Debt - Loss on Extinguishment of Debt (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Debt Instrument, Redemption [Line Items]
Loss on extinguishments of debt	$ 0.0	$ 4.4	$ 22.1	$ 33.2	$ 11.8	$ 37.1	$ 0.0	$ 0.0	$ 59.7	$ 48.9	$ 0.0
AmeriGas Partners
Debt Instrument, Redemption [Line Items]
Early redemption premiums									51.3	39.6
Write-off of unamortized debt issuance costs									8.4	9.3
Loss on extinguishments of debt									$ 59.7	$ 48.9