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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	$ (1.8)	$ (7.8)	$ (2.5)	$ (10.5)
Unrealized (losses) gains	(5.1)	0.6	(5.4)	4.2
Aluminum
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	(1.6)	(4.2)	(1.6)	(4.4)
Unrealized (losses) gains	(1.8)	(4.7)	(6.2)	0.5
Natural Gas
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	(0.1)	(2.1)	(0.8)	(3.9)
Unrealized (losses) gains	(1.9)	3.0	0.8	1.8
Electricity
Summary Of Realized And Unrealized Gains (Losses)
Realized losses	(0.1)	(1.5)	(0.1)	(2.2)
Unrealized (losses) gains	(0.6)	1.6	0.6	0.7
Foreign Currency
Summary Of Realized And Unrealized Gains (Losses)
Unrealized (losses) gains	0.1	0	(0.1)	0
Hedges Relating to the Convertible Notes | Call Options
Summary Of Realized And Unrealized Gains (Losses)
Unrealized (losses) gains	(9.1)	4.4	(3.1)	(4.4)
Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Summary Of Realized And Unrealized Gains (Losses)
Unrealized (losses) gains	$ 8.2	$ (3.7)	$ 2.6	$ 5.6