PENSION AND POST-RETIREMENT BENEFITS - Narrative (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) plan	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Retirement Benefits [Abstract]
Net periodic benefit cost	$ 1.2	$ 2.0		$ 7.2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	1.2	2.0		$ 7.2
Aggregate employer contributions during 2020	18.0
Scenario, Forecast
Retirement Benefits [Abstract]
Net periodic benefit cost			$ 5.0
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			$ 5.0
Pension Plans
Retirement Benefits [Abstract]
Net periodic benefit cost	1.0	1.8
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	1.0	1.8
Employer contributions	3.4
Pension Plans | Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions	$ 1.6
Number of qualified plans | plan	2
Pension Plans | CARES Act | Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions, expected deferral	$ 9.0
Other Post-Retirement Benefit Plans
Retirement Benefits [Abstract]
Net periodic benefit cost	0.2	0.2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	0.2	$ 0.2
Employer contributions	$ 0.2