Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Shares of common stock in ESOP	1,822,509
Defined contribution plan cost recognized	$ 71.5	$ 60.6	$ 53.3
Pension and postretirement benefits	$ 9.6	11.1
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	4.20%
U.K.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	4.30%
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	$ 2.0	6.2	1.8
ABO for all defined benefit pension plans	3,429.1	3,491.4
Company contributions	32.6
Defined Benefit Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	35.0
Defined Benefit Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	45.0
Defined Benefit Pension Plan | Unfunded Plan
Defined Benefit Plan Disclosure [Line Items]
ABO for plans with obligation in excess plan assets	54.5
PBO for plans with obligation in excess of plan assets	58.7
Defined Benefit Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 1.4	6.0	$ 1.3
Amortization period based on approximate average remaining service period	7 years
ABO for plans with obligation in excess plan assets	$ 47.1	50.5
PBO for plans with obligation in excess of plan assets	$ 2,194.5	$ 2,289.7
Expected return on plan assets	5.80%	5.80%	6.80%
Company contributions	$ 8.4	$ 23.0
Accumulated benefit obligations	2,348.8	2,450.8	$ 3,335.3
Pension and postretirement benefits	5.3	5.8
Losses arising during the period	(2.6)	152.8
Amortization of net actuarial loss	(61.1)	(72.0)
Net actuarial gain on pretax basis	(461.8)	(525.5)
Defined Benefit Pension Plan | International
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	0.6	0.2	$ 0.5
ABO for plans with obligation in excess plan assets	144.3	101.3
PBO for plans with obligation in excess of plan assets	$ 295.1	$ 284.9
Expected return on plan assets	4.20%	4.00%	4.70%
Company contributions	$ 24.2	$ 21.7
Accumulated benefit obligations	1,162.4	1,137.5	$ 1,969.6
Pension and postretirement benefits	0.6	0.4
Losses arising during the period	7.0	(9.3)
Amortization of net actuarial loss	(12.2)	(14.9)
Net actuarial gain on pretax basis	$ (506.4)	(511.6)
Defined Benefit Pension Plan | U.K.
Defined Benefit Plan Disclosure [Line Items]
Amortization period based on approximate average remaining life expectancy	23 years
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 14.0	19.9
Pension and postretirement benefits	3.7	4.9
Losses arising during the period	0.1	0.5
Amortization of net actuarial loss	2.0	1.6
Net actuarial gain on pretax basis	$ 2.4	$ 4.5