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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Counterparty Credit Risk (Details) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2025 USD ($) Customers | Sep. 30, 2024 USD ($) Customers
Derivative |  |
Receivables from power sales | $ | $ 1,908 | $ 1,683
Credit of Customers |  |
Derivative |  |
Number of customers that represent the percent of sales | Customers | 2 | 2

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