Derivatives and Other Financial Instruments - Additional Information (Detail) kt in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) kt	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) kt	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) kt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings	$ (74)	$ (27)	$ (127)	$ (64)
Unrealized gain (loss) in accumulated other comprehensive loss	$ (3,737)		(3,737)		$ (3,645)
Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings		28	$ 4	44
Foreign Exchange Forward | Norway [Member] | Euro Power Purchases [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2026-12
Foreign Exchange Forward | Norway [Member] | Krone Capital Expenditures [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2025-06
Foreign Exchange Forward | Brazil [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2025-08
Foreign Exchange Forward | Canada [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2025-03
Sales [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings		(7)		(12)
Cost of Goods Sold [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings		(4)		(4)
Derivatives Designated as Hedging Instruments [Member] | Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings		28	$ 4	44
Derivatives Designated as Hedging Instruments [Member] | Power Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Aluminum forecast sales | kt	1,344		1,344		1,456
Derivatives Designated as Hedging Instruments [Member] | Power Contract [Member] | Cash Flow Hedging [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amount of (loss) gain expected to be recognized into earnings over the next 12 months			$ (245)
Derivatives Designated as Hedging Instruments [Member] | Sales [Member] | Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings		32		48
Derivatives Designated as Hedging Instruments [Member] | Cost of Goods Sold [Member] | Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gain (loss) reclassed from Other comprehensive loss to earnings		$ (4)		$ 4