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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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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 |

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