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	Dec. 31, 2023 USD ($)	Dec. 31, 2023 PLN (zł)	Dec. 31, 2023 GBP (£)	Sep. 30, 2023 USD ($)	Sep. 30, 2023 PLN (zł)	Sep. 30, 2023 GBP (£)
Interest rate contracts
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 1,250.0			$ 2,000.0
Foreign currency forward contracts | Polish Zloty
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	34.9	zł 156.1		34.0	zł 156.1
Foreign currency forward contracts | British Pound Sterling
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 177.3		£ 144.0	$ 206.9		£ 168.0