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Asset Retirement Obligations Asset Retirement Obligations (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Liabilities Settled [Line Items]
Increase in ARO liability		$ 3,300
Change in estimate	[1]	132	$ 369
Additional obligations		3,136
Balance	[1]	10,806	7,489	$ 7,162
Asset Retirement Obligation, Liabilities Settled	[1]	257	279
Accretion (recorded as regulatory asset)	[1]	306	237
Asset Retirement Obligation, Current		283	272
Amortization and Depreciation of Decontaminating and Decommissioning Assets		188	188	137
Total ARO change due to CCR			458
Change in estimate due to Gallatin CCR closure			60
Changes in closure liabilities			15
Increase in Asset Retirement Obligation, Revisions in Estimate			9
estimate revision of SLR		(164)
Nuclear
Liabilities Settled [Line Items]
Change in estimate		(160)	7
Additional obligations		0
Balance		3,814	3,808	3,643
Asset Retirement Obligation, Liabilities Settled		4	8
Accretion (recorded as regulatory asset)		170	166
Non-nuclear
Liabilities Settled [Line Items]
Change in estimate		292	362
Additional obligations		3,136
Balance		6,992	3,681	$ 3,519
Asset Retirement Obligation, Liabilities Settled		253	271
Accretion (recorded as regulatory asset)		$ 136	$ 71
[1] (1) Includes $283 million and $272 million at September 30, 2024 and 2023, respectively, in Current liabilities.

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[Line Items] for Asset Retirement Obligation Disclosure [Table]

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Change in estimate due to Gallatin CCR closure

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Changes in closure liabilities

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estimate revision of SLR

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Increase in Asset Retirement Obligation, Revisions in Estimate

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Total ARO change due to CCR

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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
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

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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
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481999/410-20-25-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 410
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-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481850/410-20-50-1

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Current portion of 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/2009/role/commonPracticeRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481850/410-20-50-1

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Amount of asset retirement obligations incurred during the period.

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-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481850/410-20-50-1

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481850/410-20-50-1

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Amount of increase (decrease) in asset retirement obligations.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481850/410-20-50-1

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
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-URI https://asc.fasb.org/1943274/2147481850/410-20-50-1

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