Income Taxes (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2021 USD ($) Jurisdiction	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Operating Loss Carryforwards [Line Items]
Tax structuring	$ (39.5)	$ 0.0	$ 0.0
Basis differential of investment in foreign affiliates considered indefinitely invested	964.0
Potential U.S. tax if all unrealized basis differences were repatriated	202.0
Tax loss carryforwards and tax credits without expiration	12.1
Accrued interest	6.8	5.6	4.9
Deferred tax asset related to accrued interest	1.1	0.8	0.7
Penalties	$ 3.4	$ 4.0	$ 3.9
Number of foreign jurisdictions | Jurisdiction	60
Between 2018 and 2020
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards	$ 2.7