Debt (Registered Public Offerings) (Details) € in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2025 USD ($)	Sep. 30, 2025 EUR (€)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2025 EUR (€)	Feb. 28, 2025 USD ($)	Feb. 28, 2025 EUR (€)
Debt Instrument [Line Items]
Debt issuance costs	$ 3.8		$ 4.6
Repayment of debt	429.9		$ 486.2	$ 615.4
Senior Notes
Debt Instrument [Line Items]
Debt issuance costs					$ 12.0		$ 8.0
Senior Notes | U.S. Dollar-denominated Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount					1,100.0
Senior Notes | Euro-denominated Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount					$ 570.0	€ 500	$ 1,000.0	€ 1,000
Repayment of debt	$ 311.0	€ 300
Interest rate	1.00%