Segment Information - Schedule of Operating Results of Alcoa's Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Total sales	$ 7,088	$ 7,289	$ 14,247	$ 14,665
Equity income (loss)	(10)	(10)	(22)	(12)
Depreciation, depletion, and amortization	341	343	682	689
Income taxes	115	85	253	195
ATOI	304	255	655	559
Third-Party Sales [Member]
Segment Reporting Information [Line Items]
Third-party sales	5,787	5,887	11,573	11,841
Intersegment [Member]
Segment Reporting Information [Line Items]
Intersegment sales	1,301	1,402	2,674	2,824
Alumina [Member]
Segment Reporting Information [Line Items]
Total sales	1,403	1,326	2,824	2,718
Equity income (loss)	(1)	1		2
Depreciation, depletion, and amortization	115	114	224	228
Income taxes	14	(6)	28	(7)
ATOI	64	23	122	58
Alumina [Member] | Third-Party Sales [Member]
Segment Reporting Information [Line Items]
Third-party sales	822	750	1,648	1,525
Alumina [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Intersegment sales	581	576	1,176	1,193
Primary Metals [Member]
Segment Reporting Information [Line Items]
Total sales	2,297	2,586	4,782	5,291
Equity income (loss)	(7)	(9)	(16)	(11)
Depreciation, depletion, and amortization	132	133	267	268
Income taxes	(25)	(19)	(24)	(32)
ATOI	(32)	(3)	7	7
Primary Metals [Member] | Third-Party Sales [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,620	1,804	3,378	3,748
Primary Metals [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Intersegment sales	677	782	1,404	1,543
Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Total sales	1,920	1,957	3,750	3,846
Equity income (loss)	(2)	(2)	(6)	(3)
Depreciation, depletion, and amortization	55	57	112	114
Income taxes	32	34	71	85
ATOI	79	78	160	180
Global Rolled Products [Member] | Third-Party Sales [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,877	1,913	3,656	3,758
Global Rolled Products [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Intersegment sales	43	44	94	88
Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Total sales	1,468	1,420	2,891	2,810
Depreciation, depletion, and amortization	39	39	79	79
Income taxes	94	76	178	149
ATOI	193	157	366	314
Engineered Products and Solutions [Member] | Third-Party Sales [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,468	$ 1,420	$ 2,891	$ 2,810