Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 1,213.8	$ 1,142.9
Foreign Exchange Trading Income	58.7	57.0
Treasury Management Fees	9.6	9.3
Security Commissions and Trading Income	39.1	37.9
Other Operating Income	50.7	61.0
Investment Security Gains (Losses), net	0.0	(189.4)
Total Other Noninterest Income	158.1	(24.2)
Total Noninterest Income	1,371.9	1,118.7
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	485.1	467.4
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	647.4	593.9
Securities Lending
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	17.9	18.6
Other
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 63.4	$ 63.0