Contingencies and Commitments - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended									1 Months Ended					0 Months Ended
	Jul. 31, 2012 Plant	Jun. 30, 2012 USD ($) Installment	Jun. 30, 2012 EUR (€)	Mar. 26, 2012 USD ($)	Mar. 26, 2012 EUR (€)	Jun. 30, 2010 t	Feb. 21, 2013 Minimum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] EUR (€)	Nov. 30, 2006 Curtis v. Alcoa Inc. [Member] Person	Jun. 30, 2014 Alcoa [Member] USD ($)	Jun. 30, 2014 Alcoa [Member] EUR (€)	Feb. 21, 2013 Alcoa Trasformazioni [Member] USD ($)	Feb. 21, 2013 Alcoa Trasformazioni [Member] EUR (€)	Nov. 19, 2009 Italian Government [Member] USD ($) Plant	Nov. 19, 2009 Italian Government [Member] EUR (€) Plant	Dec. 31, 2012 Portovesme [Member] t
Loss Contingencies [Line Items]
Retired former employees involved in class action										13,000
Management estimate for maximum exposure from class action				$ 110	€ 85								$ 97	€ 76
Provision for contract losses							0	97	76
Charge related to European Commission announcement															250	173
Number of smelters	2														2	2
Write-off of receivable															20	14
Establishment reserve															230	159
Recovery amount		375	303
Reduction in recovery amount		65	53
Payments to Italian Government		310	250
Payments to Italian Government, installments amount		69	50
Number of installments, litigation payment		5	5
Litigation reserve		216	159								0
Range of reasonable possible loss, minimum		216	159
Range of reasonable possible loss, maximum		413	303
Noncurrent asset											$ 125	€ 91
Amount of curtailment, metric-tons-per-year						44,000											150,000