Inventories - Components of Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022
Inventory
Total inventories	$ 410	$ 665	$ 496
Non-utility LPG and natural gas
Inventory
Total inventories	189	335	261
Gas Utility natural gas
Inventory
Total inventories	37	166	84
Energy certificates
Inventory
Total inventories	68	70	70
Materials, supplies and other
Inventory
Total inventories	$ 116	$ 94	$ 81