Retirement Benefits - Defined Benefit Plan Change in Fair Value of Plan Assets Level Three (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 3,754.8
Plan assets at end of year	3,753.1	$ 3,754.8
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	84.6	77.2
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	14.2	(0.6)
Purchases, Sales, Issuances, and Settlements, Net	2.0	8.0
Plan assets at end of year	100.8	84.6
U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	2,827.3
Plan assets at end of year	2,781.3	2,827.3
U.S. Plans | Insurance contracts
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
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 | Insurance contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	79.1
Plan assets at end of year	95.4	79.1
Non-U.S. Plans | Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	4.6
Plan assets at end of year	4.5	4.6
Non-U.S. Plans | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	83.7
Plan assets at end of year	99.9	83.7
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	79.1	71.5
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	14.3	(0.4)
Purchases, Sales, Issuances, and Settlements, Net	2.0	8.0
Plan assets at end of year	95.4	79.1
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	4.8
Realized Gains (Losses)	0.0	0.0
Unrealized Gains (Losses)	(0.1)	(0.2)
Purchases, Sales, Issuances, and Settlements, Net	0.0
Plan assets at end of year	$ 4.5	$ 4.6