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Income Taxes - Additional Information (Detail) € in Millions, $ in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 AUD ($)	Dec. 31, 2021 USD ($) Filer	Dec. 31, 2021 AUD ($) Filer	Dec. 31, 2020 USD ($)	Dec. 31, 2020 AUD ($)	Dec. 31, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2021 AUD ($)	Dec. 31, 2020 AUD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 AUD ($)
Income Taxes [Line Items]
Corporate income tax rate					21.00%	21.00%	21.00%	21.00%	21.00%	21.00%
Deferred income taxes					$ 319
Deferred tax liability					583
Deferred tax assets			$ 3,168		2,964		$ 3,168
Foreign undistributed net earnings for which no deferred taxes have been provided					2,377
Noncurrent income taxes (Q)			209		$ 191		$ 209
Percentage of the effect of unrecognized tax benefit, if recorded					0.00%	0.00%	3.00%	3.00%	3.00%	(7.00%)
Reductions for tax positions of prior years					$ 0		$ 26
Interest and penalties recognized					0		0			$ 2
Income related to accrued interest and penalties							0			13	$ 1
Amount accrued for payment of interest and penalties			2		$ 2		2
Secretariat of the Federal Revenue Bureau of Brazil [Member]
Income Taxes [Line Items]
Tax credit carryforward, limitations on use					30.00%	30.00%
Tax Authority, Spain [Member]
Income Taxes [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss	$ 30	€ 26									30	€ 26
Interest recorded in provision for income taxes to establish liability for estimated loss											$ 10	€ 9
Gain recorded from reversal of 2018 entry							32		€ 26
Reductions for tax positions of prior years							$ 21		€ 17
Percentage of share of the estimated loss											49.00%	49.00%
Divesture of MRC [Member]
Income Taxes [Line Items]
Divestiture not deductible for tax purposes										65
Avilés and La Coruña Aluminum Facilities [Member]
Income Taxes [Line Items]
Divestiture not deductible for tax purposes										35
Alcoa World Alumina Brasil [Member] \| Alumar Refinery [Member]
Income Taxes [Line Items]
Corporate income tax rate					15.25%	15.25%	34.00%	34.00%	34.00%
Increase (decrease) in discrete income tax charge and benefit due tax holiday							$ (15)			$ (7)
Income tax holiday, description					The holiday related to production at the Alumar refinery will end on December 31, 2027, and the holiday related to the operation of the Juruti (Brazil) bauxite mine will end on December 31, 2026.	The holiday related to production at the Alumar refinery will end on December 31, 2027, and the holiday related to the operation of the Juruti (Brazil) bauxite mine will end on December 31, 2026.
Valuation Allowance Against Increased Deferred Tax Asset [Member] \| GILTI [Member]
Income Taxes [Line Items]
Income tax charge (benefit) due to implementing provisions of TCJA							138
U.S. Federal Net Operating Loss Carryforwards [Member] \| GILTI [Member]
Income Taxes [Line Items]
Income tax charge (benefit) due to implementing provisions of TCJA							(138)
Foreign [Member]
Income Taxes [Line Items]
Deferred income taxes					$ 318
Percentage of net deferred tax asset relates to seven of Alcoa Corporation's income tax filers					85.00%	85.00%
Number of Alcoa Corporation's income tax filers \| Filer					6	6
Deferred tax liability					$ 483
Deferred tax assets					$ 1,898
Foreign [Member] \| Latest Tax Year [Member]
Income Taxes [Line Items]
Income Tax Examination Year Under Examination					2020	2020
Foreign [Member] \| Earliest Tax Year [Member]
Income Taxes [Line Items]
Income Tax Examination Year Under Examination					2009	2009
Foreign [Member] \| Australian Taxation Office [Member]
Income Taxes [Line Items]
Assessed income tax amount exclusive of interest and penalties															$ 74	$ 107
Lower cash tax payments			169	$ 219	$ 14	$ 19
Noncurrent income taxes (Q)			$ 169		174		169						$ 238	$ 219
Foreign [Member] \| AofA [Member]
Income Taxes [Line Items]
Deferred tax liability					182
Foreign [Member] \| AofA [Member] \| Australian Taxation Office [Member]
Income Taxes [Line Items]
Assessed income tax amount exclusive of interest and penalties															$ 74	$ 107
Lower cash tax payments					14	$ 19	$ 169	$ 219
Foreign [Member] \| Alcoa World Alumina Brasil [Member]
Income Taxes [Line Items]
Deferred income taxes					68
Foreign [Member] \| Alcoa Aluminio SA [Member]
Income Taxes [Line Items]
Deferred income taxes					141
Foreign [Member] \| Alcoa Canada Company [Member]
Income Taxes [Line Items]
Deferred income taxes					148
Foreign [Member] \| Alcoa Lauralco Management Company [Member]
Income Taxes [Line Items]
Deferred income taxes					67
Foreign [Member] \| Alcoa Wolinbec Company [Member]
Income Taxes [Line Items]
Deferred income taxes					34
Foreign [Member] \| Espanola [Member]
Income Taxes [Line Items]
Deferred tax assets					103
United States [Member]
Income Taxes [Line Items]
Deferred income taxes					1
Deferred tax liability					100
Deferred tax assets					$ 1,066
United States [Member] \| Latest Tax Year [Member]
Income Taxes [Line Items]
Income Tax Examination Year Under Examination					2018	2018