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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No definition available.

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- Definition

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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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

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

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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 after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 08, 2017
Debt Instrument [Line Items]
Long-Term Debt	$ 13,770,828,000	$ 12,248,743,000
Less Amounts due in One Year	(327,411,000)	(837,319,000)
Senior Notes
Debt Instrument [Line Items]
Unamortized Premiums and Discounts, Net	(4,100,000)	(4,200,000)
Unamortized Debt Issuance Costs	(20,600,000)	(23,200,000)
Long-term debt	13,770,800,000	12,248,700,000
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-Term Debt	11,600,000	39,500,000
Fair Value Adjustment
Debt Instrument [Line Items]
Long-Term Debt	109,100,000	144,700,000
Fair Value Adjustment - Current Portion
Debt Instrument [Line Items]
Long-Term Debt	(31,300,000)	(36,200,000)
Loans Payable
Debt Instrument [Line Items]
Less Amounts due in One Year	(201,100,000)	(401,100,000)
Total Other Long-Term Debt
Debt Instrument [Line Items]
Long-Term Debt	6,054,000,000.0	5,644,700,000
CL&P
Debt Instrument [Line Items]
Long-Term Debt	3,518,136,000	3,004,016,000
Less Amounts due in One Year	0	(250,000,000)
CL&P \| 4.375% Fixed Rate Tax Exempt due 2028
Debt Instrument [Line Items]
Long-Term Debt	120,500,000	120,500,000
CL&P \| First Mortgage Bonds:
Debt Instrument [Line Items]
Long-Term Debt	3,394,800,000	3,144,800,000
Unamortized Premiums and Discounts, Net	27,800,000	10,200,000
Unamortized Debt Issuance Costs	(25,000,000.0)	(21,500,000)
Long-term debt	$ 3,518,100,000	3,004,000,000.0
CL&P \| First Mortgage Bonds: \| 7.875% 1994 Series D due 2024
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	7.875%
Long-Term Debt	$ 139,800,000	139,800,000
CL&P \| First Mortgage Bonds: \| 5.750% 2004 Series B due 2034
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.75%
Long-Term Debt	$ 130,000,000.0	130,000,000.0
CL&P \| First Mortgage Bonds: \| 5.625% 2005 Series B due 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.625%
Long-Term Debt	$ 100,000,000.0	100,000,000.0
CL&P \| First Mortgage Bonds: \| 6.350% 2006 Series A due 2036
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.35%
Long-Term Debt	$ 250,000,000.0	250,000,000.0
CL&P \| First Mortgage Bonds: \| 5.750% 2007 Series B due 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.75%
Long-Term Debt	$ 150,000,000.0	150,000,000.0
CL&P \| First Mortgage Bonds: \| 6.375% 2007 Series D due 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.375%
Long-Term Debt	$ 100,000,000.0	100,000,000.0
CL&P \| First Mortgage Bonds: \| 5.500% 2009 Series A due 2019
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.50%
Long-Term Debt	$ 0	250,000,000.0
CL&P \| First Mortgage Bonds: \| 2.500% 2013 Series A due 2023
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.50%
Long-Term Debt	$ 400,000,000.0	400,000,000.0
CL&P \| First Mortgage Bonds: \| 4.300% 2014 Series A due 2044
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.30%
Long-Term Debt	$ 475,000,000.0	475,000,000.0
CL&P \| First Mortgage Bonds: \| 4.150% 2015 Series A due 2045
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.15%
Long-Term Debt	$ 350,000,000.0	350,000,000.0
CL&P \| First Mortgage Bonds: \| 3.200% 2017 Series A due 2027
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.20%
Long-Term Debt	$ 500,000,000.0	300,000,000.0
CL&P \| First Mortgage Bonds: \| 4.000% 2018 Series A due 2048
