Derivatives, Hedging Programs and Other Financial Instruments, Notional Quantity Table (Details) mmlbs in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018 mmlbs MMBTU
Not Designated as Hedging Instrument | Aluminum | Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)				139.1
Not Designated as Hedging Instrument | Aluminum | Sale
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)				0.9
Not Designated as Hedging Instrument | Midwest premium swap contracts | Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)				100.1
Not Designated as Hedging Instrument | Natural Gas Member | Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary) | MMBTU				4,040,000
Not Designated as Hedging Instrument | Electricity | Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary) | MMBTU				219,600
Designated as Hedging Instrument | Alloy Metal Hedge | Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)				9.0
Scenario, Forecast | Natural Gas Member
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage			66.00%
Scenario, Forecast | Electricity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage	9.00%	55.00%	54.00%