Segment Information, Net Sales by Product Categories (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net Sales:
Net sales	$ 336.4	$ 338.9	$ 1,075.3	$ 1,018.1
Aero/HS products
Net Sales:
Net sales	170.0	172.5	531.4	509.1
Automotive Extrusions
Net Sales:
Net sales	49.5	44.0	153.3	129.5
GE products
Net Sales:
Net sales	100.4	103.6	331.5	323.1
Other products
Net Sales:
Net sales	$ 16.5	$ 18.8	$ 59.1	$ 56.4