Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended				12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jan. 31, 2011	Jan. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity, maximum	50.00%				50.00%
Goodwill	$ 5,251				$ 5,251	$ 5,122	$ 5,054
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill					50.00%
Market capitalization of common stock	9,207
Market price of common stock					$ 8.65	$ 15.39
Percentage of decline in market price of common stock					44.00%
Maximum hedging contracts period, in years					5
Minimum number of reporting units being subjected for goodwill impairment test					3
Number of reporting units being subjected to goodwill impairment test					9
Number of reporting units, estimated fair value of reporting units less than carrying values					6
Businesses expected to be disposed within, years					1
Percentage of total goodwill allocated to reporting units					90.00%
Effect of change in accounting principle presented on financial statement, before tax				250
Change in functional currency of certain Brazilian operations				309
Goodwill impairment threshold, maximum		50.00%	50.00%
Restructuring and other charges					281	207	237
Restructuring and other charges, after-tax and noncontrolling interests					181	130	151
Alcoa Fastening Systems [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	1,153				1,153
Alcoa Power And Propulsion [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	1,627				1,627
Alcoa World Alumina And Chemicals [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity, maximum				60.00%
Primary Metals [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	1,841				1,841
Engineered Products And Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units					5
Engineered Products And Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	2,666				2,666	2,523	2,504
Restructuring and other charges					(3)	18	64
Alumina [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	11				11	12	17
Restructuring and other charges					39	12	5
Alumina [Member] | Alcoa World Alumina And Chemicals [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity, maximum						40.00%
Alumina [Member] | Primary Metals [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units					4
Write-Off Of Capitalized Business Acquisition Costs [Member]
Summary Of Significant Accounting Policies [Line Items]
Restructuring and other charges							18
Restructuring and other charges, after-tax and noncontrolling interests							$ 12