Reporting Segments and Related Information - Narrative (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) segment state	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2
Segment reporting information, fully taxable-equivalent adjustment	$ 28.5	$ 31.8	$ 57.5
Net interest income	$ 2,411.0	2,177.1	$ 1,982.0
Asset Servicing segment | Change in allocation of net interest income
Segment Reporting Information [Line Items]
Net interest income		(132.0)
Wealth Management segment
Segment Reporting Information [Line Items]
Services provided by business units, number of states | state	19
Wealth Management segment | Change in allocation of net interest income
Segment Reporting Information [Line Items]
Net interest income		$ 132.0