Segment and Geographic Area Information - Sales by Major Product Grouping (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Product Information [Line Items]
Consolidated sales	$ 5,245	$ 5,573	$ 5,897	$ 5,819	$ 6,377	$ 6,239	$ 5,836	$ 5,454	$ 22,534	$ 23,906	$ 23,032
Alumina [Member]
Product Information [Line Items]
Consolidated sales									3,333	3,401	3,151
Primary Aluminum [Member]
Product Information [Line Items]
Consolidated sales									5,085	6,011	6,194
Flat-Rolled Aluminum [Member]
Product Information [Line Items]
Consolidated sales									6,238	7,351	7,106
Investment Castings [Member]
Product Information [Line Items]
Consolidated sales									1,812	1,784	1,807
Alcoa Fastening Systems and Rings [Member]
Product Information [Line Items]
Consolidated sales									2,168	1,647	1,505
Architectural Aluminum Systems [Member]
Product Information [Line Items]
Consolidated sales									951	1,002	977
Aluminum Wheels [Member]
Product Information [Line Items]
Consolidated sales									790	786	702
Other Extruded and Forged Products [Member]
Product Information [Line Items]
Consolidated sales									1,332	1,019	1,015
Other [Member]
Product Information [Line Items]
Consolidated sales									$ 825	$ 905	$ 575