RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 582,334	$ 538,452	$ 533,197
Public Service Company of New Hampshire
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	86,832	52,804	57,732
Interest Expense on RRB Principal (included in Interest Expense)	56,998	58,127	60,666
Variable Interest Entity, Primary Beneficiary | Public Service Company of New Hampshire | Rate Reduction Bonds
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	43,200	43,200	43,000
Interest Expense on RRB Principal (included in Interest Expense)	$ 18,400	$ 19,700	$ 21,100