INCOME TAX EXPENSE - Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract]
Income Before Income Taxes	$ 35.6	$ 88.9	$ 97.7	$ 168.3
Statutory Federal Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Income Taxes Computed at Statutory Federal Rate	$ 7.5	$ 18.7	$ 20.5	$ 35.3
Increase (Decrease) in Income Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit	3.4	8.0	10.5	15.0
Production Tax Credits	(8.3)	(7.7)	(25.0)	(28.3)
Investment Tax Credits	(0.4)	(1.6)	(1.6)	(5.2)
Regulatory Differences – Excess Deferred Tax	(2.0)	(2.3)	(7.7)	(7.5)
Non-Controlling Interest in Subsidiaries	2.4	3.0	7.6	8.9
AFUDC – Equity	(0.4)	0.0	(1.3)	0.0
Nondeductible Portion of Transaction Costs	0.7	0.0	4.0	0.0
Other	0.0	1.2	1.3	2.2
Total Income Tax Expense	$ 2.9	$ 19.3	$ 8.3	$ 20.4