Other Income Net (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Component of Operating Income [Abstract]
Interest and interest-related income	$ 3.6	$ 2.2	$ 2.4
Utility non-tariff service income	2.7	2.8	2.7
Finance charges	17.5	21.4	18.8
Gains on sales of fixed assets	5.4	1.4	1.9
Loss on private equity partnership investment	0	(6.3)	0
Other, net	6.9	11.3	14.0
Total other income, net	$ 36.1	$ 32.8	$ 39.8