Utility Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Millions	Jun. 30, 2011	Sep. 30, 2010	Jun. 30, 2010
Regulatory Asset
Regulatory Assets	$ 246.1	$ 306.7	$ 141.7
Regulatory Liability
Regulatory Liabilities	46.4	32.7	46.2
Income taxes recoverable [Member]
Regulatory Asset
Regulatory Assets	92.7	82.5	95.3
Underfunded pension and postretirement plans [Member]
Regulatory Asset
Regulatory Assets	116.0	159.2	10.3
Environmental costs [Member]
Regulatory Asset
Regulatory Assets	20.7	22.6	24.3
Deferred fuel and power costs [Member]
Regulatory Asset
Regulatory Assets	7.8	36.6	6.3
Other [Member]
Regulatory Asset
Regulatory Assets	8.9	5.8	5.5
Postretirement benefits [Member]
Regulatory Liability
Regulatory Liabilities	11.6	10.5	10.3
Environmental overcollections [Member]
Regulatory Liability
Regulatory Liabilities	6.2	7.2	8.3
Deferred fuel and power refunds [Member]
Regulatory Liability
Regulatory Liabilities	22.4	8.3	16.6
State tax benefits - distribution system repairs [Member]
Regulatory Liability
Regulatory Liabilities	$ 6.2	$ 6.7	$ 11.0