Leases - Additional cash flow information (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 102.7	$ 113.0
Operating cash flows from finance leases	1.1	0.9
Financing cash flows from finance leases	9.7	6.0
Right-of-use assets obtained in exchange for new operating leases	31.9	67.4
Right-of-use assets obtained in exchange for new finance leases	$ 18.4	$ 13.4