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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 132,705	$ 126,404	$ 264,438	$ 247,533
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	5,857	8,926	19,523	13,961
Interest Expense on RRB Principal (included in Interest Expense)	13,909	14,612	28,276	27,386
PSNH | VIE | Rate Reduction Bonds
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	10,800	6,800	21,500	6,800
Interest Expense on RRB Principal (included in Interest Expense)	$ 5,300	$ 2,800	$ 10,700	$ 2,800