$ 27,060,500
Accumulated Depreciation	(6,858,800)	(6,722,400)
Net Plant	21,641,898	21,350,510
Emission Allowances	361,779	328,721
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	4,247,000	4,197,300
Accumulated Depreciation	(1,277,700)	(1,254,700)
Net Plant	3,076,608	3,039,313
Emission Allowances	165,725	$ 162,354
Electricity Generation Plant, Non-Nuclear [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	1,192,600
Accumulated Depreciation	(564,100)
Net Plant	628,500
Fuel	98,300
Materials and Supplies	48,500
Emission Allowances	19,700
Total Generation Assets	$ 795,000