Selected Quarterly Financial Data (Unaudited) - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unusual Or Infrequent Item [Line Items]
NRV charge	$ 51.2	$ 76.0		$ 131.5	$ (25.0)	$ 35.0
NRV charge net of tax	32.0	49.5
Deferred tax asset valuation allowance charge		$ (63.9)		(68.4)
Restructuring charges				64.3	0.0	67.5
Impairment of goodwill				126.6	$ 0.0	0.0
Asset Impairment Charges	54.5					55.1
Impairment of Long-Lived Assets Held-for-use, After Tax	34.1
Restructuring costs net of tax				$ 41.6		41.2
Severance and termination benefit costs						$ 8.2
Other Postretirement Benefits [Member]
Unusual Or Infrequent Item [Line Items]
Settlements and curtailments gains			$ 25.5
Settlements and curtailments gains net of tax			$ 18.4
Flat Rolled Products [Member]
Unusual Or Infrequent Item [Line Items]
Impairment of goodwill	126.6
Impairment of goodwill net of tax	79.2
High Performance Materials & Components and Corporate [Member]
Unusual Or Infrequent Item [Line Items]
Severance and termination benefit costs	6.3
Severance and termination benefit costs net of tax	3.9
Facility Idling Costs [Member]
Unusual Or Infrequent Item [Line Items]
Restructuring costs	3.5
Restructuring costs net of tax	2.2
Inventory Valuation Reserve [Member] | Non-PQ grade titanium sponge [Member]
Unusual Or Infrequent Item [Line Items]
Lower of cost or market charges	(25.4)
Lower of cost or market charges net of tax	$ 15.9