Other Comprehensive Income (Loss) (Schedule of Changes in AOCL by Component) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Other comprehensive income (loss)
Total Other Comprehensive Income (Loss), net of tax	$ 14.6	$ 11.4	$ (13.4)	$ 2.0
Accumulated other comprehensive loss
Beginning balance			1,227.2
Net activity	14.6	11.4	(13.4)	2.0
Ending balance	1,244.7		1,244.7
Available-for-sale Securities and Hedges [Member]
Other comprehensive income (loss)
Prior to reclassification	0.4	(2.8)	16.6	(2.6)
Reclassification from	(0.5)	0.0	(0.7)	0.0
Pre-tax	(0.1)	(2.8)	15.9	(2.6)
Tax effect	(0.1)	1.0	(5.9)	0.9
Total Other Comprehensive Income (Loss), net of tax	(0.2)	(1.8)	10.0	(1.7)
Accumulated other comprehensive loss
Beginning balance	7.1	0.1	(3.1)	0.0
Net activity	(0.2)	(1.8)	10.0	(1.7)
Ending balance	6.9	(1.7)	6.9	(1.7)
Foreign Currency Translation Adjustment [Member]
Other comprehensive income (loss)
Prior to reclassification	14.0	12.6	(25.5)	2.4
Reclassification from	0.0	0.0	0.0	0.0
Pre-tax	14.0	12.6	(25.5)	2.4
Tax effect	0.0	0.0	0.0	0.0
Total Other Comprehensive Income (Loss), net of tax	14.0	12.6	(25.5)	2.4
Accumulated other comprehensive loss
Beginning balance	(154.7)	(103.0)	(115.2)	(92.8)
Net activity	14.0	12.6	(25.5)	2.4
Ending balance	(140.7)	(90.4)	(140.7)	(90.4)
Change in Pension and Postretirement Defined Benefit Plans [Member]
Other comprehensive income (loss)
Prior to reclassification	0.0	0.0	0.4	0.0
Reclassification from	1.4	1.0	2.9	2.1
Pre-tax	1.4	1.0	3.3	2.1
Tax effect	(0.6)	(0.4)	(1.2)	(0.8)
Total Other Comprehensive Income (Loss), net of tax	0.8	0.6	2.1	1.3
Accumulated other comprehensive loss
Beginning balance	(49.5)	(47.3)	(50.8)	(48.0)
Net activity	0.8	0.6	2.1	1.3
Ending balance	(48.7)	(46.7)	(48.7)	(46.7)
Accumulated Other Comprehensive Income (Loss) [Member]
Other comprehensive income (loss)
Prior to reclassification	14.4	9.8	(8.5)	(0.2)
Reclassification from	0.9	1.0	2.2	2.1
Pre-tax	15.3	10.8	(6.3)	1.9
Tax effect	(0.7)	0.6	(7.1)	0.1
Total Other Comprehensive Income (Loss), net of tax	14.6	11.4	(13.4)	2.0
Accumulated other comprehensive loss
Beginning balance	(197.1)	(150.2)	(169.1)	(140.8)
Net activity	14.6	11.4	(13.4)	2.0
Ending balance	$ (182.5)	$ (138.8)	$ (182.5)	$ (138.8)