Taxes on Income - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Examination [Line Items]
Net operating loss and state credit carry-forwards	$ 318.5	$ 317.0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	173.4	303.1
Foreign tax credit carry-forwards	128.0	103.0
Impact of reduced rates on income tax expense	$ 3.2	$ 2.7	$ 4.1
Impact of reduced rates on income tax expense, per diluted share	$ 0.01	$ 0.01	$ 0.01
Increase (decrease) in valuation allowance	$ (1.3)	$ 293.7
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	173.4	303.1
Accrued interest on uncertain tax positions	25.7	21.7
Accrued penalties on uncertain tax positions	3.9	$ 2.9
Estimated decrease in unrecognized tax benefits within the next twelve months	33.6
Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Net operating loss and state credit carry-forwards	9.9
Foreign Tax Authority [Member]
Income Tax Examination [Line Items]
Net operating loss and state credit carry-forwards	98.5
State [Member]
Income Tax Examination [Line Items]
Net operating loss and state credit carry-forwards	$ 206.1