Derivatives and Other Financial Instruments - Additional Information (Detail) kt in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) kt	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) kt	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) kt	Mar. 31, 2021 Contract
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive loss to earnings	$ (37)	$ (82)	$ (280)	$ (201)
Accumulated other comprehensive loss (G)	(3,644)		$ (3,644)		$ (4,592)
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of expected to be operational in Alumar Restart			75.00%
Accumulated other comprehensive loss (G)	18		$ 18
Level 1 Derivative Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized (loss) gain reclassed from Other comprehensive loss to earnings	32	(4)	$ 12	(7)
Commodity Contract | Level 1 [Member] | Brazil [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instrument, start date			Apr. 30, 2022
Commodity Contract | Level 1 [Member] | Brazil [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2023-12
Commodity Contract | Level 1 [Member] | San Ciprian (Spain) Strike [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2022-10
Foreign Exchange Forward | Brazil [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year			2024-12
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
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 (loss) gain reclassed from Other comprehensive loss to earnings	$ 32		$ 12	(7)
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	1,740		1,740		1,905
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			$ (148)
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 (loss) gain reclassed from Other comprehensive loss to earnings	$ 34	$ (4)	16	(6)
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 (loss) gain reclassed from Other comprehensive loss to earnings	$ (2)		$ (4)	$ (1)
Derivatives Not Designated as Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of financial contracts | Contract						4