Contingencies and Commitments - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended		12 Months Ended					12 Months Ended	1 Months Ended			1 Months Ended			1 Months Ended	12 Months Ended					12 Months Ended			1 Months Ended		6 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended		12 Months Ended						12 Months Ended				12 Months Ended					12 Months Ended												12 Months Ended				3 Months Ended	12 Months Ended						1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	0 Months Ended
	Jun. 30, 2009 D	Jan. 31, 2007 D	Dec. 31, 2012 USD ($) MW Installment Kmt	Dec. 31, 2012 EUR (€)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Nov. 08, 2011 D	Dec. 31, 2011 Aerospace Fasteners Business [Member] USD ($)	Jul. 31, 2006 Italian Government [Member] Y	Nov. 19, 2009 Italian Government [Member] USD ($)	Nov. 19, 2009 Italian Government [Member] EUR (€)	Jan. 31, 2007 Spanish Government [Member] Y	Jan. 31, 2007 Tariffs Granted by Spain [Member] USD ($)	Jan. 31, 2007 Tariffs Granted by Spain [Member] EUR (€)	Jun. 30, 2003 Massena West, Ny [Member] Y	Dec. 31, 2012 Massena West, Ny [Member] USD ($)	Dec. 31, 2012 Smelter Operation [Member] USD ($)	Dec. 31, 2012 East St. Louis, IL Site [Member] USD ($)	Dec. 31, 2005 East St. Louis, IL Site [Member] USD ($)	Dec. 31, 2012 Sherwin, TX site [Member] USD ($)	Dec. 31, 2012 Other sites [Member] USD ($)	Dec. 31, 2011 Other sites [Member] USD ($)	Dec. 31, 2011 U.S. Smelters [Member] USD ($)	Oct. 31, 2012 Grasse River [Member] USD ($)	Nov. 30, 2008 Grasse River [Member] USD ($)	Jun. 30, 2012 Grasse River [Member] USD ($)	Dec. 31, 2012 Grasse River [Member] USD ($)	Dec. 31, 2010 Grasse River [Member] USD ($)	Mar. 24, 2010 Grasse River [Member] USD ($)	Dec. 31, 2009 Fusina [Member] USD ($)	Dec. 31, 2009 Portovesme [Member] USD ($)	Aug. 31, 2012 Baie Comeau [Member] USD ($)	Sep. 30, 2012 Mosjoen [Member] USD ($)	Dec. 31, 2012 Machadinho and Barra Grande [Member] Y	Dec. 31, 2012 Serrado Facao and Estreito Projects [Member] Y	Dec. 31, 2012 Barra Grande [Member] USD ($) MWh	Dec. 31, 2012 Barra Grande [Member] BRL MWh	Dec. 31, 2011 Barra Grande [Member] USD ($)	Dec. 31, 2011 Barra Grande [Member] BRL	Dec. 31, 2012 Machadinho [Member] USD ($) MWh	Dec. 31, 2012 Machadinho [Member] BRL MWh	Dec. 31, 2011 Machadinho [Member] USD ($)	Dec. 31, 2011 Machadinho [Member] BRL	Dec. 31, 2012 Serra Do Facao Project [Member] USD ($) MWh	Dec. 31, 2012 Serra Do Facao Project [Member] ZAR	Dec. 31, 2012 Serra Do Facao Project [Member] BRL	Dec. 31, 2011 Serra Do Facao Project [Member] USD ($)	Dec. 31, 2011 Serra Do Facao Project [Member] BRL	Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] AUD	Dec. 31, 2012 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($)	Dec. 31, 2012 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD	Dec. 31, 2011 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($)	Dec. 31, 2011 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD	Dec. 31, 2012 Minimum [Member] USD ($)	Dec. 31, 2012 Maximum [Member] USD ($)	Dec. 31, 2012 Canada and Norway [Member] Smelter Operation [Member] USD ($)	Dec. 31, 2012 Energy, Raw Materials, and Other Goods and Services [Member] USD ($)	Dec. 31, 2012 Alcoa [Member] USD ($)	Dec. 31, 2012 Alcoa [Member] EUR (€)	Dec. 31, 2012 Estreito Project [Member] USD ($) MWh	Dec. 31, 2012 Estreito Project [Member] BRL	Dec. 31, 2012 Outstanding bank guarantees [Member] Minimum [Member]	Dec. 31, 2012 Outstanding bank guarantees [Member] Maximum [Member]	Jun. 30, 2012 Alba [Member] USD ($)	Dec. 31, 2012 Alba [Member] USD ($)	Oct. 09, 2012 Alba [Member] USD ($)	Feb. 27, 2008 Alba [Member] Y	Dec. 31, 2012 Alba [Member] Minimum [Member] USD ($)	Dec. 31, 2012 Alba [Member] Maximum [Member] USD ($)	May 31, 2011 Breaches of Warranty [Member] USD ($)	May 31, 2011 Negligence Award [Member] USD ($)	Dec. 31, 2012 Recurring Costs of Managing Hazardous Substances and Environmental Programs [Member]	Nov. 30, 2006 Curtis vs Alcoa [Member] Person	Dec. 31, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation of Puerto Rico [Member] USD ($)	Jan. 20, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation of Puerto Rico [Member] Breaches of Warranty [Member] USD ($)	Jan. 20, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation of Puerto Rico [Member] Punitive Damages [Member] USD ($)	Jan. 20, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation of Puerto Rico [Member] Property Damages [Member] USD ($)
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																																																																	45	40
Restructuring and other charges			87		281	207																																																											45
Restructuring and other charges, after-tax and noncontrolling interests			73		181	130																																																											18	15
