Inventories - Components of Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Inventory
Inventory, net	$ 176.5	$ 239.9	$ 201.5
Non-utility LPG and natural gas
Inventory
Inventory, net	106.7	140.7	135.8
Gas Utility natural gas
Inventory
Inventory, net	3.8	37.5	6.3
Materials, supplies and other
Inventory
Inventory, net	$ 66.0	$ 61.7	$ 59.4