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.00%
Long-Term Debt	$ 800,000,000.0	500,000,000.0
NSTAR Electric
Debt Instrument [Line Items]
Long-Term Debt	3,247,086,000	2,944,846,000
Less Amounts due in One Year	(95,000,000)	0
NSTAR Electric \| Unsecured Debt
Debt Instrument [Line Items]
Long-Term Debt	2,800,000,000.0	2,400,000,000.0
Less Amounts due in One Year	(95,000,000.0)	0
Unamortized Premiums and Discounts, Net	(4,100,000)	(2,500,000)
Unamortized Debt Issuance Costs	(18,800,000)	(17,700,000)
Long-term debt	$ 3,247,100,000	2,944,800,000
NSTAR Electric \| Unsecured Debt \| 5.750% due 2036
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.75%
Long-Term Debt	$ 200,000,000.0	200,000,000.0
NSTAR Electric \| Unsecured Debt \| 5.500% due 2040
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.50%
Long-Term Debt	$ 300,000,000.0	300,000,000.0
NSTAR Electric \| Unsecured Debt \| 2.375% due 2022
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.375%
Long-Term Debt	$ 400,000,000.0	400,000,000.0
NSTAR Electric \| Unsecured Debt \| 4.400% due 2044
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.40%
Long-Term Debt	$ 300,000,000.0	300,000,000.0
NSTAR Electric \| Unsecured Debt \| 3.250% due 2025
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.25%
Long-Term Debt	$ 250,000,000.0	250,000,000.0
NSTAR Electric \| Unsecured Debt \| 2.700% due 2026
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.70%
Long-Term Debt	$ 250,000,000.0	250,000,000.0
NSTAR Electric \| Unsecured Debt \| 3.200% due 2027
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.20%
Long-Term Debt	$ 700,000,000.0	700,000,000.0
NSTAR Electric \| Unsecured Debt \| 3.250% due 2029
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.25%
Long-Term Debt	$ 400,000,000.0	0
NSTAR Electric \| Senior Notes
Debt Instrument [Line Items]
Long-Term Debt	$ 565,000,000.0	565,000,000.0
NSTAR Electric \| Senior Notes \| 5.900% Senior Notes Series B due 2034
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.90%
Long-Term Debt	$ 50,000,000.0	50,000,000.0
NSTAR Electric \| Senior Notes \| 6.700% Senior Notes Series D due 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.70%
Long-Term Debt	$ 40,000,000.0	40,000,000.0
NSTAR Electric \| Senior Notes \| 5.100% Senior Notes Series E due 2020
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.10%
Long-Term Debt	$ 95,000,000.0	95,000,000.0
NSTAR Electric \| Senior Notes \| 3.500% Senior Notes Series F due 2021
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.50%
Long-Term Debt	$ 250,000,000.0	250,000,000.0
NSTAR Electric \| Senior Notes \| 3.880% Senior Notes Series G due 2023
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.88%
Long-Term Debt	$ 80,000,000.0	80,000,000.0
NSTAR Electric \| Senior Notes \| 2.750% Senior Notes Series H due 2026
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.75%
Long-Term Debt	$ 50,000,000.0	50,000,000.0
PSNH
Debt Instrument [Line Items]
Long-Term Debt	951,620,000	655,173,000
Less Amounts due in One Year	0	(150,000,000)
PSNH \| First Mortgage Bonds:
Debt Instrument [Line Items]
Long-Term Debt	957,000,000.0	807,000,000.0
Less Amounts due in One Year	0	(150,000,000.0)
Unamortized Premiums and Discounts, Net	(700,000)	0
Unamortized Debt Issuance Costs	(4,700,000)	(1,800,000)
Long-term debt	$ 951,600,000	655,200,000
PSNH \| First Mortgage Bonds: \| 5.600% Series M due 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.60%
Long-Term Debt	$ 50,000,000.0	50,000,000.0
PSNH \| First Mortgage Bonds: \| 4.500% Series P due 2019
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.50%
Long-Term Debt	$ 0	150,000,000.0
PSNH \| First Mortgage Bonds: \| 4.050% Series Q due 2021
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.05%
