Acquisitions - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed - Plex (Details) - USD ($) $ in Millions	Aug. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Goodwill		$ 3,625.9	$ 1,650.3	$ 1,071.1
Plex Systems
Business Acquisition [Line Items]
Accounts receivable	$ 14.8
Other assets	28.3
Goodwill	1,725.3
Intangible assets	531.4
Total assets acquired	2,299.8
Less: Contract liabilities	(29.2)
Less: Other liabilities assumed	(31.8)
Less: Deferred income taxes	(33.3)
Net assets acquired	2,205.5
Total purchase consideration, net of cash acquired	$ 2,205.5