Inventories (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Sep. 30, 2011	Jun. 30, 2011
Inventories
Total inventories	$ 317.3	$ 363.0	$ 271.6
Non-utility LPG and natural gas [Member]
Inventories
Total inventories	220.1	222.2	170.5
Gas Utility Natural Gas [Member]
Inventories
Total inventories	27.8	95.6	50.1
Materials, Supplies and Other [Member]
Inventories
Total inventories	$ 69.4	$ 45.2	$ 51.0