Goodwill and Intangible Assets - Components of Company's Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill (not subject to amortization)	$ 3,032.3	$ 2,989.0	$ 2,981.3
Intangible assets:
Customer relationships, noncompete agreements and other	801.6	773.5	778.1
Accumulated amortization	(362.8)	(324.8)	(321.3)
Intangible assets, net (definite-lived)	438.8	448.7	456.8
Trademarks and tradenames (indefinite-lived)	132.4	131.6	131.1
Total intangible assets, net	$ 571.2	$ 580.3	$ 587.9