Income Taxes - Schedule of Income Tax Data (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Components of income before income taxes
United States									$ 721.6	$ 547.2	$ 512.1
Non-United States									609.2	490.2	431.0
Total	$ 481.7	$ 251.7	$ 299.6	$ 297.8	$ 273.5	$ 276.0	$ 230.3	$ 257.6	1,330.8	1,037.4	943.1
Current income tax provision:
United States									475.3	67.3	175.9
Non-United States									131.4	109.9	91.7
State and local									18.1	0.7	16.3
Total current									624.8	177.9	283.9
Deferred income tax provision:
United States									118.6	44.6	(53.7)
Non-United States									48.0	(14.1)	(8.8)
State and local									3.9	3.3	(8.0)
Total deferred									170.5	33.8	(70.5)
Income tax provision									795.3	211.7	213.4
Total income taxes paid									$ 222.9	$ 211.9	$ 299.8