Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	$ 338.4	$ 300.4
Regulatory Liabilities	28.3	29.8
Postretirement benefits [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	13.1	11.5
Environmental overcollections [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	2.9	4.7
Deferred fuel and power refunds [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	4.4	6.6
State tax benefits - distribution system repairs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	7.4	6.3
Other regulatory liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liabilities	0.5	0.7
Income taxes recoverable [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	103.2	97.9
Underfunded pension and postretirement plans [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	188.2	150.7
Environmental costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	16.8	19.5
Deferred fuel and power costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	11.6	12.2
Removal costs, net [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	12.7	12.3
Other regulatory assets [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	$ 5.9	$ 7.8