v3.26.1
FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption $ 155,568 $ 155,568
Rate Reduction Bonds 259,257 280,862
Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 155,600 155,600
Long-Term Debt 29,111,600 28,265,400
Rate Reduction Bonds 302,500 324,100
Fair Value | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 123,700 126,100
Long-Term Debt 27,713,400 27,055,500
Rate Reduction Bonds 294,600 320,200
CL&P    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 116,200 116,200
CL&P | Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 116,200 116,200
Long-Term Debt 5,111,300 5,110,100
Rate Reduction Bonds 0 0
CL&P | Fair Value | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 91,100 92,900
Long-Term Debt 4,782,800 4,844,700
Rate Reduction Bonds 0 0
NSTAR Electric    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 43,000 43,000
NSTAR Electric | Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 43,000 43,000
Long-Term Debt 6,341,800 5,945,600
Rate Reduction Bonds 0 0
NSTAR Electric | Fair Value | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 32,600 33,200
Long-Term Debt 6,089,200 5,752,600
Rate Reduction Bonds 0 0
PSNH    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Rate Reduction Bonds 259,257 280,862
PSNH | Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 0 0
Long-Term Debt 2,234,500 2,031,300
Rate Reduction Bonds 302,500 324,100
PSNH | Fair Value | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Preferred Stock Not Subject to Mandatory Redemption 0 0
Long-Term Debt 2,054,100 1,874,800
Rate Reduction Bonds $ 294,600 $ 320,200