Income Taxes - Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Excess book basis over tax basis of property, plant and equipment	$ 966	$ 867
Utility regulatory assets	84	106
Intangible assets and goodwill	81	75
Derivative instrument assets	19	514
Other	37	33
Gross deferred tax liabilities	1,187	1,595
Investment in AmeriGas Partners	(28)	(79)
Pension plan liabilities	(14)	(21)
Employee-related benefits	(37)	(38)
Operating loss carryforwards	(75)	(48)
Foreign tax credit carryforwards	(64)	(76)
Utility regulatory liabilities	(83)	(85)
Utility environmental liabilities	(15)	(15)
Interest expense	(83)	(51)
Other	(58)	(74)
Gross deferred tax assets	(457)	(487)
Deferred tax assets valuation allowance	141	141
Net deferred tax liabilities	$ 871	$ 1,249