Retirement Benefits - Defined Benefit Plan Change in Fair Value of Plan Assets Level Three (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 3,753.1
Plan assets at end of year	3,838.0	$ 3,753.1
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	100.8	84.6
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	13.1	14.2
Purchases, Sales, Issuances, and Settlements, Net	1.8	2.0
Plan assets at end of year	115.7	100.8
U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	2,781.3
Plan assets at end of year	2,817.8	2,781.3
U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	0.9
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	971.8
Plan assets at end of year	1,020.2	971.8
Non-U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	99.9
Plan assets at end of year	114.8	99.9
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	95.4	79.1
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	13.0	14.3
Purchases, Sales, Issuances, and Settlements, Net	1.8	2.0
Plan assets at end of year	110.2	95.4
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	4.5	4.6
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	0.1	(0.1)
Purchases, Sales, Issuances, and Settlements, Net	0.0
Plan assets at end of year	$ 4.6	$ 4.5