Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	$ 4,137
Other comprehensive (loss) income before reclassification adjustments (after-tax)	63	$ 53
Amounts reclassified from AOCI	5	1
Other comprehensive income (loss) attributable to UGI	68	54
Balance, end of period	4,446	4,005
Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(26)	(26)
Other comprehensive (loss) income before reclassification adjustments (after-tax)	0	0
Amounts reclassified from AOCI	0	0
Other comprehensive income (loss) attributable to UGI	0	0
Balance, end of period	(26)	(26)
Derivative Instruments
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(54)	(25)
Other comprehensive (loss) income before reclassification adjustments (after-tax)	0	6
Amounts reclassified from AOCI	5	1
Other comprehensive income (loss) attributable to UGI	5	7
Balance, end of period	(49)	(18)
Foreign Currency
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(67)	(166)
Other comprehensive (loss) income before reclassification adjustments (after-tax)	63	47
Amounts reclassified from AOCI	0	0
Other comprehensive income (loss) attributable to UGI	63	47
Balance, end of period	(4)	(119)
Total
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(147)	(217)
Balance, end of period	$ (79)	$ (163)