Risk Management and Fair Values (Schedules Of Valuation Techniques) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Risk Management And Fair Values [Abstract]
Range From Average Percentage for Electricity Options	11.00%
Range from Average Percentage for Fair Value of Electricity Swaps	3.00%
Effect of Significant Unobservable Inputs on Fair Value of Electricity Options	$ 19.0
Effect of Significant Unobservable Inputs on Fair Value of Electricity Swaps	20.0
Fair Value of Electricity Options	93.0
Fair Value of Electricity Swaps	$ 435.0

The effect of significant unobservable inputs on the fair value of electricity options.

No definition available.

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The effect of significant unobservable inputs on the fair value of electricity swaps.

No definition available.

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The fair value of electricity options classified as Level 3 in the fair value hierarchy.

No definition available.

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The fair value of electricity swaps classified as Level 3 in the fair value hierarchy

No definition available.

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The range from the average percentage used when calculating the fair value of electricity options classified as Level 3 in the fair value hierarchy

No definition available.

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The range from the average percentage used when calculating the fair value of electricity swaps classified as Level 3 in the fair value hierarchy

No definition available.

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