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Pension Benefit Obligations - Asset Categories (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Sep. 30, 2023
--- | --- | ---
Post-retirement plan |  |
Fair values of plan assets | $ 913.3 | $ 772.1
Cash and cash equivalents |  |
Post-retirement plan |  |
Fair values of plan assets | 22.1 | 29.5
Debt securities |  |
Post-retirement plan |  |
Fair values of plan assets | 391.5 | 338.3
Diversified and equity funds |  |
Post-retirement plan |  |
Fair values of plan assets | 286.7 | 258.4
Fixed income funds |  |
Post-retirement plan |  |
Fair values of plan assets | 213.9 | 174.3
Absolute return fund |  |
Post-retirement plan |  |
Fair values of plan assets | 5.9 | 8.9
Derivative instruments and other |  |
Post-retirement plan |  |
Fair values of plan assets | (6.8) | (37.3)
Quoted Prices in Active Markets (Level 1) |  |
Post-retirement plan |  |
Fair values of plan assets | 487.6 | 412.0
Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents |  |
Post-retirement plan |  |
Fair values of plan assets | 22.1 | 20.2
Quoted Prices in Active Markets (Level 1) | Debt securities |  |
Post-retirement plan |  |
Fair values of plan assets | 391.5 | 338.3
Quoted Prices in Active Markets (Level 1) | Diversified and equity funds |  |
Post-retirement plan |  |
Fair values of plan assets | 48.5 | 30.3
Quoted Prices in Active Markets (Level 1) | Fixed income funds |  |
Post-retirement plan |  |
Fair values of plan assets | 17.3 | 21.7
Quoted Prices in Active Markets (Level 1) | Derivative instruments and other |  |
Post-retirement plan |  |
Fair values of plan assets | 8.2 | 1.5
Significant Other Observable Inputs (Level 2) |  |
Post-retirement plan |  |
Fair values of plan assets | 2.6 | (11.9)
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |
Post-retirement plan |  |
Fair values of plan assets |  | 9.3
Significant Other Observable Inputs (Level 2) | Diversified and equity funds |  |
Post-retirement plan |  |
Fair values of plan assets | 13.5 | 13.2
Significant Other Observable Inputs (Level 2) | Fixed income funds |  |
Post-retirement plan |  |
Fair values of plan assets | 4.1 | 4.4
Significant Other Observable Inputs (Level 2) | Derivative instruments and other |  |
Post-retirement plan |  |
Fair values of plan assets | (15.0) | (38.8)
Investments measured at NAV |  |
Post-retirement plan |  |
Fair values of plan assets | 423.1 | 372.0
Investments measured at NAV | Diversified and equity funds |  |
Post-retirement plan |  |
Fair values of plan assets | 224.7 | 214.9
Investments measured at NAV | Fixed income funds |  |
Post-retirement plan |  |
Fair values of plan assets | 192.5 | 148.2
Investments measured at NAV | Absolute return fund |  |
Post-retirement plan |  |
Fair values of plan assets | $ 5.9 | $ 8.9

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