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Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Regulatory Assets and Liabilities |  |  |
Non-current regulatory liabilities | $ 141 | $ 83 |
Current regulatory assets | 127 | 191 |
Regulatory assets | 8,047 | 9,408 |
Net unrealized gains (losses) | (12) | (64) |
Regulatory Assets | 8,174 | 9,599 |
Current regulatory liabilities | 228 | 174 |
Regulatory asset amount expensed | 63 | 71 | $ 31
Regulatory Liabilities | 369 | 257 |
Environmental Costs Recognized, Capitalized | 308 | 215 |
Regulatory Asset |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 168 | 154 |
Unrealized losses on interest rate derivatives |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets | 57 | 54 |
Regulatory assets | 316 | 447 |
Non-nuclear decommissioning costs |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 5,563 | 6,187 |
Pension Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 1,531 | 1,979 |
Unrealized gains/losses on commodity derivatives |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets | 59 | 102 |
Regulatory assets | 12 | 64 |
Deferred Fuel Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets | 0 | 35 |
Nuclear decommissioning costs |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory assets | 149 | 362 |
Other current assets |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets | 11 | 0 |
Unrealized gains/losses on commodity derivatives |  |  |
Regulatory Assets and Liabilities |  |  |
Non-current regulatory liabilities | 10 | 2 |
Current regulatory liabilities | 14 | 5 |
Deferred other post-retirement benefits cost |  |  |
Regulatory Assets and Liabilities |  |  |
Non-current regulatory liabilities | 131 | 81 |
Fuel cost adjustment tax equivalents |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory liabilities | 203 | 169 |
Deferred Fuel Costs [Member] |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory liabilities | $ 11 | $ 0 |

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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 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(3)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 + Details
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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-10 + Details
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- Definition Amount of costs recognized in the balance sheet for known or estimated future costs arising from requirements to perform activities to remediate one or more sites. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 25 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482049/410-30-25-18 + Details
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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478742/980-340-50-1 + 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 -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478742/980-340-50-1 + Details
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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 405 -Name Accounting Standards Codification -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477571/980-405-25-1 + Details
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