Fair Value Measurements, Fair Value Hierarchy Table (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Derivative assets
Derivative assets	$ 42.2	$ 79.1
Derivative liabilities
Derivative Liabilities	60.4	78.4
Aluminum Commodity [Member] \| Call option purchase contracts [Member]
Derivative assets
Derivative assets	0.5	9.3
Aluminum Commodity [Member] \| Call option purchase contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets	0	0
Aluminum Commodity [Member] \| Call option purchase contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets	0.5	9.3
Aluminum Commodity [Member] \| Call option purchase contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets	0	0
Aluminum Commodity [Member] \| Call option sales contracts [Member]
Derivative liabilities
Derivative Liabilities	0.5	9.3
Aluminum Commodity [Member] \| Call option sales contracts [Member] \| Level 1 [Member]
Derivative liabilities
Derivative Liabilities	0	0
Aluminum Commodity [Member] \| Call option sales contracts [Member] \| Level 2 [Member]
Derivative liabilities
Derivative Liabilities	0.5	9.3
Aluminum Commodity [Member] \| Call option sales contracts [Member] \| Level 3 [Member]
Derivative liabilities
Derivative Liabilities	0	0
Aluminum Commodity [Member] \| Put option purchase contracts [Member]
Derivative assets
Derivative assets		0.1
Aluminum Commodity [Member] \| Put option purchase contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets		0
Aluminum Commodity [Member] \| Put option purchase contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets		0.1
Aluminum Commodity [Member] \| Put option purchase contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets		0
Aluminum Commodity [Member] \| Put option sales contracts [Member]
Derivative liabilities
Derivative Liabilities		0.1
Aluminum Commodity [Member] \| Put option sales contracts [Member] \| Level 1 [Member]
Derivative liabilities
Derivative Liabilities		0
Aluminum Commodity [Member] \| Put option sales contracts [Member] \| Level 2 [Member]
Derivative liabilities
Derivative Liabilities		0.1
Aluminum Commodity [Member] \| Put option sales contracts [Member] \| Level 3 [Member]
Derivative liabilities
Derivative Liabilities		0
Aluminum Commodity [Member] \| Fixed priced purchase contracts [Member]
Derivative assets
Derivative assets	1.4	18.2
Derivative liabilities
Derivative Liabilities	5.7	0.4
Aluminum Commodity [Member] \| Fixed priced purchase contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative Liabilities	0	0
Aluminum Commodity [Member] \| Fixed priced purchase contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets	1.4	18.2
Derivative liabilities
Derivative Liabilities	5.7	0.4
Aluminum Commodity [Member] \| Fixed priced purchase contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative Liabilities	0	0
Aluminum Commodity [Member] \| Fixed priced sales contracts [Member]
Derivative assets
Derivative assets	0.5
Derivative liabilities
Derivative Liabilities	0.4	3.4
Aluminum Commodity [Member] \| Fixed priced sales contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets	0
Derivative liabilities
Derivative Liabilities	0	0
Aluminum Commodity [Member] \| Fixed priced sales contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets	0.5
Derivative liabilities
Derivative Liabilities	0.4	3.4
Aluminum Commodity [Member] \| Fixed priced sales contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets	0
Derivative liabilities
Derivative Liabilities	0	0
Aluminum Commodity [Member] \| Midwest premium swap contracts [Member]
Derivative assets
Derivative assets	0.7	0.2
Derivative liabilities
Derivative Liabilities		0.1
Aluminum Commodity [Member] \| Midwest premium swap contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative Liabilities		0
Aluminum Commodity [Member] \| Midwest premium swap contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative Liabilities		0
Aluminum Commodity [Member] \| Midwest premium swap contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets	0.7	0.2
Derivative liabilities
Derivative Liabilities		0.1
Natural Gas [Member] \| Call option purchase contracts [Member]
Derivative assets
