v3.20.2
Subsequent Events​ (Details)
$ in Millions
May 13, 2020
USD ($)
Apr. 02, 2020
USD ($)
Oct. 30, 2020
USD ($)
Mar. 01, 2020
USD ($)
Dec. 31, 2019
USD ($)
Feb. 08, 2019
company
Oct. 01, 2018
USD ($)
claimants
Subsequent Event [Line Items]              
Number of publicly traded companies | company           2  
Disposed of by sale | Hard Alloy Extrusions Plant in South Korea              
Subsequent Event [Line Items]              
Consideration received       $ 55      
Disposed of by sale | Texarkana Rolling Mill and Cast House [Member]              
Subsequent Event [Line Items]              
Consideration received             $ 302
Disposal Group, Including Discontinued Operation, Book Value             $ 63
Period of Operationalizing Rolling Mill Equipment of Transaction | claimants             36
Disposed of by sale | Texarkana Rolling Mill and Cast House [Member] | Achievement of Milestones [Member]              
Subsequent Event [Line Items]              
Consideration received         $ 25   $ 50
Disposed of by sale | Texarkana Rolling Mill and Cast House [Member] | Achievement of Milestones [Member] | Subsequent events              
Subsequent Event [Line Items]              
Consideration received     $ 25        
Senior Secured Credit Facility | First-Lien Revolving Credit Facility | Revolving Credit Facility              
Subsequent Event [Line Items]              
Proceeds from revolving credit facility $ 500 $ 500