Retirement Benefits - Defined Benefit Plan Change in Fair Value of Plan Assets Level Three (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 2,903.9
Plan assets at end of year	2,457.4	$ 2,903.9
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	58.7	111.8
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	9.6	(51.6)
Purchases, Sales, Issuances, and Settlements, Net	(0.7)	(1.5)
Plan assets at end of year	67.6	58.7
U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	2,091.3
Plan assets at end of year	1,618.8	2,091.3
U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	0.0
Plan assets at end of year	0.0	0.0
U.S. Plans | Level 3 | Insurance contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	0.0	0.9
Realized Gains (Losses)		0.0
Unrealized Gains (Losses)		0.0
Purchases, Sales, Issuances, and Settlements, Net		(0.9)
Plan assets at end of year		0.0
Non-U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	812.6
Plan assets at end of year	838.6	812.6
Non-U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	58.7
Plan assets at end of year	67.6	58.7
Non-U.S. Plans | Level 3 | Insurance contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	54.9	106.2
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	9.6	(50.9)
Purchases, Sales, Issuances, and Settlements, Net	0.7	(0.4)
Plan assets at end of year	65.2	54.9
Non-U.S. Plans | Level 3 | Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	3.8	4.7
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	0.0	(0.7)
Purchases, Sales, Issuances, and Settlements, Net	(1.4)	(0.2)
Plan assets at end of year	$ 2.4	$ 3.8