RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 533,197	$ 498,805	$ 421,755
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	57,732	80,978	(16,577)
Interest Expense on RRB Principal (included in Interest Expense)	60,666	60,634	$ 51,007
Variable Interest Entity, Primary Beneficiary | Rate Reduction Bonds | PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	43,000	27,300
Interest Expense on RRB Principal (included in Interest Expense)	$ 21,100	$ 14,400