Business, Product and Geographical Area Information and Concentration of Risk, Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Sales:
Revenues	$ 393.1	$ 332.8	$ 1,196.5	$ 1,044.4
Transferred at Point in Time
Net Sales:
Revenues	127.8		425.2
Transferred over Time
Net Sales:
Revenues	265.3		771.3
Aero/HS products
Net Sales:
Revenues	185.7	150.2	540.9	483.2
Automotive Extrusions
Net Sales:
Revenues	56.1	52.7	183.9	161.6
GE products
Net Sales:
Revenues	133.9	115.9	425.1	361.1
Other products
Net Sales:
Revenues	$ 17.4	$ 14.0	$ 46.6	$ 38.5