Segment Information (Schedule Of Reconciliation Of Segment Assets) (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Total segment assets	$ 39,598	$ 39,293
Alumina [Member]
Total segment assets	9,675	9,967
Primary Metals [Member]
Total segment assets	12,222	11,947
Flat-Rolled Products [Member]
Total segment assets	5,033	4,606
Engineered Products and Solutions [Member]
Total segment assets	5,951	5,434
Alcoa [Member]
Total segment assets	$ 32,881	$ 31,954