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Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Regulatory Assets and Liabilities
Non-current regulatory liabilities	$ 107	$ 172
Current regulatory assets	178	138
Regulatory assets	5,566	6,134
Net unrealized gains (losses)	(52)	(1)
Regulatory Assets	5,744	6,272
Current regulatory liabilities	222	391
Regulatory asset amount expensed	31	70	$ 72
Regulatory Liabilities	329	563
Change in nuclear decommissioning costs	93
Regulatory Asset
Regulatory Assets and Liabilities
Regulatory assets	152	138
Unrealized losses on interest rate derivatives
Regulatory Assets and Liabilities
Current regulatory assets	31	47
Regulatory assets	272	479
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	2,922	2,856
Pension Costs [Member]
Regulatory Assets and Liabilities
Regulatory assets	1,440	1,839
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	136	14
Regulatory assets	52	1
Deferred Fuel Costs [Member]
Regulatory Assets and Liabilities
Current regulatory assets	11	77
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	728	821
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Non-current regulatory liabilities	12	102
Current regulatory liabilities	21	173
Deferred other post-retirement benefits cost
Regulatory Assets and Liabilities
Non-current regulatory liabilities	95	70
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	$ 201	$ 218

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Regulatory Assets and Liabilities [Line Items]

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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.

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-Name Accounting Standards Codification
-Section 45
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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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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.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

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