Segment Information - Schedule of Segment ATOI to Consolidated Net Income Attributable to Alcoa (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Total segment ATOI	$ 291	$ 656
Metal price lag	1	(23)
Interest expense	(127)	(122)
Noncontrolling interests	5	(60)
Consolidated net income attributable to Alcoa	16	195
Other [Member]
Segment Reporting Information [Line Items]
Impact of LIFO	4	7
Interest expense	(83)	(80)
Noncontrolling interests	5	(60)
Corporate expense	(55)	(62)
Restructuring and other charges	(61)	(161)
Other	$ (86)	$ (82)