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, 2015	Mar. 31, 2014
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ (4.5)	$ 2.9
Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	(4.5)	2.9
Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(4.7)	2.0
Unrealized gains (losses)	(4.5)	2.0
Call Options | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	10.2	4.4
Bifurcated Conversion Feature | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	(10.2)	(3.5)
Aluminum | Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(2.7)	0.8
Unrealized gains (losses)	(4.2)	1.7
Natural Gas | Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(1.3)	0.7
Unrealized gains (losses)	(0.7)	0.8
Electricity | Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(0.7)	0.5
Unrealized gains (losses)	$ 0.4	$ (0.5)