Long-Term Debt	$ 122,000,000.0	122,000,000.0
PSNH \| First Mortgage Bonds: \| 3.200% Series R due 2021
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.20%
Long-Term Debt	$ 160,000,000.0	160,000,000.0
PSNH \| First Mortgage Bonds: \| 3.500% Series S due 2023
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.50%
Long-Term Debt	$ 325,000,000.0	325,000,000.0
PSNH \| First Mortgage Bonds: \| 3.600% Series T due 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.60%
Long-Term Debt	$ 300,000,000.0	0
Yankee Gas \| First Mortgage Bonds: \| Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2020 - 2049
Debt Instrument [Line Items]
Long-Term Debt	620,000,000.0	470,000,000.0
NSTAR Gas \| First Mortgage Bonds: \| NSTAR Gas - First Mortgage Bonds: 3.740% - 9.950% due 2020 - 2049
Debt Instrument [Line Items]
Long-Term Debt	$ 460,000,000.0	385,000,000.0
Aquarion \| Unsecured Debt \| Aquarion - Senior Note 4.000% due 2024
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.00%
Long-Term Debt	$ 360,000,000.0	360,000,000.0
Aquarion \| Unsecured Debt \| Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049
Debt Instrument [Line Items]
Long-Term Debt	335,300,000	289,500,000
Aquarion \| Unsecured Debt \| Aquarion - Secured Debt 4.100% - 9.640% due 2021 - 2035
Debt Instrument [Line Items]
Long-Term Debt	68,800,000	70,700,000
Commercial Paper
Debt Instrument [Line Items]
Commercial Paper Classified as Long-Term Debt (See Note 8, Short-Term Debt)	346,300,000	0
Commercial Paper \| NSTAR Electric
Debt Instrument [Line Items]
Commercial Paper Classified as Long-Term Debt (See Note 8, Short-Term Debt)	$ 650,000,000
Minimum \| Yankee Gas \| First Mortgage Bonds: \| Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2020 - 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.23%
Minimum \| NSTAR Gas \| First Mortgage Bonds: \| NSTAR Gas - First Mortgage Bonds: 3.740% - 9.950% due 2020 - 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.74%
Minimum \| Aquarion \| Unsecured Debt \| Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	0.00%
Minimum \| Aquarion \| Unsecured Debt \| Aquarion - Secured Debt 4.100% - 9.640% due 2021 - 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.10%
Maximum \| Yankee Gas \| First Mortgage Bonds: \| Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2020 - 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	8.48%
Maximum \| NSTAR Gas \| First Mortgage Bonds: \| NSTAR Gas - First Mortgage Bonds: 3.740% - 9.950% due 2020 - 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	9.95%
Maximum \| Aquarion \| Unsecured Debt \| Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.43%
Maximum \| Aquarion \| Unsecured Debt \| Aquarion - Secured Debt 4.100% - 9.640% due 2021 - 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	9.64%
Eversource
Debt Instrument [Line Items]
Long-Term Debt	$ 4,358,339,000	4,031,997,000
Less Amounts due in One Year	$ (23,933,000)	(378,883,000)
Eversource \| Unsecured Debt \| Eversource Parent - Debentures 4.500% due 2019
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.50%
Long-Term Debt	$ 0	350,000,000.0
Eversource \| Unsecured Debt \| Eversource Parent - Senior Notes 2.500% - 4.250% due 2021 - 2029
Debt Instrument [Line Items]
Long-Term Debt	4,000,000,000.0	$ 4,000,000,000.0
Eversource \| Commercial Paper
Debt Instrument [Line Items]
Commercial Paper Classified as Long-Term Debt (See Note 8, Short-Term Debt)	$ 1,450,000,000		$ 1,450,000,000
Eversource \| Minimum \| Unsecured Debt \| Eversource Parent - Senior Notes 2.500% - 4.250% due 2021 - 2029
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.50%
Eversource \| Maximum \| Unsecured Debt \| Eversource Parent - Senior Notes 2.500% - 4.250% due 2021 - 2029
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.25%