Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013
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	$ 1,000,000
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	1,894
Maturity year of future aluminum price	2013
Expected future oil prices	91
Maturity year of future oil price	2018
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	2,335
Maturity year of future aluminum price	2018
Expected future oil prices	110
Maturity year of future oil price	2013
Interrelationship of future aluminum prices, foreign currency exchange rates, and U.S. consumer price index [Member] | Aluminum contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	509,000,000
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]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,883
Maturity year of future aluminum price	2013
Foreign currency exchange rate	1
Foreign currency exchange rate	1.04
Foreign currency exchange rate expected year	2013
Expected consumer price index	233
Expected consumer price index, Year	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]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,172
Maturity year of future aluminum price	2016
Foreign currency exchange rate	0.94
Foreign currency exchange rate expected year	2016
Consumer price index base year	1982
Expected consumer price index	253
Consumer price index base	100
Expected consumer price index, Year	2016
Interrelationship of LME price to overall energy price [Member] | Aluminum contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	12,000,000
Interrelationship of LME price to overall energy price [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	1,928
Maturity year of future aluminum price	2013
Interrelationship of LME price to overall energy price [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	2,359
Maturity year of future aluminum price	2019
Price of electricity beyond forward curve [Member] | Energy contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, 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	78
Maturity date of electricity beyond forward curve	2023
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
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	478,000,000
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	2,569
Maturity year of future aluminum price	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	2,766
Maturity year of future aluminum price	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	$ 32,000,000
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	1.71%
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	2.06%
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]
Percentage of credit spread	1.88%