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v3.19.1

Segment Information - Narrative (Details) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 USD ($)
Segment Reporting [Abstract] |
Goodwill, amount reallocated due to restructuring | $ 110

X
- Definition Goodwill, Amount Reallocated Due To Restructuring + References No definition available. + Details
Name: | arnc_GoodwillAmountReallocatedDueToRestructuring
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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