FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 20.7	$ 21.2
Commodity contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	22.4	9.0
Derivative, Collateral, Right to Reclaim Cash	(22.4)	(6.0)
Derivative Liability	0.0	3.0
Commodity contract [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	22.4	2.3
Commodity contract [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0.0	6.7
Commodity contract [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0.0	0.0
Catalyst Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Obligations, Fair Value Disclosure	112.5	102.5
Catalyst Obligation [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0.0	0.0
Catalyst Obligation [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	112.5	102.5
Catalyst Obligation [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0.0	0.0
Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Obligations, Fair Value Disclosure	29.5	0.0
Contingent Consideration | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0.0	0.0
Contingent Consideration | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0.0	0.0
Contingent Consideration | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	29.5	0.0
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	312.4	402.3
Money market funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	312.4	402.3
Money market funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Money market funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Commodity contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	24.9	6.0
Derivative assets, Effect of Counter-party Netting	(22.4)	(6.0)
Derivative assets, Net Carrying Value on Balance Sheet	2.5	0.0
Commodity contract [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	24.9	2.5
Commodity contract [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0.0	3.5
Commodity contract [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0.0	0.0
Inventory Intermediation Agreement Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	3.3	11.3
Derivative assets, Effect of Counter-party Netting	0.0	0.0
Derivative assets, Net Carrying Value on Balance Sheet	3.3	11.3
Inventory Intermediation Agreement Obligation [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0.0	0.0
Inventory Intermediation Agreement Obligation [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	3.3	11.3
Inventory Intermediation Agreement Obligation [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 0.0	$ 0.0