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Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Net receivables which represents assets related to divested businesses to be transferred to the buyers	$ 20	$ 2

X

- Definition

Receivables excluded from pension plan assets.

+ References

No definition available.

+ Details

Name:	arnc_ReceivablesExcludedFromPensionPlanAssets
Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration