Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Income from continuing operations attributable to Alcoa common shareholders	$ 242	$ (143)	$ (2)	$ 94	$ (193)	$ 172	$ 326	$ 309	$ 191	$ 614	$ 262
Less: preferred stock dividends declared									2	2	2
Income from continuing operations available to common equity									189	612	260
Less: dividends and undistributed earnings allocated to participating securities										1	1
Income from continuing operations available to Alcoa common shareholders-basic									189	611	259
Add: interest expense related to convertible notes										30
Income from continuing operations available to Alcoa common shareholders-diluted									$ 189	$ 641	$ 259
Average shares outstanding-basic									1,067	1,061	1,018
Stock options									3	7	6
Stock and performance awards									6	4	1
Convertible notes										89
Average shares outstanding-diluted									1,076	1,161	1,025