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, 2020 USD ($) grant_recipient $ / shares shares	Sep. 30, 2019 USD ($) grant_recipient $ / shares shares	Sep. 30, 2018 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 | $	$ 95.6	$ 56.9	$ 51.0
Number of Restricted Stock Units
Outstanding at beginning of year, shares | shares	4,889,534	4,797,922	4,365,782
Granted, shares | shares	1,657,935	1,796,200	1,747,870
Vested, shares | shares	(1,651,840)	(1,430,826)	(1,149,055)
Cancelled, shares | shares	(169,928)	(273,762)	(166,675)
Outstanding at end of year, shares | shares	4,725,701	4,889,534	4,797,922
Weighted Average Grant Date Fair Value
Outstanding at beginning of year, weighted average grant date fair value, per share | $ / shares	$ 33.01	$ 31.77	$ 26.09
Granted, weighted average grant date fair value, per share | $ / shares	35.98	33.75	41.82
Vested, weighted average grant date fair value, per share | $ / shares	30.85	29.83	25.80
Cancelled, weighted average grant date fair value, per share | $ / shares	33.24	32.82	29.56
Outstanding at end of year, weighted average grant date fair value, per share | $ / shares	$ 34.79	$ 33.01	$ 31.77
Additional information - restricted stock units
Share-based compensation expense | $	$ 50.6	$ 51.8	$ 39.3
Unrecognized compensation expense | $	$ 120.6
Weighted average period over which unrecognized compensation cost is expected to be recognized	2 years 8 months 12 days
Maximum [Member]
Additional information - restricted stock units
Vesting period	5 years
Minimum [Member]
Additional information - restricted stock units
Vesting period	3 years
Fiscal 2020 Grant [Member]
Additional information - restricted stock units
RSU grant recipients | grant_recipient	960
Fiscal 2019 Grant [Member]
Additional information - restricted stock units
RSU grant recipients | grant_recipient		900
Fiscal 2018 Grant [Member]
Additional information - restricted stock units
RSU grant recipients | grant_recipient			920