Arconic Inc Separation Transaction and Discontinued Operations - Summary of Results of 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]
Sales	$ 1,576	$ 7,094	$ 7,236
Cost of goods sold	1,292	6,013	6,283
Selling, general administrative, research and development and other expenses	106	346	295
Provision for depreciation and amortization	59	241	262
Restructuring and other charges (credits)	(18)	38	(154)
Interest expense	7	0	1
Other expense, net	42	91	109
Income from discontinued operations	88	365	440
Provision for income taxes	38	21	107
Income from discontinued operations after income taxes	$ 50	$ 344	$ 333