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v3.19.3.a.u2

Segment and Geographic Area Information - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Segment Reporting Information [Line Items] |  |
Costs related to certain customer settlements |  | $ 38
Sales Revenue, Segment | Product Concentration Risk |  |
Segment Reporting Information [Line Items] |  |
Sales percentage | 70.00% |

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 Sales Percentage + References No definition available. + Details
Name: | arnc_SalesPercentage
Namespace Prefix: | arnc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_ProductConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |