Derivative Financial Instruments and Related Hedging Programs, Realized and Unrealized Gains and Losses Table (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Summary Of Realized And Unrealized Gains Losses
Total realized gains (losses)	$ 0.5	$ (1.2)	$ 8.4	$ (3.2)
Total unrealized (losses) gains	(12.7)	10.9	(19.8)	(7.1)
Aluminum Commodity [Member]
Summary Of Realized And Unrealized Gains Losses
Total realized gains (losses)	1.6	(0.9)	11.9	(2.6)
Total unrealized (losses) gains	(14.8)	17.1	(21.4)	1.1
Natural Gas [Member]
Summary Of Realized And Unrealized Gains Losses
Total realized gains (losses)	(1.1)	(0.3)	(3.5)	(0.6)
Total unrealized (losses) gains	(0.9)	(2.4)	0.6	(5.2)
Electricity [Member]
Summary Of Realized And Unrealized Gains Losses
Total unrealized (losses) gains	(1.1)	0	(1.2)	0
Hedges Relating to Notes [Member] | Call Options [Member]
Summary Of Realized And Unrealized Gains Losses
Total unrealized (losses) gains	(16.6)	10.3	(10.2)	4.7
Hedges Relating to Notes [Member] | Bifurcated Conversion Feature [Member]
Summary Of Realized And Unrealized Gains Losses
Total unrealized (losses) gains	$ 20.7	$ (14.1)	$ 12.4	$ (7.7)