RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Income Statements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 145,435	$ 134,285	$ 283,201	$ 269,000
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	(26,274)	(11,563)	(44,821)	(31,673)
Interest Expense on RRB Principal (included in Interest Expense)	13,821	14,607	28,452	29,087
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	21,600	21,600
Interest Expense on RRB Principal (included in Interest Expense)	$ 4,600	$ 5,000	$ 9,300	$ 10,000