OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES - Other Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Other Income
Total Other Income	$ 5.9	$ 2.5	$ 14.5	$ 6.6
Pension and Other Postretirement Benefit Plan Non-Service Credits
Other Income
Total Other Income	3.7	1.7	8.0	3.7
Interest and Investment Income
Other Income
Total Other Income	0.8	1.0	2.7	2.1
AFUDC - Equity
Other Income
Total Other Income	1.3	0.9	2.5	1.4
Other
Other Income
Total Other Income	$ 0.1	$ (1.1)	$ 1.3	$ (0.6)