Segment And Geographic Area Information (Schedule Of Operating Results And Assets Of Alcoa's Reportable Segments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Third-party sales	$ 24,689	$ 20,746	$ 18,171
Intersegment sales	6,137	4,989	3,483
Total sales	30,826	25,735	21,654
Equity income (loss)	16	13	(16)
Depreciation, depletion, and amortization	1,395	1,369	1,256
Income taxes	635	443	(200)
ATOI	1,893	1,424	(234)
Capital expenditures	1,287	1,015	1,617
Equity investments	1,524	1,244
Goodwill	5,251	5,122	5,054
Total assets	40,120	39,293
Alumina [Member]
Segment Reporting Information [Line Items]
Goodwill	11	12	17
Primary Metals [Member]
Segment Reporting Information [Line Items]
Goodwill	991	993	939
Flat-Rolled Products [Member]
Segment Reporting Information [Line Items]
Goodwill	208	207	210
Engineered Products And Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill	2,666	2,523	2,504
Segment Information [Member]
Segment Reporting Information [Line Items]
Capital expenditures	1,164	904
Equity investments	1,498	1,214
Goodwill	3,876	3,735
Total assets	32,039	31,870
Segment Information [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Third-party sales	3,462	2,815	2,161
Intersegment sales	2,727	2,212	1,534
Total sales	6,189	5,027	3,695
Equity income (loss)	25	10	8
Depreciation, depletion, and amortization	444	406	292
Income taxes	179	60	(22)
ATOI	607	301	112
Capital expenditures	371	295
Equity investments	450	413
Goodwill	11	12
Total assets	9,782	9,967
Segment Information [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Third-party sales	8,240	7,070	5,252
Intersegment sales	3,192	2,597	1,836
Total sales	11,432	9,667	7,088
Equity income (loss)	(7)	1	(26)
Depreciation, depletion, and amortization	556	571	560
Income taxes	92	96	(365)
ATOI	481	488	(612)
Capital expenditures	463	380
Equity investments	925	741
Goodwill	991	993
Total assets	11,867	11,947
Segment Information [Member] | Flat-Rolled Products [Member]
Segment Reporting Information [Line Items]
Third-party sales	7,642	6,277	6,069
Intersegment sales	218	180	113
Total sales	7,860	6,457	6,182
Equity income (loss)	(3)
Depreciation, depletion, and amortization	237	238	227
Income taxes	104	92	48
ATOI	266	220	(49)
Capital expenditures	157	104
Equity investments	123	60
Goodwill	208	207
Total assets	4,559	4,522
Segment Information [Member] | Engineered Products And Solutions [Member]
Segment Reporting Information [Line Items]
Third-party sales	5,345	4,584	4,689
Total sales	5,345	4,584	4,689
Equity income (loss)	1	2	2
Depreciation, depletion, and amortization	158	154	177
Income taxes	260	195	139
ATOI	539	415	315
Capital expenditures	173	125
Goodwill	2,666	2,523
Total assets	$ 5,831	$ 5,434