Segment Information - Schedule of Segment ATOI to Consolidated Net Income (Loss) Attributable to Alcoa (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Total segment ATOI	$ 568	$ 407	$ 1,224	$ 725
Interest expense	(124)	(105)	(246)	(225)
Noncontrolling interests	(67)	9	(127)	28
Net income (loss) attributable to Alcoa	140	138	335	(40)
Other [Member]
Segment Reporting Information [Line Items]
Impact of LIFO	36	(8)	43	(15)
Metal price lag	(39)	11	(62)	18
Interest expense	(80)	(69)	(160)	(147)
Noncontrolling interests	(67)	9	(127)	28
Corporate expense	(66)	(70)	(130)	(137)
Restructuring and other charges	(159)	(77)	(320)	(398)
Other	$ (53)	$ (65)	$ (133)	$ (114)