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Benefit Plans Contributions (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2026 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Defined Benefit Plan Disclosure |  |  |  |
Defined contribution plan contribution amount |  | $ 124 | $ 116 | $ 105
Other postretirement benefit contributions |  | 24 | 22 |
Contribution related to TVARS case |  | 5 | 5 |
Supplemental Employee Retirement Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined Benefit Plan, Related to SERP |  | 10 | 4 |
Other Post-retirement Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  | 24 | 22 |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  | 310 | $ 304 |
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 | Other Pension Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions | $ 300 |  |  |

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