Business, Product and Geographical Area Information - Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net sales:
Net sales	$ 748.9	$ 750.6	$ 2,651.9	$ 1,815.6
Aero/HS products
Net sales:
Net sales	140.8	142.0	492.8	387.6
Packaging
Net sales:
Net sales	341.5	367.3	1,240.2	726.1
Automotive Extrusions
Net sales:
Net sales	60.6	50.1	196.0	163.3
GE products
Net sales:
Net sales	200.3	187.1	699.2	518.4
Other products
Net sales:
Net sales	5.7	4.1	23.7	20.2
Transferred at Point in Time
Net sales:
Net sales	630.2	613.6	2,165.1	1,419.5
Transferred over Time
Net sales:
Net sales	$ 118.7	$ 137.0	$ 486.8	$ 396.1