Segment Information (Schedule Of Operating Results And Assets Of Alcoa's Reportable Segments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Segment Reporting Information [Line Items]
Third-party sales	$ 5,954		$ 5,929
Intersegment sales	1,422		1,541
Total sales	7,376		7,470
Equity income (loss)	(2)		5
Depreciation, depletion, and amortization	346		340
Income taxes	107		192
After-tax operating income (ATOI)	296		555
Segment Information [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Third-party sales	775		810
Intersegment sales	617		633
Total sales	1,392		1,443
Equity income (loss)	1		3
Depreciation, depletion, and amortization	114		103
Income taxes	(1)		44
After-tax operating income (ATOI)	35		142
Segment Information [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,944		1,980
Intersegment sales	761		839
Total sales	2,705		2,819
Equity income (loss)	(2)		1
Depreciation, depletion, and amortization	135		141
Income taxes	(13)		53
After-tax operating income (ATOI)	10		202
Segment Information [Member] | Engineered Products And Solutions [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,390		1,247
Intersegment sales
Total sales	1,390		1,247
Equity income (loss)			1
Depreciation, depletion, and amortization	40		38
Income taxes	72		62
After-tax operating income (ATOI)	155		130
Segment Information [Member] | Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,845	[1]	1,892	[1]
Intersegment sales	44	[1]	69	[1]
Total sales	1,889	[1]	1,961	[1]
Equity income (loss)	(1)	[1]		[1]
Depreciation, depletion, and amortization	57	[1]	58	[1]
Income taxes	49	[1]	33	[1]
After-tax operating income (ATOI)	$ 96	[1]	$ 81	[1]

[1] In the first quarter of 2012, Alcoa changed the name of the Flat-Rolled Products segment to the Global Rolled Products segment