v3.20.1

Restructuring and Other Charges - Narrative (Details) $ in Millions		3 Months Ended		12 Months Ended
	Mar. 01, 2020 USD ($)	Mar. 31, 2020 USD ($) employee	Mar. 31, 2019 USD ($) employee	Dec. 31, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 19
Restructuring and other charges		$ (19)	$ 2
Expected number of employees separated | employee		480
Number of employees separated | employee		270
Cash payments, restructuring		$ 4		$ 15
Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring		4		12
Allocated costs, ParentCo
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		2	$ (9)
Other miscellaneous costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		6
Cash payments, restructuring		0		$ 3
Hard Alloy Extrusions Plant in South Korea | Disposed of by sale
Restructuring Cost and Reserve [Line Items]
Gain (loss) on sale	$ 31	(31)
Aluminum Rolling Mill in Brazil | Disposed of by sale
Restructuring Cost and Reserve [Line Items]
Gain (loss) on sale		$ (6)
Rolled Products and Building and Construction Systems
Restructuring Cost and Reserve [Line Items]
Number of employees separated | employee			155
Rolled Products and Building and Construction Systems | Layoff costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 11

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