Retirement Benefits (Change in Projected Benefit Obligation) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
U.S.
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Obligation at beginning of year	$ 3,281.6	$ 2,922.8
Service cost	23.4	21.4	$ 25.5
Interest cost	91.2	113.4	107.2
Amendments	1.6	1.1
Actuarial loss (gain)	190.5	380.3
Settlements	(11.7)	(12.2)
Special termination benefits	0.0	0.7
Participant contributions	0.0	0.0
Benefits paid	(152.5)	(146.2)
Currency translation and other	(0.3)	0.3
Obligation at end of year	3,423.8	3,281.6	2,922.8
International
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Obligation at beginning of year	1,864.0	1,660.5
Service cost	23.3	19.3	25.5
Interest cost	24.8	35.8	37.3
Amendments	0.0	4.7
Actuarial loss (gain)	(11.6)	300.2
Settlements	(0.9)	(1.6)
Special termination benefits	0.0	0.1
Participant contributions	1.2	1.3
Benefits paid	(49.8)	(47.7)
Currency translation and other	98.7	(108.6)
Obligation at end of year	$ 1,949.7	$ 1,864.0	$ 1,660.5