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LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands | Jan. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 25,701,627 | $ 23,588,616
Less Amounts due Within One Year |  | (1,003,150) | (824,847)
Current Portion Classified as Long-Term Debt |  | 0 | 990,900
Senior Notes |  |  |
Debt Instrument [Line Items] |  |  |
Unamortized Premiums and Discounts, Net |  | 41,700 | 49,700
Unamortized Debt Issuance Costs |  | (76,100) | (65,000)
Long-Term Debt |  | 25,701,600 | 23,588,600
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 5,600 | 12,500
Fair Value Adjustment |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 0 | 19,300
Fair Value Adjustment - Current Portion |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 0 | (5,500)
Loans Payable |  |  |
Debt Instrument [Line Items] |  |  |
Less Amounts due Within One Year |  | (750,300) | (1,810,200)
Total Other Long-Term Debt |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 14,016,400 | 12,845,700
Commercial Paper |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  |  | 990,900
Eversource |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 10,729,256 | 9,952,351
Less Amounts due Within One Year |  | (600,000) | (364,653)
Eversource | Unsecured Debt | Eversource Parent - Senior Notes due 2025 - 2050 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 11,350,000 | 10,300,000
Eversource | Unsecured Debt | Eversource Parent - Senior Notes due 2025 - 2050 | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 0.80% |
Eversource | Unsecured Debt | Eversource Parent - Senior Notes due 2025 - 2050 | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.95% |
CL&P |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 5,108,173 | 4,814,429
Long-Term Debt, Due Within One Year |  | (400,000) | (139,800)
Less Amounts due Within One Year |  | (2,944) | 0
CL&P | Subsequent Event |  |  |
Debt Instrument [Line Items] |  |  |
Current Portion Classified as Long-Term Debt | $ 397,100 |  |
CL&P | First Mortgage Bonds |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 5,130,000 | 4,619,800
Current Portion Classified as Long-Term Debt |  | 397,100 | 139,800
Unamortized Premiums and Discounts, Net |  | 14,300 | 18,000
Unamortized Debt Issuance Costs |  | (33,200) | (30,700)
Long-Term Debt |  | $ 5,108,200 | 4,814,400
CL&P | First Mortgage Bonds | 1994 Series D due 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 7.875% |
Long-Term Debt |  | $ 0 | 139,800
CL&P | First Mortgage Bonds | 2004 Series B due 2034 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.75% |
Long-Term Debt |  | $ 130,000 | 130,000
CL&P | First Mortgage Bonds | 2005 Series B due 2035 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.625% |
Long-Term Debt |  | $ 100,000 | 100,000
CL&P | First Mortgage Bonds | 2006 Series A due 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 6.35% |
Long-Term Debt |  | $ 250,000 | 250,000
CL&P | First Mortgage Bonds | 2007 Series B due 2037 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.75% |
Long-Term Debt |  | $ 150,000 | 150,000
CL&P | First Mortgage Bonds | 2007 Series D due 2037 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 6.375% |
Long-Term Debt |  | $ 100,000 | 100,000
CL&P | First Mortgage Bonds | 2014 Series A due 2044 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.30% |
Long-Term Debt |  | $ 475,000 | 475,000
CL&P | First Mortgage Bonds | 2015 Series A due 2045 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.15% |
Long-Term Debt |  | $ 350,000 | 350,000
CL&P | First Mortgage Bonds | 2017 Series A due 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.20% |
Long-Term Debt |  | $ 500,000 | 500,000
CL&P | First Mortgage Bonds | 2018 Series A due 2048 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.00% |
Long-Term Debt |  | $ 800,000 | 800,000
CL&P | First Mortgage Bonds | 2020 Series A due 2025 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 0.75% |
Long-Term Debt |  | $ 400,000 | 400,000
CL&P | First Mortgage Bonds | 2021 Series A due 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.05% |
Long-Term Debt |  | $ 425,000 | 425,000
CL&P | First Mortgage Bonds | 2023 Series A due 2053 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.25% |
Long-Term Debt |  | $ 500,000 | 500,000
CL&P | First Mortgage Bonds | 2023 Series B due 2033 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.90% |
Long-Term Debt |  | $ 300,000 | 300,000
CL&P | First Mortgage Bonds | 2024 Series A due 2029 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.65% |
Long-Term Debt |  | $ 350,000 | 0
CL&P | First Mortgage Bonds | 2024 Series B due 2034 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.95% |
Long-Term Debt |  | $ 300,000 | 0
CL&P | Commercial Paper |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  |  | 139,800
Current Portion Classified as Long-Term Debt |  | 0 | 207,300
NSTAR Electric |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 4,844,920 | 4,496,947
Less Amounts due Within One Year |  | (250,000) | 0
NSTAR Electric | Unsecured Debt |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 5,000,000 | 4,400,000
Less Amounts due Within One Year |  | (250,000) | 0
Unamortized Premiums and Discounts, Net |  | (14,000) | (14,000)
Unamortized Debt Issuance Costs |  | (31,100) | (29,100)
Long-Term Debt |  | $ 4,844,900 | 4,496,900
NSTAR Electric | Unsecured Debt | 2006 Debentures due 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.75% |
Long-Term Debt |  | $ 200,000 | 200,000
NSTAR Electric | Unsecured Debt | 2010 Debentures due 2040 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.50% |
Long-Term Debt |  | $ 300,000 | 300,000
NSTAR Electric | Unsecured Debt | 2014 Debentures due 2044 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.40% |
