Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) - Level 3 [Member] - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	$ 2	$ 0
Derivative Liabilities, Fair value	1,293	$ 838
Energy Contracts [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	2
Derivative Liabilities, Fair value	1,293
Financial Contracts [Member] | Energy Contracts [Member] | Interrelationship Of Forward Energy Price, LME Forward Price And Consumer Price Index [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	2
Power Contract [Member] | Energy Contracts [Member] | MWh of Energy Needed to Produce Forecasted Mt of Aluminum at Rate of 4 Million MWh Per Year [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	284
Power Contract [Member] | Energy Contracts [Member] | MWh of Energy Needed to Produce Forecasted Mt of Aluminum at Rate of 17 Million MWh Per Year [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	1,006
Power Contract [Member] | Energy Contracts [Member] | Estimated Spread Between The Respective 30-Year Debt Yield Of Alcoa Corporation And The Counterparty [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	$ 3