Income Taxes - Schedule of Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Excess book basis over tax basis of property, plant and equipment	$ 1,051	$ 994
Intangible assets and goodwill	105	86
Utility regulatory assets	80	74
Investment in AmeriGas Partners	71	31
Other	113	50
Gross deferred tax liabilities	1,420	1,235
Interest expense	(150)	(118)
Operating loss carryforwards	(73)	(72)
Utility regulatory liabilities	(66)	(72)
Foreign tax credit carryforwards	(12)	(49)
Employee-related benefits	(25)	(33)
Investment tax credits	(116)	(26)
Utility environmental liabilities	(19)	(16)
Pension plan liabilities	0	(8)
Derivative instrument liabilities	(19)	(3)
Other	(121)	(58)
Gross deferred tax assets	(601)	(455)
Deferred tax assets valuation allowance	71	130
Net deferred tax liabilities	$ 890	$ 910