Business, Product and Geographical Area Information and Concentration of Risk, Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net Sales:
Revenues	$ 395.2	$ 388.0
Transferred at Point in Time
Net Sales:
Revenues	131.8	156.6
Transferred over Time
Net Sales:
Revenues	263.4	231.4
Aero/HS products
Net Sales:
Revenues	198.5	170.2
Automotive Extrusions
Net Sales:
Revenues	53.0	60.5
GE products
Net Sales:
Revenues	130.0	143.3
Other products
Net Sales:
Revenues	$ 13.7	$ 14.0