Investment Securities - Investments In Private Equity Funds Subject to Lock-Up Periods (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt and Equity Securities, FV-NI [Line Items]
1 – 3 years	$ 14.4
3 – 5 years	63.5
5 – 10 years	161.0
>10 years	16.3
Total	1,991.9	$ 1,998.2
Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 255.2