Retirement Benefits - Defined Benefit Plan Change in Fair Value of Plan Assets Level Three (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 3,838.0
Plan assets at end of year	4,192.2	$ 3,838.0
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	115.7	100.8
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	(5.6)	13.1
Purchases, Sales, Issuances, and Settlements, Net	1.7	1.8
Plan assets at end of year	111.8	115.7
U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	2,817.8
Plan assets at end of year	3,047.3	2,817.8
U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	0.9
Plan assets at end of year	0.9	0.9
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	0.9	0.9
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	0.0	0.0
Purchases, Sales, Issuances, and Settlements, Net	0.0	0.0
Plan assets at end of year	0.9	0.9
Non-U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	1,020.2
Plan assets at end of year	1,144.9	1,020.2
Non-U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	114.8
Plan assets at end of year	110.9	114.8
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	110.2	95.4
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	(5.7)	13.0
Purchases, Sales, Issuances, and Settlements, Net	1.7	1.8
Plan assets at end of year	106.2	110.2
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	4.6	4.5
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	0.1	0.1
Purchases, Sales, Issuances, and Settlements, Net	0.0	0.0
Plan assets at end of year	$ 4.7	$ 4.6