Derivative Financial Instruments and Related Hedging Programs, Realized and Unrealized Gains (Losses) Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)			$ (2.3)	$ 16.4
Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(2.3)	(5.7)	(4.8)	(16.2)
Unrealized gains (losses)	3.1	12.2	(2.3)	16.4
Aluminum | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(2.0)	(3.3)	(3.6)	(7.7)
Unrealized gains (losses)	1.7	8.3	(4.5)	8.8
Natural Gas | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(0.5)	(1.6)	(1.3)	(5.5)
Unrealized gains (losses)	0	3.0	0.8	4.7
Electricity | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	0.3	(0.8)	0.2	(3.0)
Unrealized gains (losses)	(0.3)	1.0	0.3	1.8
Foreign Currency | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(0.1)	0	(0.1)	0
Unrealized gains (losses)	0.1	0	0	0
Hedges Relating to the Convertible Notes | Call Options | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	31.0	10.2	27.9	5.8
Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ (29.4)	$ (10.3)	$ (26.8)	$ (4.7)