Business Segment Information (Reconciliation of Operating Income) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Operating income	$ 516.5		$ 455.4	$ 971.5	$ 916.1
Facility closure	0.0	$ (29.0)	0.0	(29.0)	0.0
Segment Reconciling Items
Segment Reporting Information [Line Items]
Facility closure	0.0		0.0	(29.0)	0.0
Segment Total
Segment Reporting Information [Line Items]
Operating income	$ 516.5		$ 455.4	$ 1,000.5	$ 916.1