INCOME TAXES - SUMMARY OF INCOME TAX EXPENSE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Provision for income taxes
Current tax expense (benefit)	$ (18.3)	$ 49.8	$ (66.1)
Deferred income taxes, net	51.1	5.1	125.5
Investment tax credit, net	(1.6)	(0.4)	(0.3)
Total income tax expense	$ 31.2	$ 54.5	$ 59.1