Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) mmlb in Millions	6 Months Ended
	Jun. 30, 2022 EUR (€) mmlb MMBTU MWh
Purchase | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	128.0
Purchase | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2022
Purchase | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2023
Purchase | Midwest premium swap contracts
Derivative [Line Items]
Derivative non-monetary notional amount	61.5
Purchase | Midwest premium swap contracts | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2022
Purchase | Midwest premium swap contracts | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2023
Purchase | Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	3.2
Purchase | Alloying Metals | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2022
Purchase | Alloying Metals | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2022
Purchase | Natural Gas
Derivative [Line Items]
Derivative non-monetary notional amount | MMBTU	4,320,000
Purchase | Natural Gas | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2022
Purchase | Natural Gas | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2025
Purchase | Foreign Exchange Contract
Derivative [Line Items]
Derivative notional amount | €	€ 1,160,746
Purchase | Foreign Exchange Contract | Minimum
Derivative [Line Items]
Derivative maturity period	Sep. 30, 2022
Purchase | Foreign Exchange Contract | Maximum
Derivative [Line Items]
Derivative maturity period	Feb. 29, 2024
Purchase | Electricity
Derivative [Line Items]
Derivative non-monetary notional amount | MWh	110,425
Purchase | Electricity | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2022
Purchase | Electricity | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2022
Sales | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	24.3
Sales | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2022
Sales | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2022