Income Taxes - Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Excess book basis over tax basis of property, plant and equipment	$ 830	$ 805
Utility regulatory assets	112	108
Intangible assets and goodwill	107	71
Other	32	7
Gross deferred tax liabilities	1,081	991
Investment in AmeriGas Partners	(216)	(304)
Pension plan liabilities	(48)	(50)
Employee-related benefits	(46)	(44)
Operating loss carryforwards	(34)	(21)
Foreign tax credit carryforwards	(81)	(81)
Utility regulatory liabilities	(94)	(94)
Derivative instruments	(26)	(15)
Utility environmental liabilities	(16)	(15)
Other	(54)	(34)
Gross deferred tax assets	(615)	(658)
Deferred tax assets valuation allowance	105	91
Net deferred tax liabilities	$ 571	$ 424