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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Sep. 30, 2015
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)
 
2015
 
2014
 
2013
Asset Class
 
 
 
 
 
Nuclear
2.81

 
2.90

 
2.86

Coal-fired
5.50

 
4.37

 
3.47

Hydroelectric
1.30

 
1.44

 
1.30

Gas and oil-fired
3.18

 
3.23

 
3.21

Transmission
2.78

 
2.76

 
2.76

Other
8.65

 
8.40

 
8.14