Arconic Inc. Separation Transaction - Narrative (Details) $ in Millions		3 Months Ended
	Apr. 01, 2020 company	May 05, 2020 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (D)			$ 21	$ 12
Subsequent Event
Restructuring Cost and Reserve [Line Items]
Number of independent, publicly-traded companies resulting from proposed separation transaction | company	2
Business separation | Separation Transaction [Member]
Restructuring Cost and Reserve [Line Items]
Debt issuance costs incurred			45
Capital expenditures			3
Restructuring costs incurred to date			116
Business separation | Separation Transaction [Member] | Subsequent Event
Restructuring Cost and Reserve [Line Items]
Debt issuance costs incurred		$ 45
Capital expenditures		$ 10
Business separation | Separation Transaction [Member] | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (D)			$ 38