Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Schedule of Accumulated Other Comprehensive Income Effects of Derivative Instruments (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Derivative Instruments and Hedging Activities Disclosure [Line Items] | ||||
| Amount of Gain/(Loss) Recognized in Other Comprehensive Income on Derivatives, net of tax | $ (4.0) | $ 6.3 | $ (22.1) | $ 6.0 |
| Interest rate contracts | ||||
| Derivative Instruments and Hedging Activities Disclosure [Line Items] | ||||
| Amount of Gain/(Loss) Recognized in Other Comprehensive Income on Derivatives, net of tax | (5.1) | 0.0 | (15.3) | 0.1 |
| Foreign currency forward contracts | ||||
| Derivative Instruments and Hedging Activities Disclosure [Line Items] | ||||
| Amount of Gain/(Loss) Recognized in Other Comprehensive Income on Derivatives, net of tax | $ 1.1 | $ 6.3 | $ (6.8) | $ 5.9 |