Retirement Benefits (Details) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2025 USD ($) shares	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) program shares	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Retirement and Postemployment Benefits
Number of defined benefit retirement programs in which a specified percentage of employees participate | program			1
Number of defined benefit retirement programs | program			8
Defined benefit plans
Settlement (benefit) expense			$ (1.7)	$ 35.2	$ 0.0
Funded status:
Plan assets less than benefit obligations		$ (94.4)		(94.4)
Amounts recorded in the consolidated balance sheets:
Accrued pension costs, long-term portion	$ 82.5	109.3	$ 82.5	109.3
Plan Assets
Reporting entity's common stock owned by trust (in shares) | shares	0		0
United States
Defined benefit plans
Service cost			$ 0.0	0.0	0.0
Interest cost			0.8	7.2	11.1
Expected return on plan assets			0.0	(8.3)	(13.6)
Amortization of unrecognized prior service cost, net			0.0	0.0	0.0
Amortization of actuarial loss			(0.2)	0.3	0.3
Settlement (benefit) expense			(1.7)	35.2	0.0
Net pension costs			(1.1)	34.4	(2.2)
Change in benefit obligation:
Projected benefit obligation at beginning of year			18.0	213.6
Service cost			0.0	0.0	0.0
Interest cost			0.8	7.2	11.1
Actuarial loss (gain)			(0.2)	1.5
Benefits paid			(1.7)	(54.3)
Settlements			0.0	0.0
Transfer of participants benefit obligation			0.0	(150.0)
Employee contributions			0.0	0.0
Effect of exchange rates on projected benefit obligation			0.0	0.0
Projected benefit obligation at end of year	$ 16.9	18.0	16.9	18.0	213.6
Change in plan assets:
Fair value of plan assets at beginning of year			0.0	219.2
Actual (loss) return on plan assets			0.0	(16.6)
Employee and employer contributions			1.7	1.7
Benefits paid			1.7	54.3
Annuity premium for transferred participants	0.0	(150.0)
Effect of exchange rates on plan assets			0.0	0.0
Fair value of plan assets at end of year	0.0	0.0	0.0	0.0	$ 219.2
Funded status:
Plan assets less than benefit obligations	(16.9)	(18.0)	(16.9)	(18.0)
Amounts recorded in the consolidated balance sheets:
Assets for Plan Benefits, Defined Benefit Plan	0.0	0.0	0.0	0.0
Accrued pension costs, current portion	(1.7)	(1.7)	(1.7)	(1.7)
Accrued pension costs, long-term portion	15.2	16.3	15.2	16.3
Plan assets less than benefit obligations	(16.9)	(18.0)	(16.9)	(18.0)
Accumulated Benefit Obligation
Projected benefit obligation	16.9	18.0	16.9	18.0
Accumulated benefit obligation	16.9	18.0	16.9	18.0
Fair value of plan assets	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Actuarial Assumptions
Discount rate for obligation, end of year (as a percent)	5.00%	4.60%	5.00%	4.60%	5.70%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				5.40%	5.40%
Expected rate of return on plan assets (as a percent)					5.20%
United States | Discontinued Operations
Defined benefit plans
Service cost			$ 0.0	$ 0.0	$ 0.1
Change in benefit obligation:
Service cost			0.0	0.0	0.1
Foreign Plan
Defined benefit plans
Service cost			2.4	1.8	1.5
Interest cost			3.5	4.5	4.2
Expected return on plan assets			(1.5)	(1.5)	(1.5)
Amortization of unrecognized prior service cost, net			0.1	0.1	0.1
Amortization of actuarial loss			0.2	(0.7)	(0.8)
Settlement (benefit) expense			0.5	0.5	(0.3)
Net pension costs			5.2	4.7	3.2
Change in benefit obligation:
Projected benefit obligation at beginning of year			151.0	131.5
Service cost			2.4	1.8	1.5
Interest cost			3.5	4.5	4.2
Actuarial loss (gain)			(8.5)	12.5
Benefits paid			(6.2)	(5.5)
Settlements			(7.7)	(5.0)
Transfer of participants benefit obligation			0.0	0.0
Employee contributions			1.5	1.4
Effect of exchange rates on projected benefit obligation			7.6	9.8
Projected benefit obligation at end of year	$ 122.3	$ 151.0	122.3	151.0	131.5
Change in plan assets:
Fair value of plan assets at beginning of year			56.6	49.0
Actual (loss) return on plan assets			0.5	3.2
Employee and employer contributions			10.6	10.3
Benefits paid			6.2	5.5
Annuity premium for transferred participants			0.0	0.0
Effect of exchange rates on plan assets			2.8	4.6
Fair value of plan assets at end of year	56.6	56.6	56.6	56.6	$ 49.0
Funded status:
Plan assets less than benefit obligations	(65.7)		(65.7)
Amounts recorded in the consolidated balance sheets:
Assets for Plan Benefits, Defined Benefit Plan	5.2	3.1	5.2	3.1
Accrued pension costs, current portion	(6.1)	(7.0)	(6.1)	(7.0)
Accrued pension costs, long-term portion	64.8	90.5	64.8	90.5
Plan assets less than benefit obligations	(65.7)	(94.4)	(65.7)	(94.4)
Accumulated Benefit Obligation
Projected benefit obligation	71.2	97.8	71.2	97.8
Accumulated benefit obligation	71.2	97.8	71.2	97.8
Fair value of plan assets	$ 0.3	$ 0.3	$ 0.3	$ 0.3
Actuarial Assumptions
Discount rate for obligation, end of year (as a percent)	2.80%	2.70%	2.80%	2.70%	3.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate			2.60%	3.50%	3.90%
Expected rate of return on plan assets (as a percent)			2.40%	2.90%	3.10%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase			2.00%	2.00%	2.00%
Pension Plans Defined Benefit
Accumulated other comprehensive loss
Net actuarial gains (losses)	$ (18.9)	$ 21.1	$ (18.9)	$ 21.1
Prior service cost	0.0	(0.1)	0.0	(0.1)
Aggregate tax effect	(4.9)	(5.0)	(4.9)	(5.0)
Amount that will be amortized from accumulated other comprehensive loss into net benefit costs	0.8		0.8
Accumulated Benefit Obligation
Accumulated benefit obligation	$ 139.2	$ 169.0	$ 139.2	$ 169.0