Income Taxes - Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Excess book basis over tax basis of property, plant and equipment	$ 994	$ 966
Intangible assets and goodwill	86	81
Utility regulatory assets	74	84
Investment in AmeriGas Partners	31	0
Derivative instrument assets	0	19
Other	50	37
Gross deferred tax liabilities	1,235	1,187
Interest expense	(118)	(83)
Operating loss carryforwards	(72)	(75)
Utility regulatory liabilities	(72)	(83)
Foreign tax credit carryforwards	(49)	(64)
Employee-related benefits	(33)	(37)
Investment tax credits	(26)	0
Utility environmental liabilities	(16)	(15)
Pension plan liabilities	(8)	(14)
Derivative instrument liabilities	(3)	0
Investment in AmeriGas Partners	0	(28)
Other	(58)	(58)
Gross deferred tax assets	(455)	(457)
Deferred tax assets valuation allowance	130	141
Net deferred tax liabilities	$ 910	$ 871