Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)				3 Months Ended			3 Months Ended			3 Months Ended			3 Months Ended			3 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2012	Mar. 31, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member]	Mar. 31, 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	Mar. 31, 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	Mar. 31, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member]	Mar. 31, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member]	Mar. 31, 2014 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member]	Mar. 31, 2014 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member]	Mar. 31, 2014 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Minimum [Member] Discounted Cash Flow [Member]	Mar. 31, 2014 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Maximum [Member] Discounted Cash Flow [Member]	Mar. 31, 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	$ 371,000,000	$ 390,000,000	$ 596,000,000			$ 292,000,000			$ 34,000,000			$ 11,000,000
Price of aluminum beyond forward curve																2,401	2,554
Derivative Liabilities, Fair value	440,000,000	479,000,000													384,000,000			20,000,000
Expected future aluminum prices				1,705	2,066		1,724	1,958		1,806	2,143
Maturity year of future aluminum price				2014	2018		2014	2016		2014	2019					2023	2027
Expected future oil prices				93	108
Percentage of credit spread																			0.57%	1.88%	1.23%
Price of electricity beyond forward curve													$ 82	$ 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							0.92	0.87
Foreign currency exchange rate expected year							2014	2016
Consumer price index base year								1982
Expected consumer price index							232	246
Consumer price index base								100
Expected consumer price index, Year							2014	2016