LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Long-Term Debt	$ 19,723,994	$ 17,023,577
Long-Term Debt – Current Portion	1,320,129	1,193,097
Senior Notes
Debt Instrument [Line Items]
Unamortized Premiums and Discounts, Net	40,100	43,400
Unamortized Debt Issuance Costs	(49,400)	(36,300)
Long-Term Debt	19,724,000	17,023,600
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-Term Debt	11,900	11,700
Fair Value Adjustment
Debt Instrument [Line Items]
Long-Term Debt	26,200	43,800
Fair Value Adjustment - Current Portion
Debt Instrument [Line Items]
Long-Term Debt	(7,000)	(17,700)
Loans Payable
Debt Instrument [Line Items]
Long-Term Debt – Current Portion	1,203,400	775,400
Total Other Long-Term Debt
Debt Instrument [Line Items]
Long-Term Debt	10,027,500	8,059,000
Eversource
Debt Instrument [Line Items]
Long-Term Debt	6,972,804	5,395,840
Long-Term Debt – Current Portion	1,207,047	767,681
Eversource \| Unsecured Debt \| Eversource Parent - Senior Notes due 2023 - 2050
Debt Instrument [Line Items]
Long-Term Debt	$ 8,150,000	6,100,000
Eversource \| Unsecured Debt \| Eversource Parent - Senior Notes due 2023 - 2050 \| Minimum
Debt Instrument [Line Items]
Interest rate	0.80%
Eversource \| Unsecured Debt \| Eversource Parent - Senior Notes due 2023 - 2050 \| Maximum
Debt Instrument [Line Items]
Interest rate	4.60%
CL&P
Debt Instrument [Line Items]
Long-Term Debt	$ 4,216,488	4,215,379
Long-Term Debt – Current Portion	400,000	0
CL&P \| First Mortgage Bonds
Debt Instrument [Line Items]
Long-Term Debt	4,219,800	4,219,800
Unamortized Premiums and Discounts, Net	21,500	23,100
Unamortized Debt Issuance Costs	(24,800)	(27,500)
Long-Term Debt	$ 4,216,500	4,215,400
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	$ 400,000	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 \| Commercial Paper
Debt Instrument [Line Items]
Long-Term Debt	400,000
Long-Term Debt – Current Portion	400,000	0
NSTAR Electric
Debt Instrument [Line Items]
Long-Term Debt	4,345,085	3,585,399
Long-Term Debt – Current Portion	80,000	400,000
NSTAR Electric \| Unsecured Debt
Debt Instrument [Line Items]
Long-Term Debt	4,250,000	3,800,000
Long-Term Debt – Current Portion	80,000	400,000
Unamortized Premiums and Discounts, Net	(14,800)	(11,200)
Unamortized Debt Issuance Costs	(30,100)	(23,400)
Long-Term Debt	$ 4,345,100	3,585,400
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 \| 2012 Debentures due 2022
Debt Instrument [Line Items]
Interest rate	2.375%
Long-Term Debt	$ 0	400,000
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	0
NSTAR Electric \| Unsecured Debt \| 2022 Debentures due 2052
Debt Instrument [Line Items]
Interest rate	4.95%
Long-Term Debt	$ 400,000	0
NSTAR Electric \| Senior Notes
Debt Instrument [Line Items]
Long-Term Debt	$ 220,000	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	$ 80,000	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	1,134,914	1,163,833
Long-Term Debt – Current Portion	29,668	0
PSNH \| First Mortgage Bonds
Debt Instrument [Line Items]
Long-Term Debt	1,175,000	1,175,000
Long-Term Debt – Current Portion	325,000	0
Unamortized Premiums and Discounts, Net	(2,500)	(2,600)
Unamortized Debt Issuance Costs	(7,900)	(8,600)
Long-Term Debt	$ 1,134,900	1,163,800
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	$ 325,000	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 \| Commercial Paper
Debt Instrument [Line Items]
Long-Term Debt	295,300
Long-Term Debt – Current Portion	295,300	0
Yankee Gas \| First Mortgage Bonds \| Yankee Gas - First Mortgage Bonds due 2024 - 2051
Debt Instrument [Line Items]
Long-Term Debt	$ 845,000	765,000
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	5.35%
NSTAR Gas \| First Mortgage Bonds \| NSTAR Gas - First Mortgage Bonds due 2025 - 2051
Debt Instrument [Line Items]
Long-Term Debt	$ 705,000	580,000
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 \| EGMA - First Mortgage Bonds due 2031 - 2052
Debt Instrument [Line Items]
Long-Term Debt	$ 650,000	550,000
EGMA \| First Mortgage Bonds \| EGMA - First Mortgage Bonds due 2031 - 2052 \| Minimum
Debt Instrument [Line Items]
Interest rate	2.11%
EGMA \| First Mortgage Bonds \| EGMA - First Mortgage Bonds due 2031 - 2052 \| Maximum
Debt Instrument [Line Items]
Interest rate	4.70%
Aquarion \| Unsecured Debt \| Aquarion - Unsecured Notes due 2023 - 2052
Debt Instrument [Line Items]
Long-Term Debt	$ 464,700	394,900
Aquarion \| Unsecured Debt \| Aquarion - Unsecured Notes due 2023 - 2052 \| Minimum
Debt Instrument [Line Items]
Interest rate	0.00%
Aquarion \| Unsecured Debt \| Aquarion - Unsecured Notes due 2023 - 2052 \| Maximum
Debt Instrument [Line Items]
Interest rate	6.43%
Aquarion \| Secured Debt \| Aquarion - Secured Debt due 2023 - 2044
Debt Instrument [Line Items]
Long-Term Debt	$ 34,400	39,600
Aquarion \| Secured Debt \| Aquarion - Secured Debt due 2023 - 2044 \| Minimum
Debt Instrument [Line Items]
Interest rate	2.864%
Aquarion \| Secured Debt \| Aquarion - Secured Debt due 2023 - 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

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt discount (premium).

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

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