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Asset Retirement Obligations Asset Retirement Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Liabilities Settled [Line Items] |  |  |  |
Increase in ARO liability |  | $ 160 |  |
Change in estimate | [1] | 247 | $ 203 |
Additional obligations | [1] |  | 43 |
Balance | [1] | 7,162 | 7,002 | $ 6,785
Asset Retirement Obligation, Liabilities Settled | [1] | 311 | 242 |
Accretion (recorded as regulatory asset) | [1] | 224 | 213 |
Asset Retirement Obligation, Current |  | 275 | 266 |
Amortization and Depreciation of Decontaminating and Decommissioning Assets |  | 137 | 72 | 169
Total ARO change due to CCR |  | 82 | 122 |
Change in ARO from operating CCR facilities |  |  | 30 |
Change in ARO from inactive CCR facilities |  |  | 13 |
ARO change due to groundwater monitoring |  |  | 69 |
Accounts payable and accrued liabilities |  |  |  |
Liabilities Settled [Line Items] |  |  |  |
Asset Retirement Obligation, Liabilities Settled |  | 20 |  |
Nuclear |  |  |  |
Liabilities Settled [Line Items] |  |  |  |
Change in estimate |  | 61 | 12 |
Additional obligations |  |  | 0 |
Balance |  | 3,643 | 3,428 | 3,278
Asset Retirement Obligation, Liabilities Settled |  | 2 | 11 |
Accretion (recorded as regulatory asset) |  | 156 | 149 |
Change due to cost study |  | 58 |  |
Non-nuclear |  |  |  |
Liabilities Settled [Line Items] |  |  |  |
Change in estimate |  | 186 | 191 |
Additional obligations |  |  | 43 |
Balance |  | 3,519 | 3,574 | $ 3,507
Asset Retirement Obligation, Liabilities Settled |  | 309 | 231 |
Accretion (recorded as regulatory asset) |  | 68 | $ 64 |
Change in estimate due to coal fines |  | 119 |  |
Change in estimate due to closure of coal yards |  | 57 |  |
Change in estimate due to timing of maintenance |  | 53 |  |
Change in estimate due to timing of asset retirement activities |  | 47 |  |
Change in estimate due to Gallatin CCR closure |  | 30 |  |
Change in cost estimates at Allen |  | $ 15 |  |
[1] | (1) Includes $275 million a nd $266 million at September 30, 2022 and 2021, respectively, in Current liabilities. (2) Settlements include the change in asset retirement obligation project accruals included in Accounts payable and accrued liabilities of $20 million.

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- Definition The current period expense charged against earnings on decontaminating and decommissioning of facilities used in the normal conduct of business and not intended for resale to allocate or recognize the cost of the assets over their useful lives. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -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 The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 25 -Paragraph 4 -URI https://asc.fasb.org/extlink&oid=116646717&loc=d3e6290-110844 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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