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Summary of Significant Accounting Policies (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2021 | Sep. 30, 2021
Nuclear Plant |  |
Property, Plant and Equipment [Line Items] |  |
Public utilities, property, plant and equipment, disclosure of composite depreciation rate for plants of service | 2.72% | 2.38%
Fossil Fuel Plant |  |
Property, Plant and Equipment [Line Items] |  |
Public utilities, property, plant and equipment, disclosure of composite depreciation rate for plants of service | 3.98% | 1.95%
Hydro Plant |  |
Property, Plant and Equipment [Line Items] |  |
Public utilities, property, plant and equipment, disclosure of composite depreciation rate for plants of service | 1.95% | 1.60%
Natural Gas Processing Plant |  |
Property, Plant and Equipment [Line Items] |  |
Public utilities, property, plant and equipment, disclosure of composite depreciation rate for plants of service | 3.45% | 2.98%
Electric Transmission |  |
Property, Plant and Equipment [Line Items] |  |
Public utilities, property, plant and equipment, disclosure of composite depreciation rate for plants of service | 1.45% | 1.34%
Other Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Public utilities, property, plant and equipment, disclosure of composite depreciation rate for plants of service | 3.21% | 7.12%

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