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Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Regulatory Assets and Liabilities |  |  |
Non-current regulatory liabilities | $ 172 | $ 40 |
Current regulatory assets | 138 | 196 |
Regulatory assets | 6,134 | 7,956 |
Regulatory Assets | 6,272 | 8,152 |
Current regulatory liabilities | 391 | 340 |
Regulatory asset amount expensed | 70 | 72 | $ 21
Regulatory Liabilities | 563 | 380 |
Change in nuclear decommissioning costs | 458 |  |
Deferred Project Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Gallatin coal combustion residual facilities estimated cost to cap and close | 47 | 114 |
Regulatory Asset |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 138 | 150 |
Removal Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 479 | 1,122 |
Unrealized losses on interest rate derivatives |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets | 14 | 3 |
Regulatory assets | 1 | 0 |
Non-nuclear decommissioning costs |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 2,856 | 2,653 |
Pension Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 1,839 | 3,668 |
Deferred Fuel Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets | 77 | 79 |
Nuclear decommissioning costs |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 821 | 363 |
Unrealized gains/losses on commodity derivatives |  |  |
Regulatory Assets and Liabilities |  |  |
Non-current regulatory liabilities | 102 | 40 |
Current regulatory liabilities | 173 | 210 |
Deferred other post-retirement benefits cost |  |  |
Regulatory Assets and Liabilities |  |  |
Non-current regulatory liabilities | 70 | 0 |
Fuel cost adjustment tax equivalents |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory liabilities | $ 218 | $ 130 |

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- Definition The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227 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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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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