Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,111.9	$ 1,078.7	$ 3,271.8	$ 3,390.5
Foreign Exchange Trading Income	51.8	64.7	154.9	223.2
Treasury Management Fees	7.5	9.3	23.8	31.0
Security Commissions and Trading Income	30.9	32.1	101.7	101.1
Other Operating Income	68.2	57.3	170.2	144.0
Investment Security Gains (Losses), net	0.0	(0.3)	6.9	(0.3)
Total Other Noninterest Income	158.4	163.1	457.5	499.0
Total Noninterest Income	1,270.3	1,241.8	3,729.3	3,889.5
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	459.0	435.0	1,358.7	1,383.4
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	574.1	565.3	1,673.4	1,765.8
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	20.7	21.7	61.3	62.2
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 58.1	$ 56.7	$ 178.4	$ 179.1