Contingencies and Commitments - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended			3 Months Ended				1 Months Ended								0 Months Ended
	Jul. 31, 2012 Plant	Jun. 30, 2012 USD ($) Installment	Jun. 30, 2012 EUR (€)	Mar. 31, 2014	Mar. 26, 2012 USD ($)	Mar. 26, 2012 EUR (€)	Jun. 30, 2010 t	Nov. 30, 2006 Curtis v. Alcoa Inc. [Member] Person	Feb. 21, 2013 Minimum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] EUR (€)	Feb. 21, 2013 Alcoa Trasformazioni [Member] USD ($)	Feb. 21, 2013 Alcoa Trasformazioni [Member] EUR (€)	Mar. 31, 2014 Alcoa [Member] USD ($)	Mar. 31, 2014 Alcoa [Member] EUR (€)	Nov. 19, 2009 Italian Government [Member] USD ($) Plant	Nov. 19, 2009 Italian Government [Member] EUR (€) Plant	Jul. 31, 2006 Italian Government [Member]	Dec. 31, 2012 Portovesme [Member] t
Loss Contingencies [Line Items]
Retired former employees involved in class action								13,000
Trial length, number of days				8 days
Management estimate for maximum exposure from class action					$ 110	€ 85						$ 97	€ 76
Provision for contract losses									0	97	76
Number of years operating under a power supply structure																		10 years
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		218	159											0
Range of reasonable possible loss, minimum		218	159
Range of reasonable possible loss, maximum		417	303
Noncurrent asset														$ 126	€ 91
Amount of curtailment, metric-tons-per-year							44,000												150,000