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Commitments and Contingencies - Purchase Obligations (Details) $ in Millions | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) Megawatts megawatts | Sep. 30, 2020 USD ($) | Sep. 30, 2019 USD ($) | Sep. 30, 2027 USD ($) | Sep. 30, 2026 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($)
Obligations |  |  |  |  |  |  |  |  |
Megawatts provided under power purchase obligations | Megawatts | 2,455 |  |  |  |  |  |  |  |
Remaining terms of the agreements, high end of range | 14 years |  |  |  |  |  |  |  |
Megawatts provided under transmission obligations | megawatts | 2,450 |  |  |  |  |  |  |  |
Power purchased under agreement | $ | $ 202 | $ 202 | $ 195 |  |  |  |  |  |
2019 | $ | $ 4 |  |  |  |  |  |  |  |
Scenario, Forecast |  |  |  |  |  |  |  |  |
Obligations |  |  |  |  |  |  |  |  |
Purchase Obligation | $ |  |  |  | $ 754 | $ 137 | $ 138 | $ 138 | $ 138 | $ 138
Purchase Agreements Required by Federal Law |  |  |  |  |  |  |  |  |
Obligations |  |  |  |  |  |  |  |  |
Megawatts provided under power purchase obligations | Megawatts | 270 |  |  |  |  |  |  |  |
Number of generation sources under PPAs | Megawatts | 369 |  |  |  |  |  |  |  |

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- Definition Number of megawatts provided under the power purchase obligations. + References No definition available. + Details
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- Definition Megawatts provided under transmission obligations + References No definition available. + Details
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- Definition Number of generation sources under PPAs + References No definition available. + Details
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- Definition The expense for power purchased under contractual power purchase obligations. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The high end of the range of remaining terms of the agreements. + References No definition available. + Details
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- Definition Unfunded loan commitment due in year 2 + References No definition available. + Details
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Balance Type: | credit
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier. + References No definition available. + Details
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- Details
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- Details
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