Segment Information - Reconciliation of Partnership Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Depreciation and amortization	$ (108.9)	$ (112.2)	$ (220.1)	$ (222.5)
Interest expense	(61.0)	(58.1)	(121.2)	(116.3)
Income (loss) before income taxes	487.3	521.1	$ 599.2	850.9
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	290.3	309.5	$ 500.9	503.6
Depreciation and amortization	(44.3)	(45.2)	(90.0)	(92.6)
Interest expense	(42.2)	(41.0)	(84.6)	(81.6)
Merger expense	(0.9)	0.0	(0.9)	0.0
Noncontrolling interest	1.3	2.3	3.0	3.5
Income (loss) before income taxes	204.2	225.6	328.4	332.9
Corporate & Other
Segment Reporting Information [Line Items]
Depreciation and amortization	(0.3)	(0.3)	(0.4)	(0.5)
Interest expense	0.0	(0.1)	(0.2)	(0.3)
Income (loss) before income taxes	(0.9)	(53.9)	(168.9)	(52.2)
Gains (losses) on unsettled commodity derivative instruments, net	$ 4.7	$ (48.1)	$ (161.2)	$ (41.5)