Retirement Benefits - Defined Benefit Plan Change in Fair Value of Plan Assets Level Three (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 2,779.0
Plan assets at end of year	2,810.0	$ 2,779.0
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	74.0	68.0
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	2.0	8.0
Purchases, Sales, Issuances, and Settlements, Net	(2.0)	(2.0)
Plan assets at end of year	74.0	74.0
U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	1,800.0
Plan assets at end of year	1,821.0	1,800.0
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
Non-U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	979.0
Plan assets at end of year	989.0	979.0
Non-U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	74.0
Plan assets at end of year	74.0	74.0
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	72.0	65.0
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	2.0	8.0
Purchases, Sales, Issuances, and Settlements, Net	(1.0)	(1.0)
Plan assets at end of year	73.0	72.0
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	2.0	3.0
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	0.0	0.0
Purchases, Sales, Issuances, and Settlements, Net	(1.0)	(1.0)
Plan assets at end of year	$ 1.0	$ 2.0