Derivatives, Hedging Programs and Other Financial Instruments, Material Derivative Positions (Details) mmlbs in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2019 MMBTU MWH mmlbs
Aluminum | Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative non-monetary notional amount							117.1
Aluminum | Designated as Hedging Instrument | Sales
Derivative [Line Items]
Derivative non-monetary notional amount							0.5
Midwest premium swap contracts | Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative non-monetary notional amount							89.4
Alloy Metal Hedge | Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative non-monetary notional amount							10.5
Natural Gas | Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative non-monetary notional amount | MMBTU							8,530,000
Electricity | Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative non-monetary notional amount | MWH							307,080
Scenario, Forecast | Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage	31.00%	37.00%	37.00%	66.00%	66.00%	69.00%
Scenario, Forecast | Electricity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage				27.00%	54.00%	54.00%