Other Operating Income - (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Components of Other Operating Income [Line Items]
Other operating income	$ 68.2	$ 57.3	$ 170.2	$ 144.0
Loan Service Fees
Components of Other Operating Income [Line Items]
Other operating income	21.2	17.8	61.3	52.6
Banking Service Fees
Components of Other Operating Income [Line Items]
Other operating income	15.0	12.2	40.8	37.8
Bank Owned Life Insurance
Components of Other Operating Income [Line Items]
Other operating income	17.3	17.3	51.0	44.0
Other Income
Components of Other Operating Income [Line Items]
Other operating income	$ 14.7	$ 10.0	$ 17.1	$ 9.6