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Separation Transaction, Share Distribution Ratio

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Arconic Inc. Separation Transaction and Discontinued Operations - Narrative (Details)				3 Months Ended	6 Months Ended
	Apr. 01, 2020 company	Mar. 25, 2020 USD ($)	Feb. 01, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 01, 2020 USD ($)	Feb. 07, 2020 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of independent, publicly-traded companies resulting from proposed separation transaction \| company	2
Separation, share distribution ratio	0.25
Debt issuance costs incurred					$ 61,000,000	$ 0
Aluminum Rolling Mill
Restructuring Cost and Reserve [Line Items]
Disposal group, consideration			$ 50,000,000
Gain on sale of business			$ 59,000,000
Asset impairment charges				$ 6,000,000		$ 53,000,000
Hard Alloy Extrusions Plant In South Korea
Restructuring Cost and Reserve [Line Items]
Disposal group, consideration							$ 62,000,000
Lien Notes
Restructuring Cost and Reserve [Line Items]
Debt issuance costs incurred				$ 45,000,000	$ 45,000,000
Senior Notes \| Second Lien Notes Due 2028
Restructuring Cost and Reserve [Line Items]
Aggregate principal amount								$ 600,000,000
Long-term debt, interest rate (percentage)								6.125%
Line of Credit \| Senior Secured First Lien Term B Loan Facility Due 2027 \| Secured Debt
Restructuring Cost and Reserve [Line Items]
Aggregate principal amount		$ 600,000,000
Credit Agreement term		7 years