Segment and Geographic Area Information - Schedule of Segment ATOI to Consolidated Net (Loss) Income Attributable to Alcoa (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Total segment ATOI									$ 1,906	$ 1,968	$ 1,267
Metal price lag									(133)	78	(45)
Interest expense									(498)	(473)	(453)
Noncontrolling interests									(125)	91	(41)
Impairment of goodwill	$ (25)								(25)		(1,731)
Consolidated net (loss) income attributable to Alcoa	$ (701)	$ 44	$ 140	$ 195	$ 159	$ 149	$ 138	$ (178)	(322)	268	(2,285)
Other [Member]
Segment Reporting Information [Line Items]
Impact of LIFO									136	(54)	52
Interest expense									(324)	(308)	(294)
Noncontrolling interests									(125)	91	(41)
Corporate expense									(266)	(284)	(274)
Impairment of goodwill									(25)		(1,731)
Restructuring and other charges									(943)	(894)	(607)
Other									$ (548)	$ (329)	$ (612)