Business Segment and Geographic Information (Reconciliation of Equity Affiliates' Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
India Finance Act 2020		$ 33.8							$ 33.8
Tax reform repatriation - equity method investment											$ (28.5)
Equity affiliates' income	$ 67.2	$ 51.2	$ 88.2	$ 58.2	$ 59.9	$ 56.4	$ 46.2	$ 52.9	264.8	$ 215.4	174.8
Segment Reconciling Items
Segment Reporting Information [Line Items]
India Finance Act 2020									33.8	0.0	0.0
Tax reform repatriation - equity method investment									0.0	0.0	(28.5)
Segment Total
Segment Reporting Information [Line Items]
Equity affiliates' income									$ 231.0	$ 215.4	$ 203.3