COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Jun. 30, 2012	Sep. 30, 2007	Sep. 30, 2006	Jul. 26, 2012
Commitments [Abstract]
Minimum total payments required for natural gas contracts	$ 156
Approximate contract amount of project	6
Contingencies and Indemnifications [Abstract]
Number of former manufactured gas plant (MGP) sites in Missouri	three
Number of former manufactured gas plant (MGP) sites in Shrewsbury, Missouri	one
Number of former manufactured gas plant (MGP) sites in the City of St. Louis	two
Minimum cost estimate for a one-time contractual transfer of risk	5.8
Maximum cost estimate for a one-time contractual transfer of risk	36.3
Original proposed disallowance amount related to recovery of purchased gas costs	7.2	1.5	2.8
Adjusted proposed disallowance amount related to purchase gas costs	1.7
Amount remaining on deposit with a brokerage firm				$ 1.5