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, 2025	Sep. 30, 2024
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	$ 301.4	$ 260.0
Purchases, sales, and settlements, net	(11.7)	(12.4)
Actual return on plan assets held at end of year	14.0	53.8
Fair Value at End of Year	303.7	301.4
Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	187.8	165.8
Purchases, sales, and settlements, net	(4.2)	(4.9)
Actual return on plan assets held at end of year	4.7	26.9
Fair Value at End of Year	188.3	187.8
Alternative credit pooled funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value at beginning of year	113.6	94.2
Purchases, sales, and settlements, net	(7.5)	(7.5)
Actual return on plan assets held at end of year	9.3	26.9
Fair Value at End of Year	$ 115.4	$ 113.6