Segment Information - Schedule of Operating Results of Alcoa's Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Reporting Information [Line Items]
Third-party sales	$ 5,786	$ 5,954
Intersegment sales	1,373	1,422
Total sales	7,159	7,376
Equity income (loss)	(12)	(2)
Depreciation, depletion, and amortization	341	346
Income taxes	138	110
ATOI	351	304
Segment Information [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Third-party sales	826	775
Intersegment sales	595	617
Total sales	1,421	1,392
Equity income (loss)	1	1
Depreciation, depletion, and amortization	109	114
Income taxes	14	(1)
ATOI	58	35
Segment Information [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,758	1,944
Intersegment sales	727	761
Total sales	2,485	2,705
Equity income (loss)	(9)	(2)
Depreciation, depletion, and amortization	135	135
Income taxes	1	(13)
ATOI	39	10
Segment Information [Member] | Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,779	1,845
Intersegment sales	51	44
Total sales	1,830	1,889
Equity income (loss)	(4)	(1)
Depreciation, depletion, and amortization	57	57
Income taxes	39	51
ATOI	81	102
Segment Information [Member] | Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,423	1,390
Intersegment sales
Total sales	1,423	1,390
Equity income (loss)
Depreciation, depletion, and amortization	40	40
Income taxes	84	73
ATOI	$ 173	$ 157