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Debt and Other Obligations Debt and Other Obligations - Debt Securities Activity (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2013
Debt Instrument |  |  |  |
Face Amount | $ 40 |  |  | $ 360
Discount on debt issues | (9) | $ (8) |  |
Redemptions/Maturities of variable interest entities | 35 | 39 | $ 43 |
Redemptions/Maturities of power bonds | $ 1,022 | $ 29 | $ 1,028 |
Percent of par value | 99.109% | 99.187% |  |
Total Current maturities of power bonds issued at par | $ 1,022 | $ 1,022 |  |
Short-term debt, net of discounts | 1,167 | 432 |  |
Current maturities of long-term debt of variable interest entities issued at par | 37 | 35 |  |
Long-term power bonds, net | 17,867 | 17,844 |  |
880591EF5 (12.15.20) |  |  |  |
Debt Instrument |  |  |  |
Total Current maturities of power bonds issued at par | $ 1 | 1 |  |
Interest rate | 3.77% |  |  |
Debt Instrument, Maturity Date | Dec. 15, 2024 |  |  |
880591EF5 (6.15.21) |  |  |  |
Debt Instrument |  |  |  |
Total Current maturities of power bonds issued at par | $ 21 | 21 |  |
Interest rate | 3.77% |  |  |
Debt Instrument, Maturity Date | Jun. 15, 2025 |  |  |
880591ER9 |  |  |  |
Debt Instrument |  |  |  |
Total Current maturities of power bonds issued at par | $ 0 | 1,000 |  |
Interest rate | 2.875% |  |  |
Debt Instrument, Maturity Date | Sep. 15, 2024 |  |  |
880591EW8 [Member] |  |  |  |
Debt Instrument |  |  |  |
Total Current maturities of power bonds issued at par | $ 1,000 | $ 0 |  |
Interest rate | 0.75% |  |  |
Debt Instrument, Maturity Date | May 15, 2025 |  |  |
Total |  |  |  |
Debt Instrument |  |  |  |
Debt Instrument, Redemption Period, End Date | 1,057 | 68 |  |
Percent of par value | 100.00% |  |  |
Debt of variable interest entities |  |  |  |
Debt Instrument |  |  |  |
Redemptions/Maturities of variable interest entities | $ 35 | $ 39 |  |
2009 Series B |  |  |  |
Debt Instrument |  |  |  |
Redemptions/Maturities of power bonds | 22 | 29 |  |
2012 Series A |  |  |  |
Debt Instrument |  |  |  |
Redemptions/Maturities of power bonds | 1,000 | 0 |  |
Total |  |  |  |
Debt Instrument |  |  |  |
Debt Securities Issues | $ 991 | 992 |  |
880591EY4 |  |  |  |
Debt Instrument |  |  |  |
Interest rate | 4.25% |  |  |
Debt Instrument, Maturity Date | Sep. 15, 2052 |  |  |
Long-term power bonds, net | $ 500 | 500 |  |
880591EX6 |  |  |  |
Debt Instrument |  |  |  |
Interest rate | 1.50% |  |  |
Debt Instrument, Maturity Date | Sep. 15, 2031 |  |  |
Long-term power bonds, net | $ 500 | 500 |  |
880591EZ1 |  |  |  |
Debt Instrument |  |  |  |
Face Amount | $ 0 | 1,000 |  |
Interest rate | 3.875% |  |  |
Debt Instrument, Maturity Date | Mar. 15, 2028 |  |  |
Long-term power bonds, net | $ 1,000 | 1,000 |  |
880591FB3 |  |  |  |
Debt Instrument |  |  |  |
Interest rate | 4.375% |  |  |
Debt Instrument, Maturity Date | Aug. 01, 2034 |  |  |
Long-term power bonds, net | $ 1,000 | $ 0 |  |

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