Derivative assets		0.3
Derivative liabilities
Derivative Liabilities	0.1
Natural Gas [Member] \| Call option purchase contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets		0
Derivative liabilities
Derivative Liabilities	0
Natural Gas [Member] \| Call option purchase contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets		0.3
Derivative liabilities
Derivative Liabilities	0.1
Natural Gas [Member] \| Call option purchase contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets		0
Derivative liabilities
Derivative Liabilities	0
Natural Gas [Member] \| Put option purchase contracts [Member]
Derivative assets
Derivative assets	0.9	2.5
Natural Gas [Member] \| Put option purchase contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets	0	0
Natural Gas [Member] \| Put option purchase contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets	0.9	2.5
Natural Gas [Member] \| Put option purchase contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets	0	0
Natural Gas [Member] \| Put option sales contracts [Member]
Derivative liabilities
Derivative Liabilities	4.0	4.6
Natural Gas [Member] \| Put option sales contracts [Member] \| Level 1 [Member]
Derivative liabilities
Derivative Liabilities	0	0
Natural Gas [Member] \| Put option sales contracts [Member] \| Level 2 [Member]
Derivative liabilities
Derivative Liabilities	4.0	4.6
Natural Gas [Member] \| Put option sales contracts [Member] \| Level 3 [Member]
Derivative liabilities
Derivative Liabilities	0	0
Natural Gas [Member] \| Fixed priced purchase contracts [Member]
Derivative assets
Derivative assets		0.1
Derivative liabilities
Derivative Liabilities	0.9	0.5
Natural Gas [Member] \| Fixed priced purchase contracts [Member] \| Level 1 [Member]
Derivative assets
Derivative assets		0
Derivative liabilities
Derivative Liabilities	0	0
Natural Gas [Member] \| Fixed priced purchase contracts [Member] \| Level 2 [Member]
Derivative assets
Derivative assets		0.1
Derivative liabilities
Derivative Liabilities	0.9	0.5
Natural Gas [Member] \| Fixed priced purchase contracts [Member] \| Level 3 [Member]
Derivative assets
Derivative assets		0
Derivative liabilities
Derivative Liabilities	0	0
Electricity [Member] \| Fixed priced purchase contracts [Member]
Derivative liabilities
Derivative Liabilities	1.2
Electricity [Member] \| Fixed priced purchase contracts [Member] \| Level 1 [Member]
Derivative liabilities
Derivative Liabilities	0
Electricity [Member] \| Fixed priced purchase contracts [Member] \| Level 2 [Member]
Derivative liabilities
Derivative Liabilities	1.2
Electricity [Member] \| Fixed priced purchase contracts [Member] \| Level 3 [Member]
Derivative liabilities
Derivative Liabilities	0
Hedges Relating to Notes [Member] \| Bifurcated Conversion Feature [Member]
Derivative liabilities
Derivative Liabilities	47.6	60.0
Hedges Relating to Notes [Member] \| Bifurcated Conversion Feature [Member] \| Level 1 [Member]
Derivative liabilities
Derivative Liabilities	0	0
Hedges Relating to Notes [Member] \| Bifurcated Conversion Feature [Member] \| Level 2 [Member]
Derivative liabilities
Derivative Liabilities	47.6	60.0
Hedges Relating to Notes [Member] \| Bifurcated Conversion Feature [Member] \| Level 3 [Member]
Derivative liabilities
Derivative Liabilities	0	0
Hedges Relating to Notes [Member] \| Call Options [Member]
Derivative assets
Derivative assets	38.2	48.4
Hedges Relating to Notes [Member] \| Call Options [Member] \| Level 1 [Member]
Derivative assets
Derivative assets	0	0
Hedges Relating to Notes [Member] \| Call Options [Member] \| Level 2 [Member]
Derivative assets
Derivative assets	38.2	48.4
Hedges Relating to Notes [Member] \| Call Options [Member] \| Level 3 [Member]
Derivative assets
Derivative assets	0	0
Level 1 [Member]
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative Liabilities	0	0
Level 2 [Member]
Derivative assets
Derivative assets	41.5	78.9
Derivative liabilities
Derivative Liabilities	60.4	78.3
Level 3 [Member]
Derivative assets
Derivative assets	0.7	0.2
Derivative liabilities
Derivative Liabilities	$ 0	$ 0.1

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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