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, 2024 USD ($) grant_recipient $ / shares shares	Sep. 30, 2023 USD ($) grant_recipient $ / shares shares	Sep. 30, 2022 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 | $	$ 184.7	$ 115.2	$ 120.1
Number of Restricted Stock Units
Outstanding at beginning of year, shares | shares	2,966,925	3,466,094	3,817,265
Granted, shares | shares	663,860	877,131	1,153,124
Vested, shares | shares	(1,233,866)	(1,251,785)	(1,402,642)
Cancelled, shares | shares	(87,182)	(124,515)	(101,653)
Outstanding at end of year, shares | shares	2,309,737	2,966,925	3,466,094
Weighted Average Grant Date Fair Value
Outstanding at beginning of year, weighted average grant date fair value, per share | $ / shares	$ 70.85	$ 57.50	$ 46.16
Granted, weighted average grant date fair value, per share | $ / shares	147.79	93.44	74.96
Vested, weighted average grant date fair value, per share | $ / shares	65.51	50.61	41.44
Cancelled, weighted average grant date fair value, per share | $ / shares	85.12	61.95	51.22
Outstanding at end of year, weighted average grant date fair value, per share | $ / shares	$ 95.28	$ 70.85	$ 57.50
Additional information - restricted stock units
Share-based compensation expense | $	$ 77.3	$ 65.7	$ 63.6
Unrecognized compensation expense | $	$ 170.1
Weighted average period over which unrecognized compensation cost is expected to be recognized	2 years 7 months 6 days
Minimum [Member]
Additional information - restricted stock units
Vesting period	3 years
Maximum [Member]
Additional information - restricted stock units
Vesting period	5 years
Fiscal 2022 Grant
Additional information - restricted stock units
RSU grant recipients | grant_recipient			1,200
Fiscal 2023 Grant
Additional information - restricted stock units
RSU grant recipients | grant_recipient		1,380
Fiscal 2024 Grant
Additional information - restricted stock units
RSU grant recipients | grant_recipient	1,470