Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period			$ 4,137
Other comprehensive loss before reclassification adjustments	$ (52)	$ (69)	11	$ (16)
Amounts reclassified from AOCI	5	2	10	3
Other comprehensive income (loss) attributable to UGI	(47)	(67)	21	(13)
Balance, end of period	4,828	4,090	4,828	4,090
Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(26)	(26)	(26)	(26)
Other comprehensive loss before reclassification adjustments	0	0	0	0
Amounts reclassified from AOCI	1	2	1	2
Other comprehensive income (loss) attributable to UGI	1	2	1	2
Balance, end of period	(25)	(24)	(25)	(24)
Derivative Instruments
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(49)	(18)	(54)	(25)
Other comprehensive loss before reclassification adjustments	4	(36)	4	(30)
Amounts reclassified from AOCI	4	0	9	1
Other comprehensive income (loss) attributable to UGI	8	(36)	13	(29)
Balance, end of period	(41)	(54)	(41)	(54)
Foreign Currency
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(4)	(119)	(67)	(166)
Other comprehensive loss before reclassification adjustments	(56)	(33)	7	14
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income (loss) attributable to UGI	(56)	(33)	7	14
Balance, end of period	(60)	(152)	(60)	(152)
Total
AOCI Attributable to Parent, Net of Tax
Balance, beginning of period	(79)	(163)	(147)	(217)
Balance, end of period	$ (126)	$ (230)	$ (126)	$ (230)