Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Fund Investment Capital
Loss Contingencies [Line Items]
Capital commitments	$ 5.1
Commitment period (in years)	3 years
Standby Letters of Credit
Loss Contingencies [Line Items]
Outstanding standby letters of credit	$ 899.4	$ 934.5
Amount available under unsecured credit facilities	367.4
Contingently liable for issuance of standby letters of credit and surety bonds	903.8
Surety Bond
Loss Contingencies [Line Items]
Contingently liable for issuance of standby letters of credit and surety bonds	$ 5,600.0