Segment Information - Schedule of Operating Results of Alcoa's Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Total sales	$ 6,939	$ 7,082	$ 21,186	$ 21,747
Equity income (loss)	(18)	(4)	(40)	(16)
Depreciation, depletion, and amortization	327	346	1,009	1,035
Income taxes	124	75	377	270
ATOI	338	224	993	783
Alumina [Member]
Segment Reporting Information [Line Items]
Total sales	1,359	1,339	4,183	4,057
Equity income (loss)	(2)	2	(2)	4
Depreciation, depletion, and amortization	100	120	324	348
Income taxes	17	(22)	45	(29)
ATOI	67	(9)	189	49
Primary Metals [Member]
Segment Reporting Information [Line Items]
Total sales	2,291	2,485	7,073	7,776
Equity income (loss)	(13)	(5)	(29)	(16)
Depreciation, depletion, and amortization	131	130	398	398
Income taxes	(16)	(19)	(40)	(51)
ATOI	8	(14)	15	(7)
Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Total sales	1,852	1,891	5,602	5,737
Equity income (loss)	(3)	(1)	(9)	(4)
Depreciation, depletion, and amortization	56	57	168	171
Income taxes	32	39	103	124
ATOI	71	89	231	269
Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Total sales	1,437	1,367	4,328	4,177
Depreciation, depletion, and amortization	40	39	119	118
Income taxes	91	77	269	226
ATOI	192	158	558	472
Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Intersegment sales	1,251	1,308	3,925	4,132
Intersegment Sales [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Intersegment sales	513	575	1,689	1,768
Intersegment Sales [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Intersegment sales	691	691	2,095	2,234
Intersegment Sales [Member] | Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Intersegment sales	47	42	141	130
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	5,688	5,774	17,261	17,615
Third-Party Sales [Member] | Operating Segments [Member] | Alumina [Member]
Segment Reporting Information [Line Items]
Third-party sales	846	764	2,494	2,289
Third-Party Sales [Member] | Operating Segments [Member] | Primary Metals [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,600	1,794	4,978	5,542
Third-Party Sales [Member] | Operating Segments [Member] | Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,805	1,849	5,461	5,607
Third-Party Sales [Member] | Operating Segments [Member] | Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,437	$ 1,367	$ 4,328	$ 4,177