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