Segment Information, Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net Sales:
Net sales			$ 998.7	$ 1,075.3
Aero/HS products
Net Sales:
Net sales			500.7	531.4
Automotive Extrusions
Net Sales:
Net sales			143.6	153.3
GE products
Net Sales:
Net sales			318.3	331.5
Other products
Net Sales:
Net sales			$ 36.1	$ 59.1
Fabricated Products
Net Sales:
Net sales	$ 320.6	$ 336.4
Fabricated Products | Aero/HS products
Net Sales:
Net sales	156.1	170.0
Fabricated Products | Automotive Extrusions
Net Sales:
Net sales	46.5	49.5
Fabricated Products | GE products
Net Sales:
Net sales	105.6	100.4
Fabricated Products | Other products
Net Sales:
Net sales	$ 12.4	$ 16.5