Contingencies and Commitments - Additional Information - 2 (Detail) $ in Millions				1 Months Ended	12 Months Ended
	Oct. 01, 2024 USD ($)	Oct. 01, 2024 AUD ($)	Apr. 08, 2015 USD ($) Refinery	Apr. 30, 2016 Refinery	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Aug. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Number of alumina refineries to be powered under supplied agreement | Refinery				3
Total asset					$ 225,000,000	$ 283,000,000
Guarantees of third party related to project financing					$ 0	0
Line of credit renew or expire starting year					2025
Line of credit renew or expire ending year					2026
Letters of credit, total amount committed					$ 316,000,000
Letter of credit agreement, expiration date					May 01, 2026
Total amount committed under outstanding surety bonds					$ 245,000,000
Minimum [Member]
Loss Contingencies [Line Items]
Surety bonds, expiration date					2025
Maximum [Member]
Loss Contingencies [Line Items]
Surety bonds, expiration date					2029
Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Outstanding bank guarantees and letters of credit					$ 12,000,000
Total amount committed under outstanding surety bonds					7,000,000
Parent Co [Member]
Loss Contingencies [Line Items]
Outstanding bank guarantees and letters of credit					6,000,000
Total amount committed under outstanding surety bonds					7,000,000
Standby Letter of Credit Agreement [Member]
Loss Contingencies [Line Items]
Line of credit facility, outstanding borrowings					87,000,000
Principal amount of debt								$ 200,000,000
Letter of Credit [Member]
Loss Contingencies [Line Items]
Line of credit facility, outstanding borrowings					87,000,000
AofA [Member]
Loss Contingencies [Line Items]
Bank guarantee delivered	$ 62,000,000	$ 100
AofA [Member] | Service Agreements [Member] | Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Number of alumina refineries to be powered under supplied agreement | Refinery			3
Gas supply agreement prepayment amount			$ 500,000,000
AofA [Member] | Service Agreements [Member] | Prepaid Expenses and Other Current Assets [Member] | Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Total asset					35,000,000	37,000,000
AofA [Member] | Service Agreements [Member] | Other Noncurrent Assets [Member] | Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Total asset					$ 225,000,000	283,000,000
Energy Obligation [Member]
Loss Contingencies [Line Items]
Expiration date of unconditional purchase obligations for energy starting year					2040
Expiration date of unconditional purchase obligations for energy ending year					2041
Purchase obligations due in 2025					$ 50,000,000
Purchase obligations due in 2026					53,000,000
Purchase obligations due in 2027					55,000,000
Purchase obligations due in 2028					57,000,000
Purchase obligations due in 2029					59,000,000
Purchase obligations due thereafter					740,000,000
Purchase obligations expenditures					50,000,000	$ 53,000,000	$ 58,000,000
Energy Raw Materials And Other Goods And Services [Member]
Loss Contingencies [Line Items]
Purchase obligations due in 2025					4,431,000,000
Purchase obligations due in 2026					1,764,000,000
Purchase obligations due in 2027					1,497,000,000
Purchase obligations due in 2028					1,275,000,000
Purchase obligations due in 2029					1,267,000,000
Purchase obligations due thereafter					$ 7,233,000,000