Other Operating Income - (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Components of Other Operating Income [Line Items]
Other operating income	$ 924.7		$ 55.2	$ 985.7	$ 102.0
Visa Class C shares
Components of Other Operating Income [Line Items]
Realized gains		$ 607.0		607.0
Unrealized gains		$ 286.8		286.8
Loan Service Fees
Components of Other Operating Income [Line Items]
Other operating income	13.7		21.4	29.4	40.1
Banking Service Fees
Components of Other Operating Income [Line Items]
Other operating income	13.3		13.6	26.6	25.8
Bank Owned Life Insurance
Components of Other Operating Income [Line Items]
Other operating income	21.4		17.0	42.0	33.7
Other Income
Components of Other Operating Income [Line Items]
Other operating income	$ 876.3		$ 3.2	$ 887.7	$ 2.4