PSNH GENERATION ASSET SALE - Narrative (Details) $ in Thousands	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 10, 2015 USD ($) senator
Regulatory Assets [Line Items]
Equity return related to clean air project forgone			$ 25,000
Other current liabilities	$ 591,222	$ 684,914
Accrued Pension and SERP	1,073,510	1,141,514
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Other current liabilities	46,415	43,253
Accrued Pension and SERP	101,143	$ 94,652
Electricity Generation Plant, Non-Nuclear [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Number of state senators | senator			2
Accounts payable	30,200
Other current liabilities	17,600
Asset retirement obligation	20,600
Accrued Pension and SERP	$ 23,900