Derivatives and Other Financial Instruments - Additional Information (Detail) kt in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) Member Smelter kt	Dec. 31, 2023 USD ($) kt	Dec. 31, 2022 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Minimum members required for strategic risk management committee | Member	3
Realized gain (loss) reclassed from other comprehensive (loss) income to earnings	$ (288)	$ (130)
Unrealized gain (loss) in accumulated other comprehensive loss	$ (5,110)	(3,645)
Other derivative contracts estimated term of quoted market prices, in years	10 years
Other derivative beyond market estimated quoted price of aluminum by extrapolating	10 years
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) in accumulated other comprehensive loss		11
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of smelters | Smelter	7
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) income to earnings	$ 1	86
Commodity Contract | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year	2024-12
Commodity Contract | Level 1 [Member] | Brazil [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year	2023-12
Foreign Exchange Forward | Brazil [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year	2026-10
Foreign Exchange Forward | Brazil [Member] | U.S. Dollar Aluminum Sales [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative instruments, expiration month and year	2023-12
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	2027-12
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 | Australia [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 | Canada [Member] | Canadian Dollar Expenses [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) income to earnings	$ 2	31	$ 10
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) income to earnings	(1)	(5)	$ (5)
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) income to earnings	$ 1	$ 86
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	1,230	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 gain (loss) expected to be recognized into earnings over the next 12 months	$ 251
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) income to earnings	2	$ 91
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) income to earnings	$ (1)	$ (5)