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LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 23,588,616 | $ 19,723,994
Less Amounts due Within One Year | (824,847) | (1,320,129)
Current Maturities Classified as Long-Term Debt | 990,900 | 0
Senior Notes |  |
Debt Instrument [Line Items] |  |
Unamortized Premiums and Discounts, Net | 49,700 | 40,100
Unamortized Debt Issuance Costs | (65,000) | (49,400)
Long-Term Debt | 23,588,600 | 19,724,000
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 12,500 | 11,900
Fair Value Adjustment |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 19,300 | 26,200
Fair Value Adjustment - Current Portion |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | (5,500) | (7,000)
Loans Payable |  |
Debt Instrument [Line Items] |  |
Less Amounts due Within One Year | (1,810,200) | (1,203,400)
Total Other Long-Term Debt |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 12,845,700 | 10,027,500
Commercial Paper |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 990,900 |
Eversource |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 9,952,351 | 6,972,804
Less Amounts due Within One Year | (364,653) | (1,207,047)
Eversource | Unsecured Debt | Eversource Parent - Senior Notes due 2024 - 2050 |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 10,300,000 | 8,150,000
Eversource | Unsecured Debt | Eversource Parent - Senior Notes due 2024 - 2050 | Minimum |  |
Debt Instrument [Line Items] |  |
Interest rate | 0.80% |
Eversource | Unsecured Debt | Eversource Parent - Senior Notes due 2024 - 2050 | Maximum |  |
Debt Instrument [Line Items] |  |
Interest rate | 5.95% |
CL&P |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 4,814,429 | 4,216,488
Less Amounts due Within One Year | (139,800) | (400,000)
CL&P | First Mortgage Bonds |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 4,619,800 | 4,219,800
Current Maturities Classified as Long-Term Debt | 139,800 | 400,000
Unamortized Premiums and Discounts, Net | 18,000 | 21,500
Unamortized Debt Issuance Costs | (30,700) | (24,800)
Long-Term Debt | $ 4,814,400 | 4,216,500
CL&P | First Mortgage Bonds | 1994 Series D due 2024 |  |
Debt Instrument [Line Items] |  |
Interest rate | 7.875% |
Long-Term Debt | $ 139,800 | 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 | 2013 Series A due 2023 |  |
Debt Instrument [Line Items] |  |
Interest rate | 2.50% |
Long-Term Debt | $ 0 | 400,000
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 | 0
CL&P | First Mortgage Bonds | 2023 Series B due 2033 |  |
Debt Instrument [Line Items] |  |
Interest rate | 4.90% |
Long-Term Debt | $ 300,000 | 0
CL&P | Commercial Paper |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 139,800 | 400,000
Current Maturities Classified as Long-Term Debt | 207,300 | 0
NSTAR Electric |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 4,496,947 | 4,345,085
Less Amounts due Within One Year | 0 | (80,000)
NSTAR Electric | Unsecured Debt |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 4,400,000 | 4,250,000
Less Amounts due Within One Year | 0 | (80,000)
Unamortized Premiums and Discounts, Net | (14,000) | (14,800)
Unamortized Debt Issuance Costs | (29,100) | (30,100)
Long-Term Debt | $ 4,496,900 | 4,345,100
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 | 0
NSTAR Electric | Senior Notes |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 140,000 | 220,000
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 | 2013 Senior Notes Series G due 2023 |  |
Debt Instrument [Line Items] |  |
Interest rate | 3.88% |
Long-Term Debt | $ 0 | 80,000
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 | 1,431,591 | 1,134,914
Less Amounts due Within One Year | 0 | (29,668)
PSNH | First Mortgage Bonds |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | 1,450,000 | 1,175,000
Less Amounts due Within One Year | 0 | (325,000)
Unamortized Premiums and Discounts, Net | (4,900) | (2,500)
Unamortized Debt Issuance Costs | (13,500) | (7,900)
Long-Term Debt | $ 1,431,600 | 1,134,900
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 | 2013 Series S due 2023 |  |
Debt Instrument [Line Items] |  |
Interest rate | 3.50% |
Long-Term Debt | $ 0 | 325,000
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 | 0
PSNH | First Mortgage Bonds | 2023 Series X due 2033 |  |
Debt Instrument [Line Items] |  |
Interest rate | 5.35% |
Long-Term Debt | $ 300,000 | 0
PSNH | Commercial Paper |  |
Debt Instrument [Line Items] |  |
Long-Term Debt |  | 295,300
Current Maturities Classified as Long-Term Debt | 0 | 295,300
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2024 - 2051 |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 1,015,000 | 845,000
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2024 - 2051 | Minimum |  |
Debt Instrument [Line Items] |  |
Interest rate | 1.38% |
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2024 - 2051 | Maximum |  |
Debt Instrument [Line Items] |  |
Interest rate | 5.51% |
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2025 - 2051 |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 705,000 | 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 | $ 708,000 | 650,000
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 | $ 527,000 | 464,700
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 - 2044 |  |
Debt Instrument [Line Items] |  |
Long-Term Debt | $ 39,000 | 34,400
Aquarion | Secured Debt | Aquarion - Secured Debt due 2027 - 2044 | Minimum |  |
Debt Instrument [Line Items] |  |
Interest rate | 1.55% |
Aquarion | Secured Debt | Aquarion - Secured Debt due 2027 - 2044 | 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 | $ 360,000 | $ 360,000

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