Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)					6 Months Ended			6 Months Ended			6 Months Ended			6 Months Ended					6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2012	Jun. 30, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member]	Jun. 30, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member]	Jun. 30, 2014 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] Index	Jun. 30, 2014 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] Index	Jun. 30, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member]	Jun. 30, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Price of Electricity beyond Forward Curve [Member] Energy Contracts [Member]	Jun. 30, 2014 Price of Electricity beyond Forward Curve [Member] Energy Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Price of Electricity beyond Forward Curve [Member] Energy Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Price of Aluminum beyond Forward Curve [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Price of Aluminum beyond Forward Curve [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member]	Jun. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Minimum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Maximum [Member] Discounted Cash Flow [Member]	Jun. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Median [Member] Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	$ 346,000,000	$ 390,000,000	$ 596,000,000	$ 257,000,000			$ 24,000,000			$ 24,000,000			$ 422,000,000
Price of aluminum beyond forward curve																2,453	2,594
Derivative Liabilities, Fair value	457,000,000	479,000,000																14,000,000
Expected future aluminum prices					1,871	2,141		1,858	2,019		1,846	2,183
Maturity year of future aluminum price					2014	2018		2014	2016		2014	2019				2023	2027
Expected future oil prices					99	113
Percentage of credit spread																			0.73%	1.61%	1.17%
Price of electricity beyond forward curve														$ 83	$ 154
Maturity year of future oil price					2018	2014
Maturity date of electricity beyond forward curve														2014	2036
Foreign currency exchange rate								1
Foreign currency exchange rate								0.94	0.90
Foreign currency exchange rate expected year								2014	2016
Consumer price index base year									1982
Expected consumer price index								236	248
Consumer price index base									100
Expected consumer price index, Year								2014	2016