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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net sales:
Net sales	$ 954.2	$ 741.0	$ 1,903.0	$ 1,065.0
Aero/HS products
Net sales:
Net sales	175.4	133.9	352.0	245.6
Packaging
Net sales:
Net sales	450.7	358.8	898.7	358.8
Automotive Extrusions
Net sales:
Net sales	71.6	55.6	135.4	113.2
GE products
Net sales:
Net sales	247.7	180.9	498.9	331.3
Other products
Net sales:
Net sales	8.8	11.8	18.0	16.1
Transferred at Point in Time
Net sales:
Net sales	762.9	605.7	1,534.9	805.9
Transferred over Time
Net sales:
Net sales	$ 191.3	$ 135.3	$ 368.1	$ 259.1