Employee Benefit Plans - Time-Based Restricted Stock Unit Equity Awards (Details) - Restricted Stock Units (RSUs) [Member] $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2019 USD ($) grant_recipient $ / shares shares	Sep. 30, 2018 USD ($) grant_recipient $ / shares shares	Sep. 30, 2017 USD ($) grant_recipient $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value | $	$ 56.9	$ 51.0	$ 25.0
Number of Restricted Stock Units
Outstanding at beginning of year, shares | shares	4,797,922	4,365,782	3,478,233
Granted, shares | shares	1,796,200	1,747,870	1,868,660
Vested, shares | shares	(1,430,826)	(1,149,055)	(792,941)
Cancelled, shares | shares	(273,762)	(166,675)	(188,170)
Outstanding at end of year, shares | shares	4,889,534	4,797,922	4,365,782
Weighted Average Grant Date Fair Value
Outstanding at beginning of year, weighted average grant date fair value, per share | $ / shares	$ 31.77	$ 26.09	$ 24.12
Granted, weighted average grant date fair value, per share | $ / shares	33.75	41.82	28.64
Vested, weighted average grant date fair value, per share | $ / shares	29.83	25.80	24.48
Cancelled, weighted average grant date fair value, per share | $ / shares	32.82	29.56	25.21
Outstanding at end of year, weighted average grant date fair value, per share | $ / shares	$ 33.01	$ 31.77	$ 26.09
Additional information - restricted stock units
Share-based compensation expense | $	$ 51.8	$ 39.3	$ 28.8
Unrecognized compensation expense | $	$ 99.8
Weighted average period over which unrecognized compensation cost is expected to be recognized	3 years 3 months 18 days
Maximum [Member]
Additional information - restricted stock units
Vesting period	5 years
Fiscal 2018 Grant [Member]
Additional information - restricted stock units
RSU grant recipients | grant_recipient	900
Fiscal 2017 Grant [Member]
Additional information - restricted stock units
RSU grant recipients | grant_recipient		920
Fiscal 2016 Grant [Member]
Additional information - restricted stock units
RSU grant recipients | grant_recipient			600