RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 498,805	$ 421,755	$ 400,961
Public Service Company Of New Hampshire
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	60,634	$ 51,007	$ 50,040
Variable Interest Entity, Primary Beneficiary | Public Service Company Of New Hampshire
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	27,300
Interest Expense on RRB Principal (included in Interest Expense)	$ 14,400