Employee Retirement Plans - Fair Value of U.S. Pension Plan and VEBA Trust Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 529.2	$ 493.7	$ 453.8
Pension Benefits | U.S. Pension Plan
Defined Benefit Plan Disclosure
Fair value of plan assets	498.0	463.4
Other	5.3	17.8
Pension Benefits | U.S. Pension Plan | Domestic equity investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	274.9	250.5
Other	0.0	0.0
Pension Benefits | U.S. Pension Plan | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	171.6	158.9
Other	0.0	0.0
Pension Benefits | U.S. Pension Plan | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	65.2	43.2
Other	0.0	0.0
Pension Benefits | U.S. Pension Plan | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		11.4
Other		0.0
Pension Benefits | U.S. Pension Plan | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	38.1	37.0
Other	0.0	0.0
Pension Benefits | U.S. Pension Plan | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	61.6	47.3
Other	0.0	0.0
Pension Benefits | U.S. Pension Plan | Fixed income investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	161.5	165.6
Other	5.3	17.8
Pension Benefits | U.S. Pension Plan | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	156.2	147.8
Other	0.0	0.0
Pension Benefits | U.S. Pension Plan | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	5.3	17.8
Other	5.3	17.8
Pension Benefits | U.S. Pension Plan | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	492.7	445.6
Pension Benefits | U.S. Pension Plan | Level 1 | Domestic equity investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	274.9	250.5
Pension Benefits | U.S. Pension Plan | Level 1 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	171.6	158.9
Pension Benefits | U.S. Pension Plan | Level 1 | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	65.2	43.2
Pension Benefits | U.S. Pension Plan | Level 1 | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		11.4
Pension Benefits | U.S. Pension Plan | Level 1 | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	38.1	37.0
Pension Benefits | U.S. Pension Plan | Level 1 | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	61.6	47.3
Pension Benefits | U.S. Pension Plan | Level 1 | Fixed income investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	156.2	147.8
Pension Benefits | U.S. Pension Plan | Level 1 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	156.2	147.8
Pension Benefits | U.S. Pension Plan | Level 1 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 2 | Domestic equity investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 2 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 2 | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 2 | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		0.0
Pension Benefits | U.S. Pension Plan | Level 2 | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 2 | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 2 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | Domestic equity investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | Small and midcap equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | Smallcap common stocks
Defined Benefit Plan Disclosure
Fair value of plan assets		0.0
Pension Benefits | U.S. Pension Plan | Level 3 | UGI Corporation Common Stock
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | International index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | Fixed income investments:
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
Pension Benefits | U.S. Pension Plan | Level 3 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA
Defined Benefit Plan Disclosure
Fair value of plan assets	14.8	13.7
Other	0.4	0.1
VEBA | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	9.3	9.6
Other	0.0	0.0
VEBA | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	5.1	4.0
Other	0.0	0.0
VEBA | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0.4	0.1
Other	0.4	0.1
VEBA | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	14.4	13.6
VEBA | Level 1 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	9.3	9.6
VEBA | Level 1 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	5.1	4.0
VEBA | Level 1 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA | Level 2 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA | Level 2 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA | Level 3 | S&P 500 Index equity mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA | Level 3 | Bond index mutual funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0.0	0.0
VEBA | Level 3 | Cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 0.0	$ 0.0