Segment Information - Schedule of Segment ATOI to Consolidated Net Income Attributable to Alcoa (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Total segment ATOI	$ 619	$ 338	$ 1,362	$ 993
Interest expense	(126)	(108)	(351)	(341)
Noncontrolling interests	(18)	20	(46)	12
NET INCOME ATTRIBUTABLE TO ALCOA	149	24	109	54
Unallocated Amounts (Net of Tax) [Member]
Segment Reporting Information [Line Items]
Impact of LIFO	(18)	9	(33)	12
Interest expense	(81)	(70)	(228)	(221)
Noncontrolling interests	18	(20)	46	(12)
Corporate expense	(74)	(74)	(211)	(212)
Restructuring and other charges	(189)	(108)	(587)	(324)
Other	$ (126)	$ (51)	$ (240)	$ (182)