Business Segment and Geographic Information (Reconciliation of Equity Affiliates' Income) (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017		Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Equity affiliates' income	$ 44.8	$ (36.9)	[1]	$ 34.2	$ 38.0	$ 39.3	$ 42.1	$ 32.3	$ 33.3	$ 80.1	[1]	$ 147.0	$ 152.3
Equity method investment impairment charge		$ 79.5								79.5		0.0	0.0
Segment Total
Segment Reporting Information [Line Items]
Equity affiliates' income										159.6		147.0	152.3
Segment Reconciling Items
Segment Reporting Information [Line Items]
Equity method investment impairment charge										$ (79.5)		$ 0.0	$ 0.0

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