Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)						9 Months Ended			9 Months Ended			9 Months Ended			9 Months Ended			9 Months Ended			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Aluminum Contracts [Member]	Dec. 31, 2012 Aluminum Contracts [Member]	Sep. 30, 2013 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member]	Sep. 30, 2013 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member]	Sep. 30, 2013 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	Sep. 30, 2013 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	Sep. 30, 2013 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member]	Sep. 30, 2013 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member]	Sep. 30, 2013 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member]	Sep. 30, 2013 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member]	Sep. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Minimum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Maximum [Member] Discounted Cash Flow [Member]	Sep. 30, 2013 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	$ 80,000,000	$ 117,000,000	$ 44,000,000	$ 72,000,000				$ 373,000,000			$ 5,000,000			$ 4,000,000
Price of aluminum beyond forward curve																		2,589	2,766
Derivative Liabilities, Fair value	85,000,000	86,000,000	78,000,000	69,000,000													448,000,000			28,000,000
Expected future aluminum prices						1,785	2,295		1,803	2,141		1,899	2,355
Maturity year of future aluminum price						2013	2018		2013	2016		2013	2019					2023	2027
Expected future oil prices						89	109
Percentage of credit spread																					1.18%	2.28%	1.73%
Price of electricity beyond forward curve															$ 80	$ 154
Maturity year of future oil price						2018	2013
Maturity date of electricity beyond forward curve															2013	2036
Foreign currency exchange rate									1
Foreign currency exchange rate									0.93	0.87
Foreign currency exchange rate expected year									2013	2016
Consumer price index base year										1982
Expected consumer price index									232	249
Consumer price index base										100
Expected consumer price index, Year									2013	2016