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Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Retirement Benefits [Abstract] |  |
Contributions and payments | $ 5 | $ 12

X
- Definition Defined Benefit Plan, Benefit Obligation, Contributions And Payments + References No definition available. + Details
Name: | hwm_DefinedBenefitPlanBenefitObligationContributionsAndPayments
Namespace Prefix: | hwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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