Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Sep. 30, 2011	Mar. 31, 2011
Regulatory Assets [Line Items]
Regulatory Assets	$ 295.7	$ 300.4	$ 256.4
Regulatory Liabilities [Line Items]
Regulatory Liabilities	35.4	29.8	58.3
Postretirement benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	12.1	11.5	11.2
Environmental overcollections [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3.8	4.7	6.8
Deferred fuel and power refunds [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	12.0	6.6	34.0
State tax benefits - distribution system repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6.7	6.3	6.3
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0.8	0.7
Income taxes recoverable [Member]
Regulatory Assets [Line Items]
Regulatory Assets	99.2	97.9	89.9
Underfunded pension and postretirement plans [Member]
Regulatory Assets [Line Items]
Regulatory Assets	146.6	150.7	116.0
Environmental costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	18.2	19.5	22.0
Deferred fuel and power costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	11.0	12.2	8.2
Removal costs, net [Member]
Regulatory Assets [Line Items]
Regulatory Assets	11.9	12.3	11.7
Other [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 8.8	$ 7.8	$ 8.6