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Summary of Significant Accounting Policies [Table Text Block] | 12 Months Ended
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Sep. 30, 2021
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)
| 2021 |  | 2020 |  | 2019
Asset Class |  |  |  |  |
Nuclear | 2.38 |  |  | 2.38 |  |  | 2.38 |
Coal-fired(1) | 1.95 |  |  | 3.62 |  |  | 4.96 |
Hydroelectric | 1.60 |  |  | 1.60 |  |  | 1.61 |
Gas and oil-fired | 2.98 |  |  | 3.04 |  |  | 3.00 |
Transmission | 1.34 |  |  | 1.34 |  |  | 1.34 |
Other | 7.12 |  |  | 7.26 |  |  | 7.16 |

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