Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Net income attributable to Alcoa common shareholders	$ 149	$ 94
Less: preferred stock dividends declared	1	1
Net income available to common equity	148	93
Less: dividends and undistributed earnings allocated to participating securities
Net income available to Alcoa common shareholders - basic	148	93
Add: interest expense related to convertible notes	8	8
Net income available to Alcoa common shareholders - diluted	$ 156	$ 101
Average shares outstanding - basic	1,069	1,066
Stock options	3	4
Stock and performance awards	8	5
Convertible notes	89	89
Average shares outstanding - diluted	1,169	1,164