RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 5,534,600	$ 5,514,700
Regulatory Liabilities	3,679,927	3,658,042
Accrued Interest (included in Other Current Liabilities)	694,252	836,834
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	518,517	540,122
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	543,700	565,300
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	127,600	125,400
Special Deposits
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	63,400	52,500
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)	949,200	945,800
Regulatory Liabilities	405,773	413,381
Accrued Interest (included in Other Current Liabilities)	26,958	32,736
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	518,517	540,122
PSNH | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Rate Reduction Bonds - Current Portion	43,200	43,200
Rate Reduction Bonds - Long-Term Portion	518,500	540,100
PSNH | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	543,700	565,300
PSNH | Securitized Stranded Costs | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	543,700	565,300
PSNH | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	14,800	14,700
PSNH | Other Regulatory Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Regulatory Liabilities	4,100	5,600
Accrued Interest (included in Other Current Liabilities)	8,300	8,600
PSNH | Special Deposits
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	30,900	32,500
PSNH | Special Deposits | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	30,600	32,500
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