Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,096.3	$ 1,143.4	$ 2,159.9	$ 2,311.8
Foreign Exchange Trading Income	50.1	77.6	103.1	158.5
Treasury Management Fees	7.9	10.6	16.3	21.7
Security Commissions and Trading Income	36.1	32.8	70.8	69.0
Other Operating Income	55.2	45.6	102.0	86.7
Investment Security Gains (Losses), net	0.0	0.0	6.9	0.0
Total Other Noninterest Income	149.3	166.6	299.1	335.9
Total Noninterest Income	1,245.6	1,310.0	2,459.0	2,647.7
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	458.1	464.4	899.7	948.4
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	558.8	597.3	1,099.3	1,200.5
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	21.5	21.6	40.6	40.5
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 57.9	$ 60.1	$ 120.3	$ 122.4