Acquisitions and Dispositions - Total Cash Paid and Liabilities Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
UGI International
Business Acquisition [Line Items]
Total cash paid	$ 18
Liabilities incurred	0
Total purchase price	$ 18
Midstream & Marketing
Business Acquisition [Line Items]
Total cash paid		$ 16
Liabilities incurred		7
Total purchase price		$ 23