Income Taxes - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Unamortized tax-deductible goodwill resulting from intercompany stock sales and reorganizations			$ 26,000,000
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	$ 272,000,000	$ 59,000,000
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit), one-time transition tax			16,000,000
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit), charge to record valuation allowance on U.S. foreign tax credits			$ 43,000,000
Percentage of temporary tax differences that reverse within the carryforward period			24.00%
Percentage of deferred tax asset exclusive of reversing temporary differences			76.00%
Deferred tax asset, increase (decrease), amount, foreign tax credit			$ 46,000,000	$ 9,000,000	$ 302,000,000
Deferred tax assets, tax credit carryforwards, foreign, expired during period			8,000,000	57,000,000	128,000,000
Deferred tax assets, valuation allowance, foreign tax credit			417,000,000
Valuation allowance, amount released	98,000,000	98,000,000	10,000,000	98,000,000
Valuation allowance	2,584,000,000	2,584,000,000	2,486,000,000	2,584,000,000	1,940,000,000	$ 1,291,000,000
Increase (decrease) to valuation allowance			136,000,000	831,000,000	$ 772,000,000
Valuation allowance, changes due to losses no longer supported by temporary differences			20,000,000
Net deferred tax assets other	(24,000,000)	(24,000,000)	$ (94,000,000)	$ (24,000,000)
Percentage of the effect of unrecognized tax benefit, if recorded			5.00%	15.00%	6.00%
Interest or penalties recognized			$ 22,000,000	$ 1,000,000	$ 0
Income related to accrued interest and penalties			1,000,000	2,000,000	0
Amount accrued for payment of interest and penalties	2,000,000	2,000,000	21,000,000	2,000,000
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options					0
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
Foreign Tax Authority
Income Tax Contingency [Line Items]
Increase (decrease) to valuation allowance			61,000,000	675,000,000
Internal Revenue Service IRS | Alcoa Corporation
Income Tax Contingency [Line Items]
Net deferred tax assets	925,000,000	925,000,000		925,000,000
Luxembourg
Income Tax Contingency [Line Items]
Valuation allowance	280,000,000	280,000,000		280,000,000
Luxembourg | Alcoa Corporation
Income Tax Contingency [Line Items]
Net deferred tax assets	42,000,000	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		19,000,000
Canada Revenue Agency
Income Tax Contingency [Line Items]
Net deferred tax assets	20,000,000	20,000,000		20,000,000
Australia
Income Tax Contingency [Line Items]
Valuation allowance	93,000,000	93,000,000		93,000,000
Tax Authority, Spain
Income Tax Contingency [Line Items]
Valuation allowance	$ 163,000,000	$ 163,000,000		$ 163,000,000
Tax Authority, Spain | Foreign Tax Authority
Income Tax Contingency [Line Items]
Increase (decrease) to valuation allowance			92,000,000
Other Net State Deferred Tax Asset
Income Tax Contingency [Line Items]
Valuation allowance			$ 675,000,000