Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Entity Information
Off-Balance Sheet, Credit Loss, Liability	$ 18.4	$ 16.2	$ 3.8
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)	(31.1)	(68.4)	$ 14.7
Cumulative Effect, Period of Adoption, Adjusted Balance
Entity Information
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)	2.2	12.4
Unused Credit Card Lines
Entity Information
Credit extension commitments	814.0	827.6
Standby Letters of Credit
Entity Information
Credit extension commitments	97.1	93.8
Commitments to Extend Credit
Entity Information
Credit extension commitments	$ 4,069.2	$ 5,173.3