Segment Information - Schedule of Operating Results and Assets of Alcoa's Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Third-party sales	$ 5,774	$ 6,350	$ 17,615	$ 18,805
Intersegment sales	1,308	1,597	4,132	4,845
Total sales	7,082	7,947	21,747	23,650
Equity income (loss)	(4)	(2)	(16)	24
Depreciation, depletion, and amortization	346	355	1,035	1,050
Income taxes	82	156	284	570
After-tax operating income (ATOI)	235	462	806	1,652
Segment Information [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Third-party sales	764	879	2,289	2,615
Intersegment sales	575	751	1,768	2,107
Total sales	1,339	1,630	4,057	4,722
Equity income (loss)	2	2	4	27
Depreciation, depletion, and amortization	120	117	348	332
Income taxes	(22)	42	(29)	146
After-tax operating income (ATOI)	(9)	154	49	482
Segment Information [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,794	2,124	5,542	6,249
Intersegment sales	691	798	2,234	2,559
Total sales	2,485	2,922	7,776	8,808
Equity income (loss)	(5)	(4)	(16)	(4)
Depreciation, depletion, and amortization	130	137	398	420
Income taxes	(19)	21	(51)	129
After-tax operating income (ATOI)	(14)	110	(7)	513
Segment Information [Member] | Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,849	1,974	5,607	5,951
Intersegment sales	42	48	130	179
Total sales	1,891	2,022	5,737	6,130
Equity income (loss)	(1)		(4)
Depreciation, depletion, and amortization	57	61	171	179
Income taxes	44	26	136	94
After-tax operating income (ATOI)	98	60	289	240
Segment Information [Member] | Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,367	1,373	4,177	3,990
Total sales	1,367	1,373	4,177	3,990
Equity income (loss)				1
Depreciation, depletion, and amortization	39	40	118	119
Income taxes	79	67	228	201
After-tax operating income (ATOI)	$ 160	$ 138	$ 475	$ 417