Cash Flow Information - Schedule of Cash Paid for Acquisitions Including Non-Controlling Interest (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Business Combinations [Abstract]
Assets acquired	$ 2,003	$ 3,515
Liabilities assumed	(868)	(345)
Contingent consideration liability		(130)
Equity issued	(870)	(610)
Noncontrolling interest acquired		31
Increase in Alcoa's shareholders' equity	(60)	(3)
Cash paid	205	2,458
Less: cash acquired	302	45
Net cash paid	$ (97)	$ 2,413