RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Income Statements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 137,766	$ 134,715
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	18,547	20,110
Interest Expense on RRB Principal (included in Interest Expense)	14,630	14,479
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
Interest Expense on RRB Principal (included in Interest Expense)	$ 4,700	$ 5,000