PENSION AND POST-RETIREMENT BENEFITS - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Net periodic benefit costs:
Total net periodic benefit costs	$ 1.3	$ 1.2	$ 4.0
Pension Plans
Net periodic benefit costs:
Service cost	0.3	0.4
Interest cost	2.3	3.7
Expected return on plan assets	(4.9)	(5.8)
Amortization of actuarial loss	3.4	2.7
Total net periodic benefit costs	1.1	1.0
Other Post-Retirement Benefit Plans
Net periodic benefit costs:
Service cost	0.0	0.0
Interest cost	0.0	0.1
Expected return on plan assets	0.0	0.0
Amortization of actuarial loss	0.2	0.1
Total net periodic benefit costs	$ 0.2	$ 0.2