Arconic Inc Separation Transaction and Discontinued Operations - Summary of Property, Plant and Equipment Purchases of the Discontinued Operations (Details) - Discontinued Operations, Disposed of by Means Other than Sale - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capital expenditures	$ 72	$ 210	$ 308
Proceeds from the sales of businesses	112	20	309
Provision for depreciation and amortization	$ 59	$ 241	$ 262