INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Operating Loss Carryforwards [Line Items]
Decrease in valuation allowance		$ 294.0
Increase in valuation allowance		129.0
Change in valuation allowance		165.0
Charge of valuation allowance			$ (241.6)	$ 278.6	$ 295.8
State expense (benefit) tax credits			2.4	43.2	(11.4)
Income tax expense (benefit), tax credits, return to provision process	$ (118.0)
Income tax expense (benefit), state tax, return to provision process			283.0
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount			59.5
Income tax expense (benefit) from contingent liability increase (decrease)		(44.0)
Interest expense on uncertain tax positions			2.4	1.3	0.3
Accrued interest payable	4.1		4.1	1.7
South Fork Wind And Revolution Wind
Operating Loss Carryforwards [Line Items]
Equity method investment, pre tax charge		$ 284.0
CL&P
Operating Loss Carryforwards [Line Items]
Charge of valuation allowance			(6.2)	50.8	51.3
State expense (benefit) tax credits			39.6	(2.8)	$ (10.7)
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount			0.0
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Valuation allowance for tax credit and operating loss carryforward	$ 293.4		293.4	558.2
State and Local Jurisdiction | CL&P
Operating Loss Carryforwards [Line Items]
Change in valuation allowance			0.1	23.5
State and Local Jurisdiction | Eversource
Operating Loss Carryforwards [Line Items]
Change in valuation allowance			$ 0.2	$ 27.3