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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Sep. 30, 2013
Accounting Policies [Abstract]  
Property, Plant, and Equipment Depreciation Rates
Average depreciation rates by asset class are as follows:
Property, Plant, and Equipment Depreciation Rates
At September 30
(percent)
 
2013
 
2012
 
2011
Asset Class
 
Nuclear
2.86

 
2.71

 
2.58

Coal-Fired
3.47

 
5.65

 
3.80

Hydroelectric
1.30

 
1.35

 
1.43

Gas and oil-fired
3.21

 
3.67

 
3.70

Transmission
2.76

 
2.99

 
3.39

Other
8.14

 
8.10

 
7.39