Multiemployer Pension Plans - Multiemployer Pension Plan Description and Contributions (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020 Agreement $ / shares
Multiemployer Pension Plan Disclosure [Line Items]
Green zone funding percentage	80.00%
USW Plan
Multiemployer Pension Plan Disclosure [Line Items]
Number of collective-bargaining agreements | Agreement	3
USW Plan | Newark, Ohio and Spokane (Trentwood), Washington Facilities
Multiemployer Pension Plan Disclosure [Line Items]
Percentage of employees covered by bargaining agreement	85.00%
USW Plan | Newark, Ohio and Spokane (Trentwood), Washington Facilities | Starting in July Two Thousand Twenty
Multiemployer Pension Plan Disclosure [Line Items]
Monthly contributions per hour worked by each bargaining unit employee | $ / shares	$ 1.75
USW Plan | Richmond (Bellwood), Virginia Facility
Multiemployer Pension Plan Disclosure [Line Items]
Percentage of employees covered by bargaining agreement	12.00%
USW Plan | Florence, Alabama Facility
Multiemployer Pension Plan Disclosure [Line Items]
Percentage of employees covered by bargaining agreement	3.00%