Derivative Financial Instruments and Related Hedging Programs, Realized and Unrealized Gains and Losses Table (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary Of Realized And Unrealized Gains Losses
Unrealized gains (losses)	$ 3.9	$ 16.0	$ (25.9)
Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains Losses
Realized (losses) gains	(6.5)	(19.1)	4.4
Unrealized gains (losses)	3.9	16.0	(25.9)
Not Designated as Hedging Instrument | Aluminum
Summary Of Realized And Unrealized Gains Losses
Realized (losses) gains	(5.5)	(9.0)	9.6
Unrealized gains (losses)	(3.1)	10.1	(26.5)
Not Designated as Hedging Instrument | Natural Gas
Summary Of Realized And Unrealized Gains Losses
Realized (losses) gains	(1.8)	(6.7)	(5.2)
Unrealized gains (losses)	2.6	4.3	(1.6)
Not Designated as Hedging Instrument | Electricity
Summary Of Realized And Unrealized Gains Losses
Realized (losses) gains	0.8	(3.4)	0
Unrealized gains (losses)	1.1	0.8	(1.8)
Not Designated as Hedging Instrument | Foreign Currency
Summary Of Realized And Unrealized Gains Losses
Unrealized gains (losses)	0.1	0	0
Not Designated as Hedging Instrument | Call Options relating to the Convertible Notes | Hedges Relating to the Convertible Notes
Summary Of Realized And Unrealized Gains Losses
Unrealized gains (losses)	24.2	9.0	(2.1)
Not Designated as Hedging Instrument | Bifurcated Conversion Feature of the Convertible Notes | Hedges Relating to the Convertible Notes
Summary Of Realized And Unrealized Gains Losses
Unrealized gains (losses)	$ (21.0)	$ (8.2)	$ 6.1