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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 134,285	$ 132,705	$ 269,000	$ 264,438
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	11,563	5,857	31,673	19,523
Interest Expense on RRB Principal (included in Interest Expense)	14,607	13,909	29,087	28,276
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	21,500
Interest Expense on RRB Principal (included in Interest Expense)	$ 5,000	$ 5,300	$ 10,000	$ 10,700