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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details) | 12 Months Ended
--- | ---
Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($)
Derivative |  |
Change in Unrealized gains (losses) on Interest Rate Derivatives | $ (240,000,000) | $ (728,000,000)
Fair value | 52,000,000 | 1,000,000
Interest rate swaps | 662,000,000 | $ 905,000,000
Unrealized gains/losses on derivatives | $ 0 |
Commodity Contract Derivatives |  |
Derivative |  |
Number of contracts | 54 | 44
Notional amount | 318,000,000 | 296,000,000
Fair value | $ 31,000,000 | $ 145,000,000
Commodity Contract under FHP |  |
Derivative |  |
Number of contracts | 221 | 225
Notional amount | 388 | 256
Fair value | $ (186,000,000) | $ 115,000,000
Commodity Contract under FHP | Fuel Expense |  |
Derivative |  |
Unrealized gains/losses on derivatives | 301,000,000 | 38,000,000
Commodity Contract under FHP | Purchased Power Expense |  |
Derivative |  |
Unrealized gains/losses on derivatives | 47,000,000 | 9,000,000
Accounts payable and accrued liabilities | Commodity Contract Derivatives |  |
Derivative |  |
Fair value | (1,000,000) | (6,000,000)
Accounts payable and accrued liabilities | Commodity Contract under FHP |  |
Derivative |  |
Fair value | (135,000,000) | (8,000,000)
Other Regulatory Assets (Liabilities) | Interest Rate Swap |  |
Derivative |  |
Unrealized gains/losses on derivatives | (45,000,000) | (103,000,000)
Other Regulatory Assets (Liabilities) | Commodity Contract under FHP |  |
Derivative |  |
Unrealized gains/losses on derivatives | $ (348,000,000) | $ 47,000,000

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