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Goodwill and Other Intangible Assets - Goodwill (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) reporting_unit	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 12, 2014 USD ($)
Goodwill [Line Items]
Goodwill	$ 651.4	$ 641.9	$ 651.4
Period increase (decrease) in goodwill		(9.5)
Impairment of goodwill		0.0	(126.6)	$ 0.0
Accumulated goodwill impairment	126.6	126.6	$ 126.6
Hanard Machine, Inc. [Member]
Goodwill [Line Items]
Goodwill					$ 8.4
High Performance Materials & Components [Member]
Goodwill [Line Items]
Goodwill		641.9
Impairment of goodwill		$ 0.0		$ 0.0
Number of reporting units \| reporting_unit		3
High Performance Materials & Components [Member] \| First Reporting Unit [Member]
Goodwill [Line Items]
Goodwill		$ 470.8
Percentage of fair value in excess of carrying value		14.00%
High Performance Materials & Components [Member] \| Second Reporting Unit [Member]
Goodwill [Line Items]
Goodwill		$ 114.4
Percentage of fair value in excess of carrying value		12.00%
High Performance Materials & Components [Member] \| Third Reporting Unit [Member]
Goodwill [Line Items]
Goodwill		$ 56.7
Flat Rolled Products [Member]
Goodwill [Line Items]
Impairment of goodwill	$ (126.6)