Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Tax Contingency [Line Items]
Effective tax rate	26.60%		37.70%	39.40%	1.50%
Income tax benefit recognized	35.00%		35.00%	35.00%	35.00%
Operational losses in certain foreign jurisdictions	$ 21,000,000		$ 20,000,000	$ 14,000,000	$ 36,000,000
Income tax benefit recognized	75,000,000		78,000,000	301,000,000	$ 1,000,000
Percentage of tax differences that reverse within end of 2014					(36.50%)
Russia [Member]
Income Tax Contingency [Line Items]
Income tax benefit recognized				0
Alcoa World Alumina and Chemicals [Member]
Income Tax Contingency [Line Items]
Discrete income tax charge		$ 83,000,000		85,000,000
Alumina Limited [Member] | Alcoa World Alumina and Chemicals [Member]
Income Tax Contingency [Line Items]
Percent of investment in AWAC joint venture by Alumina Limited		40.00%
Alcoa [Member] | Alcoa World Alumina and Chemicals [Member]
Income Tax Contingency [Line Items]
Percent of investment in AWAC joint venture by Aloca		60.00%
Deferred tax liability	51,000,000	$ 50,000,000		51,000,000
Deferred tax asset written off as valuation allowance		60.00%
Foreign Jurisdictions [Member]
Income Tax Contingency [Line Items]
Income tax benefit recognized	$ 0		$ 0	0	$ 0
United States [Member]
Income Tax Contingency [Line Items]
Discrete income tax benefit				$ 34,000,000