Income Taxes - Narrative (Details) - USD ($)		1 Months Ended	12 Months Ended
	Aug. 21, 2019	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Mar. 27, 2020	Sep. 30, 2017
Income Tax Examination [Line Items]
Foreign tax credits			$ 0	$ 10,000,000	$ 13,000,000
Net operating loss carryback						$ 32,000,000
Income taxes receivable			$ 80,000,000	$ 0
Tax Cuts And Jobs Act Of 2017, incomplete accounting, change in tax rate, deferred tax liability, provisional income tax benefit, including unrecognized deferred tax liability					$ 384,000,000
Effective income tax rate reconciliation, at federal statutory income tax rate, percent (as a percentage)			21.00%	21.00%	24.50%
Increase (decrease) in income tax liabilities					$ (52,000,000)
Tax Cuts And Jobs Act of 2017, transition tax for accumulated foreign earnings, provisional Income tax expense (benefit)			$ 2,000,000	$ 4,000,000
Income tax expense (benefit), continuing operations, adjustment of deferred tax (asset) liability		$ (12,000,000)		2,000,000
Deferred tax assets relating to operating loss carryforwards			34,000,000	21,000,000
Increase (decrease) in valuation allowance			14,000,000	(26,000,000)
Unrecognized income tax benefits			4,000,000	11,000,000	12,000,000		$ 12,000,000
Unrecognized tax benefits if recognized would impact the reported effective tax rate			4,000,000
Accrued Interest Included
Income Tax Examination [Line Items]
Unrecognized income tax benefits			4,000,000
Future Utilization of Foreign Tax Credits
Income Tax Examination [Line Items]
Increase (decrease) in valuation allowance				(25,000,000)
National Interest Deduction Carryover
Income Tax Examination [Line Items]
Increase (decrease) in valuation allowance			16,000,000
Flaga
Income Tax Examination [Line Items]
Deferred tax assets relating to operating loss carryforwards			2,000,000
UGI France
Income Tax Examination [Line Items]
Deferred tax assets relating to operating loss carryforwards			5,000,000
AmeriGas Propane
Income Tax Examination [Line Items]
Incentive distribution, distribution					13,000,000
Operating loss carryforwards			12,000,000
Deferred tax assets relating to operating loss carryforwards			2,000,000
Other Subsidiaries
Income Tax Examination [Line Items]
Deferred tax assets relating to operating loss carryforwards			25,000,000
Merger Sub
Income Tax Examination [Line Items]
Incentive distribution, distribution	$ 2,228,000,000
Cost for income tax purposes	2,030,000,000
Deferred tax asset, step up in tax basis of the underlying assets	$ 512,000,000			512,000,000
Foreign | Flaga
Income Tax Examination [Line Items]
Operating loss carryforwards			11,000,000
Foreign | UGI France
Income Tax Examination [Line Items]
Operating loss carryforwards			14,000,000
State
Income Tax Examination [Line Items]
Decrease in income tax expense due to state tax flow through of accelerated depreciation			11,000,000	$ 7,000,000	4,000,000
Operating loss carryforwards			$ 393,000,000
French Parliament
Income Tax Examination [Line Items]
Effective income tax rate reconciliation, at federal statutory income tax rate, percent (as a percentage)			34.43%
French Parliament | Foreign
Income Tax Examination [Line Items]
Increase (decrease) in income tax liabilities					$ 1,000,000