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Financial contributions.

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

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Notices include claims for compounded interest on the tax amount.

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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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Estimated amount of loss resulting from an adverse tax position.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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Amount of increase (decrease) to previously recorded tax expense. Includes, but is not limited to, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, and IRS tax settlement.

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Contingencies - Additional Information - 1 (Detail) € in Millions, $ in Millions			1 Months Ended			3 Months Ended								6 Months Ended			12 Months Ended	30 Months Ended
	Sep. 17, 2020 USD ($)	Sep. 17, 2020 AUD ($)	Mar. 31, 2013 USD ($)	May 31, 2012 USD ($)	May 31, 2012 BRL (R$)	Jun. 30, 2021 USD ($)	Jun. 30, 2021 AUD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 EUR (€)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 AUD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Jun. 30, 2021 USD ($)	Jun. 30, 2021 BRL (R$)	Jun. 30, 2021 AUD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2021 AUD ($)	Sep. 30, 2020 AUD ($)	Jul. 07, 2020 USD ($)	Jul. 07, 2020 AUD ($)	Mar. 31, 2013 BRL (R$)
Loss Contingencies [Line Items]
Other noncurrent liabilities and deferred credits						$ 550,000,000		$ 515,000,000						$ 550,000,000				$ 550,000,000
AWAC [Member] \| Alumina Limited [Member]
Loss Contingencies [Line Items]
Non-controlling interest, ownership percentage						40.00%								40.00%				40.00%	40.00%
Alcoa Corporation [Member] \| AWAC [Member]
Loss Contingencies [Line Items]
Ownership interest percentage						60.00%								60.00%				60.00%	60.00%
Maximum [Member] \| PARTER Capital Group AG [Member] \| Spain [Member] \| Aviles and La Coruna Smelters [Member] \| Avilés and La Coruña Aluminum Facilities [Member]
Loss Contingencies [Line Items]
Financial contributions																	$ 95,000,000
Financial contributions paid to buyer in relation to divestiture																		$ 78,000,000
Tax Authority, Spain [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss												$ 30,000,000	€ 26
Reversal of reserve recorded in provision for income taxes to establish liability for estimated loss								$ 32,000,000	€ 26
Brazilian Federal Revenue Office [Member] \| Alcoa World Alumina Brasil [Member]
Loss Contingencies [Line Items]
Disallowed tax credits			$ 110,000,000																				R$ 220,000,000
Percentage of penalty of the gross disallowed amount			50.00%
Value added tax receivable				$ 41,000,000	R$ 82,000,000
Brazilian Federal Revenue Office [Member] \| Minimum [Member] \| Alcoa World Alumina Brasil [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss														$ 0
Brazilian Federal Revenue Office [Member] \| Maximum [Member] \| Alcoa World Alumina Brasil [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss														44,000,000	R$ 220,000,000
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						$ 3,000,000	$ 5			$ 165,000,000	$ 219			7,000,000		$ 10
Other noncurrent liabilities and deferred credits						172,000,000								172,000,000				172,000,000	$ 229
Tax assessment deposit						$ 80,000,000								$ 80,000,000				$ 80,000,000	$ 107