Income Taxes (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
Components of income before income taxes
United States									$ 547.2	$ 512.1	$ 660.5
Non-United States									490.2	431.0	467.0
Total	$ 273.5	$ 276.0	$ 230.3	$ 257.6	$ 236.9	$ 252.3	$ 217.0	$ 236.9	1,037.4	943.1	1,127.5
Current income tax provision:
United States									67.3	175.9	238.6
Non-United States									109.9	91.7	73.6
State and local									0.7	16.3	17.0
Total current									177.9	283.9	329.2
Deferred income tax provision:
United States									44.6	(53.7)	(30.3)
Non-United States									(14.1)	(8.8)	2.6
State and local									3.3	(8.0)	(1.6)
Total deferred									33.8	(70.5)	(29.3)
Income tax provision									211.7	213.4	299.9
Total income taxes paid									$ 211.9	$ 299.8	$ 313.1