v3.20.2

Subsequent Events​ (Details) $ in Millions | May 13, 2020 USD ($) | Apr. 02, 2020 USD ($) | Feb. 08, 2019 company | Nov. 01, 2016 company
--- | --- | --- | --- | ---
Subsequent Event [Line Items] |  |  |  |
Number of publicly traded companies | company |  |  | 2 | 2
Senior Secured Credit Facility | First-Lien Revolving Credit Facility | Revolving Credit Facility |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Proceeds from revolving credit facility | $ | $ 500 | $ 500 |  |

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- Definition Number of Publicly Traded Companies + References No definition available. + Details
Name: | arnc_NumberofPubliclyTradedCompanies
Namespace Prefix: | arnc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=arnc_FirstLienRevolvingCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |