Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,142.9	$ 1,063.6
Foreign Exchange Trading Income	57.0	53.0
Treasury Management Fees	9.3	8.4
Security Commissions and Trading Income	37.9	34.7
Other Operating Income	61.0	46.8
Investment Security Gains (Losses), net	(189.4)	6.9
Total Other Noninterest Income	(24.2)	149.8
Total Noninterest Income	1,118.7	1,213.4
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	467.4	441.6
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	593.9	540.5
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	18.6	19.1
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 63.0	$ 62.4