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Contingencies and Commitments - Additional Information (Detail)		1 Months Ended			6 Months Ended	15 Months Ended
	Nov. 19, 2009 EUR (€) Plant	Jul. 31, 2014 Plant	Jun. 30, 2012 EUR (€) Installment	Jun. 30, 2012 USD ($)	Jun. 30, 2015 EUR (€)	Dec. 31, 2013 EUR (€)	Dec. 31, 2013 USD ($)	Jun. 30, 2015 USD ($)	Feb. 21, 2013 EUR (€)	Feb. 21, 2013 USD ($)	Dec. 31, 2012 t	Jun. 30, 2012 USD ($) Installment	Mar. 26, 2012 EUR (€)	Mar. 26, 2012 USD ($)	Sep. 30, 2010 t	Nov. 19, 2009 USD ($)
Loss Contingencies [Line Items]
Management estimate for maximum exposure from class action													€ 85,000,000	$ 110,000,000
Number of smelters		2
Recovery amount			€ 303,000,000	$ 375,000,000
Reduction in recovery amount			53,000,000									$ 65,000,000
Payments to Italian Government			€ 250,000,000	$ 310,000,000
Payments to Italian Government, installments amount						€ 50,000,000	$ 69,000,000
Number of installments, litigation payment | Installment			5									5
Litigation reserve			€ 159,000,000									$ 176,000,000
Range of reasonable possible loss, minimum			159,000,000									176,000,000
Range of reasonable possible loss, maximum			€ 303,000,000									$ 337,000,000
Amount of curtailment, metric-tons-per-year | t															44,000
Minimum [Member]
Loss Contingencies [Line Items]
Provision for contract losses | $										$ 0
Maximum [Member]
Loss Contingencies [Line Items]
Provision for contract losses									€ 76,000,000	97,000,000
Italy [Member]
Loss Contingencies [Line Items]
Number of years operating under a power supply structure					10 years
Charge related to European Commission announcement	€ 173,000,000															$ 250,000,000
Number of smelters	2
Write-off of receivable	€ 14,000,000															20,000,000
Establishment reserve	€ 159,000,000															$ 230,000,000
Portovesme [Member]
Loss Contingencies [Line Items]
Amount of curtailment, metric-tons-per-year | t											150,000
Alcoa [Member]
Loss Contingencies [Line Items]
Reduction in recovery amount					€ 53,000,000			$ 59,000,000
Noncurrent asset					€ 91,000,000			$ 102,000,000
Alcoa Trasformazioni [Member]
Loss Contingencies [Line Items]
Management estimate for maximum exposure from class action									€ 76,000,000	$ 97,000,000

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