RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Impact of Funding on the Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 7,665,400	$ 7,693,700
Other Regulatory Liabilities (included in Regulatory Liabilities)	4,323,619	4,273,465
Accrued Interest (included in Other Current Liabilities)	1,290,226	1,274,450
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	259,257	280,862
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	295,300	306,100
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	181,100	189,900
Current Derivative Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	56,200	93,600
Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	3,200	3,200
PSNH
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	971,900	961,100
Other Regulatory Liabilities (included in Regulatory Liabilities)	425,128	417,442
Accrued Interest (included in Other Current Liabilities)	71,076	62,334
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	259,257	280,862
PSNH | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Rate Reduction Bonds - Current Portion	43,200	43,200
Rate Reduction Bonds - Long-Term Portion	259,300	280,900
PSNH | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	295,300	306,100
PSNH | Securitized Stranded Costs | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	295,300	306,100
PSNH | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	2,700	3,000
PSNH | Other Regulatory Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Other Regulatory Liabilities (included in Regulatory Liabilities)	9,100	7,300
Accrued Interest (included in Other Current Liabilities)	1,900	5,100
PSNH | Current Derivative Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	22,200	38,300
PSNH | Current Derivative Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	18,400	30,600
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