Business Segment Information (Reconciliation of Operating Income) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Segment Reporting Information [Line Items]
Business separation costs	$ 0.0	$ (32.5)
Cost reduction and asset actions	0.0	(50.0)	$ (151.4)
Operating Income	460.7	328.3
Segment Total
Segment Reporting Information [Line Items]
Operating Income	460.7	410.8
Segment Reconciling Items
Segment Reporting Information [Line Items]
Business separation costs	0.0	(32.5)
Cost reduction and asset actions	$ 0.0	$ (50.0)