Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease expense	$ 109.8	$ 104.6
Variable lease expense	15.8	15.6
Finance Leases
Amortization of right-of-use assets	1.7	1.3
Interest on lease liabilities	0.4	0.4
Total lease expense	$ 127.7	$ 121.9