Employee Retirement Plans - Change in Pension Benefits and Other Postretirement Benefits Obligations (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Change in benefit obligations:
Benefit obligations — beginning of year	$ 782	$ 750
Service cost	12	11	$ 10
Interest cost	22	23	27
Actuarial (gain) loss	(30)	27
Plan amendments	2	0
Acquisitions	114	0
Curtailments	0	(2)
Foreign currency (gain) loss	(1)	3
Benefits paid	(31)	(30)
Benefit obligations — end of year	870	782	750
Change in plan assets:
Fair value of plan assets — beginning of year	585	547
Actual gain on plan assets	75	53
Foreign currency	0	1
Employer contributions	14	13
Acquisitions	92	0
Benefits paid	(30)	(29)
Fair value of plan assets — end of year	736	585	$ 547
Funded status of the plans — end of year	(134)	(197)
Amounts recorded in UGI Corporation stockholders’ equity (pre-tax):
Prior service cost	3	1
Net actuarial loss	13	24
Total	16	25
Amounts recorded in regulatory assets and liabilities (pre-tax):
Net actuarial loss	108	174
Total	108	174
ABO for the pension plans	$ 756	$ 687