Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Class of Stock [Line Items]
Purchases of treasury stock	$ 587.8	$ 330.8	$ 218.7
Cash paid for share repurchase contracts	46.4	$ 0.0	$ 0.0
Share Repurchase Contracts, Shares Expected to be Repurchased, Next Fiscal Period	0.6
Share Repurchase Contracts, Cash Expected to be Received, Next Fiscal Period	$ 47.5
Preferred Stock
Class of Stock [Line Items]
Treasury Stock, Shares, Acquired	0.0
Common Stock
Class of Stock [Line Items]
Treasury Stock, Shares, Acquired	6.1	3.3	2.8
Treasury Stock Acquired, Average Cost Per Share	$ 97.67	$ 98.78	$ 76.21
Purchases of treasury stock	$ 587.8	$ 330.8	$ 218.7
Payments for accrued repurchases of common stock	$ 7.4	$ 8.7