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Summary of Significant Accounting Policies Depreciation (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021 | Sep. 30, 2021
Property, Plant and Equipment [Line Items] |  |  |  |  |
Depreciation expense | $ 459 | $ 347 | $ 1,400 | $ 1,000 |
Increase due to new depreciation rates |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Depreciation expense |  |  | $ 309 |  |
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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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
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