PENSION AND POST-RETIREMENT BENEFITS - Narrative (Details) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) plan	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Retirement Benefits [Abstract]
Net periodic benefit cost	$ 1.5		$ 2.2	$ 4.2	$ 6.3		$ 7.2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	1.5		2.2	4.2	6.3		$ 7.2
Aggregate employer contributions during 2020	19.0			19.0
Scenario, Forecast
Retirement Benefits [Abstract]
Net periodic benefit cost						$ 5.6
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost						$ 5.6
Pension Plans
Retirement Benefits [Abstract]
Net periodic benefit cost	1.3		2.0	3.6	5.8
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	1.3		2.0	3.6	5.8
Employer contributions	1.8			7.0
Pension Plans | Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions		$ 1.6
Employer contributions, expected deferral in 2020, CARES Act	9.3			$ 9.3
Number of qualified plans | plan				2
Other Post-Retirement Benefit Plans
Retirement Benefits [Abstract]
Net periodic benefit cost	0.2		0.2	$ 0.6	0.5
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	0.2		$ 0.2	0.6	$ 0.5
Employer contributions	$ 0.2			$ 0.5