Alcoa's maximum exposure to loss in projects			375	303									90	70																										120	240										520	500													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
Court granted motion for judgment																																																																								10			20	13	6	10
Damages awarded to plaintiff, pre-judgment interest																																																																							2
Management estimate for maximum exposure from class action			110	85
Provision for contract losses				39																																																			0	50
Number of years operating under a power supply structure									10			9
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			66	50
Number of installments, litigation payment			5	5
Litigation reserve			209	159																																																							143	109
Range of reasonable possible loss, minimum			209	159
Amount of curtailment, in kmt-per-year			44	44
Days provided to submit observations and comments to the EC		30
Number of cleanup locations			More than 100	More than 100
Remediation reserve balance			532		347															30
Remediation reserve balance, classified as a current liability			74		58
Remediation reserve increase								3								206	30	14	15		12	13	31	128	40	37	1	2		12	3	25	20
Remediation reserve adjustment																165		14					18						17																												45
Payments related to remediation expenses applied against the reserve			22		19
Increase and decrease in reserves due to effects of foreign currency translation			1		(1)
Percentage of cost of goods sold																																																																									2.00%
Period of time between potential phenomenon occurrences, years															10
Commitment to taking share of output in associated projects at cost, in years																																		30	26
Investment percentage																																				42.18%	42.18%			30.99%	30.99%			34.97%	34.97%				20.00%	20.00%											25.49%	25.49%
Assured power from installed capacity																																				160	160			120	120			65	65																150	150
Total investment in projects																																				159	326	169	314	95	195	97	182	98		200	105	196
Estimated project costs																																												490	1,000																2,520	5,170
Aluminio's share of project																																												170	350																640	1,320
Additional contributions																																												170	350				141	176	12	11	5	6
Increase in estimated costs to complete project																																																													130	270
Commitment expended on the project																																																													610	1,250
Percentage of current power self-sufficiency			70.00%	70.00%
Total energy demand			690	690
Initial cash investment																																																	17	24
Required plan contributions																																																			40	40
Repayments made under the agreement for future gas transmission services																																																			363	349
Purchase obligations due in 2013			176																																																							3,502
Purchase obligations due in 2014			175																																																							2,137
Purchase obligations due in 2015			176																																																							2,085
Purchase obligations due in 2016			165																																																							1,926
Purchase obligations due in 2017			165																																																							2,496
Purchase obligations due thereafter			2,688																																																							20,717
Purchase obligations expenditures			161		227	129
Expiration date of unconditional purchase obligations for energy																																																							2015	2036
Operating leases, expense			244		255	260
Long-term operating leases, minimum annual rentals due in 2013			198
Long-term operating leases, minimum annual rentals due in 2014			155
Long-term operating leases, minimum annual rentals due in 2015			127
Long-term operating leases, minimum annual rentals due in 2016			102
Long-term operating leases, minimum annual rentals due in 2017			77
Long-term operating leases, minimum annual rentals due thereafter			597
Guarantees of third party related to project financing			605
Guarantees, expiration date																																																							2015	2019							2013	2017
Guarantees, total amount committed			494
Letters of credit, total amount committed			299
Letters of credit, expiration date			2013	2013
Total amount committed under outstanding surety bonds			$ 193
Surety bonds, expiration date																																																							2013	2014