Segment and Geographic Area Information - Schedule of Segment Reporting Information to Consolidated Net Income Attributable to Alcoa (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Total segment ATOI									$ 1,369	$ 1,893	$ 1,424
Interest expense									(490)	(524)	(494)
Noncontrolling interests									29	(194)	(138)
Discontinued operations										(3)	(8)
Consolidated net income attributable to Alcoa	242	(143)	(2)	94	(191)	172	322	308	191	611	254
Unallocated Amounts (Net of Tax) [Member]
Segment Reporting Information [Line Items]
Impact of LIFO									20	(38)	(16)
Interest expense									(319)	(340)	(321)
Noncontrolling interests									29	(194)	(138)
Corporate expense									(282)	(290)	(291)
Restructuring and other charges									(75)	(196)	(134)
Discontinued operations										(3)	(8)
Other									$ (551)	$ (221)	$ (262)