COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	$ 631.3	$ 591.4	$ 581.4
Natural Gas Procurement	888.0	695.0	695.8
Capacity and Purchased Power	67.2	70.5	69.0
Peaker CfDs	19.6	23.1	20.1
Transmission Support Commitments	17.4	16.7	14.2
CL&P
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	567.4	529.0	474.1
Capacity and Purchased Power	64.4	67.6	65.5
Peaker CfDs	19.6	23.1	20.1
Transmission Support Commitments	6.9	6.6	5.6
NSTAR Electric
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	63.9	62.4	60.0
Capacity and Purchased Power	2.8	2.9	2.9
Peaker CfDs	0.0	0.0	0.0
Transmission Support Commitments	6.8	6.6	5.6
PSNH
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	0.0	0.0	47.3
Capacity and Purchased Power	0.0	0.0	0.6
Peaker CfDs	0.0	0.0	0.0
Transmission Support Commitments	$ 3.7	$ 3.5	$ 3.0