Employee Benefit Plans - Stock Options (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Stock Options
Outstanding at beginning of year, shares	8,431,348	11,395,917	15,337,656
Exercised, shares	(2,547,139)	(2,770,569)	(3,504,989)
Canceled or expired, shares	(27,250)	(194,000)	(436,750)
Outstanding at end of year, shares	5,856,959	8,431,348	11,395,917
Exercisable at end of year, shares	4,955,392	5,772,214	6,645,967
Weighted Average Exercise Price
Outstanding at beginning of year, weighted average exercise price, per share	$ 16.92	$ 16.69	$ 17.50
Exercised, weighted average exercise price, per share	16.10	15.83	20.02
Canceled or expired, weighted average exercise price, per share	22.08	18.83	18.45
Outstanding at end of year, weighted average exercise price, per share	17.25	16.92	16.69
Exercisable at end of year, weighted average exercise price, per share	$ 17.07	$ 16.01	$ 14.99
Additional information - stock options
Expiration period	10 years
Total intrinsic value of options exercised	$ 76.8	$ 49.5	$ 39.2
Aggregate intrinsic value of options outstanding	146.0
Aggregate intrinsic value of options exercisable	$ 124.4
Lower range of options outstanding exercise price	$ 9.03
Upper range of options outstanding exercise price	$ 23.86
Weighted average remaining contractual term of options outstanding	3 years 6 months
Stock based compensation expense	$ 6.9	$ 15.1	$ 20.5
Unrecognized compensation expense related to options	$ 1.0