Employee Retirement Plans - Change in Pension Benefits and Other Postretirement Benefits Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Change in benefit obligations:
Benefit obligations — beginning of year	$ 750	$ 669
Service cost	11	10	$ 11
Interest cost	23	27	26
Actuarial loss	27	89
Curtailments	(2)	(1)
Settlements	0	(13)
Foreign currency	3	(3)
Benefits paid	(30)	(28)
Benefit obligations — end of year	782	750	669
Change in plan assets:
Fair value of plan assets — beginning of year	547	563
Actual gain on plan assets	53	13
Foreign currency	1	(1)
Employer contributions	13	12
Settlements	0	(13)
Benefits paid	(29)	(27)
Fair value of plan assets — end of year	585	547	563
Funded status of the plans — end of year	(197)	(203)
Assets (liabilities) recorded in the balance sheet:
Assets in excess of liabilities — included in other noncurrent assets	0	0
Unfunded liabilities — included in other noncurrent liabilities	(197)	(203)
Net amount recognized	(197)	(203)
Amounts recorded in UGI Corporation stockholders’ equity (pre-tax):
Prior service cost (benefit)	1	1
Net actuarial loss	24	26
Total	25	27
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost		1
Net actuarial loss	174	177
Total	174	178
Other Postretirement Benefits
Change in benefit obligations:
Benefit obligations — beginning of year	23	19
Interest cost	1	1
Actuarial loss	1	4
Curtailments	0	0
Settlements	0	0
Foreign currency	0	0
Benefits paid	(1)	(1)
Benefit obligations — end of year	24	23	19
Change in plan assets:
Fair value of plan assets — beginning of year	16	15
Actual gain on plan assets	2	1
Foreign currency	0	0
Settlements	0	0
Benefits paid	(1)
Fair value of plan assets — end of year	17	16	$ 15
Funded status of the plans — end of year	(7)	(7)
Assets (liabilities) recorded in the balance sheet:
Assets in excess of liabilities — included in other noncurrent assets	3	3
Unfunded liabilities — included in other noncurrent liabilities	(10)	(10)
Net amount recognized	(7)	(7)
Amounts recorded in UGI Corporation stockholders’ equity (pre-tax):
Prior service cost (benefit)	(1)	(1)
Total	(1)	(1)
Amounts recorded in regulatory assets and liabilities (pre-tax):
Net actuarial loss	1	1
Total	$ 1	$ 1