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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
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COMMITMENTS AND CONTINGENCIES - Guarantees and Indemnifications (Details) - USD ($) $ in Millions	Mar. 31, 2026	Jan. 31, 2026	Sep. 30, 2024
Guarantor Obligations [Line Items]
Maximum exposure (up to)			$ 850.0
North East Offshore, Revolution Wind, LLC and South Fork Wind, LLC
Guarantor Obligations [Line Items]
Ownership interest (percent)	50.00%
South Fork Class B Member, LLC
Guarantor Obligations [Line Items]
Ownership interest (percent)	50.00%
Eversource Investment LLC, Eversource Investment Service Company LLC and South Fork Class B Member, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 1,620.0
South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 7.1
Ownership interest (percent)	50.00%
Performance Guarantee \| Eversource Investment Service Company LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)			$ 100.0
Tax Equity \| Eversource TEI LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 50.0
Revolution Wind, LLC and TurbineCo, LLC \| Construction-related purchase agreements with third-party contractors
Guarantor Obligations [Line Items]
Maximum exposure (up to)	122.3
Eversource Investment LLC, Eversource Investment Service Company LLC and South Fork Class B Member, LLC \| Funding and indemnification obligations of North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	143.0
Eversource Investment LLC \| Revolution Wind Tax Positions
Guarantor Obligations [Line Items]
Maximum exposure (up to)	300.0
Eversource Investment LLC \| Performance Guarantee
Guarantor Obligations [Line Items]
Maximum exposure (up to)		$ 900.0
Eversource TEI LLC \| South Fork Wind Tax Equity
Guarantor Obligations [Line Items]
Maximum exposure (up to)	50.0
South Fork Wind, LLC \| Power Purchase Guarantee
Guarantor Obligations [Line Items]
Maximum exposure (up to)	7.1
Various Eversource subsidiaries \| Surety Bond
Guarantor Obligations [Line Items]
Maximum exposure (up to)	34.1
North East Offshore, Revolution Wind, LLC, TurbineCo, LLC \| Performance Guarantee
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 682.7