Retirement Benefits - Schedule of Net Periodic Pension and Postretirement Benefit Cost (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
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| Pension Benefits | ||||
| Components of net periodic benefit cost (income) | ||||
| Service cost | $ 10 | $ 10 | $ 28 | $ 31 |
| Interest cost | 34 | 34 | 103 | 102 |
| Expected return on plan assets | (42) | (42) | (127) | (125) |
| Amortization of net actuarial loss | 3 | 7 | 11 | 20 |
| Net periodic pension and postretirement benefit cost | 5 | 9 | 15 | 28 |
| Other Postretirement Benefits | ||||
| Components of net periodic benefit cost (income) | ||||
| Service cost | 0 | 0 | 1 | 0 |
| Interest cost | 0 | 1 | 1 | 1 |
| Amortization of net actuarial loss | 1 | 0 | 2 | 2 |
| Net periodic pension and postretirement benefit cost | $ 1 | $ 1 | $ 4 | $ 3 |
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References No definition available.
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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