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Significant Accounting Policies (Details Textuals) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Sep. 30, 2011
Dec. 31, 2010
Finite-Lived Intangible Assets [Line Items]  
Intangible Assets Emission Allowance$ 9$ 9
Intangible Assets Renewable Energy Credits2617
Gross Carrying amount of accumulated amortization of intangible assets6563
Accumulated amortization of intangible assets$ 26$ 22
Finite Lived Intangible Assets Useful Life Minimum4 
Finite Lived Intangible Assets Useful Life Maximum30