Retirement Benefits - Schedule of Net Periodic Pension and Postretirement Benefit Cost (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2026 |
Mar. 31, 2025 |
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| Pension Benefits | ||||
| Components of net periodic benefit cost (income) | ||||
| Service cost | $ 9 | $ 11 | $ 18 | $ 21 |
| Interest cost | 35 | 34 | 69 | 68 |
| Expected return on plan assets | (43) | (42) | (85) | (83) |
| Amortization of net actuarial loss | 4 | 7 | 8 | 13 |
| Net periodic pension and postretirement benefit cost | 5 | 10 | 10 | 19 |
| Other Postretirement Benefits | ||||
| Components of net periodic benefit cost (income) | ||||
| Service cost | 1 | 0 | 1 | 0 |
| Interest cost | 1 | 0 | 1 | 0 |
| Amortization of net actuarial loss | 0 | 1 | 1 | 2 |
| Net periodic pension and postretirement benefit cost | $ 2 | $ 1 | $ 3 | $ 2 |
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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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