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Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Income Tax Contingency [Line Items]
Effective tax rate	48.50%		60.30%		41.40%	76.00%
U.S federal statutory rate			35.00%			35.00%
Income tax benefit recognized	$ 100,000,000		$ 199,000,000		$ 401,000,000	$ 200,000,000
Discrete income tax charge						56,000,000
Operational losses in certain foreign jurisdictions			8,000,000			44,000,000
Discrete income tax benefit			9,000,000
Alcoa World Alumina and Chemicals [Member]
Income Tax Contingency [Line Items]
Discrete income tax charge		$ 83,000,000		$ 85,000,000
Alcoa World Alumina and Chemicals [Member] | Alumina Limited [Member]
Income Tax Contingency [Line Items]
Percent of investment in AWAC joint venture by Alumina Limited		40.00%
Suriname [Member]
Income Tax Contingency [Line Items]
U.S federal statutory rate	35.00%
Income tax benefit recognized	$ 0
Net discrete income tax charge					$ 34,000,000
Brazil [Member]
Income Tax Contingency [Line Items]
Discrete income tax charge			56,000,000
Italy [Member]
Income Tax Contingency [Line Items]
Income tax benefit recognized			$ 0
Russia [Member]
Income Tax Contingency [Line Items]
U.S federal statutory rate					35.00%
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		$ 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

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