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, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$ 160.4	$ 223.2	$ 299.5	$ 1,358.3
Less: Distributed and undistributed income available to participating securities, Basic				(0.2)
Net income attributable to common stockholders, basic	160.4	223.2	299.5	1,358.1
Less: Distributed and undistributed income available to participating securities, Diluted				(0.2)
Net income attributable to common stockholders, diluted	$ 160.4	$ 223.2	$ 299.5	$ 1,358.1
Basic weighted average shares outstanding	256.6	256.1	255.7	255.5
Effect of dilutive stock options and non- participating securities	2.8	4.2	3.7	4.2
Diluted weighted average shares outstanding	259.4	260.3	259.4	259.7
Basic earnings per share attributable to common stockholders	$ 0.63	$ 0.87	$ 1.17	$ 5.32
Diluted earnings per share attributable to common stockholders	$ 0.62	$ 0.86	$ 1.15	$ 5.23