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Income tax payable, possible unrecorded assessed amount from taxing authority.

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Payment amount refund percentage.

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Percentage of penalty on amount of additional taxes due.

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Proposed administrative penalties.

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Tax assessment deposit.

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Tax credit previously claimed and disallowed by tax authority.

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Carrying amount as of the balance sheet date of unearned revenue or income, not otherwise specified in the taxonomy, which is expected to be taken into income after one year or beyond the normal operating cycle, if longer and noncurrent obligations not separately disclosed in the balance sheet (other liabilities, noncurrent).

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A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions.

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Contingencies - Additional Information - 1 (Detail) $ in Millions			1 Months Ended							3 Months Ended
	Sep. 17, 2020 USD ($)	Sep. 17, 2020 AUD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 BRL (R$)	Feb. 28, 2022 USD ($)	Feb. 28, 2022 BRL (R$)	Mar. 31, 2013 USD ($)	May 31, 2012 USD ($)	May 31, 2012 BRL (R$)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 AUD ($)	Mar. 31, 2022 BRL (R$)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 AUD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 AUD ($)	Mar. 31, 2022 AUD ($)	Feb. 28, 2022 BRL (R$)	Dec. 31, 2021 USD ($)	Sep. 30, 2020 AUD ($)	Jul. 07, 2020 USD ($)	Jul. 07, 2020 AUD ($)	Mar. 31, 2013 BRL (R$)
Loss Contingencies [Line Items]
Other noncurrent liabilities and deferred credits			$ 601,000,000							$ 601,000,000									$ 599,000,000
Aviles And La Coruna Facilities [Member]
Loss Contingencies [Line Items]
Restructuring Charges										$ 77,000,000
AWAC [Member] \| Alumina Limited [Member]
Loss Contingencies [Line Items]
Non-controlling interest, ownership percentage			40.00%							40.00%							40.00%
Australian Taxation Office [Member] \| Foreign Jurisdiction [Member] \| AofA [Member]
Loss Contingencies [Line Items]
Additional income tax payable, exclusive of interest and penalties																					$ 160,000,000	$ 214
Notices include claims for compounded interest on the tax amount																					$ 530,000,000	$ 707
Proposed administrative penalties	$ 96,000,000	$ 128
Payment of dispute resolution practices income tax percentage															50.00%	50.00%
Assessed income tax amount exclusive of interest and penalties															$ 74,000,000					$ 107
Payment amount refund percentage															50.00%	50.00%
Reduction in current year cash tax payment										$ 4,000,000	$ 5		$ 14,000,000	$ 19	$ 169,000,000	$ 219
Other noncurrent liabilities and deferred credits			$ 182,000,000							182,000,000							$ 243
Tax assessment deposit			80,000,000							$ 80,000,000							$ 107
Alcoa World Alumina Brasil [Member] \| Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Disallowed tax credits					$ 4,000,000		$ 110,000,000											R$ 19,000,000					R$ 220,000,000
Percentage of penalty of the gross disallowed amount							50.00%
Value added tax receivable			$ 9,000,000	R$ 44,000,000	$ 14,000,000	R$ 65,000,000		$ 41,000,000	R$ 82,000,000
Alcoa Corporation [Member] \| AWAC [Member]
Loss Contingencies [Line Items]
Ownership interest percentage			60.00%							60.00%							60.00%
Minimum [Member] \| Alcoa World Alumina Brasil [Member] \| Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss										$ 0
Maximum [Member] \| Alcoa World Alumina Brasil [Member] \| Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss										$ 50,000,000		R$ 239,000,000