Inventories (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Sep. 30, 2011	Mar. 31, 2011
Inventories
Total inventories	$ 347.8	$ 363.0	$ 222.1
Non-utility LPG and natural gas [Member]
Inventories
Total inventories	261.5	222.2	160.9
Gas Utility Natural Gas [Member]
Inventories
Total inventories	12.8	95.6	7.9
Materials, Supplies and Other [Member]
Inventories
Total inventories	$ 73.5	$ 45.2	$ 53.3