Goodwill and Intangible Assets - Components of Company's Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill (not subject to amortization)	$ 2,948.4	$ 2,989.0	$ 2,998.6	[1]
Intangible assets:
Customer relationships, noncompete agreements and other	764.3	773.5	778.3
Accumulated amortization	(342.4)	(324.8)	(312.3)
Intangible assets, net (definite-lived)	421.9	448.7	466.0
Trademarks and tradenames (indefinite-lived)	129.1	131.6	132.2
Total intangible assets, net	$ 551.0	$ 580.3	$ 598.2

[1] Restated to reflect (1) the current-year changes in the presentation of our UGI International and Midstream & Marketing reportable segments and (2) the adoption of new accounting guidance related to debt issuance costs (see Note 2).