Goodwill and Intangible Assets - Components of Company's Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill (not subject to amortization)	$ 2,998.6	$ 2,953.4	$ 2,731.2	[1]
Intangible assets:
Customer relationships, noncompete agreements and other	778.3	761.1	670.2
Accumulated amortization	(312.3)	(282.4)	(254.1)
Intangible assets, net (definite-lived)	466.0	478.7	416.1
Trademarks and tradenames (indefinite-lived)	132.2	131.4	121.4
Total intangible assets, net	$ 598.2	$ 610.1	$ 537.5

[1] Certain amounts have been restated to reflect the current-year changes in our segment presentation as described above.