Earnings Per Share - Reconciliation Of Information Used To Compute Basic And Diluted EPS (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share Basic And Diluted By Common Class [Line Items]
(Loss) income from continuing operations attributable to Alcoa common shareholders	$ (143)	$ 172	$ (51)	$ 807
Less: preferred stock dividends declared	1	1	2	2
(Loss) income from continuing operations available to common equity	(144)	171	(53)	805
Less: dividends and undistributed earnings allocated to participating securities				2
(Loss) income from continuing operations available to Alcoa common shareholders - basic	(144)	171	(53)	803
Add: interest expense related to convertible notes		8		22
(Loss) income from continuing operations available to Alcoa common shareholders - diluted	$ (144)	$ 179	$ (53)	$ 825
Average shares outstanding - basic	1,067	1,064	1,066	1,060
Stock options		7		8
Stock and performance awards		4		3
Convertible notes		89		89
Average shares outstanding - diluted	1,067	1,164	1,066	1,160