STOCKHOLDER'S EQUITY (Details) (USD $)	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Stockholder's Equity [Abstract]
Common stock outstanding (in shares)	12,804	11,717
Increase in common stock and paid-in capital	$ 44,400,000	$ 4,800,000
Shares sold to parent company	1,087	43
Proceeds from sale of stock used to reduce short-term borrowings	42,700,000	1,600,000
Dividend payment restriction formula component - fixed amount	8,000,000
Dividend payment restriction formula resulting calculation - available to pay dividends in period	355,000,000	299,000,000
SEC effective shelf registration Form S-3 for issuance of bonds, unsecured debt, and preferred stock - maximum available	350,000,000
MoPSC authorized debt issuance through June 30, 2013 - maximum available	518,000,000
MoPSC authorized debt issuance - remaining available	473,100,000
Accumulated other comprehensive income (loss) [Abstract]
Balance, beginning balance	(2,473,000)	(2,875,000)
Current period change	372,000	402,000	(256,000)
Balance, ending balance	(2,101,000)	(2,473,000)	(2,875,000)
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated other comprehensive income (loss) [Abstract]
Balance, beginning balance	(53,000)	15,000
Current period change	182,000	(68,000)
Balance, ending balance	129,000	(53,000)
Defined Benefit Pension and Other Postretirement Benefit Plans [Member]
Accumulated other comprehensive income (loss) [Abstract]
Balance, beginning balance	(2,420,000)	(2,890,000)
Current period change	190,000	470,000
Balance, ending balance	$ (2,230,000)	$ (2,420,000)