COMMITMENTS AND CONTINGENCIES - Guarantees and Indemnifications (Details) - USD ($) $ in Millions	Mar. 31, 2022	Oct. 23, 2019	Jan. 25, 2017
North East Offshore LLC
Guarantor Obligations [Line Items]
Ownership interest	50.00%
Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 420.6
Ownership interest	50.00%
Revolution Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 268.5
Ownership interest	50.00%
South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 184.0
Eversource Investment LLC | North East Offshore LLC
Guarantor Obligations [Line Items]
Ownership interest	50.00%
Construction-related purchase agreements with third-party contractors | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Ownership interest	50.00%
Construction-related purchase agreements with third-party contractors | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 936.3
Construction-related purchase agreements with third-party contractors | Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	330.6
Construction-related purchase agreements with third-party contractors | Revolution Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	254.7
Construction-related purchase agreements with third-party contractors | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	165.3
Funding and indemnification obligations of North East Offshore LLC | Eversource Investment LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	107.8
Funding and indemnification obligations of North East Offshore LLC | Eversource Investment LLC | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	910.0
Power Purchase Agreement | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 7.1		$ 7.1
Ownership interest	50.00%
OREC capacity production | Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 2.2	$ 15.4
Ownership interest	50.00%
Real estate purchase | Bay State Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 2.5
Transmission interconnection | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	1.2
Letter of Credit | Eversource Investment LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	4.3
Surety bonds | Various
Guarantor Obligations [Line Items]
Maximum exposure (up to)	35.0
Lease payments for real estate | Eversource Service
Guarantor Obligations [Line Items]
Maximum exposure (up to)	0.7
Performance guarantee | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 1,300.0
Percent of obligations guaranteed	50.00%
Payment guarantee | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 62.5
Percent of obligations guaranteed	50.00%