Investment Securities - Held-To-Maturity Allowance For Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0.8	$ 1.9	$ 0.8	$ 1.9	$ 0.7	$ 1.9	$ 1.6	$ 0.0
Debt Securities, Held-to-Maturity, Credit Loss Expense (Reversal)	$ 0.1	$ 0.3	$ (1.1)	$ 1.9