RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Income Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 135,216	$ 125,201	$ 399,654	$ 372,734
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	20,421	27,357	39,944	41,318
Interest Expense on RRB Principal (included in Interest Expense)	16,378	16,593	44,654	43,977
PSNH | VIE | Rate Reduction Bonds
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	10,800	10,200	32,200	17,100
Interest Expense on RRB Principal (included in Interest Expense)	$ 5,200	$ 6,000	$ 15,900	$ 8,800