Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	$ 3,827	$ 4,101
Other comprehensive income (loss) before reclassification adjustments (after-tax)	58	(103)	$ (19)
Amounts reclassified from AOCI:
Reclassification adjustments (pre-tax)	17	6	4
Reclassification adjustments tax benefit	(5)	(3)	(2)
Reclassification adjustments (after-tax)	12	3	2
Other comprehensive income (loss) attributable to UGI	70	(100)	(17)
Reclassification of stranded income tax effects related to TCJA		(7)
Balance, end of year	4,137	3,827	4,101
Postretirement Benefit Plans
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(26)	(11)	(19)
Other comprehensive income (loss) before reclassification adjustments (after-tax)	(3)	(13)	10
Amounts reclassified from AOCI:
Reclassification adjustments (pre-tax)	4	2	(3)
Reclassification adjustments tax benefit	(1)	(1)	1
Reclassification adjustments (after-tax)	3	1	(2)
Other comprehensive income (loss) attributable to UGI	0	(12)	8
Reclassification of stranded income tax effects related to TCJA		(3)
Balance, end of year	(26)	(26)	(11)
Derivative Instruments
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(25)	(16)	(21)
Other comprehensive income (loss) before reclassification adjustments (after-tax)	(38)	(7)	1
Amounts reclassified from AOCI:
Reclassification adjustments (pre-tax)	13	4	7
Reclassification adjustments tax benefit	(4)	(2)	(3)
Reclassification adjustments (after-tax)	9	2	4
Other comprehensive income (loss) attributable to UGI	(29)	(5)	5
Reclassification of stranded income tax effects related to TCJA		(4)
Balance, end of year	(54)	(25)	(16)
Foreign Currency
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(166)	(83)	(53)
Other comprehensive income (loss) before reclassification adjustments (after-tax)	99	(83)	(30)
Amounts reclassified from AOCI:
Reclassification adjustments (pre-tax)	0	0	0
Reclassification adjustments tax benefit	0	0	0
Reclassification adjustments (after-tax)	0	0	0
Other comprehensive income (loss) attributable to UGI	99	(83)	(30)
Reclassification of stranded income tax effects related to TCJA		0
Balance, end of year	(67)	(166)	(83)
Accumulated other comprehensive income (loss)
AOCI Including Portion Attributable to NCI [Roll Forward]:
Balance, beginning of year	(217)	(110)	(93)
Amounts reclassified from AOCI:
Reclassification of stranded income tax effects related to TCJA		(7)
Balance, end of year	$ (147)	$ (217)	$ (110)

Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, after Tax [Abstract] [Abstract]

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