Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Fair Value of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Designated as Hedging Instrument | Purchase
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	$ (2.7)	$ (3.3)
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	3.3	5.9
Liabilities	(5.0)	(5.3)
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	3.3	5.9
Liabilities	(5.0)	(5.3)
Net Amount	(1.7)	0.6
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.1
Net Amount	0.1
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument | Purchase | Alloying Metals
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.1
Net Amount	0.1
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	3.2	5.9
Liabilities	(5.0)	(5.3)
Net Amount	(1.8)	0.6
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Natural Gas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	1.7	4.7
Liabilities	(0.3)
Net Amount	1.4	4.7
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.8	0.7
Liabilities	(3.0)	(3.9)
Net Amount	(2.2)	(3.2)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Midwest premium purchase contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.2	0.5
Liabilities	(1.7)	(1.4)
Net Amount	(1.5)	$ (0.9)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Midwest premium sale contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.5
Net Amount	$ 0.5