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REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | $ 6,731,900 | $ 7,070,700
Less: Current Portion | 1,823,417 | 2,189,660
Total Long-Term Regulatory Assets | 4,908,519 | 4,880,974
Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 2,003,000 | 2,039,400
Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 1,450,000 | 1,781,600
Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 991,500 | 968,400
Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 985,800 | 967,400
Securitized Stranded Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 327,700 | 349,300
Goodwill-related |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 238,800 | 247,200
Cost of Removal |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 232,600 | 198,400
Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 156,400 | 150,200
Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 26,300 | 57,200
Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 319,800 | 311,600
CL&P |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 2,093,400 | 2,325,500
Less: Current Portion | 408,514 | 638,529
Total Long-Term Regulatory Assets | 1,684,883 | 1,687,029
CL&P | Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 979,800 | 971,100
CL&P | Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 301,200 | 507,700
CL&P | Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 530,100 | 521,000
CL&P | Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 169,100 | 168,800
CL&P | Securitized Stranded Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
CL&P | Goodwill-related |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
CL&P | Cost of Removal |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
CL&P | Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 42,700 | 41,200
CL&P | Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 26,300 | 57,200
CL&P | Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 44,200 | 58,500
NSTAR Electric |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 2,056,600 | 2,107,100
Less: Current Portion | 900,764 | 902,770
Total Long-Term Regulatory Assets | 1,155,758 | 1,204,337
NSTAR Electric | Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 554,000 | 609,800
NSTAR Electric | Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 648,800 | 650,000
NSTAR Electric | Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 153,900 | 145,400
NSTAR Electric | Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 304,500 | 293,600
NSTAR Electric | Securitized Stranded Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
NSTAR Electric | Goodwill-related |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 205,000 | 212,300
NSTAR Electric | Cost of Removal |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 8,300 | 8,500
NSTAR Electric | Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 81,400 | 78,300
NSTAR Electric | Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
NSTAR Electric | Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 100,700 | 109,200
PSNH |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 1,014,100 | 1,065,700
Less: Current Portion | 125,497 | 173,267
Total Long-Term Regulatory Assets | 888,626 | 892,411
PSNH | Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 469,200 | 458,500
PSNH | Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 123,800 | 162,800
PSNH | Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 20,000 | 20,700
PSNH | Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 64,800 | 65,600
PSNH | Securitized Stranded Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 327,700 | 349,300
PSNH | Goodwill-related |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
PSNH | Cost of Removal |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
PSNH | Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 5,300 | 5,100
PSNH | Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
PSNH | Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | $ 3,300 | $ 3,700

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