RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 5,701,400	$ 5,715,800
Regulatory Liabilities	3,894,768	3,866,251
Accrued Interest (included in Other Current Liabilities)	925,467	830,620
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	432,097	453,702
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	468,100	478,900
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	162,100	150,000
Current Derivative Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	73,300	78,200
Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	19,100	44,700
PSNH
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	779,200	786,400
Regulatory Liabilities	388,838	381,366
Accrued Interest (included in Other Current Liabilities)	64,356	63,005
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	432,097	453,702
PSNH | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Rate Reduction Bonds - Current Portion	43,200	43,200
Rate Reduction Bonds - Long-Term Portion	432,100	453,700
PSNH | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	468,100	478,900
PSNH | Securitized Stranded Costs | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	468,100	478,900
PSNH | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	14,700	15,800
PSNH | Other Regulatory Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Regulatory Liabilities	6,000	5,400
Accrued Interest (included in Other Current Liabilities)	2,900	7,500
PSNH | Current Derivative Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	16,600	31,400
PSNH | Current Derivative Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	16,300	31,100
PSNH | Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	3,200	3,200
PSNH | Other Long-Term Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	$ 3,200	$ 3,200