Derivative Financial Instruments and Related Hedging Programs, Realized and Unrealized Gains (Losses) Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)			$ 4.9	$ (5.4)
Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	1.3	(1.8)	3.3	(2.5)
Unrealized gains (losses)	2.0	(5.1)	4.9	(5.4)
Aluminum | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	1.3	(1.6)	2.1	(1.6)
Unrealized gains (losses)	0.6	(1.8)	2.3	(6.2)
Natural Gas | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	0.5	(0.1)	1.2	(0.8)
Unrealized gains (losses)	(0.2)	(1.9)	0.6	0.8
Electricity | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(0.5)	(0.1)	0	(0.1)
Unrealized gains (losses)	1.2	(0.6)	0.7	0.6
Foreign Currency | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	(0.1)	0.1	(0.1)	(0.1)
Hedges Relating to the Convertible Notes | Call Options | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	2.5	(9.1)	6.9	(3.1)
Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ (2.0)	$ 8.2	$ (5.5)	$ 2.6