Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,111.0	$ 1,003.8	$ 3,250.1	$ 2,968.9
Foreign Exchange Trading Income	66.4	61.6	215.7	221.8
Treasury Management Fees	11.2	11.6	33.7	34.0
Security Commissions and Trading Income	36.5	26.0	104.3	100.9
Other Operating Income	62.3	53.5	171.6	144.4
Investment Security Gains, net	0.0	0.0	0.0	0.1
Total Other Noninterest Income	176.4	152.7	525.3	501.2
Total Noninterest Income	1,287.4	1,156.5	3,775.4	3,470.1
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	485.9	416.4	1,434.8	1,231.7
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	549.2	519.3	1,586.8	1,515.2
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	20.2	19.8	58.0	70.7
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 55.7	$ 48.3	$ 170.5	$ 151.3