Segment and Geographical Area Information, Schedule of net sales by end market segment applications (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer
Net sales	$ 331.9	$ 320.6	$ 334.9	$ 343.2	$ 316.6	$ 336.4	$ 367.2	$ 371.7	$ 1,330.6	$ 1,391.9	$ 1,356.1
Aero/HS products
Revenue from External Customer
Net sales									675.4	695.5	686.3
Automotive Extrusions
Revenue from External Customer
Net sales									188.8	199.2	173.5
GE products
Revenue from External Customer
Net sales									420.1	426.1	419.5
Other products
Revenue from External Customer
Net sales									$ 46.3	$ 71.1	$ 76.8