RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 6,389,200	$ 5,578,300
Regulatory Liabilities	4,022,923	3,930,305
Accrued Interest (included in Other Current Liabilities)	1,081,981	989,053
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	$ 367,282	$ 410,492
Other Current Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash and Cash Equivalents, Statement of Financial Position [Extensible Enumeration]	Prepayments and Other Current Assets	Prepayments and Other Current Assets
Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	$ 17,300	$ 19,600
Restricted Cash and Cash Equivalents, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Assets	Other Long-Term Assets
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 392,500	$ 435,700
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	339,000	322,500
PSNH
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	963,300	696,200
Regulatory Liabilities	393,574	391,628
Accrued Interest (included in Other Current Liabilities)	72,328	59,616
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	367,282	410,492
PSNH | Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	3,200	3,200
PSNH | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	392,500	435,700
PSNH | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	8,000	14,400
Variable Interest Entity, Primary Beneficiary | PSNH
Condensed Balance Sheet Statements, Captions [Line Items]
Rate Reduction Bonds - Current Portion	43,200	43,200
Rate Reduction Bonds - Long-Term Portion	367,300	410,500
Variable Interest Entity, Primary Beneficiary | PSNH | Other Current Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	30,000	32,400
Variable Interest Entity, Primary Beneficiary | PSNH | Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	3,200	3,200
Variable Interest Entity, Primary Beneficiary | PSNH | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	392,500	435,700
Variable Interest Entity, Primary Beneficiary | PSNH | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Regulatory Liabilities	5,300	6,000
Accrued Interest (included in Other Current Liabilities)	$ 6,300	$ 6,900