Earnings Per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$ 148.1	$ 160.4	$ 286.6	$ 299.5
Less: Distributed and undistributed income available to participating securities, Basic	(0.1)		(0.1)
Distributed and undistributed income available to common stockholders, Basic	148.0	160.4	286.5	299.5
Less: Distributed and undistributed income available to participating securities, Diluted	(0.1)		(0.1)
Distributed and undistributed income available to common stockholders, Diluted	$ 148.0	$ 160.4	$ 286.5	$ 299.5
Basic weighted average shares outstanding	259.0	256.6	258.6	255.7
Effect of dilutive stock options and non- participating securities	1.2	2.8	1.5	3.7
Diluted weighted average shares outstanding	260.2	259.4	260.1	259.4
Basic earnings per share attributable to common stockholders	$ 0.57	$ 0.63	$ 1.11	$ 1.17
Diluted earnings per share attributable to common stockholders	$ 0.57	$ 0.62	$ 1.10	$ 1.15