Derivative Financial Instruments and Related Hedging Programs, Realized and Unrealized Gains (Losses) Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ 4.0	$ (4.5)
Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	4.0	(4.5)
Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(4.4)	(4.7)
Unrealized gains (losses)	4.0	(4.5)
Foreign Currency Member | Operational Risk Hedges | Designated as Hedging Instrument [Member]
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	0.2	0.0
Aluminum | Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(2.7)	(2.7)
Unrealized gains (losses)	3.2	(4.2)
Natural Gas | Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	(1.7)	(1.3)
Unrealized gains (losses)	0.8	(0.7)
Electricity | Operational Risk Hedges | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Realized (losses) gains	0.0	(0.7)
Unrealized gains (losses)	0.0	0.4
Hedges Relating To Notes Member | Call Options | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	0.0	10.2
Hedges Relating To Notes Member | Bifurcated Conversion Feature | Not Designated as Hedging Instrument
Summary Of Realized And Unrealized Gains (Losses)
Unrealized gains (losses)	$ 0.0	$ (10.2)