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Revenue from Contracts with Customers - Narrative (Details) $ in Millions | 9 Months Ended
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Sep. 30, 2018 USD ($)
Revenue from Contract with Customer [Abstract] |
Revenue, shipping payment terms | 30 days
Customer claims for new product introductions | $ 38

X
- Definition Contract with Customer, Claims for New Product Introductions + References No definition available. + Details
Name: | arnc_ContractwithCustomerClaimsforNewProductIntroductions
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Revenue, Terms Of Payment, Period + References No definition available. + Details
Name: | arnc_RevenueTermsOfPaymentPeriod
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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