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Derivative Instruments (Gross Derivative Contract Positions Outstanding Relating To Energy And Weather Derivatives Trading Activities) (Details)
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Jun. 30, 2012
Btu
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Dec. 31, 2011
Btu
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Energy [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount | 170,095,670 | [1] | 240,363,364 | [1] | ||
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Temperature [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount Per Unit | 24,141,394 | [1] | 14,917,438 | [1] | ||
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Agriculture [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount | 29,798,000 | [1] | 6,098,000 | [1] | ||
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Precipitation [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount Per Unit | 1,799,475 | [1] | 65,000 | [1] | ||
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Wind [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount Per Unit | 146 | [1] | 712 | [1] | ||
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