Average percentage of credit spread.

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- Definition

Base year consumer price index.

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No definition available.

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Consumer price index base year.

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No definition available.

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- Definition

Expected consumer price index.

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No definition available.

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Expected date of consumer price index.

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No definition available.

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- Definition

Foreign currency derivatives maturity date.

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No definition available.

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- Definition

Maturity data of future oil price.

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No definition available.

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- Definition

Maturity date of electricity beyond forward curve.

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No definition available.

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- Definition

Maturity data of future aluminum price.

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No definition available.

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- Definition

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226003-175313

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 4B
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-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
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-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=51814546&loc=SL51823488-111719

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract but not the derivative contract itself.

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No definition available.

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Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative asset contract but not the derivative contract itself.

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No definition available.

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- Definition

Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in energy volume but not the derivative contract itself.

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No definition available.

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Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in mass but not the derivative contract itself.

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No definition available.

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Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in volume but not the derivative contract itself.

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No definition available.

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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Index $ / Metric_Ton $ / MWh $ / Barrels $ / AUD $ / lb	Dec. 31, 2014 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value \| $	$ 1,137	$ 268
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 \| $	1,060
Derivative Liabilities, Fair value \| $	$ 169
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	2,060
Maturity year of future aluminum price	2026
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	2,128
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	2,060
Maturity year of future aluminum price	2026
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	0.0940
Foreign currency exchange rate expected year	2021
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	0.0940
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 \| $	$ 69
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]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Maturity year of future aluminum price	2016
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	1,525
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	1,550
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]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Foreign currency exchange rate \| $ / AUD	0.73
Foreign currency exchange rate expected year	2016
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]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Consumer price index base year	1982
Consumer price index base \| Index	100
Expected consumer price index, Year	2016
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 \| Index	233
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]
Expected consumer price index \| Index	236
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 \| $	$ 6
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	1,512
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	1,686
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]
Expected future aluminum prices	1,525
Maturity year of future aluminum price	2016
Expected future oil prices \| $ / Barrels	38
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	1,652
Maturity year of future aluminum price	2018
Expected future oil prices \| $ / Barrels	53
Maturity year of future oil price	2018
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]
Foreign currency exchange rate 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	2,534
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]
Foreign currency exchange rate expected year	2036
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 \| $	$ 35
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	3.85%
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	3.41%
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	4.29%
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 Liabilities, Fair value \| $	$ 2
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	45
Maturity date of electricity beyond forward curve	2019
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	121
Maturity date of electricity beyond forward curve	2036