Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Accumulated Other Comprehensive Income Effects of Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Amount of Gain Recognized in Other Comprehensive Income on Derivatives, net of tax	$ 20.7	$ 14.7
Interest rate contracts
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Amount of Gain Recognized in Other Comprehensive Income on Derivatives, net of tax	12.6	(1.4)
Foreign currency forward contracts
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Amount of Gain Recognized in Other Comprehensive Income on Derivatives, net of tax	$ 8.1	$ 16.1