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Benefit Plans Components of Benefit Plans (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2026
Defined Benefit Plan Disclosure |  |  |  |
Fixed and variable fund annual maximum contribution | $ 10,000 |  |  |
Defined contribution plan contribution amount | 124,000,000 | $ 116,000,000 | $ 105,000,000 |
Nonqualified Excess 401(k) Plan | 2,000,000 | 1,000,000 | $ 1 |
Accounts Payable and Accrued Liabilities, Current | 3,299,000,000 | $ 2,910,000,000 |  |
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience | 37,000,000 |  |  |
Actuarial Gain (Loss) from Changes in Mortality Assumptions | 5,000,000 |  |  |
Actuarial Gain (Loss) from pre-Medicare Trend Rate Assumptions | 30,000,000 |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Discount rate |  | 5.00% | 6.05% |
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption |  | $ 46,000,000 |  |
Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions | 18,000,000 |  |  |
Actuarial Gain (Loss) due to Adoption of a Retiree Persistency Assumption | 13,000,000 |  |  |
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience | 37,000,000 |  |  |
Accounts payable and accrued liabilities |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Postemployment Benefits Liability |  | 28,000,000 |  |
Other Post-retirement Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Accounts Payable and Accrued Liabilities, Current | $ 17,000,000 | $ 20,000,000 |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Discount rate | 5.62% | 5.00% |  |
Actuarial Gain (Loss) from Delaying post-Medicare Trend Rate Assumption | $ 28,000,000 |  |  |
Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions | 3,000,000 |  |  |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Accounts Payable and Accrued Liabilities, Current | 9,000,000 | $ 6,000,000 |  |
Amount of defined benefit plan actuarial gain (loss) from discount rate change | 514,000,000 | $ 981,000,000 |  |
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience | $ 18,000,000 |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Discount rate | 5.47% | 4.95% | 5.95% |
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption | $ 39,000,000 |  |  |
Actual Return on Plan Assets | 4.90% | 12.72% | 6.13% |
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience | $ 18,000,000 |  |  |
Minimum |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage | 300.00% |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match | 150.00% |  |  |
Maximum |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage | 600.00% |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match | 600.00% |  |  |
Minimum |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach | 10.00% |  |  |
Scenario, Forecast | Pension Benefits |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract] |  |  |  |
Defined Benefit Plan, Cost of Living Adjustment Assumption Next Fiscal Year |  |  |  | 2.49%

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- Definition Actuarial Gain (Loss) due to Adoption of a Retiree Persistency Assumption + References No definition available. + Details
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- Definition Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience + References No definition available. + Details
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- Definition The maximum annual contribution that employees can make to the fixed and variable fund benefit. The fixed fund benefit is a benefit that earns a specified rate of interest on contributions made by employees. The variable fund is a benefit that invests employee contributions in the Spartan U.S. Equity Index Fund-Fidelity Advantage Class (Spartan). + References No definition available. + Details
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- Definition Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(20)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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