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Business Segments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Total direct international sales		$ 1,577.0	$ 1,607.5	$ 1,585.1
Sales by U.S. operations to foreign countries		1,215.8	1,201.8	1,175.1
LIFO-related net realizable value charge	$ (136.4)	(136.4)	(4.8)
Inventory valuation reserves	206.3	206.3	68.8
Closed company and other expense		22.1	28.3	30.9
Closed companies environmental costs		4.5	8.0	3.9
Closed companies insurance obligations			3.8
Other corporate expense		15.3	9.4	10.3
Asset Impairment Charges	$ 54.5			55.1
Flat Rolled Products [Member]
Segment Reporting Information [Line Items]
Income (loss) from equity method investments		$ (0.1)	(8.9)	(7.1)
High Performance Materials & Components [Member]
Segment Reporting Information [Line Items]
Asset Impairment Charges				8.0
STAL Precision Stainless Steel Company Limited [Member]
Segment Reporting Information [Line Items]
Joint venture ownership percentage	60.00%	60.00%
Corporate Joint Venture [Member]
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50.00%	50.00%
Revenue from related parties		$ 55.4	75.3	95.9
Corporate Joint Venture [Member] \| VSMPO [Member]
Segment Reporting Information [Line Items]
Joint venture ownership percentage by unaffiliated entity	50.00%	50.00%
Corporate, Non-Segment [Member] \| Closed Company and Other [Member]
Segment Reporting Information [Line Items]
Retirement Benefit Expense		$ 2.3	$ 7.1	$ 16.7
Inventory Valuation Reserve [Member] \| Non-PQ grade titanium sponge [Member]
Segment Reporting Information [Line Items]
Lower of cost or market charges	$ (25.4)