Inventories - Components of Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015
Inventory
Inventory, net	$ 184.2	$ 239.9	$ 208.7
Non-utility LPG and natural gas
Inventory
Inventory, net	107.9	140.7	124.6
Gas Utility natural gas
Inventory
Inventory, net	13.5	37.5	19.2
Materials, supplies and other
Inventory
Inventory, net	$ 62.8	$ 61.7	$ 64.9