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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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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.

+ References

No definition available.

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- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

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- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3291-108585

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SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended					6 Months Ended
	Jun. 30, 2021	May 31, 2021	Apr. 30, 2021	Mar. 31, 2021	Feb. 28, 2021	Jun. 30, 2021	Jun. 30, 2020
Debt Instrument [Line Items]
Repayments						$ (1,022,000)	$ (270,456)
Senior Notes \| Eversource Parent 2.50% Series I Senior Notes \| Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage					2.50%
Repayments					$ (450,000)
Senior Notes \| Eversource Parent 2.55% Series S Senior Notes \| Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage				2.55%
Issuances				$ 350,000
CL&P \| Senior Notes \| 2.05% Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage	2.05%					2.05%
Issuances	$ 425,000
NSTAR Electric
Debt Instrument [Line Items]
Repayments						$ (250,000)	(95,000)
NSTAR Electric \| Senior Notes \| 3.10% 2021 Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage		3.10%
Issuances		$ 300,000
NSTAR Electric \| Senior Notes \| 3.50% Series F Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage	3.50%					3.50%
Repayments	$ (250,000)
PSNH
Debt Instrument [Line Items]
Repayments						$ (282,000)	$ 0
PSNH \| Senior Notes \| 4.05% Series Q First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage				4.05%
Repayments				$ (122,000)
PSNH \| Senior Notes \| 3.20% Series R First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage	3.20%					3.20%
Repayments	$ (160,000)
PSNH \| Senior Notes \| 2.20% Series V First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage	2.20%					2.20%
Issuances	$ 350,000
Aquarion \| Senior Notes \| Aquarion Water Company of Connecticut 3.31% Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage			3.31%
Issuances			$ 100,000
Aquarion \| Senior Notes \| Aquarion Water Company of Connecticut 5.50% Notes
Debt Instrument [Line Items]
Interest rate, stated percentage			5.50%
Repayments			$ (40,000)