Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,166.1	$ 1,096.3	$ 2,309.0	$ 2,159.9
Foreign Exchange Trading Income	58.4	50.1	115.4	103.1
Treasury Management Fees	9.0	7.9	18.3	16.3
Security Commissions and Trading Income	34.3	36.1	72.2	70.8
Other Operating Income	924.7	55.2	985.7	102.0
Investment Security Gains (Losses), net	0.1	0.0	(189.3)	6.9	$ (176.4)
Total Other Noninterest Income	1,026.5	149.3	1,002.3	299.1
Total Noninterest Income	2,192.6	1,245.6	3,311.3	2,459.0
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	477.2	458.1	944.6	899.7
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	609.6	558.8	1,203.5	1,099.3
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	16.9	21.5	35.5	40.6
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 62.4	$ 57.9	$ 125.4	$ 120.3