Business, Product and Geographical Area Information and Concentration of Risk - Schedule of Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Net sales:
Net sales	$ 3,024.0	$ 3,087.0	$ 3,427.9
Aero/HS Products
Net sales:
Net sales	883.0	899.3	676.1
Packaging
Net sales:
Net sales	1,260.9	1,315.2	1,585.3
Automotive Extrusions
Net sales:
Net sales	251.9	254.9	254.8
GE Products
Net sales:
Net sales	618.1	596.5	883.8
Other Products
Net sales:
Net sales	10.1	21.1	27.9
Products Transferred at a Point in Time
Net sales:
Net sales	2,326.5	2,394.8	2,782.9
Products Transferred Over Time
Net sales:
Net sales	$ 697.5	$ 692.2	$ 645.0