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