Retirement Plans - Schedule of Changes in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Prepaid pension asset	$ 368.7	$ 224.7
Pension liabilities, net of current portion	(305.2)	(294.0)
Postretirement benefit liabilities, net of current portion	(145.4)	(162.1)
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	52.6	42.8	$ 44.8
Interest cost	198.6	232.6	204.6
Pension Plan [Member] | United States [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	5,048.9	3,783.5
Service cost	44.2	36.0
Interest cost	165.0	189.2
Amendments	25.2	0.4
Actuarial (gain) loss	214.3	694.4
Plan participant contributions	0.0	0.0
Benefits paid	(233.1)	(216.8)
Business combinations	0.0	561.2
Curtailments	0.0	1.0
Settlements	0.0	0.0
Foreign currency rate changes	0.0	0.0
Benefit obligation at end of fiscal year	5,264.5	5,048.9	3,783.5
Fair value of plan assets at beginning of fiscal year	5,005.3	3,921.2
Actual gain on plan assets	582.6	731.7
Employer contributions	14.9	13.0
Plan participant contributions	0.0	0.0
Benefits paid	(233.1)	(216.8)
Business combinations	0.0	556.2
Settlements	0.0	0.0
Foreign currency rate changes	0.0	0.0
Fair value of plan assets at end of fiscal year	5,369.7	5,005.3	3,921.2
Funded status	105.2	(43.6)
Prepaid pension asset	290.6	143.3
Other current liabilities	(10.7)	(14.6)
Pension liabilities, net of current portion	(174.7)	(172.3)
Over (under) funded status at end of fiscal year	105.2	(43.6)
Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	1,443.1	1,340.2
Service cost	8.4	6.8
Interest cost	33.6	43.4
Amendments	(0.2)	3.1
Actuarial (gain) loss	41.9	181.0
Plan participant contributions	2.0	2.2
Benefits paid	(72.0)	(78.3)
Business combinations	0.0	0.7
Curtailments	3.2	0.0
Settlements	(9.0)	(1.7)
Foreign currency rate changes	20.5	(54.3)
Benefit obligation at end of fiscal year	1,471.5	1,443.1	1,340.2
Fair value of plan assets at beginning of fiscal year	1,400.9	1,350.2
Actual gain on plan assets	65.4	172.9
Employer contributions	7.6	12.1
Plan participant contributions	2.0	2.2
Benefits paid	(72.0)	(78.3)
Business combinations	0.0	0.0
Settlements	(9.0)	(1.7)
Foreign currency rate changes	23.1	(56.5)
Fair value of plan assets at end of fiscal year	1,418.0	1,400.9	1,350.2
Funded status	(53.5)	(42.2)
Prepaid pension asset	78.1	81.4
Other current liabilities	(1.1)	(1.9)
Pension liabilities, net of current portion	(130.5)	(121.7)
Over (under) funded status at end of fiscal year	(53.5)	(42.2)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	1.3	1.2	1.5
Interest cost	6.9	7.7	7.9
Other Postretirement Benefits Plan [Member] | United States [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	98.3	91.0
Service cost	0.6	0.7
Interest cost	3.2	4.1
Amendments	(0.1)	0.4
Actuarial (gain) loss	(3.1)	1.6
Benefits paid	(5.3)	(6.6)
Business combinations	0.0	7.1
Foreign currency rate changes	0.0	0.0
Benefit obligation at end of fiscal year	93.6	98.3	91.0
Fair value of plan assets at beginning of fiscal year	0.0	0.0
Employer contributions	5.3	6.6
Benefits paid	(5.3)	(6.6)
Fair value of plan assets at end of fiscal year	0.0	0.0	0.0
Funded status	(93.6)	(98.3)
Other current liabilities	(8.0)	(8.9)
Postretirement benefit liabilities, net of current portion	(85.6)	(89.4)
Over (under) funded status at end of fiscal year	(93.6)	(98.3)
Other Postretirement Benefits Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	75.7	55.5
Service cost	0.7	0.5
Interest cost	3.7	3.6
Amendments	2.0	0.0
Actuarial (gain) loss	(5.3)	22.2
Benefits paid	(2.9)	(2.9)
Business combinations	0.0	0.0
Foreign currency rate changes	(11.4)	(3.2)
Benefit obligation at end of fiscal year	62.5	75.7	55.5
Fair value of plan assets at beginning of fiscal year	0.0	0.0
Employer contributions	2.9	2.9
Benefits paid	(2.9)	(2.9)
Fair value of plan assets at end of fiscal year	0.0	0.0	$ 0.0
Funded status	(62.5)	(75.7)
Other current liabilities	(2.7)	(3.0)
Postretirement benefit liabilities, net of current portion	(59.8)	(72.7)
Over (under) funded status at end of fiscal year	$ (62.5)	$ (75.7)