Other Comprehensive Income (Loss) (Schedule of Items Reclassified out of AOCL) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified	$ (21.5)	$ (41.3)	$ (52.3)	$ (76.6)
Tax effect	(7.0)	7.3	(64.5)	19.1
Net of tax	(28.5)	(34.4)	(116.8)	(58.2)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale Securities and Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified	(0.5)	(0.5)	(0.9)	(0.7)
Tax effect	0.0	0.1	0.2	0.2
Net of tax	(0.5)	(0.4)	(0.7)	(0.5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified			2.2	2.9
Tax effect			(0.4)	(1.1)
Net of tax			$ 1.8	$ 1.8
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified	1.0	1.4
Tax effect	(0.1)	(0.6)
Net of tax	$ 0.9	$ 0.8