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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, 2022 USD ($) | Sep. 30, 2021 USD ($)
Derivative |  |
Change in Unrealized gains (losses) on Interest Rate Derivatives | $ (728,000,000) | $ (402,000,000)
Interest rate swaps | 905,000,000 | 1,639,000,000
Unrealized gains/losses on derivatives | 0 |
Interest Rate Swap |  |
Derivative |  |
Fair value | (233,000,000) | (455,000,000)
Commodity Contract Derivatives |  |
Derivative |  |
Fair value | $ 145,000,000 | $ 247,000,000
Natural Gas Contract Derivatives |  |
Derivative |  |
Number of contracts | 44 | 40
Notional amount | 296,000,000 | 263,000,000
Fair value | $ 145,000,000 | $ 247,000,000
Commodity Contract under FHP |  |
Derivative |  |
Number of contracts | 225 | 0
Notional amount | 256 |
Fair value | $ 115,000,000 | $ 0
Accounts payable and accrued liabilities |  |
Derivative |  |
Fair value | 12,000,000 | 7,000,000
Interest rate swaps | 54,000,000 | 115,000,000
Accounts payable and accrued liabilities | Interest Rate Swap |  |
Derivative |  |
Fair value | (3,000,000) | (22,000,000)
Accounts payable and accrued liabilities | Commodity Contract Derivatives |  |
Derivative |  |
Fair value |  | (3,000,000)
Accounts payable and accrued liabilities | Commodity Contract under FHP |  |
Derivative |  |
Fair value | (8,000,000) |
Other Regulatory Assets (Liabilities) | Interest Rate Swap |  |
Derivative |  |
Unrealized gains/losses on derivatives | (103,000,000) | (115,000,000)
Other Regulatory Assets (Liabilities) | Commodity Contract under FHP |  |
Derivative |  |
Unrealized gains/losses on derivatives | $ 47,000,000 | $ 0

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