Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2021	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Foreign tax credits			$ 40.9	$ 25.6	$ 63.0
Undistributed earnings of foreign subsidiaries	$ 119.7		$ 119.7
Income Taxes
Corporate income tax rate			25.30%	31.20%	30.00%
Deferred tax assets relating to operating loss carryforwards	30.9		$ 30.9	$ 31.5
Increase (decrease) in valuation allowance	7.6		(7.2)
Valuation allowance provided for deferred tax assets related to state net operating loss carryforwards and other state deferred tax assets of certain subsidiaries	0.2		0.2
Credits to expire before utilization	98.5		98.5
Unrecognized income tax benefits	12.2		12.2	7.2	$ 3.2	$ 2.4
Accrued interest included in unrecognized income tax benefits	0.5		0.5
Unrecognized tax benefits if recognized would impact the reported effective tax rate	8.1		8.1
Accrued Interest Included
Income Taxes
Unrecognized income tax benefits	12.2		12.2
Future Utilization of Foreign Tax Credits
Income Taxes
Increase (decrease) in valuation allowance			(7.6)
Foreign Operating Loss Carryforwards
Income Taxes
Increase (decrease) in valuation allowance			(1.5)
Foreign Tax Credits
Income Taxes
Increase (decrease) in valuation allowance			1.1
State Capital Loss Carryforwards
Income Taxes
Increase (decrease) in valuation allowance			0.8
State Operating Loss Carryforwards
Income Taxes
Increase (decrease) in valuation allowance				(5.5)
Flaga
Income Taxes
Deferred tax assets relating to operating loss carryforwards	5.6		5.6
UGI International Holdings BV
Income Taxes
Deferred tax assets relating to operating loss carryforwards	0.7		0.7
UGI France
Income Taxes
Deferred tax assets relating to operating loss carryforwards	7.8		7.8
AmeriGas Propane
Income Taxes
Operating loss carryforwards	19.7		19.7
Deferred tax assets relating to operating loss carryforwards	6.8		6.8
Other Subsidiaries
Income Taxes
Deferred tax assets relating to operating loss carryforwards	10.0		10.0
UGI International
Income Taxes
Valuation allowance operating loss carryforwards	7.5		$ 7.5
French Parliament
Income Taxes
Corporate income tax rate			34.43%
Deferred tax benefit			$ 29.0
French Parliament | Forecast
Income Taxes
Corporate income tax rate		28.92%
State
Income Taxes
Operating loss carryforwards	187.9		187.9
Decrease in income tax expense due to state tax flow through of accelerated depreciation			2.5	1.3	$ 1.5
Deferred tax assets and associated valuation allowance for unrealized state tax benefits for equity compensation deductions				$ 7.7
Foreign
Income Taxes
Foreign tax credit carryforwards	106.1		106.1
Foreign | Flaga
Income Taxes
Operating loss carryforwards	24.5		24.5
Foreign | UGI International Holdings BV
Income Taxes
Operating loss carryforwards	2.5		2.5
Foreign | UGI France
Income Taxes
Operating loss carryforwards	$ 22.6		$ 22.6