Earnings Per Share - Schedule of Anti Dilutive Securities Excluded From Computation of Average Shares Outstanding (Parenthetical) (Detail) - $ / shares	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share [Abstract]
Average option price of shares	$ 33.32	$ 38.22

The weighted average exercise price of stock options whose individual exercise prices were greater than the average market price of an entity's common stock during the period.

No definition available.

Name:	arnc_WeightedAverageExercisePriceOfUnderwaterOptions
Namespace Prefix:	arnc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration