INCOME TAXES - COMPONENTS OF TAX EXPENSE (BENEFIT) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Current tax expense (benefit)	$ 7.4	$ 4.0	$ (44.5)	$ 13.3
Deferred tax expense	29.8	7.5	89.3	22.1
Income tax expense calculated based on estimated annual effective tax rate	37.2	11.5	44.8	35.4
Carryback of net operating losses to years with a higher statutory corporate rate pursuant to provisions of the CARES Act (as defined below)	0.0	0.0	(34.0)	0.0
Total income tax expense	$ 37.2	$ 11.5	$ 10.8	$ 35.4