Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Narrative (Details) £ in Millions, zł in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 PLN (zł)	Dec. 31, 2022 GBP (£)	Sep. 30, 2022 GBP (£)
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Financial instruments sold, not yet purchased	$ 2,208,500,000	$ 2,469,600,000
Foreign currency forward contracts, gain (loss) recognized in income	$ 1,200,000	8,900,000
Interest rate contracts
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Maximum length of time hedged in cash flow hedge	2 years
Derivative liability gain (loss) recognized in income	$ 35,700,000	9,700,000
Derivative asset gain (loss) recognized in income	500,000
Interest rate contracts | Designated as Hedging Instrument
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 2,000,000,000	$ 1,500,000,000
Foreign currency forward contracts
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Maximum length of time hedged in cash flow hedge	2 years	2 years
Foreign currency forward contracts, zloty
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 33,000,000		zł 156.1
Foreign currency forward contracts, pound sterling
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	206,800,000	$ 207,300,000		£ 168.0	£ 168.0
Fair Value, Recurring | Derivatives
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Financial instruments sold, not yet purchased	$ 272,400,000	$ 313,400,000