Business, Product and Geographical Area Information and Concentration of Risk, Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Sales:
Net sales	$ 374.9	$ 393.1	$ 1,145.4	$ 1,196.5
Transferred at Point in Time
Net Sales:
Net sales	115.9	127.8	378.7	425.2
Transferred over Time
Net Sales:
Net sales	259.0	265.3	766.7	771.3
Aero/HS products
Net Sales:
Net sales	198.9	185.7	586.8	540.9
Automotive Extrusions
Net Sales:
Net sales	47.5	56.1	146.0	183.9
GE products
Net Sales:
Net sales	117.1	133.9	375.3	425.1
Other products
Net Sales:
Net sales	$ 11.4	$ 17.4	$ 37.3	$ 46.6