Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012
Interrelationship Of Future Aluminum And Oil Prices [Member] | Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair Value	$ 2,000,000
Interrelationship Of Future Aluminum And Oil Prices [Member] | Aluminum Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,084
Maturity year of future aluminum price	2012
Expected future oil prices	91
Interrelationship Of Future Aluminum And Oil Prices [Member] | Aluminum Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,600
Maturity year of future aluminum price	2018
Expected future oil prices	112
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair Value	607,000,000
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Consumer price index base year	1982
Consumer price index base	100
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,090
Maturity year of future aluminum price	2012
Foreign currency exchange rate	1
Foreign currency exchange rate	1.03
Foreign currency exchange rate expected year	2012
Expected Consumer price index	227
Expected Consumer price index, Year	2012
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,602
Price of aluminum beyond forward curve	2,018
Foreign currency exchange rate	0.89
Foreign currency exchange rate expected year	2016
Expected Consumer price index	250
Expected Consumer price index, Year	2016
Price Of Aluminum Beyond Forward Curve [Member] | Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair Value	668,000,000
Price Of Aluminum Beyond Forward Curve [Member] | Aluminum Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of aluminum beyond forward curve	2,828
Maturity data of aluminum beyond forward curve	2023
Price Of Aluminum Beyond Forward Curve [Member] | Aluminum Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of aluminum beyond forward curve	3,048
Maturity data of aluminum beyond forward curve	2027
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair Value	35,000,000
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	1.97%
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	1.45%
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	2.49%
Price Of Electricity Beyond Forward Curve [Member] | Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair Value	8,000,000
Price Of Electricity Beyond Forward Curve [Member] | Energy Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of electricity beyond forward curve	77
Maturity date of electricity beyond forward curve	2012
Price Of Electricity Beyond Forward Curve [Member] | Energy Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of electricity beyond forward curve	$ 170
Maturity date of electricity beyond forward curve	2036