Regulatory Assets and Liabilities (Details) $ in Millions	Jun. 30, 2023 USD ($) Units	Sep. 30, 2022 USD ($) Units
Regulatory Assets and Liabilities
Current regulatory assets	$ 236	$ 138
Non-current regulatory assets	5,666	6,134
Regulatory assets	5,902	6,272
Current regulatory liabilities	224	391
Regulatory Liability, Noncurrent	59	172
Regulatory Liabilities	283	563
Fair value	$ 78	$ 1
Power Purchase Agreement with Option to Settle
Regulatory Assets and Liabilities
Number of contracts \| Units	2	0
Derivative, Nonmonetary Notional Amount	351	0
Fair value	$ (7)	$ 0
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	203	218
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities	21	173
Regulatory Liability, Noncurrent	1	102
Postretirement Benefit Costs
Regulatory Assets and Liabilities
Regulatory Liability, Noncurrent	58	70
Unrealized losses on interest rate derivatives [Member]
Regulatory Assets and Liabilities
Current regulatory assets	32	47
Non-current regulatory assets	473	479
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	180	14
Non-current regulatory assets	78	1
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory assets	24	77
Pension Costs [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	1,746	1,839
Nuclear desommissioning costs [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	592	821
Non-nuclear decommissioning [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	2,638	2,856
Other non-current regulatory assets [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	$ 139	$ 138

Regulatory Assets and Liabilities [Line Items]

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Nominal number of units used to calculate payment on derivative.

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Number of price risk derivative instruments held by the entity at the reporting date.

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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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