EMPLOYEE BENEFIT PLANS - Components of Net Period Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service Cost		$ 4.7	$ 3.0	$ 0.5
Interest Cost		14.2	15.3	18.2
Expected return on plan assets		(26.9)	(25.3)	(23.7)
Mark-to-market actuarial net losses (gains)		11.9	(10.8)	(9.7)
Curtailment	$ (5.3)	(0.6)	(6.4)	0.0
Net periodic cost (benefit)		3.3	(24.2)	(14.7)
Health Care Benefits
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service Cost		0.1	0.1	0.0
Interest Cost		0.5	0.4	0.2
Expected return on plan assets		0.0	0.0	0.0
Mark-to-market actuarial net losses (gains)		(1.7)	0.0	0.1
Curtailment		(0.2)	0.0	0.0
Net periodic cost (benefit)		$ (1.3)	$ 0.5	$ 0.3