Other Income Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Component of Operating Income [Abstract]
Interest and interest-related income	$ 0.8	$ 3.6	$ 2.2
Utility non-tariff service income	4.8	2.7	2.8
Finance charges	12.7	17.5	21.4
Gains on sales of fixed assets	11.1	5.4	1.4
Loss on private equity partnership investment	0.0	0.0	(6.3)
Other, net	15.0	6.9	11.3
Total other income, net	$ 44.4	$ 36.1	$ 32.8