Investment Securities - Investments In Private Equity Funds Subject to Lock-Up Periods (Details) - Private equity funds $ in Millions	Sep. 30, 2021 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 132.0
1 – 3 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0.3
3 – 5 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	14.0
5 – 10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	109.0
Greater than 10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 8.7