INCOME TAX EXPENSE - Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract]
Income Before Income Taxes	$ 21.1	$ 40.3	$ 62.1	$ 79.4
Statutory Federal Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Income Taxes Computed at Statutory Federal Rate	$ 4.4	$ 8.5	$ 13.0	$ 16.7
Increase (Decrease) in Income Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit	2.5	3.6	7.1	7.0
Production tax credits	(5.1)	(10.2)	(16.7)	(20.6)
Investment tax credits	(0.9)	(1.4)	(1.2)	(3.6)
Regulatory Differences – Excess Deferred Tax	(2.2)	(2.4)	(5.7)	(5.2)
Non-Controlling Interest in Subsidiaries	2.4	2.1	5.2	5.9
AFUDC – Equity	(0.3)	0.0	(0.9)	0.0
Transaction Costs	3.3	0.0	3.3	0.0
Other	(2.7)	(0.6)	1.3	0.9
Total Income Tax Expense (Benefit)	$ 1.4	$ (0.4)	$ 5.4	$ 1.1