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Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Fair Value of Derivative Financial Assets and Liabilities (Details) - USD ($) $ in Millions | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Designated as Hedging Instrument | Purchase |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Liabilities | $ (2.3) | $ (1.0)
Fair Value, Measurements, Recurring |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets | 6.9 | 5.9
Liabilities | (4.1) | (2.9)
Fair Value, Measurements, Recurring | Level 1 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets | 6.9 | 5.9
Liabilities | (4.1) | (2.9)
Net Amount | 2.8 | 3.0
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 |
Liabilities | (2.3) |
Net Amount | (2.2) |
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument | Purchase | Electricity |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets | 0.1 |
Liabilities | (2.3) |
Net Amount | (2.2) |
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets | 6.8 | 5.9
Liabilities | (1.8) | (2.9)
Net Amount | 5.0 | 3.0
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 | 0.5 | 0.3
Liabilities | (0.7) | (0.9)
Net Amount | (0.2) | (0.6)
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 | 3.4 | 3.4
Liabilities | (0.7) | (0.6)
Net Amount | 2.7 | 2.8
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Fixed Price Purchase Contracts for MWTP |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets | 0.3 | 0.4
Liabilities | (0.3) | (0.3)
Net Amount |  | 0.1
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Fixed Price Sale Contracts for MWTP |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets |  | 0.1
Liabilities |  | (0.2)
Net Amount |  | (0.1)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Foreign Currency |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets |  | 0.5
Liabilities | (0.1) |
Net Amount | (0.1) | 0.5
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Alloying Metals |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets | 2.6 | 0.7
Liabilities |  | (0.1)
Net Amount | $ 2.6 | 0.6
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Electricity |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Assets |  | 0.5
Liabilities |  | (0.6)
Net Amount |  | (0.1)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Sales | Aluminum |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Liabilities |  | (0.2)
Net Amount |  | $ (0.2)

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