Arconic Inc. Separation Transaction and Discontinued Operations - Summary of Property, Plant and Equipment Purchases of the Discontinued Operations (Details) - Arconic Corporation - Discontinued Operations, Disposed of by Means Other than Sale $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capital expenditures	$ 72
Proceeds from the sales of businesses	112
Provision for depreciation and amortization	$ 58