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Pension Benefit Obligations - Schedule of Fair Values of Pension Plan Assets By Major Asset Categories (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | $ 913.3
Cash and cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | 22.1
Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | $ 0.0 | 391.5
Diversified and equity funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | 286.7
Fixed income funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | 213.9
Absolute return fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | 5.9
Derivative instruments and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | (6.8)
Fair Value, Inputs, Level 1, 2 and 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 876.8 |
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 20.5 |
Fair Value, Inputs, Level 1, 2 and 3 | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 361.4 |
Fair Value, Inputs, Level 1, 2 and 3 | Diversified and equity funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 272.5 |
Fair Value, Inputs, Level 1, 2 and 3 | Fixed income funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 220.5 |
Fair Value, Inputs, Level 1, 2 and 3 | Absolute return fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 5.1 |
Fair Value, Inputs, Level 1, 2 and 3 | Derivative instruments and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | (3.2) |
Quoted Prices in Active Markets (Level 1) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 486.0 | 487.6
Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 20.5 | 22.1
Quoted Prices in Active Markets (Level 1) | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 361.4 | 391.5
Quoted Prices in Active Markets (Level 1) | Diversified and equity funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 71.5 | 48.5
Quoted Prices in Active Markets (Level 1) | Fixed income funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 22.7 | 17.3
Quoted Prices in Active Markets (Level 1) | Absolute return fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Quoted Prices in Active Markets (Level 1) | Derivative instruments and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 9.9 | 8.2
Significant Other Observable Inputs (Level 2) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 5.4 | 2.6
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Other Observable Inputs (Level 2) | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Other Observable Inputs (Level 2) | Diversified and equity funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 14.1 | 13.5
Significant Other Observable Inputs (Level 2) | Fixed income funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 4.4 | 4.1
Significant Other Observable Inputs (Level 2) | Absolute return fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Other Observable Inputs (Level 2) | Derivative instruments and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | (13.1) | (15.0)
Significant Unobservable Inputs (Level 3) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Unobservable Inputs (Level 3) | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Unobservable Inputs (Level 3) | Diversified and equity funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Unobservable Inputs (Level 3) | Fixed income funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Unobservable Inputs (Level 3) | Absolute return fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Significant Unobservable Inputs (Level 3) | Derivative instruments and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Investments measured at NAV |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 385.4 | 423.1
Investments measured at NAV | Cash and cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.0 | 0.0
Investments measured at NAV | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total |  | 0.0
Investments measured at NAV | Diversified and equity funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 186.9 | 224.7
Investments measured at NAV | Fixed income funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 193.4 | 192.5
Investments measured at NAV | Absolute return fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 5.1 | 5.9
Investments measured at NAV | Derivative instruments and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | $ 0.0 | $ 0.0

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