Inventories - Components of Inventories (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2013
Inventory
Total inventories	$ 332.0	$ 365.5	$ 304.0
Non-utility LPG and Natural Gas
Inventory
Total inventories	222.6	230.0	194.6
Gas Utility Natural Gas
Inventory
Total inventories	45.7	78.9	43.1
Materials, Supplies and Other
Inventory
Total inventories	$ 63.7	$ 56.6	$ 66.3