Summary of Significant Accounting Policies - Average Composite Depreciation Rates (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory assets	$ 0	$ 0
Depreciation	$ 416,000,000	$ 389,000,000	$ 397,000,000
Amortization period	5 years
Gas Utility
Public Utility, Property, Plant and Equipment [Line Items]
Average composite depreciation rates (as a percentage)	2.50%	2.20%	2.30%
Electric Utility
Public Utility, Property, Plant and Equipment [Line Items]
Average composite depreciation rates (as a percentage)	2.20%	2.10%	2.20%
UGI Utilities
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory assets	$ 397,000,000	$ 396,000,000
Computer software | UGI Utilities
Public Utility, Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years