Earnings Per Share (Reconciliation Of Information Used To Compute Basic And Diluted EPS) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share
Income from continuing operations attributable to Alcoa common shareholders	$ 172	$ 61	$ 807	$ 4
Less: preferred stock dividends declared	1	1	2	2
Income from continuing operations available to common equity	171	60	805	2
Less: dividends and undistributed earnings allocated to participating securities			2
Income from continuing operations available to Alcoa common shareholders - basic	171	60	803	2
Add: interest expense related to convertible notes	8		22
Income from continuing operations available to Alcoa common shareholders - diluted	$ 179	$ 60	$ 825	$ 2
Average shares outstanding - basic	1,064	1,021	1,060	1,017
Stock options	7	5	8	5
Stock and performance awards	4	1	3	1
Convertible notes	89		89
Average shares outstanding - diluted	1,164	1,027	1,160	1,023