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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Net income (loss) attributable to Alcoa common shareholders	$ 24	$ (143)	$ 54	$ (51)
Less: preferred stock dividends declared	1	1	2	2
Net income (loss) available to common equity	23	(144)	52	(53)
Less: dividends and undistributed earnings allocated to participating securities
Net income (loss) available to Alcoa common shareholders - basic	23	(144)	52	(53)
Add: interest expense related to convertible notes			(1)
Net income (loss) available to Alcoa common shareholders - diluted	23	(144)	52	(53)
Average shares outstanding - basic	1,070	1,067	1,069	1,066
Stock options			1
Stock and performance awards	9		9
Convertible notes
Average shares outstanding - diluted	1,079	1,067	1,079	1,066
Convertible Debt [Member]
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Add: interest expense related to convertible notes