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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
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Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($)
Derivative |  |
Change in Unrealized gains (losses) on Interest Rate Derivatives | $ (182,000,000) | $ (240,000,000)
Fair value | 64,000,000 | 52,000,000
Interest rate swaps | 840,000,000 | 662,000,000
Interest Rate Swap |  |
Derivative |  |
Unrealized gains/losses on derivatives | (31,000,000) | $ (45,000,000)
Unrealized gains/losses on derivatives | $ 0 |
Commodity Contract Derivatives |  |
Derivative |  |
Number of contracts | 45 | 54
Notional amount | 321,000,000 | 318,000,000
Fair value | $ 2,000,000 | $ 31,000,000
Commodity Contract under FHP |  |
Derivative |  |
Unrealized gains/losses on derivatives | $ (295,000,000) | $ (348,000,000)
Number of contracts | 126 | 221
Notional amount | 230 | 388
Fair value | $ (161,000,000) | $ (186,000,000)
Commodity Contract under FHP | Fuel Expense |  |
Derivative |  |
Unrealized gains/losses on derivatives | (245,000,000) | 301,000,000
Commodity Contract under FHP | Purchased Power Expense |  |
Derivative |  |
Unrealized gains/losses on derivatives | (50,000,000) | 47,000,000
Accounts payable and accrued liabilities | Commodity Contract Derivatives |  |
Derivative |  |
Fair value | (3,000,000) | (1,000,000)
Accounts payable and accrued liabilities | Commodity Contract under FHP |  |
Derivative |  |
Fair value | $ (99,000,000) | $ (135,000,000)

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