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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 147,962	$ 134,066	$ 431,162	$ 403,067
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	(17,922)	(7,360)	(62,744)	(39,034)
Interest Expense on RRB Principal (included in Interest Expense)	14,321	14,942	42,774	44,029
PSNH | VIE | Rate Reduction Bonds
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	10,800	10,800	32,400	32,400
Interest Expense on RRB Principal (included in Interest Expense)	$ 4,500	$ 4,900	$ 13,900	$ 14,900