Debt - Short-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Short-term debt	$ 5	$ 14

Short-Term Debt, Excluding Current Maturities Of Long-Term Debt

No definition available.

Name:	hwm_ShortTermDebtExcludingCurrentMaturitiesOfLongTermDebt
Namespace Prefix:	hwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant