Contingencies and Commitments - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		12 Months Ended				1 Months Ended								1 Months Ended	3 Months Ended						1 Months Ended
	Jun. 30, 2009 D	Mar. 31, 2013 USD ($) Kmt	Mar. 31, 2012 USD ($)	Dec. 31, 2012 USD ($) Installment	Dec. 31, 2012 EUR (€)	Mar. 31, 2013 EUR (€)	Nov. 08, 2011 D	Nov. 30, 2006 Curtis v. Alcoa Inc. [Member] Person	Mar. 31, 2013 Minimum [Member] USD ($)	Mar. 31, 2013 Maximum [Member] USD ($)	Mar. 31, 2013 Maximum [Member] EUR (€)	Feb. 21, 2013 Alcoa Trasformazioni [Member] USD ($)	Feb. 21, 2013 Alcoa Trasformazioni [Member] EUR (€)	Mar. 31, 2013 Alcoa [Member] USD ($)	Mar. 31, 2013 Alcoa [Member] EUR (€)	Oct. 09, 2012 Alba [Member] USD ($)	Mar. 31, 2013 Alba [Member] USD ($)	Sep. 30, 2012 Alba [Member] USD ($)	Jun. 30, 2012 Alba [Member] USD ($)	Feb. 27, 2008 Alba [Member] Y	Mar. 31, 2013 Alba [Member] Minimum [Member] USD ($)	Mar. 31, 2013 Alba [Member] Maximum [Member] USD ($)	Jul. 31, 2006 Italian Government [Member] Y	Nov. 19, 2009 Italian Government [Member] USD ($)	Nov. 19, 2009 Italian Government [Member] EUR (€)
Loss Contingencies [Line Items]
Period of alleged conspiracy, years																				15
Damages claimed, value																	$ 1,000
Number of days required to dismiss lawsuit							30
Cash payment for suit settlement																		40	45
Restructuring and other charges		7	10																45
Restructuring and other charges, after-tax and noncontrolling interests		5	7															15	18
Estimated additional reasonably possible charge				387	303														75
Contingency settlement agreement amount, total																85
Contingency settlement agreement amount paid																42.5
Contingency settlement agreement amount payable																42.5
Contingency settlement agreement future payable date																	October 9, 2013
Percentage of equity interest																	40.00%
Estimated contingency settlement changes, net of tax																					25	30
Retired former employees involved in class action								13,000
Trial length, number of days	8
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
Charge related to European Commission announcement																								250	173
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				64	50
Number of installments, litigation payment				5	5
Litigation reserve				203	159									75	59
Range of reasonable possible loss, minimum				$ 203	€ 159
Amount of curtailment, in kmt-per-year		44