Other Comprehensive Income (Loss) (Schedule of Items Reclassified out of AOCL) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified	$ (41.3)	$ (28.1)	$ (76.6)	$ (33.9)
Tax effect	7.3	6.0	19.1	7.5
Net of tax	(34.4)	(22.3)	(58.2)	(27.1)
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)	0.0	(0.7)	0.0
Tax effect	0.1	0.0	0.2	0.0
Net of tax	(0.4)	0.0	(0.5)	0.0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Change in Pension and Postretirement Defined Benefit Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified	1.4	1.0	2.9	2.1
Tax effect	(0.6)	(0.4)	(1.1)	(0.8)
Net of tax	$ 0.8	$ 0.6	$ 1.8	$ 1.3