Business Segment Information (Reconciliation of Equity Affiliates' Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Equity affiliates' income	$ 43.7	$ 34.2	$ 57.5	$ 72.2
Segment Total
Segment Reporting Information [Line Items]
Equity affiliates' income	43.7	34.2	90.0	72.2
Segment Reconciling Items
Segment Reporting Information [Line Items]
Tax reform repatriation - equity method investment	$ 0.0	$ 0.0	$ (32.5)	$ 0.0