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v3.19.3.a.u2

Debt - Short-Term Borrowings (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Disclosure [Abstract] |  |
Short-term debt | $ 31 | $ 29
Accounts payable settlement arrangements | $ 29 | $ 29

X
- Definition Accounts payable settlement arrangements. + References No definition available. + Details
Name: | arnc_AccountsPayableSettlementArrangements
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Short-Term Debt, Excluding Current Maturities Of Long-Term Debt + References No definition available. + Details
Name: | arnc_ShortTermDebtExcludingCurrentMaturitiesOfLongtermDebt
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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