Inventories - Components of Inventories (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013
Inventory
Total inventories	$ 324.4	$ 365.5	$ 292.4
Non-utility LPG and Natural Gas
Inventory
Total inventories	251.4	230.0	220.3
Gas Utility Natural Gas
Inventory
Total inventories	7.5	78.9	5.4
Materials, Supplies and Other
Inventory
Total inventories	$ 65.5	$ 56.6	$ 66.7