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Benefit Plans Contributions (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Defined Benefit Plan Disclosure |  |  |  |
Defined contribution plan contribution amount |  | $ 97 | $ 92 | $ 88
Other postretirement benefit contributions |  | 28 | 25 |
Contribution related to TVARS case |  | 4 | 5 |
Supplemental Employee Retirement Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined Benefit Plan, Related to SERP |  | 8 | 6 |
Other Post-retirement Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  | 28 | 27 |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  | 308 | $ 306 |
Other Pension Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  | 300 |  |
Minimum | Other Pension Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  | $ 300 |  |
Scenario, Forecast |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined contribution plan contribution amount | $ 101 |  |  |
Scenario, Forecast | Other Pension Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions | $ 300 |  |  |

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