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REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | $ 7,018,000 | $ 6,389,200
Less: Current Portion | 2,024,897 | 1,674,196
Total Long-Term Regulatory Assets | 4,993,145 | 4,714,970
Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 2,077,200 | 1,785,900
Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 1,638,100 | 1,319,200
Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 1,096,000 | 1,117,300
Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 944,900 | 912,400
Securitized Stranded Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 360,100 | 392,500
Goodwill-related |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 251,500 | 264,100
Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 147,000 | 137,900
Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 72,600 | 120,900
Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 430,600 | 339,000
CL&P |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 2,426,700 | 2,143,200
Less: Current Portion | 672,835 | 480,369
Total Long-Term Regulatory Assets | 1,753,887 | 1,662,778
CL&P | Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 998,300 | 896,600
CL&P | Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 529,300 | 354,500
CL&P | Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 198,200 | 197,400
CL&P | Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 522,700 | 512,600
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 | Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 40,500 | 38,500
CL&P | Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 72,600 | 120,900
CL&P | Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 65,100 | 22,700
NSTAR Electric |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 2,049,800 | 1,957,900
Less: Current Portion | 778,916 | 676,083
Total Long-Term Regulatory Assets | 1,270,882 | 1,281,836
NSTAR Electric | Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 626,300 | 609,100
NSTAR Electric | Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 572,600 | 482,900
NSTAR Electric | Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 313,800 | 336,700
NSTAR Electric | Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 141,600 | 128,600
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 | 215,900 | 226,700
NSTAR Electric | Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 76,800 | 72,300
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 | 102,800 | 101,600
PSNH |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 1,075,200 | 963,300
Less: Current Portion | 170,501 | 189,450
Total Long-Term Regulatory Assets | 904,717 | 773,783
PSNH | Storm Costs, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 452,600 | 280,200
PSNH | Regulatory Tracking Mechanisms |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 153,900 | 182,200
PSNH | Benefit Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 79,700 | 79,300
PSNH | Income Taxes, Net |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 19,100 | 16,400
PSNH | Securitized Stranded Costs |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 360,100 | 392,500
PSNH | Goodwill-related |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
PSNH | Asset Retirement Obligations |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 5,000 | 4,700
PSNH | Derivative Liabilities |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | 0 | 0
PSNH | Other Regulatory Assets |  |
Regulatory Assets [Line Items] |  |
Total Regulatory Assets | $ 4,800 | $ 8,000

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