Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	$ 4,137	$ 3,827
Other comprehensive (loss) income before reclassification adjustments (after-tax)	(13)	58	$ (103)
Amounts reclassified from AOCI	20	12	3
Other comprehensive (loss) income attributable to UGI	7	70	(100)
Reclassification of stranded income tax effects related to TCJA			(7)
Balance, end of year	5,531	4,137	3,827
Postretirement Benefit Plans
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(26)	(26)	(11)
Other comprehensive (loss) income before reclassification adjustments (after-tax)	7	(3)	(13)
Amounts reclassified from AOCI	2	3	1
Other comprehensive (loss) income attributable to UGI	9	0	(12)
Reclassification of stranded income tax effects related to TCJA			(3)
Balance, end of year	(17)	(26)	(26)
Derivative Instruments
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(54)	(25)	(16)
Other comprehensive (loss) income before reclassification adjustments (after-tax)	3	(38)	(7)
Amounts reclassified from AOCI	18	9	2
Other comprehensive (loss) income attributable to UGI	21	(29)	(5)
Reclassification of stranded income tax effects related to TCJA			(4)
Balance, end of year	(33)	(54)	(25)
Foreign Currency
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(67)	(166)	(83)
Other comprehensive (loss) income before reclassification adjustments (after-tax)	(23)	99	(83)
Amounts reclassified from AOCI	0	0	0
Other comprehensive (loss) income attributable to UGI	(23)	99	(83)
Reclassification of stranded income tax effects related to TCJA			0
Balance, end of year	(90)	(67)	(166)
Accumulated other comprehensive income (loss)
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(147)	(217)	(110)
Reclassification of stranded income tax effects related to TCJA			(7)
Balance, end of year	$ (140)	$ (147)	$ (217)