Income Taxes - Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Excess book basis over tax basis of property, plant and equipment	$ 937	$ 830
Utility regulatory assets	105	112
Intangible assets and goodwill	77	107
Derivative instrument assets	322	0
Other	36	32
Gross deferred tax liabilities	1,477	1,081
Investment in AmeriGas Partners	(102)	(216)
Pension plan liabilities	(29)	(48)
Employee-related benefits	(45)	(46)
Operating loss carryforwards	(53)	(34)
Foreign tax credit carryforwards	(79)	(81)
Utility regulatory liabilities	(102)	(94)
Derivative instrument liabilities	0	(26)
Utility environmental liabilities	(16)	(16)
Other	(107)	(54)
Gross deferred tax assets	(533)	(615)
Deferred tax assets valuation allowance	138	105
Net deferred tax liabilities	$ 1,082	$ 571