Derivatives and Other Financial Instruments - Schedule of Fair Values of Level 3 Derivative Instruments Outstanding (Detail) - Level 3 [Member]	12 Months Ended
	Dec. 31, 2023
Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Forward Sales One [Member] | LME Plus Midwest Premium [Member]
Derivative Instruments Gain Loss [Line Items]
Description	Embedded derivative that indexes the price of power to the LME price of aluminum plus the Midwest premium
Contract Termination	Mar. 31, 2026
Sensitivity to Inputs	Increase in LME price and/or the Midwest premium results in a higher cost of power and an increase to the derivative liability
Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Forward Sales Two [Member] | LME Plus Midwest Premium [Member]
Derivative Instruments Gain Loss [Line Items]
Description	Embedded derivative that indexes the price of power to the LME price of aluminum plus the Midwest premium
Contract Termination	Dec. 31, 2029
Sensitivity to Inputs	Increase in LME price and/or the Midwest premium results in a higher cost of power and an increase to the derivative liability
Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Forward Sales Three [Member] | LME Plus Midwest Premium [Member]
Derivative Instruments Gain Loss [Line Items]
Description	Embedded derivative that indexes the price of power to the LME price of aluminum plus the Midwest premium
Contract Termination	Feb. 29, 2036
Sensitivity to Inputs	Increase in LME price and/or the Midwest premium results in a higher cost of power and an increase to the derivative liability
Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Forward Sales Four [Member] | London Metal Exchange [Member]
Derivative Instruments Gain Loss [Line Items]
Description	Embedded derivative that indexes the price of power to the LME price of aluminum
Contract Termination	Sep. 30, 2027
Sensitivity to Inputs	Increase in LME price results in a higher cost of power and an increase to the derivative liability
Energy Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Estimated Credit Spread [Member]
Derivative Instruments Gain Loss [Line Items]
Description	Embedded derivative that indexes the price of power to the credit spread between the Company and the counterparty
Contract Termination	Oct. 31, 2028
Sensitivity to Inputs	Wider credit spread results in a higher cost of power and increase in the derivative liability
Financial Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member] | LME Price and Power Price [Member]
Derivative Instruments Gain Loss [Line Items]
Description	Hedge power prices
Contract Termination	Jun. 30, 2026
Sensitivity to Inputs	Lower prices in the power market or higher LME prices result in an increase in the derivative liability