Business Segments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Total sales	$ 5,177.9	$ 5,365.4	$ 4,182.4
Intersegment sales	146.4	182.4	134.6
Sales to external customers	5,031.5	5,183.0	4,047.8
Segment Operating Profit (Loss)	537.9	612.0	356.5
Depreciation and amortization	194.0	174.4	141.5
High Performance Metals [Member]
Segment Reporting Information [Line Items]
Total sales	2,274.7	2,061.0	1,410.5
Intersegment sales	84.1	105.1	73.0
Sales to external customers	2,190.6	1,955.9	1,337.5
Segment Operating Profit (Loss)	371.6	364.5	257.8
Depreciation and amortization	128.5	110.4	77.7
Flat-Rolled Products [Member]
Segment Reporting Information [Line Items]
Total sales	2,378.8	2,759.0	2,360.2
Intersegment sales	29.6	33.0	21.7
Sales to external customers	2,349.2	2,726.0	2,338.5
Segment Operating Profit (Loss)	126.9	213.4	85.9
Income Loss From Equity Method Investments	4.9	7.4	2.5
Depreciation and amortization	48.2	48.3	48.1
Engineered Products [Member]
Segment Reporting Information [Line Items]
Total sales	524.4	545.4	411.7
Intersegment sales	32.7	44.3	39.9
Sales to external customers	491.7	501.1	371.8
Segment Operating Profit (Loss)	39.4	34.1	12.8
Depreciation and amortization	15.6	14.5	14.3
Corporate [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 1.7	$ 1.2	$ 1.4