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 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capital expenditures	$ 72	$ 210
Proceeds from the sales of businesses	$ 112	$ 20