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Securitization - Narrative (Details) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2023 | Mar. 31, 2023 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Variable Interest Entity [Line Items] |  |  |  |  |
Proceeds from issuance of securitized long-term debt by AEK |  |  | $ 0 | $ 0 | $ 95,000,000
Long-term debt, fair value |  |  | 8,272,978,000 |  |
State of Texas | Extraordinary Gas Cost | Winter Storm Uri |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Regulatory asset, authorized |  | $ 3,500,000,000 |  |  |
Regulatory asset, proceeds from customer rate relief bonds |  | $ 2,020,000,000.00 |  |  |
State of Texas | Extraordinary Gas Cost | Winter Storm Uri | Minimum |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Regulatory asset, maturity period |  | 12 years |  |  |
State of Texas | Extraordinary Gas Cost | Winter Storm Uri | Maximum |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Regulatory asset, maturity period |  | 18 years |  |  |
Variable Interest Entity, Primary Beneficiary |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Long-term debt |  |  | $ 77,003,000 |  |
Variable Interest Entity, Primary Beneficiary | Securitized Utility Tariff Property |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Proceeds from sale of intangible assets | $ 92,300,000 |  |  |  |
Initial consolidation, gain (loss) | $ 0 |  |  |  |
Intangible asset, useful life | 10 years |  |  |  |
Intangible assets, amortization period |  |  | 4 years 25 days |  |
Series 2023-A Securitized Utility Tariff Bonds Due March 2033 | Senior Notes | Variable Interest Entity, Primary Beneficiary |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Debt face amount | $ 95,000,000 |  |  |  |
Debt instrument, interest rate | 5.155% |  |  |  |
Debt instrument, term | 10 years |  |  |  |
Proceeds from issuance of securitized long-term debt by AEK | $ 93,700,000 |  |  |  |
Long-term debt |  |  | $ 77,000,000.0 | 85,100,000 |
Long-term debt, fair value |  |  | $ 78,800,000 | $ 87,800,000 |

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