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Summary of Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Summary of Significant Accounting Policies [Abstract]      
Excise taxes and a portion of utility receipts taxes $ 29.3 $ 33.8 $ 36.3
Number of operating segments in Utility group 3    
Number of operating segments in Nonutility group 5