Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Shares of common stock in ESOP	1,501,888
Defined contribution plan cost recognized	$ 81.0	$ 82.6	$ 71.5
Pension and postretirement benefits	$ 15.8	11.3
U.S.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.80%
International
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	4.80%
U.K.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.00%
Percentage of plan assets as component of total international plan assets	80.00%
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 1.3	2.3	2.0
ABO for all defined benefit pension plans	3,715.6	3,860.4
ABO for plans with obligation in excess plan assets	59.7
PBO for plans with obligation in excess of plan assets	66.5
Company contributions	29.9
Defined Benefit Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	25.0
Defined Benefit Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	35.0
Defined Benefit Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 0.8	1.1	$ 1.4
Amortization period based on approximate average remaining service period	6 years
ABO for plans with obligation in excess plan assets	$ 2,313.9	2,394.5
PBO for plans with obligation in excess of plan assets	$ 2,356.3	$ 2,446.5
Expected return on plan assets	5.80%	5.80%	5.80%
Company contributions	$ 6.7	$ 7.3
Obligation at end of year	2,515.7	2,613.1	$ 2,348.8
Pension and postretirement benefits	9.8	7.3
Net actuarial (gain) loss arising during the period	37.0	11.9
Amortization of net actuarial gain (loss)	(48.8)	(58.4)
Net actuarial (gain) loss on pretax basis	403.5	415.3
Defined Benefit Pension Plan | International
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	0.5	1.2	$ 0.6
ABO for plans with obligation in excess plan assets	152.0	139.8
PBO for plans with obligation in excess of plan assets	$ 315.3	$ 326.1
Expected return on plan assets	4.80%	4.30%	4.20%
Company contributions	$ 23.2	$ 27.4
Obligation at end of year	1,279.6	1,338.7	$ 1,162.4
Pension and postretirement benefits	2.7	0.9
Net actuarial (gain) loss arising during the period	2.4	(56.5)
Amortization of net actuarial gain (loss)	(10.2)	(14.1)
Net actuarial (gain) loss on pretax basis	$ 428.0	435.8
Defined Benefit Pension Plan | U.K.
Defined Benefit Plan Disclosure [Line Items]
Amortization period based on approximate average remaining life expectancy	22 years
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Obligation at end of year	$ 8.3	12.0
Pension and postretirement benefits	3.3	3.1
Net actuarial (gain) loss arising during the period	2.8	1.7
Amortization of net actuarial gain (loss)	0.4	0.5
Net actuarial (gain) loss on pretax basis	$ 3.0	$ (0.2)