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Common Stock and Equity-Based Compensation - Weighted Average Assumption Used to Determine the Fair Value of AmeriGas Performance Unit Awards and Related Compensation Costs (Details) - AmeriGas Performance Units
12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award      
Risk-free rate 2.00% 1.50% 1.30%
Expected life 3 years 3 years 3 years
Expected volatility (as a percent) 21.10% 21.70% 20.60%
Dividend yield (as a percent) 8.20% 7.80% 10.70%