Fair Value - Unfunded Loan and Lease Commitments and Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Unfunded loan and lease commitments and letters of credit
Aggregate commitments to extend credit, standby letters of credit and commercial letters of credit	$ 6,500.0	$ 7,000.0	$ 6,700.0
Fair Value, Inputs, Level 3 [Member]
Unfunded loan and lease commitments and letters of credit
Estimated fair value of unfunded loan and lease commitments and letters of credit	$ 49.8	$ 48.5