Retirement Benefits (Summary of Changes in Pension Plan Assets Fair Value Classified as Level 3) (Details) - Defined Benefit Pension Plan - Level 3 - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	$ 260.0	$ 209.0
Purchases, sales, and settlements, net	(12.4)	30.8
Actual return on plan assets held at end of year	53.8	20.2
Fair Value at End of Year	301.4	260.0
Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	165.8	155.5
Purchases, sales, and settlements, net	(4.9)	(3.7)
Actual return on plan assets held at end of year	26.9	14.0
Fair Value at End of Year	187.8	165.8
Fixed Income Pooled Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	94.2	53.5
Purchases, sales, and settlements, net	(7.5)	34.5
Actual return on plan assets held at end of year	26.9	6.2
Fair Value at End of Year	$ 113.6	$ 94.2