Regulatory Assets and Liabilities (Details) $ in Millions	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Regulatory Assets and Liabilities
Current regulatory assets	$ 251	$ 178
Non-current regulatory assets	5,551	5,566
Regulatory assets	5,802	5,744
Current regulatory liabilities	259	222
Regulatory Liability, Noncurrent	103	107
Regulatory Liabilities	362	329
Fair value	$ 98	$ 52
Commodity Contract Derivatives
Regulatory Assets and Liabilities
Number of contracts	45	54
Derivative, Nonmonetary Notional Amount	366,000,000	318,000,000
Fair value	$ 29	$ 31
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	190	201
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory liabilities	50	0
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities	19	21
Regulatory Liability, Noncurrent	12	12
Postretirement Benefit Costs
Regulatory Assets and Liabilities
Regulatory Liability, Noncurrent	91	95
Unrealized losses on interest rate derivatives [Member]
Regulatory Assets and Liabilities
Current regulatory assets	37	31
Non-current regulatory assets	459	272
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	213	136
Non-current regulatory assets	98	52
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory assets	0	11
Pension Costs [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	1,438	1,440
Nuclear desommissioning costs [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	543	728
Non-nuclear decommissioning [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	2,838	2,922
Other non-current regulatory assets [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets	175	152
Other Regulatory Assets (Liabilities)
Regulatory Assets and Liabilities
Current regulatory assets	$ 1	$ 0

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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