RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 125,201	$ 108,719	$ 372,734	$ 319,477
Public Service Company of New Hampshire
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	16,593	$ 12,896	43,977	$ 38,676
Variable Interest Entity, Primary Beneficiary | Rate Reduction Bonds | Public Service Company of New Hampshire
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	10,200		17,100
Interest Expense on RRB Principal (included in Interest Expense)	$ 6,000		$ 8,800