Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Sep. 30, 2012	Jun. 30, 2012
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	$ 320.9	$ 338.4	$ 291.0
Regulatory Liabilities	40.0	28.3	34.0
Postretirement benefits [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	14.2	13.1	12.3
Environmental overcollections [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	2.9	2.9	3.7
Deferred fuel and power refunds [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	14.2	4.4	10.3
State tax benefits - distribution system repairs [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	8.0	7.4	7.0
Other [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Liabilities	0.7	0.5	0.7
Income taxes recoverable [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	104.7	103.2	99.9
Underfunded pension and postretirement plans [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	177.8	188.2	144.6
Environmental costs [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	16.6	16.8	16.6
Deferred fuel and power costs [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	4.1	11.6	9.8
Removal costs, net [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	12.1	12.7	11.8
Other [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	$ 5.6	$ 5.9	$ 8.3