Income Taxes - Schedule of Income Tax Data (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
Components of income before income taxes
United States									$ 556.2	$ 280.8	$ 721.6
Non-United States									579.9	620.2	609.2
Total	$ 299.6	$ 334.5	$ 167.4	$ 334.6	$ 56.4	$ 321.4	$ 402.4	$ 120.8	1,136.1	901.0	1,330.8
Current income tax provision:
United States									68.1	105.6	475.3
Non-United States									96.6	112.1	131.4
State and local									13.9	16.5	18.1
Total current									178.6	234.2	624.8
Deferred income tax provision:
United States									(32.8)	(27.0)	118.6
Non-United States									(24.7)	(0.1)	48.0
State and local									(8.2)	(1.9)	3.9
Total deferred									(65.7)	(29.0)	170.5
Income tax provision									112.9	205.2	795.3
Total income taxes paid									$ 187.9	$ 293.3	$ 222.9