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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Loss (Gain) Associated with Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Loss in which the effects of cash flow hedges are recorded	$ 898.4	$ 673.3	$ 1,764.3	$ 935.8
Cost of Products Sold \| Not Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss	2.4	(1.1)	0.8	(2.5)
Cost of Products Sold \| Not Designated as Hedging Instrument \| Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss	(0.5)	(1.5)	(1.1)	(2.6)
(Gain) loss recognized in our Statements of Consolidated Loss Unrealized loss	2.9	0.4	1.9	0.1
Cash Flow Hedges
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Loss in which the effects of cash flow hedges are recorded	898.4	673.3	1,764.3	935.8
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss	2.9	(8.7)	(17.0)	(11.4)
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Electricity
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss	(1.1)	(0.7)	(1.4)	(0.7)
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Aluminum
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss	5.9	(8.1)	(12.8)	(11.0)
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss		0.2		0.4
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Natural Gas
Derivative Instruments Gain Loss [Line Items]
Loss (gain) recognized in our Statements of Consolidated Loss	$ (1.9)	$ (0.1)	$ (2.8)	$ (0.1)