Business Segment and Geographic Information (Reconciliation of Equity Affiliates' Income) (Details) - USD ($) $ in Millions	3 Months Ended											12 Months Ended
	Sep. 30, 2018	[1]	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	[2]	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Segment Reporting Information [Line Items]
Equity method investment impairment charge												$ 0.0		$ (79.5)		$ 0.0
Tax reform repatriation - equity method investment												(28.5)
Equity affiliates' income	$ 59.2		$ 58.1	$ 43.7	$ 13.8		$ 44.8	$ (36.9)		$ 34.2	$ 38.0	174.8	[1]	80.1	[2]	147.0
Segment Reconciling Items
Segment Reporting Information [Line Items]
Equity method investment impairment charge												0.0		(79.5)		0.0
Tax reform repatriation - equity method investment												(28.5)		0.0		0.0
Segment Total
Segment Reporting Information [Line Items]
Equity affiliates' income												$ 203.3		$ 159.6		$ 147.0

[1] Includes the impacts of the Tax Act. For additional information, refer to Note 22, Income Taxes.

[2] Includes the impact of an other-than-temporary impairment of an investment in an equity affiliate. For additional information, refer to Note 8, Summarized Financial Information of Equity Affiliates.