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Risk Management Activities (Commodity Price Risk Program Derivative Contracted Gross Volumes) (Details) (USD $)
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6 Months Ended | 12 Months Ended | ||||||
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Jun. 30, 2011
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Dec. 31, 2010
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Gas Price Volatility Program [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | $ 31.0 | $ 28.4 | ||||||
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Price Protection Service Program [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | 1.0 | 1.6 | ||||||
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DependaBill Program [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | 0.3 | 0.4 | ||||||
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Regulatory Incentive Program [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | 4.9 | 2.0 | ||||||
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Gas Marketing Program [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | 35.0 | [1] | 48.2 | [1] | ||||
| Basis contract volumes, MMDth | 30.3 | 42.0 | ||||||
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Gas Marketing Forward Physical Derivatives [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | 34.9 | [2] | 48.0 | [2] | ||||
| Basis contract volumes, MMDth | 36.8 | 52.1 | ||||||
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Electric Energy Program [Member]
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| Commodity price risk program derivative contracted gross volumes, MMDth | $ 15,972.0 | $ 8,279.1 | ||||||
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