Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Notional Values For Derivatives Instrument (Details) - Designated as Hedging Instrument £ in Millions, zł in Millions, $ in Millions	Jun. 30, 2023 USD ($)	Jun. 30, 2023 PLN (zł)	Jun. 30, 2023 GBP (£)	Sep. 30, 2022 USD ($)	Sep. 30, 2022 PLN (zł)	Sep. 30, 2022 GBP (£)
Interest rate contracts
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 2,000.0			$ 1,500.0
Foreign currency forward contracts | Polish Zloty
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	33.7	zł 156.1		0.0	zł 0.0
Foreign currency forward contracts | British Pound Sterling
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 207.2		£ 168.0	$ 207.3		£ 168.0