Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Corporate income tax rate	21.00%	21.00%	35.00%	35.00%	35.00%
Net deferred tax assets	$ 517		$ 517
Deferred tax assets	3,112		3,112	$ 3,088
Deferred tax liabilities	668		668
Deferred tax assets, valuation allowance	1,927		1,927	1,755	$ 712	$ 486
Valuation allowance	0		0	$ 0
Foreign undistributed net earnings for which no deferred taxes have been provided	940		940
Earnings generated during 2017 deemed to be permanently reinvested	150		$ 150
Percentage of the effect of unrecognized tax benefit, if recorded			1.00%	10.00%	4.00%
Interest and penalties recognized			$ 1	$ 1	$ 7
Income related to accrued interest and penalties			6	2	$ 1
Amount accrued for payment of interest and penalties	2		$ 2	$ 6
Income tax rate on global intangible low tax income		10.50%
Net operating losses carry forward period		0 years	20 years
Net operating losses carryback period		0 years	2 years
Percentage of taxable income related to net operating losses carry forward and carryback period		80.00%	100.00%
Charge resulting from preliminary analysis of provisions of TCJA			$ 22
Change in deferred tax assets related to TCJA			(506)
Change in valuation allowance related to TCJA			(433)
Change in deferred tax liabilities related to TCJA			$ (51)
Threshold percentage related to Tax Cuts and Jobs Act of 2017			3.00%
Alcoa World Alumina Brasil [Member]
Income Taxes [Line Items]
Decrease in deferred tax asset due to tax holiday			$ 26
Decrease in discrete income tax charge due tax holiday			26
Decrease in deferred tax asset due to tax holiday after noncontrolling interest			15
Decrease in discrete income tax charge due to tax holiday after noncontrolling interest			$ 15
Corporate income tax rate			15.25%
Tax holiday period			10 years
Iceland [Member]
Income Taxes [Line Items]
Deferred tax assets, valuation allowance	94		$ 94
Discrete income tax charge charge			60
Tax charge to Accumulated other comprehensive loss	34		34
Valuation allowance	56		56
Iceland And Suriname [Member]
Income Taxes [Line Items]
Discrete income tax charge charge			141
Suriname [Member]
Income Taxes [Line Items]
Deferred tax assets, valuation allowance	85		$ 85
Minimum [Member]
Income Taxes [Line Items]
One-time deemed repatriation of foreign undistributed net earnings, percentage			8.00%
Tax rate on base erosion payments		5.00%
Percentage of deductible expenses			3.00%
Maximum [Member]
Income Taxes [Line Items]
One-time deemed repatriation of foreign undistributed net earnings, percentage			15.50%
Tax rate on base erosion payments		10.00%
Secretariat of the Federal Revenue Bureau of Brazil [Member]
Income Taxes [Line Items]
Tax credit carryforward, limitations on use			30.00%
Tax Authority, Spain [Member]
Income Taxes [Line Items]
Tax credit carryforward, limitations on use			25.00%
Foreign [Member]
Income Taxes [Line Items]
Net deferred tax assets	511		$ 511
Deferred tax assets	1,948		1,948
Deferred tax liabilities	560		560
Deferred tax assets, valuation allowance	877		877
Foreign [Member] | Alcoa Aluminio [Member]
Income Taxes [Line Items]
Deferred tax assets	252		252
Foreign [Member] | Alcoa World Alumina Brasil [Member]
Income Taxes [Line Items]
Deferred tax assets	153		153
Foreign [Member] | Alumina Espanola, S.A. [Member]
Income Taxes [Line Items]
Deferred tax assets	112		112
Foreign [Member] | Other Foreign Countries [Member]
Income Taxes [Line Items]
Deferred tax liabilities	$ 6		$ 6
State and Local Jurisdiction [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Income tax return, year under examination			2006
State and Local Jurisdiction [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Income tax return, year under examination			2015