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, 2013	Mar. 31, 2012
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	$ (0.7)	$ (2.7)
Unrealized (losses) gains	(0.3)	3.6
Aluminum
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	0	(0.2)
Unrealized (losses) gains	(4.4)	5.2
Natural Gas
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	(0.7)	(1.8)
Unrealized (losses) gains	2.7	(1.2)
Electricity
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	0	(0.7)
Unrealized (losses) gains	1.2	(0.9)
Foreign Currency
Summary Of Realized And Unrealized Gains (Losses)
Unrealized (losses) gains	(0.2)	0
Call Options | Hedges Relating to the Convertible Notes
Summary Of Realized And Unrealized Gains (Losses)
Unrealized (losses) gains	6.0	(8.8)
Bifurcated Conversion Feature | Hedges Relating to the Convertible Notes
Summary Of Realized And Unrealized Gains (Losses)
Unrealized (losses) gains	$ (5.6)	$ 9.3