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Segment Information - Schedule of Segment ATOI to Consolidated Net Income Attributable to Alcoa (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Total segment ATOI	$ 444	$ 567	$ 735	$ 1,223
Metal price lag	7	(39)	8	(62)
Interest expense	(129)	(124)	(256)	(246)
Noncontrolling interests	(43)	(67)	(38)	(127)
Consolidated net income attributable to Alcoa	135	140	151	335
Other [Member]
Segment Reporting Information [Line Items]
Impact of LIFO	(10)	36	(6)	43
Interest expense	(84)	(80)	(167)	(160)
Noncontrolling interests	(43)	(67)	(38)	(127)
Corporate expense	(77)	(65)	(132)	(127)
Restructuring and other charges	(15)	(159)	(76)	(320)
Other	$ (87)	$ (53)	$ (173)	$ (135)

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