Derivative Instruments - Derivatives Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses)	$ 6.0	$ 12.8	$ (74.2)	$ 63.7
Not Designated as Hedging Instrument | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on economic hedges	(19.4)	0.5	9.2	(30.1)
Unrealized Gain (Loss) on Cash Flow Hedging Instruments that have matured but not cash settled			0.4	(13.0)
Not Designated as Hedging Instrument | Commodity contracts | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on commodity derivatives not designated as hedging instruments	5.1	34.2	(85.8)	118.5
Not Designated as Hedging Instrument | Commodity contracts | Other Operating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on commodity derivatives not designated as hedging instruments	0.1	(0.3)	7.9	0.2
Designated as Hedging Instrument | Commodity contracts | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains (losses) reclassified out of accumulated other comprehensive income and into cost of materials and other on commodity derivatives designated as cash flow hedging instruments	$ 0.8	$ (21.1)	$ 3.7	$ (55.0)