Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Shares of common stock in ESOP	1,941,938
Defined contribution plan cost recognized	$ 53.3	$ 45.6	$ 40.6
Pension and postretirement benefits	$ 25.6	17.9
U.S.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	6.75%
International
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	4.73%
U.K.
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.30%
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	$ (1.3)	(5.0)	(6.2)
ABO for all defined benefit pension plans	5,140.0	5,166.5
Company contributions	44.6
Defined Benefit Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	40.0
Defined Benefit Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions for next fiscal year	50.0
Defined Benefit Pension Plan | Unfunded Plan
Defined Benefit Plan Disclosure [Line Items]
ABO for plans with obligation in excess plan assets	86.2
PBO for plans with obligation in excess of plan assets	91.7
Defined Benefit Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 1.3	5.0	$ 6.2
Amortization period based on approximate average remaining service period	7 years
ABO for plans with obligation in excess plan assets	$ 79.2	3,081.4
PBO for plans with obligation in excess of plan assets	$ 82.1	$ 3,202.2
Expected return on plan assets	6.80%	7.00%	7.00%
Company contributions	$ 6.9	$ 15.5
Prior service cost arising during the period	0.5	1.6
Accumulated benefit obligations	3,335.3	3,423.8	$ 3,281.6
Pension and postretirement benefits	19.6	10.5
Gains arising during the period	(273.2)	14.6
Amortization of net actuarial loss	(79.8)	(88.7)
Net actuarial loss on pretax basis	444.7	797.7
Defined Benefit Pension Plan | International
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	0.5	0.2	$ 0.2
ABO for plans with obligation in excess plan assets	416.8	475.8
PBO for plans with obligation in excess of plan assets	$ 456.6	$ 1,949.7
Expected return on plan assets	4.70%	5.00%	5.30%
Company contributions	$ 37.7	$ 22.0
Prior service cost arising during the period	0.0	0.0
Accumulated benefit obligations	1,969.6	1,949.7	$ 1,864.0
Pension and postretirement benefits	0.5	0.2
Gains arising during the period	(87.6)	68.9
Amortization of net actuarial loss	(19.8)	(19.7)
Net actuarial loss on pretax basis	$ 535.8	643.2
Defined Benefit Pension Plan | U.K.
Defined Benefit Plan Disclosure [Line Items]
Amortization period based on approximate average remaining life expectancy	24 years
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 27.4	38.6
Pension and postretirement benefits	5.5	7.2
Gains arising during the period	(5.4)	(1.3)
Amortization of net actuarial loss	1.8	0.0
Net actuarial loss on pretax basis	$ (6.6)	$ (3.0)