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Utility Regulatory Assets and Liabilities and Regulatory Matters (Details Textual) (USD $)
In Millions, unless otherwise specified
6 Months Ended 9 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Sep. 30, 2011
Regulatory Assets [Line Items]      
Fair value of electric utility electricity supply contracts $ 136.5 $ 24.6  
Maximum Percentage of Incremental Operating Margin Traditional Ratemaking 5.00%    
Number of years to be eligible for a distribution system improvement charge a utility must have filed a general rate filing 5    
Number of regulated utilities on which there is potential effect of legislation. 4    
Deferral Fuel and Power [Member]
     
Regulatory Assets [Line Items]      
Unrealized gains (losses) on derivative financial instrument contracts (3.1) 1.5 (3.1)
Electric Utility Electric Supply Contracts [Member]
     
Regulatory Assets [Line Items]      
Fair value of electric utility electricity supply contracts $ 14.7 $ 10.7 $ 8.7