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

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- Definition 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. + References No definition available. + Details
Name: | arnc_WeightedAverageExercisePriceOfUnderwaterOptions
Namespace Prefix: | arnc_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_EarningsPerShareAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration