PENSION AND POST-RETIREMENT BENEFITS - Fair Value of Asset Categories (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	$ 463.0	$ 462.4
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	463.0	462.4	$ 432.4
Pension Plans | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	387.9	377.4
Pension Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	189.7	179.0
Pension Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	198.2	198.4
Pension Plans | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Investments measured at Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	75.1	85.0
Pension Plans | Common and preferred stock, US small/mid cap equity | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and preferred stock, US small/mid cap equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and preferred stock, US small/mid cap equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and preferred stock, US small/mid cap equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Corporate Bonds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	10.8	10.8
Pension Plans | Mutual Funds, Corporate Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	10.8	10.8
Pension Plans | Mutual Funds, Corporate Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Corporate Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Government Bonds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	15.8	15.8
Pension Plans | Mutual Funds, Government Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	15.8	15.8
Pension Plans | Mutual Funds, Government Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Government Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, U.S. Large Cap Equiy | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.2
Pension Plans | Mutual Funds, U.S. Large Cap Equiy | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.2
Pension Plans | Mutual Funds, U.S. Large Cap Equiy | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, U.S. Large Cap Equiy | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, International Equities | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	21.7	16.3
Pension Plans | Mutual Funds, International Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	21.7	16.3
Pension Plans | Mutual Funds, International Equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, International Equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Emerging Markets International Equity | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.7	5.9
Pension Plans | Mutual Funds, Emerging Markets International Equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.7	5.9
Pension Plans | Mutual Funds, Emerging Markets International Equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Emerging Markets International Equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, U.S., Small/Mid Cap Equity | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.1
Pension Plans | Mutual Funds, U.S., Small/Mid Cap Equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.1
Pension Plans | Mutual Funds, U.S., Small/Mid Cap Equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0
Pension Plans | Mutual Funds, U.S., Small/Mid Cap Equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0
Pension Plans | Mutual Funds, Cash and Cash Equivalents | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	6.0	1.6
Pension Plans | Mutual Funds, Cash and Cash Equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	6.0	1.6
Pension Plans | Mutual Funds, Cash and Cash Equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Cash and Cash Equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Other | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.2	2.0
Pension Plans | Mutual Funds, Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.2	2.0
Pension Plans | Mutual Funds, Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Mutual Funds, Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Fixed Income Securities, Corporate Bonds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Fixed Income Securities, Corporate Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Fixed Income Securities, Corporate Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Fixed Income Securities, Corporate Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Fixed Income Securities, Government Bonds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	68.1	72.2
Pension Plans | Fixed Income Securities, Government Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Fixed Income Securities, Government Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	68.1	72.2
Pension Plans | Fixed Income Securities, Government Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Corporate Bonds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	34.6	33.6
Pension Plans | Common and Collective Funds, Corporate Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	20.7	19.4
Pension Plans | Common and Collective Funds, Corporate Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	13.9	14.2
Pension Plans | Common and Collective Funds, Corporate Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Government Bonds | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	38.7	38.9
Pension Plans | Common and Collective Funds, Government Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	4.8	9.1
Pension Plans | Common and Collective Funds, Government Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	33.9	29.8
Pension Plans | Common and Collective Funds, Government Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, U.S. Large Cap Equity | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	59.0	55.5
Pension Plans | Common and Collective Funds, U.S. Large Cap Equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	51.0	48.7
Pension Plans | Common and Collective Funds, U.S. Large Cap Equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	8.0	6.8
Pension Plans | Common and Collective Funds, U.S. Large Cap Equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, U.S. Small/Mid Cap Equity | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	24.6	18.2
Pension Plans | Common and Collective Funds, U.S. Small/Mid Cap Equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	24.6	18.2
Pension Plans | Common and Collective Funds, U.S. Small/Mid Cap Equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, U.S. Small/Mid Cap Equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, International Equities | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	72.7	70.8
Pension Plans | Common and Collective Funds, International Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	4.4	3.4
Pension Plans | Common and Collective Funds, International Equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	68.3	67.4
Pension Plans | Common and Collective Funds, International Equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Emerging Markets International Equity | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	24.5	18.1
Pension Plans | Common and Collective Funds, Emerging Markets International Equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	19.1	13.0
Pension Plans | Common and Collective Funds, Emerging Markets International Equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	5.4	5.1
Pension Plans | Common and Collective Funds, Emerging Markets International Equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Cash and Cash Equivalents | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.8	1.7
Pension Plans | Common and Collective Funds, Cash and Cash Equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	1.8	1.7
Pension Plans | Common and Collective Funds, Cash and Cash Equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Cash and Cash Equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Other | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.6	2.9
Pension Plans | Common and Collective Funds, Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds, Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.6	2.9
Pension Plans | Common and Collective Funds, Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	5.0	12.9
Pension Plans | Cash and Cash Equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	5.0	12.9
Pension Plans | Cash and Cash Equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Cash and Cash Equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	0.0	0.0
Pension Plans | Common and Collective Funds | Investments measured at Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	45.9	52.4
Pension Plans | Hedge Funds | Investments measured at Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Fair Value	$ 29.2	$ 32.6