Regulatory Assets and Liabilities (Details) $ in Millions	3 Months Ended
Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Regulatory Assets and Liabilities
Current regulatory assets		$ 178	$ 178
Non-current regulatory assets		8,809	5,566
Environmental Remediation Costs Recognized [Abstract]		169
Regulatory assets		8,987	5,744
Current regulatory liabilities		182	222
Regulatory Liability, Noncurrent		91	107
Regulatory Liabilities		273	329
Fair value		$ 59	$ 52
Commodity Contract Derivatives
Regulatory Assets and Liabilities
Number of contracts		52	54
Derivative, Nonmonetary Notional Amount		353,000,000	318,000,000
Fair value		$ 14	$ 31
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities		173	201
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities		9	21
Regulatory Liability, Noncurrent		9	12
Postretirement Benefit Costs
Regulatory Assets and Liabilities
Regulatory Liability, Noncurrent		82	95
Unrealized losses on interest rate derivatives [Member]
Regulatory Assets and Liabilities
Current regulatory assets		34	31
Non-current regulatory assets		344	272
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets		122	136
Non-current regulatory assets		59	52
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory assets		22	11
Pension Costs [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets		1,432	1,440
Nuclear desommissioning costs [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets		471	728
Non-nuclear decommissioning [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets		6,183	2,922
Increase (Decrease) in Deferred Charges	$ 3,100
Other non-current regulatory assets [Member]
Regulatory Assets and Liabilities
Non-current regulatory assets		$ 151	$ 152

Regulatory Assets and Liabilities [Line Items]

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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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Amount of costs recognized in the balance sheet for known or estimated future costs arising from requirements to perform activities to remediate one or more sites.

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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.

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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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