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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income attributable to Alcoa common shareholders	$ 149	$ 24	$ 109	$ 54
Less: preferred stock dividends declared		1	1	2
Net income available to Alcoa common shareholders - basic	149	23	108	52
Add: preferred dividends related to mandatory convertible preferred stock
Add: interest expense related to convertible notes	0	0	0	0
Net income available to Alcoa common shareholders - diluted	149	23	108	52
Average shares outstanding - basic	1,177	1,070	1,150	1,069
Stock options	8		6	1
Stock and performance awards	12	9	11	9
Mandatory convertible preferred stock	$ 8		$ 3
Average shares outstanding - diluted	1,205	1,079	1,170	1,079