LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Jan. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Long-Term Debt	$ 26,872,433		$ 25,701,627
Less Amounts due Within One Year	(1,392,948)		(1,003,150)
Senior Notes
Debt Instrument [Line Items]
Unamortized Premiums and Discounts, Net	37,800		41,700
Unamortized Debt Issuance Costs	(64,500)		(76,100)
Long-Term Debt	26,872,400		25,701,600
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-Term Debt	5,900		5,600
Fair Value Adjustment
Debt Instrument [Line Items]
Long-Term Debt	11,600		0
Fair Value Adjustment - Current Portion
Debt Instrument [Line Items]
Long-Term Debt	(2,400)		0
Loans Payable
Debt Instrument [Line Items]
Less Amounts due Within One Year	(1,090,500)		(750,300)
Total Other Long-Term Debt
Debt Instrument [Line Items]
Long-Term Debt	14,085,400		14,016,400
Eversource
Debt Instrument [Line Items]
Long-Term Debt	10,346,488		10,729,256
Less Amounts due Within One Year	(1,002,439)		(600,000)
Eversource | Senior Notes | Eversource Parent - Senior Notes due 2026 - 2050
Debt Instrument [Line Items]
Long-Term Debt	$ 11,350,000		11,350,000
Eversource | Senior Notes | Eversource Parent - Senior Notes due 2026 - 2050 | Minimum
Debt Instrument [Line Items]
Interest Rate	1.40%
Eversource | Senior Notes | Eversource Parent - Senior Notes due 2026 - 2050 | Maximum
Debt Instrument [Line Items]
Interest Rate	5.95%
CL&P
Debt Instrument [Line Items]
Long-Term Debt	$ 5,110,067		5,108,173
Long-Term Debt, Due Within One Year	0		(400,000)
Current Portion Classified as Long-Term Debt		$ 397,100
Less Amounts due Within One Year	0		(2,944)
CL&P | First Mortgage Bonds
Debt Instrument [Line Items]
Long-Term Debt	5,130,000		5,130,000
Current Portion Classified as Long-Term Debt	0		397,100
Unamortized Premiums and Discounts, Net	12,400		14,300
Unamortized Debt Issuance Costs	(32,300)		(33,200)
Long-Term Debt	$ 5,110,100		5,108,200
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	$ 0		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		350,000
CL&P | First Mortgage Bonds | 2024 Series B due 2034
Debt Instrument [Line Items]
Interest Rate	4.95%
Long-Term Debt	$ 300,000		300,000
CL&P | First Mortgage Bonds | 2025 Series A due 2030
Debt Instrument [Line Items]
Interest Rate	4.95%
Long-Term Debt	$ 400,000		0
NSTAR Electric
Debt Instrument [Line Items]
Long-Term Debt	5,645,638		4,844,920
Less Amounts due Within One Year	(300,000)		(250,000)
NSTAR Electric | Unsecured Debt
Debt Instrument [Line Items]
Long-Term Debt	5,850,000		5,000,000
Unamortized Premiums and Discounts, Net	(8,100)		(14,000)
Unamortized Debt Issuance Costs	(36,300)		(31,100)
Less Amounts due Within One Year	(300,000)		(250,000)
Long-Term Debt	$ 5,645,600		4,844,900
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	$ 0		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		600,000
NSTAR Electric | Unsecured Debt | 2025 Debentures due 2030
Debt Instrument [Line Items]
Interest Rate	4.85%
Long-Term Debt	$ 400,000		0
NSTAR Electric | Unsecured Debt | 2025 Debentures due 2035
Debt Instrument [Line Items]
Interest Rate	5.20%
Long-Term Debt	$ 700,000		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	2,031,323		1,732,066
PSNH | First Mortgage Bonds
Debt Instrument [Line Items]
Long-Term Debt	2,050,000		1,750,000
Unamortized Premiums and Discounts, Net	(2,800)		(2,600)
Unamortized Debt Issuance Costs	(15,900)		(15,300)
Long-Term Debt	$ 2,031,300		1,732,100
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		600,000
PSNH | First Mortgage Bonds | 2025 Series Y due 2028
Debt Instrument [Line Items]
Interest Rate	4.40%
Long-Term Debt	$ 300,000		0
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2026 - 2051
Debt Instrument [Line Items]
Long-Term Debt	$ 1,205,000		1,095,000
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2026 - 2051 | Minimum
Debt Instrument [Line Items]
Interest Rate	1.38%
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds due 2026 - 2051 | Maximum
Debt Instrument [Line Items]
Interest Rate	5.74%
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2029 - 2051
Debt Instrument [Line Items]
Long-Term Debt	$ 1,055,000		905,000
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2029 - 2051 | Minimum
Debt Instrument [Line Items]
Interest Rate	2.25%
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds due 2029 - 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	$ 933,000		808,000
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	$ 596,600		596,800
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	$ 47,900		$ 40,700
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%