Goodwill And Other Intangible Assets (Changes In The Carrying Amount Of Goodwill) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Goodwill [Line Items]
Goodwill gross, beginning balance	$ 5,150		$ 5,082
Accumulated impairment losses	(28)		(28)
Goodwill, net	5,122		5,054
Acquisition of businesses	150		76
Translation	(21)		(8)
Goodwill gross, ending balance	5,279		5,150
Accumulated impairment losses	(28)		(28)
Goodwill, net	5,251		5,122
Alumina [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	12		17
Goodwill, net	12		17
Translation	(1)		(5)
Segment reporting, goodwill	163
Goodwill gross, ending balance	11		12
Goodwill, net	11		12
Primary Metals [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	993		939
Goodwill, net	993		939
Acquisition of businesses			48
Translation	(2)		6
Segment reporting, goodwill	850
Goodwill gross, ending balance	991		993
Goodwill, net	991		993
Flat-Rolled Products [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	207		210
Goodwill, net	207		210
Translation	1		(3)
Segment reporting, goodwill	63
Goodwill gross, ending balance	208		207
Goodwill, net	208		207
Engineered Products And Solutions [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	2,551		2,532
Accumulated impairment losses	(28)		(28)
Goodwill, net	2,523		2,504
Acquisition of businesses	150		28
Translation	(7)		(9)
Segment reporting, goodwill	273
Goodwill gross, ending balance	2,694		2,551
Accumulated impairment losses	(28)		(28)
Goodwill, net	2,666		2,523
Corporate [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	1,387	[1]	1,384	[1]
Goodwill, net	1,387	[1]	1,384	[1]
Translation	(12)	[1]	3	[1]
Segment reporting, goodwill	1,349
Goodwill gross, ending balance	1,375	[1]	1,387	[1]
Goodwill, net	$ 1,375	[1]	$ 1,387	[1]

[1] As of December 31, 2011, $1,349 of the amount reflected in Corporate is allocated to each of Alcoa's four reportable segments ($163 to Alumina, $850 to Primary Metals, $63 to Flat-Rolled Products, and $273 to Engineered Products and Solutions) included in the table above for purposes of impairment testing (see Note A). This goodwill is reflected in Corporate for segment reporting purposes because it is not included in management's assessment of performance by the four reportable segments.