Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Millions	Sep. 30, 2011	Sep. 30, 2010
Regulatory Assets [Line Items]
Regulatory Assets	$ 300.4	$ 319.7
Regulatory Liabilities [Line Items]
Regulatory Liabilities	29.8	32.7
Income taxes recoverable [Member]
Regulatory Assets [Line Items]
Regulatory Assets	97.9	82.5
Underfunded pension and postretirement plans [Member]
Regulatory Assets [Line Items]
Regulatory Assets	150.7	159.2
Environmental costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	19.5	22.6
Deferred fuel and power costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	12.2	36.6
Removal costs, net [Member]
Regulatory Assets [Line Items]
Regulatory Assets	12.3	13.0
Other Regulatory assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets	7.8	5.8
Postretirement benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	11.5	10.5
Environmental overcollections [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4.7	7.2
Deferred Fuel and Power Refunds [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6.6	8.3
State tax benefits - distribution system repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6.3	6.7
Other Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 0.7