v3.22.0.1

Other Expenses (Income), Net - Narrative (Details) - Tax Matters Agreement $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Reversal of liability previously established	$ 20
Percentage of potential loss responsible for in event of unfavorable ruling	34.00%

X

- Definition

Loss Contingency, Percentage Of Potential Loss Responsible For In Event Of Unfavorable Ruling

+ References

No definition available.

+ Details

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Namespace Prefix:	arnc_
Data Type:	dtr-types: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_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of increase (decrease) in loss contingency liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: