Income Taxes - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended	9 Months Ended
	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective tax rate		41.30%	90.20%		34.80%	456.40%
Estimated effective tax rate		34.20%		31.90%	34.20%
Statutory rate			35.00%		35.00%	35.00%
Pretax income		$ 288	$ 102	$ 655	$ 943	$ (39)
Discrete income tax charge		13			11
Favorable impact of interim period treatment of operational losses		8			6
Tax holiday amount		10			10
Deferred income taxes assets		862			862		$ 741
Deferred income taxes					64	$ 6
Income tax reconciliation, tax credits with no tax benefit realizable						(491.40%)
Net deferred tax asset		$ 562			$ 562		449
Percentage of net deferred tax asset that relates to four of foreign income tax filers					90.00%
Foreign [Member]
Income Tax Disclosure [Abstract]
Net deferred tax asset							$ 432
Brazil [Member]
Income Tax Disclosure [Abstract]
Statutory rate	34.00%	15.25%
Foreign tax credits carry forward period		10 years
Deferred income taxes assets		$ 10			$ 10
Deferred income taxes		10
Deferred income taxes assets, net of minority interest		6
Deferred income taxes, net of minority interest		6			$ 6
Brazil [Member] | Maximum [Member]
Income Tax Disclosure [Abstract]
Percentage of utilization of existing tax loss carryforward to taxable income					30.00%
Brazil [Member] | Foreign [Member] | Alcoa Aluminio S.A. [Member]
Income Tax Disclosure [Abstract]
Net deferred tax asset		259			$ 259
Brazil [Member] | Foreign [Member] | Alcoa World Alumina Brasil Ltda. [Member]
Income Tax Disclosure [Abstract]
Net deferred tax asset		195			$ 195
Spain [Member] | Maximum [Member]
Income Tax Disclosure [Abstract]
Percentage of utilization of existing tax loss carryforward to taxable income					25.00%
Spain [Member] | Foreign [Member]
Income Tax Disclosure [Abstract]
Net deferred tax asset		554			$ 554
Spain [Member] | Foreign [Member] | Alumina Espanola, S.A. [Member]
Income Tax Disclosure [Abstract]
Net deferred tax asset		108			108
Australia [Member] | Foreign [Member] | Alcoa of Australia Limited [Member]
Income Tax Disclosure [Abstract]
Net deferred tax liability		$ 177			$ 177