Employee Retirement Plans - Change in Pension Benefits and Other Postretirement Benefits Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits
Change in benefit obligations:
Benefit obligations — beginning of year	$ 707.7	$ 614.7
Service cost	11.9	10.1	$ 10.0
Interest cost	25.0	26.8	25.5
Actuarial (gain) loss	(19.6)	83.3
Plan amendments	1.2	0.0
Curtailment	(3.6)	(1.4)
Foreign currency	2.9	0.1
Benefits paid	(27.7)	(25.9)
Benefit obligations — end of year	697.8	707.7	614.7
Change in plan assets:
Fair value of plan assets — beginning of year	493.7	453.8
Actual gain on plan assets	47.0	53.4
Foreign currency	1.6	0.1
Employer contributions	14.6	11.4
Benefits paid	(27.7)	(25.0)
Fair value of plan assets — end of year	529.2	493.7	453.8
Funded status of the plans — end of year	(168.6)	(214.0)
Assets (liabilities) recorded in the balance sheet:
Assets in excess of liabilities — included in other noncurrent assets	0.0	0.0
Unfunded liabilities — included in other noncurrent liabilities	(168.6)	(214.0)
Net amount recognized	(168.6)	(214.0)
Amounts recorded in UGI Corporation stockholders’ equity (pre-tax):
Prior service cost (credit)	0.7	(0.6)
Net actuarial loss (gain)	21.3	31.4
Total	22.0	30.8
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost (credit)	1.0	1.2
Net actuarial loss	139.5	181.0
Total	140.5	182.2
Other Postretirement Benefits
Change in benefit obligations:
Benefit obligations — beginning of year	30.9	25.4
Service cost	1.0	0.7	0.7
Interest cost	0.8	0.9	0.8
Actuarial (gain) loss	(4.8)	6.6
Plan amendments	0.0	(1.5)
Curtailment	(0.4)	(0.3)
Foreign currency	0.4	0.0
Benefits paid	(0.9)	(0.9)
Benefit obligations — end of year	27.0	30.9	25.4
Change in plan assets:
Fair value of plan assets — beginning of year	13.7	12.5
Actual gain on plan assets	1.3	1.3
Foreign currency	0.0	0.0
Employer contributions	0.6	0.6
Benefits paid	(0.8)	(0.7)
Fair value of plan assets — end of year	14.8	13.7	$ 12.5
Funded status of the plans — end of year	(12.2)	(17.2)
Assets (liabilities) recorded in the balance sheet:
Assets in excess of liabilities — included in other noncurrent assets	5.4	4.1
Unfunded liabilities — included in other noncurrent liabilities	(17.6)	(21.3)
Net amount recognized	(12.2)	(17.2)
Amounts recorded in UGI Corporation stockholders’ equity (pre-tax):
Prior service cost (credit)	(1.5)	(1.5)
Net actuarial loss (gain)	(0.6)	3.8
Total	(2.1)	2.3
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost (credit)	(1.6)	(2.2)
Net actuarial loss	1.2	2.4
Total	$ (0.4)	$ 0.2