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, 2023	Sep. 30, 2022
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	$ 209.0	$ 246.6
Purchases, sales, and settlements, net	30.8	80.3
Actual return on plan assets held at end of year	20.2	(117.9)
Fair Value at End of Year	260.0	209.0
Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	155.5	246.6
Purchases, sales, and settlements, net	(3.7)	0.0
Actual return on plan assets held at end of year	14.0	(91.1)
Fair Value at End of Year	165.8	155.5
Fixed Income Pooled Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	53.5	0.0
Purchases, sales, and settlements, net	34.5	80.3
Actual return on plan assets held at end of year	6.2	(26.8)
Fair Value at End of Year	$ 94.2	$ 53.5