Segment and Geographic Area Information - Schedule of Operating Results and Assets of Alcoa's Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Third-party sales	$ 23,427	$ 24,689	$ 20,746
Intersegment sales	5,350	6,137	4,989
Total sales	28,777	30,826	25,735
Equity income (loss)	(28)	16	13
Depreciation, depletion, and amortization	1,374	1,395	1,369
Income taxes	543	635	443
ATOI	1,369	1,893	1,424
Capital expenditures	1,261	1,287	1,015
Equity investments	1,782	1,524
Goodwill	5,170	5,157	5,028
Total assets	40,179	40,120
Alumina [Member]
Segment Reporting Information [Line Items]
Goodwill	10	11	12
Primary Metals [Member]
Segment Reporting Information [Line Items]
Goodwill	997	991	993
Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill	2,677	2,666	2,523
Segment Information [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Third-party sales	3,092	3,462	2,815
Intersegment sales	2,310	2,727	2,212
Total sales	5,402	6,189	5,027
Equity income (loss)	5	25	10
Depreciation, depletion, and amortization	455	444	406
Income taxes	(27)	179	60
ATOI	90	607	301
Capital expenditures	374	371
Equity investments	658	450
Goodwill	10	11
Total assets	9,709	9,782
Segment Information [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Third-party sales	7,432	8,240	7,070
Intersegment sales	2,877	3,192	2,597
Total sales	10,309	11,432	9,667
Equity income (loss)	(27)	(7)	1
Depreciation, depletion, and amortization	532	556	571
Income taxes	106	92	96
ATOI	309	481	488
Capital expenditures	318	463
Equity investments	917	925
Goodwill	997	991
Total assets	11,709	11,867
Segment Information [Member] | Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Third-party sales	7,378	7,642	6,277
Intersegment sales	163	218	180
Total sales	7,541	7,860	6,457
Equity income (loss)	(6)	(3)
Depreciation, depletion, and amortization	229	237	238
Income taxes	167	104	92
ATOI	358	266	220
Capital expenditures	258	157
Equity investments	188	123
Goodwill	214	208
Total assets	4,603	4,559
Segment Information [Member] | Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Third-party sales	5,525	5,345	4,584
Total sales	5,525	5,345	4,584
Equity income (loss)		1	2
Depreciation, depletion, and amortization	158	158	154
Income taxes	297	260	195
ATOI	612	539	415
Capital expenditures	200	173
Goodwill	2,677	2,666
Total assets	$ 5,891	$ 5,831