Segment Information - Reconciliation of Partnership Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Depreciation and amortization	$ (111.2)	$ (110.3)
Interest expense	(60.2)	(58.2)
(Loss) income before income taxes	$ 111.9	329.8
AmeriGas Propane | AmeriGas OLP
Segment Reporting Information [Line Items]
General partnership interest (percentage)	1.01%
Operating Segments | AmeriGas Propane
Segment Reporting Information [Line Items]
Partnership Adjusted EBITDA	$ 210.7	194.1
Depreciation and amortization	(45.7)	(47.4)
Interest expense	(42.4)	(40.6)
Noncontrolling interest	1.6	1.2
(Loss) income before income taxes	124.2	107.3
Corporate & Other
Segment Reporting Information [Line Items]
Depreciation and amortization	(0.1)	(0.2)
Interest expense	(0.2)	(0.2)
(Loss) income before income taxes	(168.0)	1.7
Gains (losses) on unsettled commodity derivative instruments, net	$ (165.9)	$ 6.6