Income Taxes - Additional Information (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Jul. 12, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Tax benefit (charge) realized from exercise of employee stock options				$ (1,000,000)	$ 0	$ 2,000,000
Unamortized tax-deductible goodwill resulting from intercompany stock sales and reorganizations				$ 24,000,000
Unamortized tax-deduction rate on goodwill				25.00%
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)		$ 272,000,000
Percentage of temporary tax differences that reverse within the carryforward period					30.00%
Percentage of deferred tax asset exclusive of reversing temporary differences					70.00%
Increase (decrease) to valuation allowance			$ 1,267,000,000	$ 831,000,000	$ 772,000,000	180,000,000
Valuation allowance		2,584,000,000	1,940,000,000	2,584,000,000	1,940,000,000	$ 1,291,000,000	$ 1,151,000,000
Tax credit carryforward, valuation allowance		379,000,000		379,000,000
Net deferred tax assets other		(24,000,000)	(164,000,000)	$ (24,000,000)	$ (164,000,000)
Percentage of tax rate decreased				52.50%	(15.70%)	(1.00%)
Percentage of the effect of unrecognized tax benefit, if recorded				15.00%	6.00%	7.00%
Interest or penalties recognized				$ 1,000,000	$ 0	$ 0
Income related to accrued interest and penalties				2,000,000	0	1,000,000
Amount accrued for payment of interest and penalties		2,000,000	2,000,000	2,000,000	2,000,000
Alcoa Corporation
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards, foreign, expired during period					302,000,000
Discrete income tax charge for valuation allowances					1,267,000,000
Net deferred tax assets other			(2,000,000)		(2,000,000)
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Increase (decrease) to valuation allowance				98,000,000
Valuation allowance		750,000,000		750,000,000
Foreign Tax Authority
Income Tax Contingency [Line Items]
Foreign tax credits carry forward period	10 years
Tax credit carryforward, valuation allowance		302,000,000		302,000,000		134,000,000
Deferred tax assets, tax credit carryforwards, foreign, expired during period				57,000,000	128,000,000	15,000,000
Iceland And Suriname
Income Tax Contingency [Line Items]
Discrete income tax charge for valuation allowances						141,000,000
Suriname
Income Tax Contingency [Line Items]
Valuation allowance						$ 85,000,000
Suriname | Minimum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2016
Suriname | Maximum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2022
Iceland
Income Tax Contingency [Line Items]
Valuation allowance						$ 56,000,000
Iceland | Minimum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2017
Iceland | Maximum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2023
Internal Revenue Service IRS | Alcoa Corporation
Income Tax Contingency [Line Items]
Net deferred tax assets			925,000,000		925,000,000
Luxembourg
Income Tax Contingency [Line Items]
Valuation allowance			280,000,000		280,000,000
Discrete income tax charge for valuation allowances					42,000,000
Luxembourg | Alcoa Corporation
Income Tax Contingency [Line Items]
Net deferred tax assets			42,000,000		42,000,000
Federal Tax Services of Russia
Income Tax Contingency [Line Items]
Net deferred tax assets			19,000,000		19,000,000
Canada Revenue Agency
Income Tax Contingency [Line Items]
Net deferred tax assets			20,000,000		20,000,000
Australia
Income Tax Contingency [Line Items]
Valuation allowance			93,000,000		93,000,000
Tax Authority, Spain
Income Tax Contingency [Line Items]
Valuation allowance			$ 163,000,000		$ 163,000,000
Tax Authority, Spain | Foreign Tax Authority
Income Tax Contingency [Line Items]
Increase (decrease) to valuation allowance				675,000,000
Excess Foreign Tax Credits
Income Tax Contingency [Line Items]
Tax credit carryforward, valuation allowance		23,000,000		23,000,000
Tax Credits, Other Adjustments
Income Tax Contingency [Line Items]
Tax credit carryforward, valuation allowance		$ (14,000,000)		$ (14,000,000)