Retirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
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| Pension Benefits | ||||
| Components of net periodic benefit cost (income) | ||||
| Service cost | $ 10.0 | $ 8.0 | $ 31.0 | $ 27.0 |
| Interest cost | 34.0 | 37.0 | 102.0 | 110.0 |
| Expected return on plan assets | (42.0) | (42.0) | (125.0) | (127.0) |
| Amortization of net actuarial loss | 7.0 | 0.0 | 20.0 | 0.0 |
| Net periodic postretirement benefit cost | 9.0 | 3.0 | 28.0 | 10.0 |
| Other Postretirement Benefits | ||||
| Components of net periodic benefit cost (income) | ||||
| Service cost | 0.0 | 1.0 | 0.0 | 1.0 |
| Interest cost | 1.0 | 1.0 | 1.0 | 2.0 |
| Amortization of net actuarial loss | 0.0 | 0.0 | 2.0 | 1.0 |
| Net periodic postretirement benefit cost | $ 1.0 | $ 2.0 | $ 3.0 | $ 4.0 |
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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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