Goodwill and Intangible Assets - Components of Company's Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill (not subject to amortization)	$ 2,886.0	$ 2,871.0	$ 2,813.8
Intangible assets:
Customer relationships, noncompete agreements and other	727.5	706.4	690.0
Trademarks and tradenames (not subject to amortization)	132.3	131.3	137.0
Gross carrying amount	859.8	837.7	827.0
Accumulated amortization	(251.6)	(227.1)	(197.1)
Intangible assets, net	$ 608.2	$ 610.6	$ 629.9