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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Sep. 30, 2019
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)
 
2019
 
2018
 
2017
Asset Class
 
 
 
 
 
Nuclear
2.38

 
2.64

 
2.66

Coal-fired(1)
4.96

 
2.32

 
2.33

Hydroelectric
1.61

 
1.57

 
1.58

Gas and oil-fired
3.00

 
2.93

 
3.27

Transmission
1.34

 
1.32

 
1.34

Other
7.16

 
5.90

 
6.12