Investments (Narrative) (Details) In Millions, unless otherwise specified	12 Months Ended				1 Months Ended		12 Months Ended		1 Months Ended		1 Months Ended			12 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended					1 Months Ended				1 Months Ended			12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Jun. 30, 2009 USD ($)	Mar. 31, 2010 Aluminum Financing Limited Noncontrolling Interests [Member] USD ($)	Dec. 31, 2011 Other Noncurrent Liabilities And Deferred Credits [Member] USD ($)	Dec. 31, 2011 Smelting And Rolling Mill Companies [Member] USD ($)	Dec. 31, 2010 Smelting And Rolling Mill Companies [Member] USD ($)	Oct. 31, 2011 Refining And Mining Company [Member] USD ($)	Dec. 31, 2011 Refining And Mining Company [Member] USD ($)	Oct. 31, 2011 Ma'aden Joint Venture [Member]	Mar. 31, 2010 Ma'aden Joint Venture [Member]	Dec. 31, 2009 Ma'aden Joint Venture [Member] years	Dec. 31, 2011 Ma'aden Joint Venture [Member] USD ($)	Dec. 31, 2010 Ma'aden Joint Venture [Member] USD ($)	Dec. 31, 2009 Saudi Arabia Joint Venture [Member]	Mar. 31, 2010 Alcoa Joint Venture [Member]	Dec. 31, 2011 Alcoa Joint Venture [Member] USD ($)	Dec. 31, 2011 Alcoa Joint Venture [Member] SAR	Dec. 31, 2009 Alcoa Joint Venture [Member] USD ($)	Dec. 31, 2010 Alcoa Joint Venture [Member] USD ($)	Dec. 31, 2009 Aluminum Financing Limited Joint Venture [Member]	Dec. 31, 2009 Aluminum Financing Limited [Member]	Dec. 31, 2011 Fixed Income Securities [Member] USD ($)	Dec. 31, 2010 Equity Securities [Member] USD ($)	Dec. 31, 2011 Alumina Limited [Member]	Dec. 31, 2009 Alumina Refinery [Member]	Dec. 31, 2011 Smelter Operation [Member] Pechiney Reynolds Quebec, Inc. [Member]	Dec. 31, 2011 Bauxite Mining [Member] Halco Mining, Inc. [Member]	Dec. 31, 2011 Bauxite Mining [Member] Minerao Rio Do Norte S.A. [Member]	Dec. 31, 2009 Mine [Member]	Dec. 31, 2009 Primary Aluminum Smelter [Member]	Dec. 31, 2009 Rolling Mill [Member]	Dec. 31, 2011 Scenario One [Member] Saudi Arabia Joint Venture [Member] USD ($)	Dec. 31, 2011 Scenario Two [Member] Saudi Arabia Joint Venture [Member] USD ($)
Schedule of Equity Method Investments [Line Items]
Joint venture shareholders agreement period, years													30
Joint venture shareholders agreement, automatic extension additional period, years													20
Projected capacity amount of processed bauxite, in kmt																											1,800				4,000	740	380
Dividends from equity investments	$ 100	$ 33	$ 56
Redemption of notes receivable					40
Ownership interest in joint venture at fair market value														14.90%
Percent of equity investments in other entity, maximum	50.00%																	60.00%	60.00%							40.00%		25.05%	45.00%	18.20%
Ownership interest in joint venture								25.10%	25.10%		74.90%	74.90%			74.90%	60.00%	25.10%			40.00%
Economic interest in joint venture			40.00%																	20.00%		20.00%
Business acquisition cost	240			3	60
Initial investment																				80
Percentage share of convertible securities of subsidiary																							50.00%
Capital investment	1,626	1,340																10,800	40,500
Project financing								4,035	1,992
Portion of project financing representing Alcoa interest in venture								1,013	500
Payment for pro rata share of pre-incorporation costs														22.0	34.0
Outstanding receivable for labor and other employee-related expenses	25
Amount invested by Alcoa and Aluminum Financing Limited																		1,100
Term of investment by Alcoa and Aluminum Financing Limited, years																		4	4
Potential forfeiture of letter of credit																																		350	60
Combined fair value of guarantees										4
Equity investments	1,524	1,244																565			285
Capital investment commitment paid-to-date	249	160
Other investments	102	96																						92	93
Fair value of guarantee included in other noncurrent liabilities and deferred credits	436					8
Debt service requirements, principal							108		60
Debt service requirements, interest maximum							$ 50		$ 25