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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) Mmlb in Millions	9 Months Ended
	Sep. 30, 2025 EUR (€) Mmlb MMBTU
Purchase | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	64.1
Purchase | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Purchase | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	Nov. 30, 2026
Purchase | Fixed Price Purchase Contracts for MWTP
Derivative [Line Items]
Derivative non-monetary notional amount	64.1
Purchase | Fixed Price Purchase Contracts for MWTP | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Purchase | Fixed Price Purchase Contracts for MWTP | Maximum
Derivative [Line Items]
Derivative maturity period	Nov. 30, 2026
Purchase | Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	6.8
Purchase | Alloying Metals | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Purchase | Alloying Metals | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2027
Purchase | Natural Gas
Derivative [Line Items]
Derivative non-monetary notional amount | MMBTU	3,300,000
Purchase | Natural Gas | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Purchase | Natural Gas | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2027
Purchase | Euro
Derivative [Line Items]
Derivative notional amount | €	€ 1,700,000
Purchase | Euro | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Purchase | Euro | Maximum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2027
Sales | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	23.5
Sales | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Sales | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	Mar. 31, 2026
Sales | Fixed Price Sale Contracts for MWTP
Derivative [Line Items]
Derivative non-monetary notional amount	23.5
Sales | Fixed Price Sale Contracts for MWTP | Minimum
Derivative [Line Items]
Derivative maturity period	Oct. 31, 2025
Sales | Fixed Price Sale Contracts for MWTP | Maximum
Derivative [Line Items]
Derivative maturity period	Apr. 30, 2026

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