Long-Term Debt |  | $ 300,000 | 300,000
NSTAR Electric | Unsecured Debt | 2015 Debentures due 2025 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.25% |
Long-Term Debt |  | $ 250,000 | 250,000
NSTAR Electric | Unsecured Debt | 2016 Debentures due 2026 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.70% |
Long-Term Debt |  | $ 250,000 | 250,000
NSTAR Electric | Unsecured Debt | 2017 Debentures due 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.20% |
Long-Term Debt |  | $ 700,000 | 700,000
NSTAR Electric | Unsecured Debt | 2019 Debentures due 2029 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.25% |
Long-Term Debt |  | $ 400,000 | 400,000
NSTAR Electric | Unsecured Debt | 2020 Debentures due 2030 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.95% |
Long-Term Debt |  | $ 400,000 | 400,000
NSTAR Electric | Unsecured Debt | 2021 Debentures due 2051 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.10% |
Long-Term Debt |  | $ 300,000 | 300,000
NSTAR Electric | Unsecured Debt | 2021 Debentures due 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 1.95% |
Long-Term Debt |  | $ 300,000 | 300,000
NSTAR Electric | Unsecured Debt | 2022 Debentures due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.55% |
Long-Term Debt |  | $ 450,000 | 450,000
NSTAR Electric | Unsecured Debt | 2022 Debentures due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.95% |
Long-Term Debt |  | $ 400,000 | 400,000
NSTAR Electric | Unsecured Debt | 2023 Debentures due 2028 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.60% |
Long-Term Debt |  | $ 150,000 | 150,000
NSTAR Electric | Unsecured Debt | 2024 Debentures due 2034 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.40% |
Long-Term Debt |  | $ 600,000 | 0
NSTAR Electric | Senior Notes |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 140,000 | 140,000
NSTAR Electric | Senior Notes | 2004 Senior Notes Series B due 2034 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.90% |
Long-Term Debt |  | $ 50,000 | 50,000
NSTAR Electric | Senior Notes | 2007 Senior Notes Series D due 2037 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 6.70% |
Long-Term Debt |  | $ 40,000 | 40,000
NSTAR Electric | Senior Notes | 2016 Senior Notes Series H due 2026 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.75% |
Long-Term Debt |  | $ 50,000 | 50,000
PSNH |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 1,732,066 | 1,431,591
PSNH | First Mortgage Bonds |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | 1,750,000 | 1,450,000
Unamortized Premiums and Discounts, Net |  | (2,600) | (4,900)
Unamortized Debt Issuance Costs |  | (15,300) | (13,500)
Long-Term Debt |  | $ 1,732,100 | 1,431,600
PSNH | First Mortgage Bonds | 2005 Series M due 2035 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.60% |
Long-Term Debt |  | $ 50,000 | 50,000
PSNH | First Mortgage Bonds | 2019 Series T due 2049 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.60% |
Long-Term Debt |  | $ 300,000 | 300,000
PSNH | First Mortgage Bonds | 2020 Series U due 2050 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.40% |
Long-Term Debt |  | $ 150,000 | 150,000
PSNH | First Mortgage Bonds | 2021 Series V due 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.20% |
Long-Term Debt |  | $ 350,000 | 350,000
PSNH | First Mortgage Bonds | 2023 Series W due 2053 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.15% |
Long-Term Debt |  | $ 300,000 | 300,000
PSNH | First Mortgage Bonds | 2023 Series X due 2033 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.35% |
Long-Term Debt |  | $ 600,000 | 300,000
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2025 - 2051 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 1,095,000 | 1,015,000
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2025 - 2051 | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 1.38% |
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2025 - 2051 | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.74% |
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2025 - 2051 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 905,000 | 705,000
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2025 - 2051 | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.25% |
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2025 - 2051 | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 7.11% |
EGMA | First Mortgage Bonds | Aquarion - Unsecured Notes due 2028 - 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 808,000 | 708,000
EGMA | First Mortgage Bonds | Aquarion - Unsecured Notes due 2028 - 2052 | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 2.11% |
EGMA | First Mortgage Bonds | Aquarion - Unsecured Notes due 2028 - 2052 | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 5.73% |
Aquarion | Unsecured Debt | Aquarion - Unsecured Notes due 2028 - 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 596,800 | 527,000
Aquarion | Unsecured Debt | Aquarion - Unsecured Notes due 2028 - 2052 | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 3.00% |
Aquarion | Unsecured Debt | Aquarion - Unsecured Notes due 2028 - 2052 | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 6.43% |
Aquarion | Secured Debt | Aquarion - Secured Debt due 2027 - 2045 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt |  | $ 40,700 | 39,000
Aquarion | Secured Debt | Aquarion - Secured Debt due 2027 - 2045 | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 1.296% |
Aquarion | Secured Debt | Aquarion - Secured Debt due 2027 - 2045 | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 9.29% |
Aquarion | Senior Notes | Aquarion - Senior Notes due 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate |  | 4.00% |
Long-Term Debt |  | $ 0 | $ 360,000

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