Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	$ 209	$ 268
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	140
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,798
Maturity year of future aluminum price	2015
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,869
Maturity year of future aluminum price	2016
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Estimated Foreign Currency Exchange Rate [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency exchange rate	0.77
Foreign currency exchange rate expected year	2015
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Estimated Foreign Currency Exchange Rate [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency exchange rate	0.78
Foreign currency exchange rate expected year	2016
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Consumer Price Index [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected consumer price index	231
Expected consumer price index, Year	2015
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Consumer Price Index [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Consumer price index base year	1982
Consumer price index base	100
Expected consumer price index	239
Expected consumer price index, Year	2016
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,798
Maturity year of future aluminum price	2015
Expected future oil prices	56
Maturity year of future oil price	2015
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,983
Maturity year of future aluminum price	2018
Expected future oil prices	71
Maturity year of future oil price	2018
Assets [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,320
Maturity year of future aluminum price	2025
Assets [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,425
Maturity year of future aluminum price	2027
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,830
Maturity year of future aluminum price	2015
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,003
Maturity year of future aluminum price	2019
Assets [Member] | Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value	8
Assets [Member] | Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of electricity beyond forward curve	43
Maturity date of electricity beyond forward curve	2018
Assets [Member] | Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of electricity beyond forward curve	130
Maturity date of electricity beyond forward curve	2036
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	344
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,320
Maturity year of future aluminum price	2025
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium	0.1725
Foreign currency exchange rate expected year	2020
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium	0.1725
Liability [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	16
Liability [Member] | Embedded Aluminum Derivative [Member] | Two Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,533
Maturity year of future aluminum price	2029
Liability [Member] | Embedded Aluminum Derivative [Member] | Two Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency exchange rate expected year	2029
Liability [Member] | Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,870
Maturity year of future aluminum price	2036
Liability [Member] | Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency exchange rate expected year	2036
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	16
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	1.44%
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	1.17%
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	1.70%
Liability [Member] | Embedded Aluminum Derivatives [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value	$ 4