Commitments and Contingencies - Legal Proceedings (Details) $ in Millions	12 Months Ended
Sep. 30, 2021 USD ($) Groups Agreements
Legal Proceedings
Possible additional future costs for compliance with CCR requirements	$ 789
Amount spent under environmental agreements	281
Contribution related to TVARS case	5
Possible additional future costs for compliance with Clean Water requirements.	148
Amount remaining to be spent under environmental agreements	10
Loss Contingency, Damages Sought, Value	30
Compensatory damages - Kingston Case	8
Punitive Damages - Kingston Case	10
Down payment from Nuclear Development	22
Compensated costs to Nuclear Development	1
General
Legal Proceedings
Legal loss contingency accrual	$ 13
Environmental Agreements
Legal Proceedings
Number of similar environmental agreements entered into \| Agreements	2
Number of environmental agreements entered into with the EPA \| Agreements	1
Number of environmental agreements entered into with environmental advocacy groups \| Groups	3
Amount to be invested in certain environmental projects	$ 290
Other long-term liabilities \| General
Legal Proceedings
Legal loss contingency accrual	12
Accounts payable and accrued liabilities \| General
Legal Proceedings
Legal loss contingency accrual	$ 1

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Amount spent under environmental agreements

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Compensated costs to Nuclear Development

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Compensatory damages - Kingston Case

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Down payment from Nuclear Development

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Number of environmental agreements entered into with the EPA

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Number of similar environmental agreements entered into

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Number environmental advocacy groups with which there is an environmental agreement.

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The possible additional future costs for compliance with CCR requirements

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The possible additional future costs for compliance with Clean Water requirements.

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Punitive Damages - Kingston Case

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