Commitments And Contingencies (Investments) (Details) In Millions, unless otherwise specified	6 Months Ended				6 Months Ended		3 Months Ended	6 Months Ended			6 Months Ended					12 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended	6 Months Ended		12 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended				12 Months Ended
	Jun. 30, 2011 USD ($)	Dec. 31, 2010 USD ($)	Jun. 30, 2011 Non Current Liabilities and Deferred Credits [Member] USD ($)	Dec. 31, 2010 Non Current Liabilities and Deferred Credits [Member] USD ($)	Jun. 30, 2011 Smelting and Rolling Mill Companies [Member] USD ($)	Jun. 30, 2011 Maaden Joint Venture [Member]	Jun. 30, 2011 Alcoa Joint Venture [Member] USD ($)	Jun. 30, 2011 Alcoa Joint Venture [Member] USD ($)	Jun. 30, 2011 Alcoa Joint Venture [Member] SAR	Dec. 31, 2010 Alcoa Joint Venture [Member] USD ($)	Jun. 30, 2011 Brazilian Real [Member]	Jun. 30, 2011 Barra Grande [Member]	Jun. 30, 2011 Machadinho [Member]	Jun. 30, 2011 Machadinho and Barra Grande [Member] USD ($) MWH	Jun. 30, 2011 Machadinho and Barra Grande [Member] BRL	Dec. 31, 2010 Machadinho and Barra Grande [Member] USD ($)	Dec. 31, 2010 Machadinho and Barra Grande [Member] BRL	Mar. 31, 2010 Estreito Project [Member] USD ($)	Mar. 31, 2010 Estreito Project [Member] BRL	Jun. 30, 2011 Estreito Project [Member] USD ($) MWH	Jun. 30, 2011 Estreito Project [Member] BRL	Dec. 31, 2006 Estreito Project [Member] Alcoa Aluminio [Member]	Jun. 30, 2011 Serra do Facao Project [Member] USD ($) MWH	Jun. 30, 2011 Serra do Facao Project [Member] BRL	Dec. 31, 2010 Serra do Facao Project [Member] USD ($)	Dec. 31, 2010 Serra do Facao Project [Member] BRL	Dec. 31, 2006 Serra do Facao Project [Member] Alcoa Aluminio [Member]	Jun. 30, 2011 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] USD ($)	Jun. 30, 2011 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] AUD	Jun. 30, 2011 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] USD ($)	Jun. 30, 2011 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] AUD	Dec. 31, 2004 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] USD ($)	Dec. 31, 2004 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] AUD	Dec. 31, 2011 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] USD ($)	Dec. 31, 2011 Dampier to Bunbry Natural Gas Pipeline (DBNGP) [Member] AUD	Dec. 31, 2006 Alcoa Aluminio [Member]	Jun. 30, 2011 Alcoa Aluminio [Member] USD ($) MWH	Jun. 30, 2011 Alcoa Aluminio [Member] BRL	Jun. 30, 2011 Alcoa [Member] USD ($)
Ownership interest in joint venture at fair market value						74.90%		25.10%
Capital investment	$ 1,596	$ 1,340			$ 4,000		$ 10,800	$ 10,800	40,500
Amount invested by Alcoa and Aluminum Financing Limited							1,100	1,100
Amount invested by Alcoa and Aluminum Financing Limited, over year	4
Capital investment commitment paid-to-date							311	311															210	330
Capital investment commitment paid in period							74	152
Duration of sharing capital commitment														30	30
Power self sufficiency											70.00%			40.00%	40.00%
Investment in SPPL as an equity method investment							447	447		285
Guarantee issued on behalf of smelting and rolling mill companies			8	8																																			1,004
Ownership interest issued as a guarantee for smelting and rolling companies						74.90%	25.10%	25.10%
Debt service requirements, principal					108
Debt service requirements, interest					50
Investment percentage												42.18%	30.99%
Total energy demand														690	690
Total investment in project														305	480	274	461
Aluminio's share of Serra do Facao																							230	350
Additional acquired share																						6.41%
Increase in estimated cost to complete Estreito project																		720	1,300
Aluminio's share of Estreito project																				790	1,250
Estimated project costs																				3,100	4,900		650	1,000
Total investment in Serra do Facao																							122	192	116	195
Percent interest in a consortium																											34.97%									25.49%
Assured energy																							65	65													38	38
Energy capacity installed																				280.00%	280.00%
Assured power from installed capacity																				150.00%	150.00%
Initial cash investment																																17	24
Additional contributions																												1	1	16	16	141	176
Additional amount committed to invest																																		10	9
Amount contributed																																					710	1,100
Alcoa's maximum exposure to loss in projects														$ 360	560													$ 520	490	$ 520	490						$ 260	410
Interest in consortium	20.00%