Contingencies and Commitments - Additional Information - 2 (Detail) In Millions, unless otherwise specified	3 Months Ended						3 Months Ended								3 Months Ended				3 Months Ended			12 Months Ended			3 Months Ended				3 Months Ended				12 Months Ended			12 Months Ended	3 Months Ended								12 Months Ended		1 Months Ended		3 Months Ended
	Mar. 31, 2013 USD ($) MW	Dec. 31, 2012 USD ($)	Dec. 31, 2012 EUR (€)	Dec. 31, 2010 USD ($)	Mar. 31, 2013 Other noncurrent liabilities and deferred credits [Member] USD ($)	Dec. 31, 2012 Other noncurrent liabilities and deferred credits [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] BRL	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] Minimum [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] Minimum [Member] Fixed Assets [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] Maximum [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] Maximum [Member] Fixed Assets [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] Maximum [Member] Fixed Assets [Member] BRL	Dec. 31, 2012 Alcoa [Member] USD ($)	Mar. 31, 2013 Barra Grande [Member] USD ($) MWh	Mar. 31, 2013 Barra Grande [Member] BRL MWh	Dec. 31, 2012 Barra Grande [Member] USD ($)	Dec. 31, 2012 Barra Grande [Member] BRL	Mar. 31, 2013 Estreito project [Member] USD ($) MWh	Mar. 31, 2013 Estreito project [Member] BRL	Mar. 31, 2012 East St. Louis, IL site [Member] USD ($)	Dec. 31, 2005 East St. Louis, IL site [Member] USD ($)	Dec. 31, 2009 Fusina [Member] USD ($)	Dec. 31, 2009 Portovesme [Member] USD ($)	Sep. 30, 2012 Baie Comeau [Member] USD ($)	Sep. 30, 2012 Mosjoen [Member] USD ($)	Mar. 31, 2013 Ma'aden joint venture [Member]	Dec. 31, 2011 Ma'aden joint venture [Member]	Mar. 31, 2013 Alcoa [Member] USD ($) Y	Mar. 31, 2013 Alcoa [Member] SAR	Dec. 31, 2012 Alcoa [Member] USD ($)	Dec. 31, 2011 Alcoa [Member]	Dec. 31, 2010 Smelting and rolling mill companies [Member] USD ($)	Mar. 31, 2013 Smelting and rolling mill companies [Member] Other noncurrent liabilities and deferred credits [Member] USD ($)	Dec. 31, 2012 Smelting and rolling mill companies [Member] Other noncurrent liabilities and deferred credits [Member] USD ($)	Dec. 31, 2011 Refining and mining company [Member] USD ($)	Mar. 31, 2013 Alumina Limited [Member]	Mar. 31, 2013 Machadinho and Barra Grande [Member] Y	Mar. 31, 2013 Serrado Facao and Estreito Projects [Member] Y	Mar. 31, 2013 Machadinho [Member] MWh	Mar. 31, 2013 Serra Do Facao Project [Member] USD ($) MWh	Mar. 31, 2013 Serra Do Facao Project [Member] BRL	Dec. 31, 2012 Serra Do Facao Project [Member] USD ($)	Dec. 31, 2012 Serra Do Facao Project [Member] BRL	Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] AUD	Mar. 31, 2013 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($)	Mar. 31, 2013 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD	Mar. 31, 2013 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($)	Mar. 31, 2013 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD
Loss Contingencies [Line Items]
Remediation reserve increase (decrease)																					$ 14	$ 15	$ 12	$ 3	$ 25	$ 20
Disallowed tax credits							110	220		0		90	175
Percentage of penalty of the gross disallowed amount							50.00%	50.00%
Value added tax receivable							41	82
Estimated range of reasonably possible loss, minimum								155	0		75
Administrative appeal, assessment period							2 years	2 years
Ownership interest issued as guarantee for smelting and rolling mill companies																											74.90%	74.90%	25.10%		25.10%	25.10%
Capital investment	1,862	1,860																											10,800	40,500			4,035			1,992
Amount invested by Alcoa and Aluminum Financing Limited																													1,100
Term of investment by Alcoa and Aluminum Financing Limited, years																													5
Capital investment commitment paid-to-date																													740
Capital investment commitment paid in period																													79
Equity method investment, carrying value																													890		816
Guarantee issued on behalf of smelting and rolling mill companies					4	4								1,013																				10	10	500
Project financing				480
Portion of project financing representing Alcoa interest in venture				120
Debt service requirements, principal																																	121			60
Debt service requirements, interest maximum																																	60			25
Ownership interest in joint venture at fair market value																																					40.00%
Commitment to taking share of output in associated projects at cost, in years																																						30	26
Investment percentage															42.18%	42.18%			25.49%	25.49%																				30.99%	34.97%	34.97%			20.00%	20.00%
Assured power from installed capacity															160	160			150	150																				120	65	65
Total investment in project															160	324	159	326																							98	198	98	200
Estimated project costs																			2,560	5,170																					500	1,000
Aluminio's share of project																			650	1,320																					170	350
Additional contributions																																									175	350			141	176	21	21	4	4
Increase in estimated costs to complete project																			130	270
Commitment expended on the project																			620	1,250
Percentage of power self-sufficiency upon completion of project with full operating capacity	70.00%
Total energy demand	690
Initial cash investment																																													17	24
Required plan contributions																																																	40	40
Repayments made under the agreement for future gas transmission services																																																	364	350
Alcoa's maximum exposure to loss in projects		$ 387	€ 303																																												$ 520	500	$ 520	500