Segment Information - Schedule of Segment ATOI to Consolidated Net Income (Loss) Attributable to Alcoa (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Total segment ATOI	$ 633	$ 325
Interest expense	(122)	(120)
Noncontrolling interests	(60)	19
Net income (loss) attributable to Alcoa	195	(178)
Other [Member]
Segment Reporting Information [Line Items]
Impact of LIFO	7	(7)
Interest expense	(80)	(78)
Noncontrolling interests	(60)	19
Corporate expense	(64)	(67)
Restructuring and other charges	(161)	(321)
Other	$ (80)	$ (49)