Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2024
Regulatory Assets and Liabilities
Non-current regulatory liabilities	$ 107	$ 107		$ 83
Current regulatory assets	178	178		191
Regulatory assets	5,566	5,566		9,408
Net unrealized gains (losses)	(52)	(52)		(64)
Regulatory Assets	5,744	5,744		9,599
Current regulatory liabilities	222	222		174
Regulatory asset amount expensed		31	$ 70
Regulatory Liabilities	329	329		257
Regulatory Asset
Regulatory Assets and Liabilities
Regulatory assets	152	152		154
Unrealized losses on interest rate derivatives
Regulatory Assets and Liabilities
Current regulatory assets	31	31		54
Regulatory assets	272	272		447
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	2,922	2,922		6,187
Increase (Decrease) in Deferred Charges	3,100
Pension Costs [Member]
Regulatory Assets and Liabilities
Regulatory assets	1,440	1,440		1,979
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	136	136		102
Regulatory assets	52	52		64
Deferred Fuel Costs [Member]
Regulatory Assets and Liabilities
Current regulatory assets	11	11		35
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	728	728		362
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Non-current regulatory liabilities	12	12		2
Current regulatory liabilities	21	21		5
Deferred other post-retirement benefits cost
Regulatory Assets and Liabilities
Non-current regulatory liabilities	95	95		81
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	$ 201	$ 201		$ 169

Regulatory Assets and Liabilities [Line Items]

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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
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-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 2
-Subparagraph (SX 210.5-03(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

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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

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The increase (decrease) during the reporting period in the value of expenditures made during the current reporting period for benefits that will be received over a period of years. Deferred charges differ from prepaid expenses in that they usually extend over a long period of time and may or may not be regularly recurring costs of operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 45
-Paragraph 28
-Subparagraph (a)
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-Topic 230
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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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.

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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.

+ References

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
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-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477571/980-405-25-1

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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