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Segment Information - Corporate and Other segment information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information
Loss on extinguishments of debt	$ (4.2)		$ (6.1)	$ 0.0	$ (59.7)
Impairment of Partnership tradenames and trademarks			0.0	(75.0)	0.0
Corporate & Other
Segment Reporting Information
Loss on extinguishments of debt			(6.1)		(59.7)
Corporate & Other \| AmeriGas Propane
Segment Reporting Information
Loss on extinguishments of debt			0.0		(59.7)
Acquisition costs				0.0	0.0
LPG business transformation costs			(14.5)
Corporate & Other \| UGI International
Segment Reporting Information
Loss on extinguishments of debt			(6.1)		0.0
Acquisition costs				(30.5)	(39.9)
LPG business transformation costs			(9.3)
Corporate & Other \| Midstream & Marketing
Segment Reporting Information
Loss on extinguishments of debt			0.0		0.0
Acquisition costs				0.0	0.0
LPG business transformation costs			0.0
Commodity contracts \| Corporate & Other \| AmeriGas Propane
Segment Reporting Information
Net income (loss) on derivative instruments			(116.8)	12.5	31.1
Commodity contracts \| Corporate & Other \| UGI International
Segment Reporting Information
Net income (loss) on derivative instruments			(142.5)	92.9	19.0
Commodity contracts \| Corporate & Other \| Midstream & Marketing
Segment Reporting Information
Net income (loss) on derivative instruments			(31.0)	(1.5)	55.7
Foreign currency contracts \| Corporate & Other \| AmeriGas Propane
Segment Reporting Information
Net income (loss) on derivative instruments			0.0	0.0	0.0
Foreign currency contracts \| Corporate & Other \| UGI International
Segment Reporting Information
Net income (loss) on derivative instruments			32.2	28.9	(23.8)
Foreign currency contracts \| Corporate & Other \| Midstream & Marketing
Segment Reporting Information
Net income (loss) on derivative instruments			0.0	0.0	$ 0.0
Merger Sub \| Corporate & Other \| AmeriGas Propane
Segment Reporting Information
Acquisition costs			(6.3)
Merger Sub \| Corporate & Other \| UGI International
Segment Reporting Information
Acquisition costs			0.0
Merger Sub \| Corporate & Other \| Midstream & Marketing
Segment Reporting Information
Acquisition costs			0.0
Trademarks and tradenames
Segment Reporting Information
Impairment of Partnership tradenames and trademarks		$ (14.5)
Trademarks and tradenames \| Corporate & Other \| AmeriGas Propane
Segment Reporting Information
Impairment of Partnership tradenames and trademarks				(75.0)
Trademarks and tradenames \| Corporate & Other \| UGI International
Segment Reporting Information
Impairment of Partnership tradenames and trademarks				0.0
Trademarks and tradenames \| Corporate & Other \| Midstream & Marketing
Segment Reporting Information
Impairment of Partnership tradenames and trademarks				$ 0.0
Affiliated Entity \| CMG \| Pennant \| Corporate & Other \| AmeriGas Propane
Segment Reporting Information
Acquisition costs			0.0
Affiliated Entity \| CMG \| Pennant \| Corporate & Other \| UGI International
Segment Reporting Information
Acquisition costs			0.0
Affiliated Entity \| CMG \| Pennant \| Corporate & Other \| Midstream & Marketing
Segment Reporting Information
Acquisition costs			$ (15.6)