Segment Information (Reconciliation Of Segment Assets) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Total segment assets	$ 41,466	$ 39,293
Alumina [Member]
Total segment assets	10,560	9,967
Primary Metals [Member]
Total segment assets	12,749	11,947
Flat-Rolled Products [Member]
Total segment assets	5,248	4,606
Engineered Products and Solutions [Member]
Total segment assets	5,995	5,434
Alcoa [Member]
Total segment assets	$ 34,552	$ 31,954