Employee Benefit Plans - Stock Options (Details) - Share-based Payment Arrangement, Option [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Stock Options
Outstanding at beginning of year, shares	3,184,157	5,856,959	8,431,348
Exercised, shares	(959,742)	(2,634,802)	(2,547,139)
Canceled or expired, shares	0	(38,000)	(27,250)
Outstanding at end of year, shares	2,224,415	3,184,157	5,856,959
Exercisable at end of year, shares	2,224,415	3,184,157	4,955,392
Weighted Average Exercise Price
Outstanding at beginning of year, weighted average exercise price, per share	$ 19.53	$ 17.25	$ 16.92
Exercised, weighted average exercise price, per share	18.58	14.47	16.10
Canceled or expired, weighted average exercise price, per share	0	18.98	22.08
Outstanding at end of year, weighted average exercise price, per share	19.94	19.53	17.25
Exercisable at end of year, weighted average exercise price, per share	$ 19.94	$ 19.53	$ 17.07
Additional information - stock options
Expiration period	10 years
Total intrinsic value of options exercised	$ 41.2	$ 70.6	$ 76.8
Aggregate intrinsic value of options outstanding	$ 123.9
Lower range of options outstanding exercise price	$ 9.97
Upper range of options outstanding exercise price	$ 23.86
Weighted average remaining contractual term of options outstanding	2 years 4 months 24 days
Stock based compensation expense	$ 0.0	$ 1.0	$ 6.9