Derivative Financial Instruments and Related Hedging Programs, Realized and Unrealized Gains (Losses) Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ 2.9	$ (0.3)
Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	2.0	(0.7)
Unrealized gains (losses)	2.9	(0.3)
Aluminum | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	0.8	0
Unrealized gains (losses)	1.7	(4.4)
Natural Gas | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	0.7	(0.7)
Unrealized gains (losses)	0.8	2.7
Electricity | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	0.5	0
Unrealized gains (losses)	(0.5)	1.2
Foreign Currency | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	0	(0.2)
Hedges Relating to the Convertible Notes | Call Options | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	4.4	6.0
Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ (3.5)	$ (5.6)