Restructuring and Other Charges - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012 Person	Sep. 30, 2011 Person	Sep. 30, 2012 Person	Sep. 30, 2011 Person	Dec. 31, 2011
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 2	$ 9	$ 27	$ 49	$ 130
Restructuring and other charges	2	5	19	26
Number of employees associated with layoff costs	20	150	350	630
Minimum amount of cash payments expected to be paid beyond the end of the current annual period			70
Maximum amount of cash payments expected to be paid beyond the end of the current annual period			75
Primary Metals [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3	(6)	9	(4)
Number of employees associated with layoff costs		40	180	110
Engineered Products and Solutions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		(2)	3	1
Number of employees associated with layoff costs			70	30
Alumina [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		6	1	32
Number of employees associated with layoff costs		30	25	60
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	(1)	6	13	13
Number of employees associated with layoff costs		10	75	10
Other miscellaneous charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				4
Restructuring and other charges				3
Restructuring reserve, other adjustment		1	2
Restructuring reserve, other adjustment, after-tax		1	2
Global Rolled Products [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		5	1	7
Number of employees associated with layoff costs		70		420
Lease Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3
Restructuring and other charges	2
Restructuring reserve, other adjustment			9
Restructuring reserve, other adjustment, after-tax			5
Small Layoff Reserves Related To Prior Periods [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				14
Restructuring and other charges				9
Restructuring reserve, other adjustment	1	10	4
Restructuring reserve, other adjustment, after-tax	1	6	2
Layoff Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			20	31	93
Restructuring and other charges			14	19
Smelter Curtailments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			9	8
Restructuring and other charges			6	5
Number of employees associated with layoff costs			160
Restructuring Programs Layoffs 2012 [Member]
Restructuring Cost and Reserve [Line Items]
Total number of employees already laid off	90		90
Number of positions terminated			350
Cash payments made against the layoff reserves	3		6
Restructuring Programs Layoffs 2011 [Member]
Restructuring Cost and Reserve [Line Items]
Total number of employees already laid off	770		770
Number of positions terminated			1,600
Cash payments made against the layoff reserves	7		21
Restructuring Programs Layoffs 2010 [Member]
Restructuring Cost and Reserve [Line Items]
Total number of employees already laid off	820		820
Number of positions terminated			875
Cash payments made against the layoff reserves	1		3
Restructuring Programs Layoffs 2009 [Member]
Restructuring Cost and Reserve [Line Items]
Total number of employees already laid off	5,900		5,900
Number of positions terminated			6,000
Litigation Matter [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		18		20
Restructuring and other charges		$ 11		$ 8