Other Comprehensive Income (Loss) (Schedule of Changes in AOCL by Component) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Other comprehensive income (loss)
Total Other Comprehensive Income (Loss), net of tax	$ 25.2	$ 14.6	$ 35.5	$ (13.4)
Accumulated other comprehensive loss
Beginning balance			1,358.2
Net activity	25.2	14.6	35.5	(13.4)
Ending balance	1,510.4		1,510.4
Available-for-sale Securities and Hedges [Member]
Other comprehensive income (loss)
Prior to reclassification	9.7	0.4	15.5	16.6
Reclassification from	(0.5)	(0.5)	(0.9)	(0.7)
Pre-tax	9.2	(0.1)	14.6	15.9
Tax effect	(1.3)	(0.1)	(3.3)	(5.9)
Total Other Comprehensive Income (Loss), net of tax	7.9	(0.2)	11.3	10.0
Accumulated other comprehensive loss
Beginning balance	7.7	7.1	4.3	(3.1)
Net activity	7.9	(0.2)	11.3	10.0
Ending balance	15.6	6.9	15.6	6.9
Foreign Currency Translation Adjustment [Member]
Other comprehensive income (loss)
Prior to reclassification	16.5	14.0	22.6	(25.5)
Reclassification from	0.0	0.0	0.0	0.0
Pre-tax	16.5	14.0	22.6	(25.5)
Tax effect	0.0	0.0	0.0	0.0
Total Other Comprehensive Income (Loss), net of tax	16.5	14.0	22.6	(25.5)
Accumulated other comprehensive loss
Beginning balance	(75.2)	(154.7)	(81.3)	(115.2)
Net activity	16.5	14.0	22.6	(25.5)
Ending balance	(58.7)	(140.7)	(58.7)	(140.7)
Change in Pension and Postretirement Defined Benefit Plans [Member]
Other comprehensive income (loss)
Prior to reclassification	(0.1)	0.0	(0.2)	0.4
Reclassification from	1.0	1.4	2.2	2.9
Pre-tax	0.9	1.4	2.0	3.3
Tax effect	(0.1)	(0.6)	(0.4)	(1.2)
Total Other Comprehensive Income (Loss), net of tax	0.8	0.8	1.6	2.1
Accumulated other comprehensive loss
Beginning balance	(32.2)	(49.5)	(33.0)	(50.8)
Net activity	0.8	0.8	1.6	2.1
Ending balance	(31.4)	(48.7)	(31.4)	(48.7)
Accumulated Other Comprehensive Income (Loss) [Member]
Other comprehensive income (loss)
Prior to reclassification	26.1	14.4	37.9	(8.5)
Reclassification from	0.5	0.9	1.3	2.2
Pre-tax	26.6	15.3	39.2	(6.3)
Tax effect	(1.4)	(0.7)	(3.7)	(7.1)
Total Other Comprehensive Income (Loss), net of tax	25.2	14.6	35.5	(13.4)
Accumulated other comprehensive loss
Beginning balance	(99.7)	(197.1)	(110.0)	(169.1)
Net activity	25.2	14.6	35.5	(13.4)
Ending balance	$ (74.5)	$ (182.5)	$ (74.5)	$ (182.5)