Segment Information, Net Sales by Product Categories (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Sales:
Net sales	$ 367.2	$ 344.1	$ 738.9	$ 679.2
Aero/HS products
Net Sales:
Net sales	181.1	173.0	361.4	336.6
Automotive Extrusions
Net Sales:
Net sales	53.7	44.7	103.8	85.5
GE products
Net Sales:
Net sales	112.0	107.3	231.1	219.5
Other products
Net Sales:
Net sales	$ 20.4	$ 19.1	$ 42.6	$ 37.6