Restructuring and Other Charges - Schedule of Restructuring and other Charges by Reportable Segments, Pretax (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges	$ 2	$ 9	$ 27	$ 49	$ 130
Alumina [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges		6	1	32
Primary Metals [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges	3	(6)	9	(4)
Global Rolled Products [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges		5	1	7
Engineered Products and Solutions [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges		(2)	3	1
Segment Total [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges	3	3	14	36
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring and other charges	$ (1)	$ 6	$ 13	$ 13