Leases - Additional cash flow information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 221.4	$ 208.7
Operating cash flows from finance leases	2.0	1.8
Financing cash flows from finance leases	13.7	14.7
Right-of-use assets obtained in exchange for new operating leases	102.7	126.9
Right-of-use assets obtained in exchange for new finance leases	$ 28.5	$ 26.4