Investment Securities - Held-to-Maturity Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0.8	$ 1.9	$ 0.0	$ 0.0
Debt Securities, Held-to-maturity, Credit Loss Expense (Reversal)	(1.1)	1.9	$ 0.0
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	$ 0.0	$ 0.0