Business, Product and Geographical Area Information and Concentration of Risk, Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Sales:
Net sales	$ 375.3	$ 415.4	$ 770.5	$ 803.4
Transferred at Point in Time
Net Sales:
Net sales	131.0	140.8	262.8	297.4
Transferred over Time
Net Sales:
Net sales	244.3	274.6	507.7	506.0
Aero/HS products
Net Sales:
Net sales	189.4	185.0	387.9	355.2
Automotive Extrusions
Net Sales:
Net sales	45.5	67.3	98.5	127.8
GE products
Net Sales:
Net sales	128.2	147.9	258.2	291.2
Other products
Net Sales:
Net sales	$ 12.2	$ 15.2	$ 25.9	$ 29.2