Quarterly Data - Schedule of Quarterly Data (Detail) (USD $) In Millions, except Per Share data, 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
Schedule Of Quarterly Financial Information [Line Items]
Sales	$ 5,898	$ 5,833	$ 5,963	$ 6,006	$ 5,989	$ 6,419	$ 6,585	$ 5,958	$ 23,700	$ 24,951	$ 21,013
Amounts Attributable to Alcoa Common Shareholders:
Income (loss) from continuing operations	242	(143)	(2)	94	(193)	172	326	309	191	614	262
(Loss) income from discontinued operations					2		(4)	(1)		(3)	(8)
Net income (loss) Attributable to Alcoa	$ 242	$ (143)	$ (2)	$ 94	$ (191)	$ 172	$ 322	$ 308	$ 191	$ 611	$ 254
Basic:
Income (loss) from continuing operations	$ 0.23	$ (0.13)		$ 0.09	$ (0.18)	$ 0.16	$ 0.31	$ 0.29	$ 0.18	$ 0.58	$ 0.25
(Loss) income from discontinued operations							$ (0.01)			$ (0.01)
Net income (loss)	$ 0.23	$ (0.13)		$ 0.09	$ (0.18)	$ 0.16	$ 0.30	$ 0.29	$ 0.18	$ 0.57	$ 0.25
Diluted:
Income (loss) from continuing operations	$ 0.21	$ (0.13)		$ 0.09	$ (0.18)	$ 0.15	$ 0.28	$ 0.27	$ 0.18	$ 0.55	$ 0.25
(Loss) income from discontinued operations											$ (0.01)
Net income (loss)	$ 0.21	$ (0.13)		$ 0.09	$ (0.18)	$ 0.15	$ 0.28	$ 0.27	$ 0.18	$ 0.55	$ 0.24