Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 1,341.4	$ 1,213.8
Foreign Exchange Trading Income	87.7	58.7
Security Commissions and Trading Income	52.1	39.1
Other Operating Income	70.4	60.3
Investment Security Gains (Losses), net	0.0	0.0
Total Other Noninterest Income	210.2	158.1
Total Noninterest Income	1,551.6	1,371.9
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	531.7	485.1
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	717.5	647.4
Securities Lending
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	23.6	17.9
Other
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 68.6	$ 63.4