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Benefit Plans Obligations and Funded Status (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022
Pension Benefits |  |  |  |
Change in benefit obligation |  |  |  |
Benefit obligation |  | $ 10,099 | $ 10,536 |
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation |  | 11,002 | 10,099 |
Service cost |  | 29 | 32 | $ 53
Plan participants' contributions |  | 3 | 4 |
Change in Plan Assets due to Collections |  | 0 | 0 |
Collections | [1] | 0 | 0 |
Actuarial loss (gain) |  | (1,059) | (284) |
Net transfers from variable fund/401(k) plan |  | 5 | 4 |
Expenses paid |  | (6) | (7) |
Benefits paid |  | 766 | 754 |
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets |  | 8,673 | 8,129 |
Change in plan assets |  |  |  |
Fair value of net plan assets |  | 8,129 | 8,094 |
Actual return on plan assets |  | 1,004 | 482 |
Employer contributions |  | 304 | 306 |
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract] |  |  |  |
Funded status |  | $ (2,329) | $ (1,970) |
Discount rate |  | 4.95% | 5.95% | 5.60%
Amount of defined benefit plan actuarial gain (loss) from discount rate change |  | $ (981) | $ (334) |
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption |  | (46) | (12) |
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience |  | 37 |  |
Other Post-retirement Benefits |  |  |  |
Change in benefit obligation |  |  |  |
Benefit obligation |  | 353 | 347 |
Postconfirmation, Other Postretirement Obligations |  |  | 388 |
Service cost |  | 11 | 10 | $ 17
Plan participants' contributions |  | 0 | 0 |
Change in Plan Assets due to Collections |  | 12 | 13 |
Collections | [1] | 12 | 13 |
Actuarial loss (gain) |  | 4 | 44 |
Net transfers from variable fund/401(k) plan |  | 0 | 0 |
Expenses paid |  | 0 | 0 |
Benefits paid |  | 34 | 38 |
Actuarial Gain (Loss) from Changes in Discount Rate |  | 43 |  |
Actuarial Gain (Loss) from pre-Medicare Trend Rate Assumptions |  |  | 27 |
Actuarial Gain (Loss) from Changes in Mortality Assumptions |  |  | 17 |
Change in plan assets |  |  |  |
Fair value of net plan assets |  | 0 | 0 |
Actual return on plan assets |  | 0 | 0 |
Employer contributions |  | 22 | 25 |
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract] |  |  |  |
Funded status |  | $ (353) | $ (347) |
Discount rate |  | 5.00% | 6.05% | 565.00%
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience |  |  | $ 10 |
Amount of defined benefit plan actuarial gain (loss) from assumption change in elections |  |  | $ 61 |
[1] | Collections include retiree contributions as well as provider discounts and rebates.

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- Definition Amount of defined benefit plan actuarial gain (loss) from assumption change in elections + References No definition available. + Details
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- Definition The amount of contributions made by plan participants, federal reinsurance payments, and provider discounts and rebates. This item represents a periodic increase to the plan obligation and an increase to plan assets. + References No definition available. + Details
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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 60 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480266/715-60-50-4 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(6) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of contributions received by defined benefit plan from participant which increase benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of projected benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-3 + Details
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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