Business Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Sales	$ 738.9	$ 832.7	$ 1,022.5	$ 1,125.5	$ 1,047.5	$ 1,069.6	$ 1,119.0	$ 987.3	$ 3,719.6	$ 4,223.4	$ 4,043.5
External Sales [Member]
Segment Reporting Information [Line Items]
Sales									3,719.6	4,223.4	4,043.5
Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales									3,870.6	4,404.8	4,163.3
Operating Segments [Member] | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales									151.0	181.4	119.8
Operating Segments [Member] | External Sales [Member]
Segment Reporting Information [Line Items]
Sales									3,719.6	4,223.4	4,043.5
Operating Segments [Member] | High Performance Materials & Components [Member]
Segment Reporting Information [Line Items]
Sales									2,062.7	2,084.6	2,016.7
Operating Segments [Member] | High Performance Materials & Components [Member] | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales									76.8	77.8	71.9
Operating Segments [Member] | High Performance Materials & Components [Member] | External Sales [Member]
Segment Reporting Information [Line Items]
Sales									1,985.9	2,006.8	1,944.8
Operating Segments [Member] | Flat Rolled Products [Member]
Segment Reporting Information [Line Items]
Sales									1,807.9	2,320.2	2,146.6
Operating Segments [Member] | Flat Rolled Products [Member] | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales									74.2	103.6	47.9
Operating Segments [Member] | Flat Rolled Products [Member] | External Sales [Member]
Segment Reporting Information [Line Items]
Sales									$ 1,733.7	$ 2,216.6	$ 2,098.7