Business, Product and Geographical Area Information - Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Net sales:
Net sales	$ 814.1	$ 954.2	$ 1,621.7	$ 1,903.0
Aero/HS products
Net sales:
Net sales	225.1	175.4	439.1	352.0
Packaging
Net sales:
Net sales	354.7	450.7	708.9	898.7
Automotive Extrusions
Net sales:
Net sales	68.4	71.6	139.2	135.4
GE products
Net sales:
Net sales	159.4	247.7	321.5	498.9
Other products
Net sales:
Net sales	6.5	8.8	13.0	18.0
Transferred at Point in Time
Net sales:
Net sales	622.6	762.9	1,247.4	1,534.9
Transferred over Time
Net sales:
Net sales	$ 191.5	$ 191.3	$ 374.3	$ 368.1