Segment and Geographic Area Information - Sales by Major Product Grouping (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
Product Information [Line Items]
Sales revenue	$ 5,898	$ 5,833	$ 5,963	$ 6,006	$ 5,989	$ 6,419	$ 6,585	$ 5,958	$ 23,700	$ 24,951	$ 21,013
Alumina [Member]
Product Information [Line Items]
Sales revenue									2,962	3,350	2,740
Primary aluminum [Member]
Product Information [Line Items]
Sales revenue									7,121	7,907	6,842
Flat-rolled aluminum [Member]
Product Information [Line Items]
Sales revenue									7,378	7,642	6,277
Investment castings [Member]
Product Information [Line Items]
Sales revenue									1,747	1,700	1,521
Alcoa Fastening Systems [Member]
Product Information [Line Items]
Sales revenue									1,414	1,313	1,070
Architectural aluminum systems [Member]
Product Information [Line Items]
Sales revenue									970	973	884
Aluminum wheels [Member]
Product Information [Line Items]
Sales revenue									692	656	475
Other extruded aluminum and forged products [Member]
Product Information [Line Items]
Sales revenue									955	1,010	930
Other [Member]
Product Information [Line Items]
Sales revenue									$ 461	$ 400	$ 274