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Assets and Liabilities with Recurring Fair Value Measurements Quantitative Information about Level 3 Fair Value Measurements (Details)
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Dec. 31, 2012
MW
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|---|---|
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Physical Power [Member]
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| Quantitative Information about Level 3 fair Value Measurements [Line Items] | |
| Fair Value Inputs Quantitative Information Power | 11,000,000 |
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Minimum [Member]
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| Quantitative Information about Level 3 fair Value Measurements [Line Items] | |
| Fair Value Inputs Quantitative Information Power | 23.75 |
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Maximum [Member]
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| Quantitative Information about Level 3 fair Value Measurements [Line Items] | |
| Fair Value Inputs Quantitative Information Power | 53.82 |