Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to Arconic	$ 166	$ 44	$ 317	$ 379
Less: preferred stock dividends declared	18	18	52	52
Net income available to Arconic common shareholders - basic	148	26	265	327
Add: interest expense related to convertible notes	2
Add: dividends related to mandatory convertible preferred stock	0	0	0	0
Net income available to Arconic common shareholders - diluted	$ 150	$ 26	$ 265	$ 327
Average shares outstanding - basic	438	427	438	414
Stock options	1		1	1
Stock and performance awards	5	4	4	4
Convertible notes	9
Mandatory convertible preferred stock	0	0	0	0
Average shares outstanding - diluted	453	431	443	419