Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) MWh $ / MWh $ / Metric_Ton $ / lb $ / Barrels	Dec. 31, 2015 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value | $	$ 317	$ 1,137
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 Assets, Fair value | $	306
Derivative Liabilities, Fair value | $	$ 242
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,197
Maturity year of future aluminum price	2027
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,229
Maturity year of future aluminum price	2027
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	2,197
Maturity year of future aluminum price	2027
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 | $ / lb	0.0630
Midwest Premium expected year	2016
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 | $ / lb	0.075
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	1,680
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 Assets, Fair value | $	$ 4
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	1,662
Maturity year of future aluminum price	2016
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	1,802
Maturity year of future aluminum price	2019
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]
Maturity year of future aluminum price	2016
Expected future oil prices | $ / Barrels	49
Maturity year of future oil price	2016
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	1,762
Maturity year of future aluminum price	2018
Expected future oil prices | $ / Barrels	55
Maturity year of future oil price	2018
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value | $	$ 30
Megawatt hours per year | MWh	2,000,000
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [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	1,662
Maturity year of future aluminum price	2016
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [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	1,785
Maturity year of future aluminum price	2019
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Midwest Premium | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium | $ / lb	0.063
Midwest Premium expected year	2016
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium | $ / lb	0.075
Midwest Premium expected year	2019
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	2,337
Maturity year of future aluminum price	2029
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]
Midwest Premium expected year	2029
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	2,633
Maturity year of future aluminum price	2036
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]
Midwest Premium expected year	2036
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 | $	$ 7
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 | $ / MWh	57
Maturity date of electricity beyond forward curve	2016
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 | $ / MWh	58
Maturity date of electricity beyond forward curve	2017
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 | $	$ 24
Percentage of credit spread	2.52%
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	2.15%
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	2.89%