Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	$ 322.3	$ 338.4	$ 295.7
Regulatory Liabilities	56.7	28.3	35.4
Postretirement benefits [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	13.9	13.1	12.1
Environmental overcollections [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	3.0	2.9	3.8
Deferred fuel and power refunds [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	31.2	4.4	12.0
State tax benefits - distribution system repairs [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	7.9	7.4	6.7
Other [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	0.7	0.5	0.8
Income taxes recoverable [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	104.2	103.2	99.2
Underfunded pension and postretirement plans [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	181.3	188.2	146.6
Environmental costs [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	16.8	16.8	18.2
Deferred fuel and power costs [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	2.1	11.6	11.0
Removal costs, net [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	11.9	12.7	11.9
Other [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	$ 6.0	$ 5.9	$ 8.8