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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, 2020 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2020 USD ($)
Derivative |  |  |
Unrealized gains/losses on derivatives | $ 0 |  |
Change in Unrealized gains (losses) on Interest Rate Derivatives | 272,000,000 | $ (565,000,000) |
Interest rate swaps | 2,041,000,000 | 1,764,000,000 |
Interest Rate Swap |  |  |
Derivative |  |  |
Amount of gain (loss) recognized in income on derivatives | (97,000,000) | (79,000,000) |
Fair value | (588,000,000) | (498,000,000) |
Commodity Contract Derivatives |  |  |
Derivative |  |  |
Amount of gain (loss) recognized in income on derivatives | (1,000,000) | 0 |
Fair value | $ 46,000,000 | $ (41,000,000) |
Coal Contract Derivatives |  |  |
Derivative |  |  |
Number of contracts | 0 | 8 |
Notional amount | 0 | 9,000,000 |
Fair value | $ 0 | $ (4,000,000) | $ 10,000,000
Natural Gas Contract Derivatives |  |  |
Derivative |  |  |
Number of contracts | 42 | 65 |
Notional amount | 302,000,000 | 330,000,000 |
Fair value | $ 46,000,000 | $ (37,000,000) |
Accounts payable and accrued liabilities |  |  |
Derivative |  |  |
Interest rate swaps | 114,000,000 | 88,000,000 |
Accounts payable and accrued liabilities | Interest Rate Swap |  |  |
Derivative |  |  |
Fair value | (32,000,000) | (24,000,000) |
Accounts payable and accrued liabilities | Commodity Contract Derivatives |  |  |
Derivative |  |  |
Fair value | $ (3,000,000) | $ (37,000,000) |

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