Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,063.7	$ 1,003.6
Foreign Exchange Trading Income	78.7	88.9
Treasury Management Fees	11.2	11.0
Security Commissions and Trading Income	34.8	41.7
Other Operating Income	54.9	34.4
Total Other Noninterest Income	179.6	176.0
Total Noninterest Income	1,243.3	1,179.6
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	469.7	417.6
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	516.4	510.5
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	18.3	23.5
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 59.3	$ 52.0