v3.26.1
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Components of Other Income, Net (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Summary of Accounting Policies [Line Items]        
Other Income, Net $ 144,033 $ 95,363 $ 245,192 $ 187,706
Proceeds from sale of intangible assets 36,000      
Pension, SERP and PBOP Non-Service   Income Components, Net of Deferred Portion        
Summary of Accounting Policies [Line Items]        
Other Income, Net 42,300 35,500 86,500 68,100
AFUDC Equity        
Summary of Accounting Policies [Line Items]        
Other Income, Net 30,900 25,600 54,800 49,500
Equity in Earnings of Unconsolidated Affiliates        
Summary of Accounting Policies [Line Items]        
Other Income, Net 5,100 4,800 8,900 10,800
Investment (Loss)/Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net (3,400) (2,000) (3,100) (4,000)
Interest Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net 32,600 30,800 61,000 64,800
Other        
Summary of Accounting Policies [Line Items]        
Other Income, Net 36,500 700 37,100 (1,500)
CL&P        
Summary of Accounting Policies [Line Items]        
Other Income, Net 17,216 12,498 34,831 30,096
CL&P | Pension, SERP and PBOP Non-Service   Income Components, Net of Deferred Portion        
Summary of Accounting Policies [Line Items]        
Other Income, Net 11,300 9,300 23,200 17,600
CL&P | AFUDC Equity        
Summary of Accounting Policies [Line Items]        
Other Income, Net 6,800 1,500 11,400 5,100
CL&P | Equity in Earnings of Unconsolidated Affiliates        
Summary of Accounting Policies [Line Items]        
Other Income, Net 0 0 0 0
CL&P | Investment (Loss)/Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net (1,500) (900) (1,600) (800)
CL&P | Interest Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net 600 2,500 1,800 8,100
CL&P | Other        
Summary of Accounting Policies [Line Items]        
Other Income, Net 0 100 0 100
NSTAR Electric        
Summary of Accounting Policies [Line Items]        
Other Income, Net 54,098 47,715 105,783 94,009
NSTAR Electric | Pension, SERP and PBOP Non-Service   Income Components, Net of Deferred Portion        
Summary of Accounting Policies [Line Items]        
Other Income, Net 18,300 15,400 37,300 30,200
NSTAR Electric | AFUDC Equity        
Summary of Accounting Policies [Line Items]        
Other Income, Net 16,800 14,700 32,500 28,800
NSTAR Electric | Equity in Earnings of Unconsolidated Affiliates        
Summary of Accounting Policies [Line Items]        
Other Income, Net 100 200 200 400
NSTAR Electric | Investment (Loss)/Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net (100) (200) 300 (2,000)
NSTAR Electric | Interest Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net 19,000 17,600 35,400 36,600
NSTAR Electric | Other        
Summary of Accounting Policies [Line Items]        
Other Income, Net 0 0 100 0
PSNH        
Summary of Accounting Policies [Line Items]        
Other Income, Net 10,358 13,725 20,861 24,484
PSNH | Pension, SERP and PBOP Non-Service   Income Components, Net of Deferred Portion        
Summary of Accounting Policies [Line Items]        
Other Income, Net 5,100 4,600 10,300 8,700
PSNH | AFUDC Equity        
Summary of Accounting Policies [Line Items]        
Other Income, Net 2,700 4,500 5,000 8,400
PSNH | Equity in Earnings of Unconsolidated Affiliates        
Summary of Accounting Policies [Line Items]        
Other Income, Net 0 0 0 0
PSNH | Investment (Loss)/Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net (700) (400) (700) (300)
PSNH | Interest Income        
Summary of Accounting Policies [Line Items]        
Other Income, Net 3,200 5,000 6,200 7,700
PSNH | Other        
Summary of Accounting Policies [Line Items]        
Other Income, Net $ 100 $ 0 $ 100 $ 0