Nature of Operations (Details)				6 Months Ended	9 Months Ended
	Aug. 01, 2019 USD ($)	Jun. 30, 2019	Apr. 01, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) county	Jun. 30, 2018 USD ($)
Investment [Line Items]
General Partner incentive distribution					$ 34,300,000	$ 34,000,000.0
Number of counties of operation | county					1
AmeriGas Propane | AmeriGas Partners
Investment [Line Items]
General Partner held a general partner interest in AmeriGas Partners (percentage)		1.00%			1.00%
Percentage of limited partnership interest in AmeriGas Partners (percentage)		25.30%
General public as limited partner interests in AmeriGas Partners (percentage)		73.70%			73.70%
AmeriGas Propane | AmeriGas OLP
Investment [Line Items]
Effective ownership interest in AmeriGas OLP (percentage)		27.00%			27.00%
Merger Sub
Investment [Line Items]
Dividends declared per common share (in USD per share, no less than) | $ / shares			$ 0.95
Termination fee payable to parent			$ 20,000,000
Expense reimbursement amount to parent, maximum			5,000,000
Expense reimbursement amount from parent, maximum			$ 5,000,000
Merger Sub | Forecast
Investment [Line Items]
Proposed consideration				$ 530,000,000
Subsequent Event | CMG
Investment [Line Items]
Proposed consideration	$ 1,275,000,000
Common Stock | Merger Sub | Forecast
Investment [Line Items]
Proposed consideration issuable (in shares) | shares				34,600,000
Units issuable (in units) | shares				10,615,711
Proposed Consideration One | Common Stock | Merger Sub | Forecast
Investment [Line Items]
Number of shares issuable per acquiree stock (in shares) | shares				0.6378
Proposed Consideration Two | Common Stock | Merger Sub | Forecast
Investment [Line Items]
Number of shares issuable per acquiree stock (in shares) | shares				0.500
Proposed Consideration Two | Cash Without Interest | Merger Sub | Forecast
Investment [Line Items]
Cash issuable per acquiree stock (in dollars per share) | $ / shares				$ 7.63
Proposed Consideration Three | Cash Without Interest | Merger Sub | Forecast
Investment [Line Items]
Cash issuable per acquiree stock (in dollars per share) | $ / shares				$ 35.325