Revenue from Contracts with Customers - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue, shipping payment terms		30 days
Customer claims for new product introductions	$ 38	$ 38

Contract with Customer, Claims for New Product Introductions

No definition available.

Name:	arnc_ContractwithCustomerClaimsforNewProductIntroductions
Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration