Earnings Per Share (Reconciliation Of Information Used To Compute Basic And Diluted EPS) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share [Abstract]
Income (loss) from continuing operations attributable to Alcoa common shareholders	$ (193)	$ 172	$ 326	$ 309	$ 258	$ 61	$ 137	$ (194)	$ 614	$ 262	$ (985)
Less: preferred stock dividends declared									2	2	2
Income (loss) from continuing operations available to common equity									612	260	(987)
Less: dividends and undistributed earnings allocated to participating securities									1	1
Income (loss) from continuing operations available to Alcoa common shareholders-basic									611	259	(987)
Add: interest expense related to convertible notes									30
Income (loss) from continuing operations available to Alcoa common shareholders-diluted									$ 641	$ 259	$ (987)
Average shares outstanding-basic									1,061	1,018	935
Stock options									7	6
Stock and performance awards									4	1
Convertible notes									89
Average shares outstanding-diluted									1,161	1,025	935