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.

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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=118932676&loc=d3e3255-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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=118932676&loc=d3e3291-108585

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Balance Type:	credit
Period Type:	duration

LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($) $ in Thousands				1 Months Ended							12 Months Ended
	Nov. 15, 2019	Nov. 01, 2019	Feb. 01, 2019	Jan. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jul. 31, 2019	Jun. 30, 2019	May 31, 2019	Apr. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Repayments of debt											$ (801,078)	$ (1,050,330)	$ (745,000)
Senior Notes
Debt Instrument [Line Items]
Long-term debt					$ 13,770,800						13,770,800	12,248,700
CL&P
Debt Instrument [Line Items]
Repayments of debt											(250,000)	(300,000)	(250,000)
CL&P \| Senior Notes \| 4.00% 2018 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Issuance										$ 300,000
CL&P \| Senior Notes \| 3.20% 2017 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Issuance						$ 200,000
CL&P \| Senior Notes \| 5.50% 2009 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Repayments of debt			$ (250,000)
NSTAR Electric
Debt Instrument [Line Items]
Repayments of debt											0	0	(400,000)
NSTAR Electric \| Senior Notes \| 3.25% 2019 Debentures
Debt Instrument [Line Items]
Issuance									$ 400,000
PSNH
Debt Instrument [Line Items]
Repayments of debt											(150,000)	(199,250)	(70,000)
PSNH \| Senior Notes \| 3.60% 2019 Series T First Mortgage Bonds
Debt Instrument [Line Items]
Issuance								$ 300,000
PSNH \| Senior Notes \| 4.50% 2009 Series P First Mortgage Bonds
Debt Instrument [Line Items]
Repayments of debt					(150,000)
NSTAR Gas \| Senior Notes \| NSTAR Gas 3.74% Series Q First Mortgage Bonds
Debt Instrument [Line Items]
Issuance							$ 75,000
Yankee Gas \| Senior Notes \| Yankee Gas 2.23% Series P First Mortgage Bonds
Debt Instrument [Line Items]
Issuance						100,000
Yankee Gas \| Senior Notes \| Yankee Gas 3.30% Series Q First Mortgage Bonds
Debt Instrument [Line Items]
Issuance						$ 100,000
Yankee Gas \| Senior Notes \| Yankee Gas 5.26% Series H First Mortgage Bonds
Debt Instrument [Line Items]
Repayments of debt		$ (50,000)
Aquarion \| Senior Notes \| Aquarion 3.54% Senior Notes
Debt Instrument [Line Items]
Issuance					45,000
Eversource
Debt Instrument [Line Items]
Repayments of debt											(350,000)	$ (450,000)	$ 0
Eversource \| Senior Notes \| Eversource Parent 4.50% Debentures
Debt Instrument [Line Items]
Repayments of debt	$ (350,000)
Eversource \| Senior Notes \| Eversource Parent 3.45% Series P Senior Notes \| Subsequent Event
Debt Instrument [Line Items]
Issuance				$ 350,000
Eversource \| CL&P \| Senior Notes \| 4.00% 2018 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Long-term debt					800,000						800,000
Eversource \| CL&P \| Senior Notes \| 3.20% 2017 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Long-term debt					$ 500,000						$ 500,000