COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints Narrative (Details) $ in Millions					3 Months Ended	15 Months Ended	30 Months Ended	36 Months Ended
	Apr. 30, 2026	Mar. 19, 2026 complaint	Oct. 16, 2018 complaint	Apr. 29, 2016 complaint	Mar. 31, 2026 USD ($)	Dec. 31, 2012	Apr. 14, 2017	Oct. 15, 2014	Dec. 31, 2025 USD ($)	Jul. 31, 2014 complaint
Loss Contingencies [Line Items]
Percentage of base ROE reasonably justified (in percent)			10.41%
Percentage of incentive cap on total ROE			13.08%
Regulatory liabilities					$ 6,063.6				$ 5,538.1
CL&P
Loss Contingencies [Line Items]
Regulatory liabilities					2,104.3				1,862.6
NSTAR Electric
Loss Contingencies [Line Items]
Regulatory liabilities					2,557.8				2,352.9
PSNH
Loss Contingencies [Line Items]
Regulatory liabilities					$ 559.2				$ 535.8
Proposed ROE | Subsequent Event
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period	11.39%
Proposed Cap | Subsequent Event
Loss Contingencies [Line Items]
Maximum percentage cap of ROE for incentive projects	12.89%
FERC ROE Complaints
Loss Contingencies [Line Items]
Loss contingency, pending claims, number | complaint		4	4	4
Period of complaint					15 months
Loss contingency, estimate of possible earnings impact					$ 871.0
Regulatory liabilities					60.4
FERC ROE Complaints | CL&P
Loss Contingencies [Line Items]
Regulatory liabilities					28.7
FERC ROE Complaints | NSTAR Electric
Loss Contingencies [Line Items]
Regulatory liabilities					24.2
FERC ROE Complaints | PSNH
Loss Contingencies [Line Items]
Regulatory liabilities					7.5
FERC ROE Complaints | Minimum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact					60.4
Estimated of Interest					28.8
FERC ROE Complaints | Maximum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact					932.0
Estimated of Interest					$ 256.0
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Loss contingency, pending claims, number | complaint										3
Base ROE percentage challenged by complainants					11.14%
FERC ROE First, Second and Third Complaints | Minimum
Loss Contingencies [Line Items]
Maximum percentage cap of ROE for incentive projects								11.14%
FERC ROE First, Second and Third Complaints | Maximum
Loss Contingencies [Line Items]
Maximum percentage cap of ROE for incentive projects								13.10%
FERC ROE Fourth Complaint
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period				10.57%
Maximum percentage cap of ROE for incentive projects				11.74%
FERC ROE Second Complaint
Loss Contingencies [Line Items]
Percentage of base ROE							10.57%
FERC ROE First Complaint
Loss Contingencies [Line Items]
Percentage of ROE for any incentive							11.74%
Regulatory liabilities					$ 60.4
FERC ROE First Complaint | CL&P
Loss Contingencies [Line Items]
Interest component of regulatory liability					13.7
FERC ROE First Complaint | NSTAR Electric
Loss Contingencies [Line Items]
Interest component of regulatory liability					11.5
FERC ROE First Complaint | PSNH
Loss Contingencies [Line Items]
Interest component of regulatory liability					$ 3.6
FERC ROE First Complaint | Original ROE
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period		11.14%				11.14%
Percentage of base ROE		11.14%						11.14%
FERC ROE First Complaint | Revised ROE
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period						9.57%
Percentage of base ROE								10.57%
FERC ROE First Complaint | Incentive Cap
Loss Contingencies [Line Items]
Maximum percentage cap of ROE for incentive projects					12.09%	12.09%
FERC ROE First Complaint | Previous Order ROE
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period					10.57%
FERC ROE First Complaint | Previous Incentive Cap
Loss Contingencies [Line Items]
Maximum percentage cap of ROE for incentive projects					11.74%
FERC ROE First Complaint | Final ROE
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period		9.57%			9.57%